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1
De, Ory Zoé. „Un non-désir qui dit son nom : enquête sur une auto-identification émergente, l'asexualité“. Electronic Thesis or Diss., Paris, EHESS, 2024. http://www.theses.fr/2024EHES0048.
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À la croisée de la sociologie de la « déviance », de la sociologie de la sexualité et du genre, et de la critique des sciences, cette thèse porte sur un groupe social émergent : les personnes qui s'identifient en tant qu'asexuelles. Venant compléter d'un A le sigle LGBTQIA (+), ces personnes revendiquent une absence de désir et/ou d'attirance sexuelle pour autrui. La recherche s'appuie principalement sur une enquête qualitative par entretiens. Ont été recueillis et analysés les discours, revendications et récits autobiographiques de personnes asexuelles auto-identifiées résidant en France, militantes ou non. Ont aussi été interrogés un ensemble de sexologues et de psychothérapeutes, ainsi qu'un groupe témoin de personnes ne s'identifiant pas à l'asexualité et rapportant des « problèmes » dans leur vie sexuelle. Des événements collectifs (réunions, Marche des fiertés, congrès de sexologie) ont également été observés. L'idée, par ce travail et l'articulation de ces divers matériaux, était d'une part de s'intéresser en profondeur à cette auto-identification historiquement très récente, d'en mieux cerner les contours, les caractéristiques et les enjeux, et d'autre part de questionner le traitement social ordinaire du non-désir sexuel pour autrui, le plus souvent impensé ou implicitement problématisé, à la lumière des normes d'hier et d'aujourd'hui, de sexualité, de genre, de santé, d'identitéThis thesis uses tools from labelling theory, sociology of “deviance”, sociology of sexuality and gender and criticism of science to focus on an emergent social group: individuals who self-identify as asexual, completing the acronym LGBTQIA(+) and reporting an absence of sexual desire for and/or sexual attraction to others. The dissertation is based on a qualitative survey and on a series of interviews. Discourses and trajectories of French self-identified asexuals (vocal activists or not) have been collected and analyzed. Sexologists and psychotherapists, and individuals having reported some sexual “issues” (without asexual self-identification) have also been interviewed. Finally, collective/community events (meetings, LGBT/Gay Pride, sexology conference in France) have been observed. The purpose of this research was, first of all, to study in detail this recent self-identification (asexuality) in order to better understand its characteristics and its implications, its words and its actions. Moreover, this work tries to highlight the ordinary conception of non-desire, and to propose a reflection, through asexuality, on sexuality, gender, health and identity standards
2
Ricci, Lorenzo. „A new model to study alternative developments : asexual propagation and regeneration in the basal chordate Botryllus schlosseri“. Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066683.
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Chez l’ascidie coloniale Botryllus schlosseri, en plus de l’embryogénèse existent deux voies de développement aboutissant à la production de la même structure : l’organisme adulte ou zooide. Ces développements alternatifs ont lieu lors de processus biologiques distincts : le bourgeonnement palléal (BP) et le bourgeonnement vasculaire (BV). Le BP est un processus de multiplication asexuée présentant une ontogénèse stéréotypée. En revanche, le BV est un phénomène régénératif, induit dans les vaisseaux sanguins de la colonie par l’ablation de tous les zooides et bourgeons palléaux. Mes travaux de recherche ont eu pour objectif de caractériser les bases moléculaires et cellulaires régissant le BP et le BV chez B. schlosseri. L’étude de gènes marqueurs des lignées méso-, endo- et ectodermiques a révélé l’existence de territoires présomptifs pour chacune de ces lignées, dès les premiers stades du BV et du BP, et suggéré l’existence d’un programme unique aux deux processus. Les lignées neurales et musculaires ont été étudiées plus en détail lors du BP, indiquant un double rôle potentiel, neuro- et myo-génétique, au tube dorsal, une structure jusqu’à présent uniquement associée au système nerveux. Une caractérisation morphologique poussée a mené à l’identification de stades précoces stéréotypés du BV lors de la régénération. Enfin, l’analyse de transcriptomes de différents stades du BP et de la régénération ont initié l’étude non biaisée des bases moléculaires du bourgeonnement chez Botryllus. L’objectif à long terme de ces travaux est de décrypter les bases moléculaires et génétiques facilitant, chez les métazoaires, l’évolution de voies de développement alternativesIn addition to embryogenesis, the colonial ascidians Botryllus schlosseri evolved two alternative developmental pathways leading to the same final structure: the adult body, or zooid. These non-embryonic ontogenesis occur during distinct biological processes: palleal budding (PB) and vascular budding (VB). PB is a process of asexual propagation, with a very stereotyped morphogenesis. Conversely, VB is a purely regenerative phenomenon, induced in the vascular system of the colony by the ablation of all zooids and palleal buds. My research work followed the objective to characterize the molecular and cellular basis of both PB and VB in B. schlosseri. The study of meso-, endo- and ectodermal lineage marker genes revealed the existence of presumptive territories of these lineages in the early palleal and vascular buds and that a single developmental program was launched in both VB and PB. Neural and muscle fates were studied in more detail for PB, indicating a potential double function, both neuro- and myo-genic for the dorsal tube, a structure so far associated with the nervous system only. A detailed morphological description of VB allowed to identify stereotyped stages during early regeneration. Eventually, a transcriptomic characterization of early VB and PB processes initiated an unbiased study of the molecular basis underlying the budding phenomenon in Botryllus. The overall goal of these research works is to unravel the molecular and genetic basis that facilitated, in Botryllus and globally in metazoan, the evolution of alternative developmental pathways
3
Puisay, Antoine. „La reproduction sexuée et asexuée des coraux face aux changements environnementaux : Implications pour la conservation et la restauration des récifs coralliens“. Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEP030.
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Le changement climatique et l’augmentation des températures globales perturbent l’abondance et la distribution de milliers d’organismes, aquatiques et terrestres, et certains écosystèmes sont particulièrement sensibles à ces changements environnementaux. L’augmentation de température est la principale menace au maintien des populations de coraux, véritables ingénieurs écologiques de ces écosystèmes. Bien que la recherche sur les récifs coralliens se soit d’abord attachée à l’étude des coraux adultes, de nombreuses informations manquent sur la reproduction sexuée et asexuée, et leur rôle dans la conservation et restauration récifale. Le premier axe de ma thèse s’est donc construit sur la réponse des jeunes stades de vie à l’augmentation de température, pour d’abord évaluer les modifications de leur performance et ensuite évaluer dans quelles mesures les jeunes stades seraient capables de s’acclimater à des conditions de températures plus élevées. Au travers de différentes expérimentations en laboratoire sur le genre Acropora, j’ai ainsi mis en évidence 1) une résistance thermique importante (+2-3°C au-dessus des températures ambiantes) des gamètes face à l’augmentation de température, 2) une résistance thermique différente entre spermatozoïdes et ovocytes: ovocytes < spermatozoïdes, 3) et la mise en évidence du rôle majeur de l’environnement dans lequel se rencontre les gamètes une fois libérés, sur la qualité et la quantité de la fécondation. Enfin, j’ai identifié les conditions optimales thermiques de pré-exposition des gamètes pour maximiser leur succès de fécondation. Bien qu’un intérêt croissant soit porté sur la reproduction sexuée ces dernières années, l’utilisation de la reproduction asexuée demeure la méthode la plus utilisée pour restaurer les récifs coralliens, plus connue sous le nom de bouturage. Ainsi le second axe de ma thèse a cherché à mettre en évidence la plasticité phénotypique des coraux en cultivant des boutures provenant de 3 espèces dans 3 environnements différents et en analysant leur taux de croissance, leur état de santé et leur survie. Cet axe a pu montrer qu’il existait des différences à plusieurs échelles, entre espèces, mais aussi au sein d’une même espèce. Mes travaux montrent qu’une sélection des individus basée sur l’étude de la plasticité phénotypique de certains traits d’histoires de vie comme la croissance ou l’état de santé dans des environnements variables permettrait d’améliorer l’efficacité de la restauration récifale. Ainsi le choix des individus au sein d’une même espèce afin de réaliser du bouturage (reproduction asexuée) et le conditionnement de la phase de vie gamètes (reproduction sexuée) peut permettre d’augmenter l’efficacité des méthodes de restaurations tout en nous donnant des informations nouvelles sur la biologie et la physiologie des coraux scléractiniaires face aux changements environnementauxClimate change and increasing temperature impact abundance and distribution of thousands of organisms, aquatic and terrestrial, and some ecosystems are particularly sensitive to these global changes. Increasing temperature is the principal threat for coral populations, which are ecological engineers of coral reef ecosystems. While research on coral reefs has first sought to study adult corals, data are still lacking on early life stages of corals. As sexual and asexual reproduction may play a key role in the conservation and restoration of coral reefs, my doctoral research aims to better understand changes on sexual and asexual reproduction in the face of rising temperature. The first axis of my Ph. D. was built on the response of early life stages to increasing temperature, in order to assess whether pre-exposure of early life may improve their ulterior performance. Among the different experiments performed on the genus Acropora, I highlighted 1) a high thermal tolerance (+2-3°C above ambient temperature) of gametes, 2) a higher sensibility of oocytes than sperm to rising temperature exposure, and 3) the pivotal role of gamete thermal history on fertilization output. Finally, I identified optimal pre-exposure conditions in order to maximize fertilization success. While an increasing interest in sexual reproduction was observed these last years, asexual reproduction and fragmentation still remain the main tool to restore damaged reefs. Thus, in the second axis of my doctoral project, I investigated the phenotypic plasticity of corals by growing 3 different species of corals across 3 different environments. Their growth rates, health status and survival probability were determined. Results from this axis showed that differences were observed at the interspecific and intraspecific levels. This work revealed that a selection based on phenotypic plasticity among different life-traits (growth rates and health status) and different environments should allow to increase coral reef restoration strategies. Hence the selection of individuals (asexual reproduction) in a species based on coral common garden experiment allow to identify individuals of interest to use as restoration biological materials. Additionally, thermal pre-conditioning of early life stages (sexual reproduction) is another way to increase efficiency of restoration measures in the face of rising temperature. My doctoral research provided new information regarding physiological and biological processes of scleractinian corals facing environmental changes and proposed new solutions for restorations based on sexual and/or asexual reproduction
4
Kozlowski, Djampa. „Contribution des éléments transposables à l’adaptabilité de ravageurs de cultures en absence de reproduction sexuée“. Electronic Thesis or Diss., Université Côte d'Azur, 2020. http://www.theses.fr/2020COAZ6028.
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Les nématodes à galles (genre Meloidogyne) sont parmi les parasites de plantes les plus nuisibles. Ces organismes se distinguent par la diversité de leurs modes de reproduction. Étonnement, il a été observé que les espèces les plus néfastes se reproduisent de manière strictement asexuée et certaines sont capables de contourner la résistance de la plante hôte en un nombre de générations restreint. Ainsi, bien qu'incapables de combiner des mutations bénéfiques provenant de différents individus, ces espèces peuvent s'adapter à des changements du milieu. L’adaptabilité et le succès parasitaire de ces espèces malgré l’absence de reproduction sexuée semblent paradoxaux et doivent reposer sur d’autres mécanismes capables de générer de la plasticité génétique.Les éléments transposables (ETs) sont des fragments d’ADN capables de se déplacer et de se multiplier dans les génomes. De ce fait, les ETs peuvent avoir des répercussions fonctionnelles et structurales sur les génomes. Les ETs pourraient constituer un des mécanismes permettant de générer la diversité génétique nécessaire à l’adaptabilité chez Meloidogyne.En réalisant une analyse de génomique comparative entre 7 espèces de Meloidogyne, j’ai montré que le contenu en ETs actuellement observé chez ces espèces semble suivre leur histoire évolutive et la dérive entre espèces, plutôt que des traits d’histoires de vie tels que le mode de reproduction. Par ailleurs, cette analyse soutient une activité récente des ETs au sein de la plupart des espèces. Ces résultats suggèrent que bien que les ETs aient récemment été actifs au sein du genre Meloidogyne, leur dynamique dans les génomes semble spécifique à chaque espèce et nécessite donc une étude ciblée.Dans cette optique, j’ai concentré mes efforts sur M. incognita, l’espèce à reproduction asexuée la plus préjudiciable pour l’agriculture. Dans un premier temps, j’ai annoté en détail le contenu en ETs du génome de M. incognita. L’analyse du contenu en ETs a confirmé que ces éléments ont probablement été récemment actifs dans le génome. Afin de mieux caractériser cette activité et ses potentiels effets, j’ai ensuite estimé la mobilité de ces ETs via une analyse de génomique comparative portant sur 12 isolats géographiques. J’ai pu identifier plusieurs milliers de loci dans le génome où les fréquences de présence d'ETs varient entre les différents isolats. Par une approche phylogénétique, j’ai montré que ces variations de fréquence d’ETs suivent l’histoire évolutive des isolats étudiés. Par rapport au génome de référence, j’ai prédit des néo-insertions d’ETs, certaines ayant un potentiel impact fonctionnel. Les validations expérimentales réalisées pour plusieurs de ces insertions confirment le rôle probable des ETs dans la plasticité du génome de cette espèce.Lors de cette analyse, j’ai également identifié des ETs présents à des fréquences intermédiaires (différentes de 0 ou 1) au sein de chaque isolat, signe d’une variabilité entre individus. Or M. incognita est un organisme supposé clonal et chaque isolat étudié est issu d’une seule femelle. En nous concentrant sur l’analyse d’un de ces isolats, nous avons validé expérimentalement plusieurs polymorphismes de présence, ce qui confirme qu’il existe une hétérogénéité génétique non négligeable au sein d’un même isolat. Par ailleurs, en comparant des données de séquençage issues du même isolat à deux points de cinétique différents, nous avons pu prédire que quelques ETs varient en fréquences au sein de l’isolat en un faible nombre de générations, ce qui sous-entend que ces ETs participent à la dynamique de la diversité génétique de cet organisme. Ces résultats posent les bases pour de futures analyses visant à déterminer si l'activité des ETs joue un rôle actif dans la capacité d’espèces à s'adapter à leur environnement en absence de reproduction sexuéeRoot-knot nematodes (genus Meloidogyne) are among the most devastating plant parasites. These organisms present an important diversity of reproductive modes. Surprisingly, it has been observed that the most damaging species reproduce in a strictly asexual manner and some can bypass the host plant's resistance in a limited number of generations. Thus, although being unable to combine beneficial mutations from different individuals, these species can adapt to environmental changes. The adaptability and parasitic success of these species despite the absence of sexual reproduction seem paradoxical and must rely on other mechanisms capable of generating genetic plasticity. Transposable Elements (TEs) are DNA fragments capable of moving and multiplying in genomes. As a result, TEs can have functional and structural repercussions on genomes. Hence, TEs could be one of the mechanisms involved in generating the genetic diversity necessary for adaptability in Meloidogyne.By performing a comparative genomics analysis between 7 Meloidogyne species, I have shown that the TE landscape currently observed in these species seems to follow their evolutionary history and interspecies drift rather than life-history traits such as the reproduction mode. Furthermore, this analysis supports recent TE activity within all these species. The results also suggest that although TEs have recently been active within the genus Meloidogyne, their dynamics in the genomes appear to be species-specific and thus require targeted study.With this in mind, I have focused my efforts on M. incognita, arguably the most detrimental asexually reproductive species to agriculture. As a first step, I have annotated in detail the TE content in the genome of M. incognita. The TE content analysis confirmed these elements have probably been recently active in the genome. To better characterize this activity and its potential effects, I then estimated the mobility of these TEs through a comparative genomics analysis of 12 geographic isolates. I was able to identify several thousand loci in the genome where the frequencies of TE presence varied substantially between different isolates. Using a phylogenetic approach, I showed that these TE frequency variations followed the evolutionary history of the studied isolates. Compared to the reference genome, I have predicted TE neo-insertions, some with potential functional impact. Experimental validations carried out for several of these insertions confirmed the potential role of TEs in the genome plasticity in this species.During this analysis, I also identified TEs present at intermediate frequencies (different from 0 or 1) within each isolate, indicating variability between individuals despite the fact M. incognita is a supposedly clonal organism and that each isolate studied was derived from a single female. Focusing on the analysis of one of these isolates, we have experimentally validated several TE polymorphisms, confirming that there is significant genetic heterogeneity within the same isolate. Furthermore, by comparing sequencing data from the same isolate at two different time points, we predicted that a few TEs varied in frequency within the isolate within a small number of generations, implying these TEs participate in the dynamics of genetic diversity in this organism. These results lay the foundation for future analyses to determine whether TEs play an active role in the ability of species to adapt to their environment in the absence of sexual reproduction
5
Ricci, Lorenzo. „A new model to study alternative developments : asexual propagation and regeneration in the basal chordate Botryllus schlosseri“. Electronic Thesis or Diss., Paris 6, 2015. http://www.theses.fr/2015PA066683.
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Chez l’ascidie coloniale Botryllus schlosseri, en plus de l’embryogénèse existent deux voies de développement aboutissant à la production de la même structure : l’organisme adulte ou zooide. Ces développements alternatifs ont lieu lors de processus biologiques distincts : le bourgeonnement palléal (BP) et le bourgeonnement vasculaire (BV). Le BP est un processus de multiplication asexuée présentant une ontogénèse stéréotypée. En revanche, le BV est un phénomène régénératif, induit dans les vaisseaux sanguins de la colonie par l’ablation de tous les zooides et bourgeons palléaux. Mes travaux de recherche ont eu pour objectif de caractériser les bases moléculaires et cellulaires régissant le BP et le BV chez B. schlosseri. L’étude de gènes marqueurs des lignées méso-, endo- et ectodermiques a révélé l’existence de territoires présomptifs pour chacune de ces lignées, dès les premiers stades du BV et du BP, et suggéré l’existence d’un programme unique aux deux processus. Les lignées neurales et musculaires ont été étudiées plus en détail lors du BP, indiquant un double rôle potentiel, neuro- et myo-génétique, au tube dorsal, une structure jusqu’à présent uniquement associée au système nerveux. Une caractérisation morphologique poussée a mené à l’identification de stades précoces stéréotypés du BV lors de la régénération. Enfin, l’analyse de transcriptomes de différents stades du BP et de la régénération ont initié l’étude non biaisée des bases moléculaires du bourgeonnement chez Botryllus. L’objectif à long terme de ces travaux est de décrypter les bases moléculaires et génétiques facilitant, chez les métazoaires, l’évolution de voies de développement alternativesIn addition to embryogenesis, the colonial ascidians Botryllus schlosseri evolved two alternative developmental pathways leading to the same final structure: the adult body, or zooid. These non-embryonic ontogenesis occur during distinct biological processes: palleal budding (PB) and vascular budding (VB). PB is a process of asexual propagation, with a very stereotyped morphogenesis. Conversely, VB is a purely regenerative phenomenon, induced in the vascular system of the colony by the ablation of all zooids and palleal buds. My research work followed the objective to characterize the molecular and cellular basis of both PB and VB in B. schlosseri. The study of meso-, endo- and ectodermal lineage marker genes revealed the existence of presumptive territories of these lineages in the early palleal and vascular buds and that a single developmental program was launched in both VB and PB. Neural and muscle fates were studied in more detail for PB, indicating a potential double function, both neuro- and myo-genic for the dorsal tube, a structure so far associated with the nervous system only. A detailed morphological description of VB allowed to identify stereotyped stages during early regeneration. Eventually, a transcriptomic characterization of early VB and PB processes initiated an unbiased study of the molecular basis underlying the budding phenomenon in Botryllus. The overall goal of these research works is to unravel the molecular and genetic basis that facilitated, in Botryllus and globally in metazoan, the evolution of alternative developmental pathways
6
Cortes, Blanca R. „Horizontal genetic transfer in asexual fungi“. FIU Digital Commons, 2000. http://digitalcommons.fiu.edu/etd/2644.
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Four aspects of horizontal genetic transfer during heterokaryon formation were examined in the asexual pathogen Fusarium oxysporum f.sp. cubense (Foe): 1) variability based on method of heterokaryon formation 2) differences in nuclear and mitochondrial inheritance 3) the occurrence of recombination without nuclear fusion 4) the occurrence of horizontal genetic transfer between distantly related isolates. The use of non- pathogenic strains of Fusarium oxysporum as biocontrol agents warrants a closer examination at the reproductive life cycle of this fungus, particularly if drag resistance or pathogenicity genes can be transmitted horizontally. Experiments were divided into three phases. Phase I looked at heterokaryon formation by hyphal anastomosis and protoplast fusion. Phase II was a time course of heterokaryon formation to look at patterns of nuclear and mitochondrial inheritance. Phase III examined the genetic relatedness of the different vegetative compatibility groups using a multilocus analysis approach. Heterokaryon formation was evident within and between vegetative compatibility groups. Observation of non-parental genotypes after heterokaryon formation confirmed that, although a rare event, horizontal genetic transfer occurred during heterokaryon formation. Uniparental mitochondria inheritance was observed in heterokaryons formed either by hyphal anastomosis or protoplast fusion. Drag resistance was expressed during heterokaryon formation, even across greater genetic distances than those distances imposed by vegetative compatibility. Phytogenies inferred from different molecular markers were incongruent at a significant level, challenging the clonal origins of Foe. Mating type genes were identified in this asexual pathogen Polymorphisms were detected within a Vegetative Compatibility Group (VCG) suggesting non-clonal inheritance and/or sexual recombination in Foe. This research was funded in part by a NIH-NIGMS (National Institutes of Health-National Institute of General Medical Sciences) Grant through the MBRS (Minority Biomedical Research Support), the Department of Biological Sciences and the Tropical Biology Program at FIU.
7
Laaka-Lindberg, Sanna. „Ecology of asexual reproduction in hepatics /“. Helsinki : Yliopistopaino, 2000. http://ethesis.helsinki.fi/julkaisut/mat/ekolo/vk/laaka-lindberg.
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8
Polak, Eline. „Asexual sporulation in the basidiomycete Coprinus cinereus /“. [S.l.] : [s.n.], 1999. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=13125.
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9
Gingas, Vicki Marie. „Asexual embryogenesis and plant regeneration in Quercus /“. The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487588939088322.
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10
Anciaux, Yoann. „Dynamiques éco-évolutives en populations asexuées : sauvetage évolutif dans le paysage adaptatif de Fisher“. Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTT135/document.
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La capacité de persistance d’une population face à un changement environnemental stressant est une question complexe à l’interface entre l’écologie et l’évolution. Le processus par lequel une population échappe à l’extinction en s’adaptant aux nouvelles conditions environnementales stressantes est nommé sauvetage évolutif. Ce cas particulier de dynamique éco-évolutive est de plus en plus étudié autant théoriquement, qu’expérimentalement, entre autres dans le contexte des changements environnementaux d’origines anthropiques. Cependant, les études modélisant ce processus négligent les interactions entre génotypes et environnements impactant le potentiel évolutif des populations faisant aux changements environnementaux. Dans le cadre de cette thèse, j’ai développé des modèles intégrant ces interactions. Pour cela, j’ai modélisé le processus de sauvetage évolutif de populations à reproduction asexuée, face à des changements environnementaux abruptes, en utilisant le paysage adaptatif de Fisher (modèle géométrique de Fisher (1930)). Ce paysage nous a permis de modéliser ces interactions génotypes-environnement et leur impact sur la proportion de mutations pouvant sauver une population. A travers deux modèles, considérant soit le sauvetage d’une population par une mutation d’effet fort, soit par un grand nombre de mutations d’effets faibles, nous avons pu dégager des prédictions pour la probabilité de sauvetage évolutif en fonction des conditions environnementales et des caractéristiques de l’organisme étudié. Ces modèles peuvent être paramétrés sur des données d’évolution expérimentale et leurs prédictions comparées à des données de traitement antibiotiques visant des pathogènes asexués. Au-delà du sauvetage évolutif, les modèles développés nous ont également permis d’établir des outils permettant de modéliser d’autres dynamiques éco-évolutives, intégrant des interactions génotype-environnement et leurs effets sur la distribution d’effets des mutationsThe persistence ability of a population facing a stressing environmental change is a complex question at the connection between ecology and evolution. The process by which a population avoid extinction by adapting to the new stressing environmental conditions is termed evolutionary rescue. This particular case of eco-evolutionary dynamic is increasingly investigated both theoretically and experimentally, among other things in the context of the environmental changes from human activity. However, the studies modelling this process neglect the interactions between genotypes and environments impacting the evolutionary potential of the populations facing environmental changes. In the context of this thesis, I developed models integrating these interactions. To this end, I modelled the process of evolutionary rescue in asexual populations, facing abrupt environmental changes, using the adaptive landscape of Fisher (Fisher’s geometric model (1930)). This landscape allowed us to model the genotypes-environments interactions and their impact on the proportion of mutations able to save a population. Using two models, considering either the rescue of a population by a mutation of strong effect, either by a large number of mutation of small effect, we derived predictions for the probability of evolutionary rescue, which depends on the environmental conditions and the characteristics of the studied organism. These models can be parametrized on data from evolutionary experiments and their predictions compared to data of antibiotic treatments aiming on asexual pathogens. Beyond evolutionary rescue, the models developed in this thesis also gave tools to model other eco-evolutionary dynamics, integrating genotype-environment interactions and their effects on the distribution of mutations effects
11
Jenkins, Christina. „Resource limitation in sexual vs. asexual Potamopyrgus antipodarum“. Thesis, University of Iowa, 2010. https://ir.uiowa.edu/etd/521.
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The question of why sexual reproduction is so prevalent in natural populations has been called the "queen of questions" in evolutionary biology (Bell, 1982). One potential answer to this question may come from studying whether sexuals and asexuals respond differently to a resource-limited environment. If asexuals require more resources to grow and reproduce at the same rate as sexuals, it could negate the two-fold cost of sexual reproduction. Here, I use Potamopyrgus antipodarum, to empirically address this possibility. First, I consider whether differences in genetic diversity between sexual and asexual components of a population could help to maintain sex in a resource-limited environment. This possible advantage associated with asexuality requires that genetically identical individuals compete more for the same resources than genetically diverse individuals. I evaluated this possibility by comparing fitness-related traits in genetically homogeneous vs. heterogeneous populations of asexual female P. antipodarum, and found that adult size was a more important determinant of individual growth and reproduction than population genetic diversity per se. Next, I used manipulations of density of experimental populations of P. antipodarum to assess whether asexual females experienced a sharper decline in fitness-related traits under high-density conditions, as expected if high sensitivity of asexual individuals to food limitation might contribute to the maintenance of sex. Counter to these predictions, I found that sexual females in fact suffered even more in high-density predictions. Finally, I considered that asexuals may respond differently to food quality, instead of quantity. Ecological stoicheometry postulates that individual growth and reproduction is associated with their bodily phosphorous (P) and the available P in food found in their environment. Because asexuals have more bodily P they may require more P rich food than sexuals to grow and reproduce at the same rate. Although asexuals reproduced less than sexuals, it was not a significant difference.
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Söderberg, Jonas. „Surviving the ratchet : Modelling deleterious mutations in asexual populations“. Doctoral thesis, Uppsala universitet, Molekylär evolution, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-157897.
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One of the most unforgiving processes in nature is that of Muller's ratchet, a seemingly irreversible accumulation of deleterious mutations that all organisms have to deal with or face extinction. The most obvious way to avoid fitness collapse is recombination, though asexual populations usually do not have the luxury of recombining freely. With the aid of computational and mathematical models, we have studied other situations where this threat is averted and the organism can survive the ratchet. The results show that a ratchet where all mutations have the same deleterious fitness effect is very effectively stalled for large effects. However, if mutations are allowed to have a broad range of effects, the fitness-loss rate can be substantial even with the same mean effect as the one-type ratchet, but we have identified parameter regions where even the broad-range effects are effectively stopped. The fitness-loss from a ratchet is very sensitive to the mutation rate and a mutation that increases the mutation rate (mutator) can easily start an otherwise stalled ratchet. Large effect mutators are heavily counter-selected, but smaller mutators can spread in the population. They can be stopped by reversals (antimutators), but even if the mutation rate is equilibrated in this way, there will be large fluctuations in mutation rate and even larger in the fitness-loss rate due to the feedback amplification in their coupling. Another way of preventing the ratchet is by reversal of the deleterious mutations themselves through back-mutations or compensatory mutations. The rate required to stop the ratchet using only back-mutations before the fitness collapses is very large. A detailed comparison between the deleterious mutations in the ratchet and in a sexual population was made and the difference was found to be greatest for large populations with large genomes. There are obviously many ways to survive the ratchet, but even more ways to drive a species to extinction by enhancing and speeding up the ratchet. By modelling and testing the ratchet for numerous different situations, we show the effects of some of these threats and benefits.
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Fierro-Constain, Laura. „La reproduction chez Oscarella lobularis (Porifera - Homoscleromorpha) : gènes impliqués et effets de l'environnement“. Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4088.
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Les Porifères et les Cténophores sont probablement les deux lignées animales les plus anciennes. Leur étude permet de retracer l’histoire précoce des métazoaires, et d’aborder l'origine de la distinction entre les lignées somatique et germinale. En effet, chez les éponges cette distinction n’existe pas: les archéocytes et choanocytes pouvant donner les cellules somatiques et les gamètes.Après avoir établi la liste des gènes considérés comme impliqués dans la gamétogenèse chez les métazoaires, j’ai caractérisé leurs séquences et retracé leur histoire grâce à des analyses comparatives intégrant les principales lignées animales. Enfin, un suivi in situ d'Oscarella lobularis m’a permis d’affiner son cycle de vie et d’accéder à toutes les étapes du développement pour étudier l’expression de ces gènes et de tester leur implication dans la gamétogenèse.Ainsi, j'ai montré que 18 gènes du GMP (Germline Multipotency Program) sont présents ancestralement chez les animaux. Parmi ceux-ci 11 s’expriment pendant la gamétogenèse, au cours de l’embryogenèse, de la reproduction asexuée et de la régénération. Enfin, le suivi in situ a montré l’influence de la variation de la température et de la matière organique sur le déclenchement de la gamétogenèse.Mon travail suggère d’une part, que la spécification des cellules germinales est régie par des mécanismes génétiques communs à l’échelle de métazoaires, et d’autre part que ces gènes pourraient être impliqués dans la multipotence. Ces résultats renforcent l’hypothèse proposant une origine commune de la lignée germinale et des cellules souches somatiquesPorifera and Ctenophora are probably the two most ancient animal lineages. Their study therefore allows to trace back the early history of metazoans and to address the origin of the distinction between somatic and germ lines. Indeed, in sponges this distinction does not exist: archeocytes and choanocytes can give rise to both somatic cells and gametes.After establishing the list of genes considered to be involved in gametogenesis in metazoans, I searched for these candidate genes (by local blast) in the transcriptomes of two sponge species (Oscarella lobularis and Oopsacas minuta). I thereby managed to characterize their sequences (phylogenetic and protein domain analyzes) and to trace their evolution through comparative analyzes including all main animal phyla. Finally, the in situ monitoring of O. lobularis enabled me to refine its life cycle and access all key developmental stages in order to study the expression of candidate genes in order to test their possible involvement in gametogenesis in this species.I have shown that 18 GMP (Germline Multipotency Program) genes are present ancestrally in animals. Among them, at least 11 are expressed not only during gametogenesis but also during embryogenesis, asexual reproduction and regeneration. Finally, in situ monitoring showed the influence of temperature variations and organic matter availability on gametogenesis.My work suggests, firstly that the specification of germ cells is controlled by common genetic mechanisms across metazoans, and secondly that these ancestral genes might be involved in pluripotency. These results reinforce the hypothesis suggesting a common origin of the germline and somatic stem cells
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Docking, T. Roderick. „The evolution of retrotransposon sequences in four asexual plant species /“. Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=81327.
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Since their discovery, transposable elements (TEs) have been regarded either as useful building blocks of genomes, or as "selfish DNA": genetic parasites that exploit the sexual cycle to spread in copy number within populations to the detriment of their hosts. If the "selfish DNA" hypothesis is correct, TEs are expected to deteriorate and be lost from asexual populations. This thesis tests the predictions of the "selfish DNA" hypothesis in four asexual plant species, focusing on patterns of nucleotide diversity and nucleotide substitution. Sequences bearing strong resemblance to known TE families including Ty1/copia, Ty3/gypsy, and LINE-like elements were successfully isolated from all four plant species, and showed patterns of nucleotide substitution consistent with a long history of purifying selection. Stochastic simulations were also conducted, and suggested that this result is expected if the host species has been asexual for less than tens of thousands of generations.
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Luk, Ka Wing. „An exploratory study of asexual marriage on a Chinese website“. HKBU Institutional Repository, 2013. https://repository.hkbu.edu.hk/etd_oa/30.
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The process of individualization is increasingly permeating all levels of Chinese society. This research attempts to highlight some aspects on how Chinese individualization is emerging in marriage and the family through the prism of China’s emerging “asexual marriage” – a consensual partnership that has no sex or a limited amount of sex. Collecting qualitative data in different ways, this study first examines the less obvious and less studied effects of China’s sexual revolution as part of the individualization process brought to the asexual individuals on a specific matchmaking website WX920. One can see that these individuals undergo great suffering and are under pressure to find a partner in light of the sexual imperative in the couple relationship. My study also focuses on the idealized view of asexual marriage currently promoted by the rhetoric of affection. What is particularly striking is that the same ideal is perceived as equally worthy of a relationship in a proforma marriage with a homosexually inclined person, when one cannot meet an asexual partner. In addition, this study suggests the reintegration of individuals into a new type of collectivity – the family, which is primarily structured as a unit of emotional importance to the individual’s marital decision. Nevertheless, the other side of family connection constitutes a crucial dilemma for some non-conformist individuals, who are confronted with a dual demand for satisfying personal aspirations and family expectations. Drawing on the concept of “negotiated familism”, this study reveals how these individuals are by no means passive recipients and they actively engage in negotiation about their ideal of personal life through a marriage in form only. Finally, I will engage a discussion on individualizing trends by exploring asexual people’s reorganization of conventional norms of marriage and other expectations such as reproduction is given.
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Dench, Jonathan. „New Computational Approaches to Study the Evolution of Asexual Haploids“. Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/40415.
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Numerous factors can influence the evolutionary fate of mutations. Despite this,
we tend to study strong evolutionary drivers, or evolution under simple contexts, in
part because they are the conditions we have a means to study. My thesis evaluates
novel computational approaches to advance detection, and study, of factors that
influence a mutation’s evolutionary outcome. First, I present the novel
computational tool AEGIS that I use to detect phylogenetic signals of correlated
evolution followed by an experimental approach to evaluate the role of epistasis as a
potential cause of correlated evolution among sites associated with antibiotic
resistance in Pseudomonas aeruginosa. Second, I developed rSHAPE, a novel in
silico approach for experimental evolution with asexual haploids, to complement
empirical work by providing a common framework in which to test various
evolutionary scenarios. After demonstrating that rSHAPE replicates the expected
evolutionary dynamics of de novo mutations, I provide evidence that the common
laboratory practice of serial passaging may increase stochasticity of evolutionary
outcome. Through my work, I have demonstrated that a marriage of computational
and experimental approaches will offer new opportunities to understand how the
interaction of evolutionary factors influence the fate of mutations.
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Hagen, R. H., und D. A. Palzkill. „Air-layering as a Method of Asexual Propagation of Mesquite“. College of Agriculture, University of Arizona (Tucson, AZ), 1989. http://hdl.handle.net/10150/216058.
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Three 12-year-old Prosopis chilensis were successfully layered in spring and late summer. The best rooting occurred with 1 cm stems treated with either 5,000 or 15,000 ppm IBA. Air-layers treated with IBA had a higher rooting rate and better root quality than untreated air-layers.
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Carrillo, Medrano Claudia del Carmen. „Mathematical models for the coexistence of sexual and asexual conspecifics“. Thesis, University of Bath, 2002. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269840.
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Rice, Christopher Steven. „Evolution of meiosis genes in sexual vs. asexual Potamopyrgus antipodarum“. Thesis, University of Iowa, 2015. https://ir.uiowa.edu/etd/1739.
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How asexual reproduction affects genome evolution, and how organisms that are ancestrally sexual alter their reproductive machinery upon becoming asexual are both central unanswered questions in evolutionary biology. While these questions have been addressed to some extent in organisms such as asexual clams, rotifers, ostracods, arthropods, and fungi, the most powerful and direct tests of how sex and its absence influence evolution requires direct comparisons between closely related and otherwise similar sexual and asexual taxa. Here, I quantify the rates and patterns of molecular evolution in the meiosis-specific genes Msh4, Msh5, and Spo11 in multiple sexual and asexual lineages of Potamopyrgus antipodarum, a New Zealand freshwater snail. Because asexual P. antipodarum reproduce apomictically (without recombination), genes used only for meiosis should be under relaxed selection relative to meiosis-specific genes in sexual P. antipodarum, allowing me to directly study how asexuality affects the evolution of meiosis-specific genes. Contrary to expectations under relaxed selection, I found no evidence that these meiosis-specific genes are degrading in asexual P. antipodarum; instead they display molecular patterns consistent with purifying selection. The presence of intact meiosis-specific genes in asexual P. antipodarum hints that the asexuals may maintain the ability to perform meiosis despite reproducing apomictically. Asexual meiotic capability suggests that some meiotic components may persist or acquire a new role in these asexuals.
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Loewe, Laurence. „Evolutionary bioinformatics predicting genetic stability of asexual genomes by global computing /“. [S.l.] : [s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=969894201.
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21
Johnston, Amal Joseph. „Functional genomics of sexual and asexual reproduction in Arabidopsis and relatives /“. Zürich, 2007. http://opac.nebis.ch/cgi-bin/showAbstract.pl?sys=000254731.
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22
Tiley, Anna Mystica Mendez. „Investigating asexual sporulation in Zymoseptoria tritici, a fungal pathogen of wheat“. Thesis, University of Bristol, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.715767.
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23
Maxwell, Danielle. „It's not just about sex : asexual identity and intimate relationship practices“. Thesis, University of York, 2017. http://etheses.whiterose.ac.uk/18006/.
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Queer and feminist scholars frequently claim that non-heteronormative sexualities, like asexuality, challenge heteronormative practices within intimate relationships. They argue that these sexualities lead to the emergence of new intimate practice and have the potential to revolutionise what is understood as the sexual “public story”—one in which a sexual assumption is repeatedly performed and an absence is culturally denied, sometimes to the point of pathologisation (Carrigan, 2011; Przybylo, 2011; Jamieson, 1998). A more recent analysis of asexuality suggests that there is very little evidence of specific asexual practices and that many asexuals are in fact not challenging heteronormative practices (see Dawson et al., 2016). Neither of these contradicting arguments fully details the nuances of how asexuality operates within intimate relationships, straddling both of these positions in practice. This thesis investigates the complexity of an asexual identity to capture the way it sometimes does and does not engage with and/or challenge heteronormativity within intimate relationships. Drawing on 68 online surveys and 29 online interviews, I thematically analysed participants’ stories to (1) understand how asexuality functions as a meaningful label, including the adoption of an asexual identity and (2) investigate patterns of intimate practices—partner selection, relationship types and forms of intimacy—and their connection to heteronormativity, an asexual identity or both. I demonstrate the presence of asexual-specific preferences, and how these preferences are often compromised for largely heteronormative practices. However, among asexual intimate practices I found a potential for the creation of more varied understandings that, while not fully challenging heteronormativity, offer more complex intimate relationship practices and understanding(s).
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Brandt, Alexander [Verfasser]. „No sex, No problem? Mutation accumulation in asexual animals / Alexander Brandt“. Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://d-nb.info/1234848937/34.
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25
Cianciolo, Jennifer M. „Evolutionary persistence and co-existence of sexual and asexual oribatid mites“. [Bloomington, Ind.] : Indiana University, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3331269.
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Thesis (Ph.D.)--Indiana University, Dept. of Biology, 2008.Title from PDF t.p. (viewed on Jul 27, 2009). Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 6533. Advisers: Michael Wade; Curt Lively.
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Bui, Linh Thuy. „Molecular dissection of asexual reproduction in the model fern Ceratopteris richardii“. Diss., University of Iowa, 2014. https://ir.uiowa.edu/etd/6380.
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The life cycle of all land plants is characterized by the alternation between two multicellular generations: haploid gametophytes and diploid sporophytes. Whereas meiotic recombination and fertilization via sexual reproduction is known to confer adaptive evolutionary benefits, some plant species can reproduce asexually bypassing meiosis and fertilization yet still undergo alternation of generations. In ferns, the two asexual reproductive pathways are termed apogamy and apospory, i.e. the asexual reproduction of sporophytes and gametophytes, respectively. Although understanding the process of asexual reproduction in flowering plants would be of considerable agricultural value, the molecular mechanisms underlying this process have yet to be identified. Similarly, the genes in ferns that underlie apogamy and apospory are unknown. Knowledge of such genes will provide invaluable information not only for the evolutionary study of asexual reproduction in land plants, but also insight into the developmental program for each generation. My PhD research focuses on the investigation of candidate genes involved in asexual reproduction in the model fern Ceratopteris richardii.
Though the molecular mechanisms underlying asexual reproduction are not understood, it is hypothesized that asexual reproduction is the result of altered regulation of certain sexual reproduction-related genes. Therefore, I selected candidate genes for asexual reproduction in C. richardii, CrEMS1, CrKNOX3 and CrANT, based on the functions of their respective homologs during sexual reproduction in two other model systems: Arabidopsis thaliana and Physcomitrella patens. I showed that, in C. richardii, CrEMS1 is expressed during key events of sexual reproduction, including sporogenesis, gametogenesis and embryo development; CrKNOX3 expression is specific for the mature egg cells and CrANT expression is restricted to sperm cells. The presence of CrEMS1 during early embryo development made it a suitable candidate for an embryonic marker for future research.
To study the function of the candidate genes, I overexpressed CrKNOX3 and BnBBM, a flowering plant BBM gene that has similar expression patterns in Brassica to CrANT. The overexpression of CrKNOX3 results in unique cell outgrowth from the antheridia, and overexpression of BnBBM results in spontaneous apogamy induction. Whole mount in situ also showed CrEMS1 expression, marking embryonic identity, in pre-apogamous cells undergoing sugar-induced and overexpression of BnBBM-induced apogamy.
The results of my PhD research provides, for the first time, insight into the molecular mechanisms underlying asexual reproduction in the model fern C. richardii, and invaluable tools, transient and stable Agrobacterium-mediated transformation protocols, for functional genomics research in this fern. The spontaneous apogamy induction on BnBBM-expressing gametophytes and the presence of CrEMS1 in pre-apogamous cells confirm the hypothesis that asexual reproduction is the result of the alteration in expression of sexual-related genes, verifying that the two pathways share a common set of genes.
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Tvedte, Eric S. „Genome evolution in parasitic wasps: comparisons of sexual and asexual species“. Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6516.
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The fate of any lineage is contingent on the rate at which its genome changes over time. Genome dynamics are influenced by patterns of mutation and recombination. Mutations as the raw force of variation can be acted on independently during exchanges of homologous genetic regions via meiotic recombination. While molecular evolution in sexual lineages is impacted by both mutation and recombination, asexual lineage fate is primarily influenced by the mutation rate; recombination is often altered or absent in asexuals. Although multiple studies show accelerated mutation accumulation in asexual lineages that have lost recombination, virtually nothing is known about rate patterns when meiosis is retained. Here, I use parasitic wasps in genus Diachasma to investigate genome evolution in a recently-derived asexual lineage. I provide evidence that asexual Diachasma possess a canonical set of meiosis genes as well as high levels of genomic homozygosity. Taken together, these observations support an active, albeit modified, form of meiosis in this asexual lineage. In addition, I present the first documentation of accelerated mutation accumulation in the nuclear genome of a naturally-occurring, meiotically- reproducing organism. If harmful, these mutations could impede asexual lineage persistence and contribute strong support for the long-term benefits of sex.
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Griffin, Clare Louise, und clare griffin@flinders edu au. „A comparison of the ecology and behaviour of parthenogenetic and sexual taxa of the Australian skink, Menetia greyii: implications for coexistence“. Flinders University. School of Biological Sciences, 2006. http://catalogue.flinders.edu.au./local/adt/public/adt-SFU20070202.132116.
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Menetia greyii, a small Australian skink, has recently been determined to be a species complex that consists of both sexual and parthenogenetic taxa (Adams et al. 2003). In total, seven distinct taxa have been identified in the south-central region of Australia. This includes three sexual taxa, three apparent parthenogen lineages, and one lizard of uncertain status
The study population occurs near Bundey Bore station in the semi-arid region of South Australia (approximately 160km north east of Adelaide). At this site, one sexual taxon (SAS) and two all-female parthenogenetic taxa (WP and RP3) were found to occur in sympatry. In a search for ecological differences, I examined spatial, thermal, physiological and morphological niche relationships in the parthenogenetic and sexual forms. Capture rates were used to determine microhabitat and macrohabitat use in the field. The use of different microhabitats and the amount of time spent occupying different exposures (sun vs. shade) were also examined under laboratory conditions. Thermal preferences, physiological performance (sprint speed ability) and daily activity periods were investigated in the laboratory. The study failed to find any major differences among the different taxa that would indicate they are partitioning resources and therefore explain how the sexual and parthenogenetic forms are coexisting. The only difference observed was that the parthenogens expressed superior sprinting ability, running faster than the sexuals over a range of temperatures. In addition, I found that sexual and parthenogenetic females within this population differed very little in their reproductive effort and output, indicating that RP3 and WP parthenogens possess a reproductive advantage over sexual females as a result of not having to produce males (Williams 1975, Maynard-Smith 1978, Bell 1982). In staged interactions between pairs of sexual and parthenogen individuals, the parthenogens were more aggressive and dominated the sexuals. As a result, the parthenogens were able to outcompete the sexuals for food items. This had serious consequences on fitness, with the sexuals losing significantly more weight than the parthenogens. All of these factors would suggest that the parthenogens should eliminate the sexuals at Bundey Bore. Despite this, the parthenogenetic females at Bundey Bore do not outnumber the sexual subpopulation. This raises the question of how the sexuals are persisting. An examination of endoparasites in the scats of parthenogen and sexual M. greyii found that WP parthenogens had significantly higher parasite prevalence than sexuals. Further to this, there is evidence of matings occurring within the study population between sexual males and WP parthenogen females with five tetraploid males being captured. Therefore, WP parthenogens may be suffering from destabilising hybridization. These factors may account for why the parthenogens (or at least the WP parthenogens) have not competitively excluded sexual M. greyii from Bundey Bore. Other possible reasons are discussed in the general discussion in Chapter 8.
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Renaut, Sébastien. „Mean fitness of long-term sexual and asexual populations of Chlamydomonas in benign environments“. Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=80862.
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Populations of Chlamydomonas were maintained in a benign laboratory environment as obligatory sexual or asexual populations for five years. Sexual reproduction is expected to facilitate the elimination of mildly deleterious mutations and thereby increase the mean fitness of a sexual population relative to an asexual population (Kondrashov 1988). Fitness in competition and in pure culture was measured. In neither of the fitness assays, both in solid and liquid cultures of Chlamydomonas, was a fitness advantage of sexual reproduction seen, even though the results varied depending on the definition of fitness. I hypothesized that the effect of mutation clearance could be masked by different forces acting on the selection strain (such as an antagonistic relationship between sexual and vegetative fitness).
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Hunter, Shenae. „Asexual cultivation techniques of the red macroalgae Asparagopsis taxiformis for commercial application“. Thesis, Hunter, Shenae (2022) Asexual cultivation techniques of the red macroalgae Asparagopsis taxiformis for commercial application. Masters by Research thesis, Murdoch University, 2022. https://researchrepository.murdoch.edu.au/id/eprint/65504/.
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Asparagopsis is a genus of red macroalgae (seaweed) endemic to coastal waters in Australia and characterised by its complex heteromorphic life history. Previous research discovered Asparagopsis metabolites such as bromoform reduce methanogenesis in livestock rumen by up to 99%. Agriculture accounts for 14% of Australia's total greenhouse gas emissions, predominantly derived from enteric fermentation from ruminant livestock. Cultivating this macroalga is of environmental significance, given the urgency of emission reductions for climate change mitigation while meeting market demand for meat. Understanding manual cultivation techniques is necessary due to limitations of abundance in the wild. There is limited research into cultivation of the asexual lifecycle of Asparagopsis.
This research aimed to identify if fragmentation of Asparagopsis is viable, and if growth can be sustained for nearshore cultivation, by mimicking naturally occurring conditions in lab-based cultivation. Light exposure, salinity, temperature, and a lack of nutrients experienced in ocean environments was emulated. Fragments of Asparagopsis taxiformis gametophytes were collected from Perth coastal waters in June and September and cultivated in aquaria at varying temperatures, substrates, and fragment types.
Growth rates were overall negatively correlated, with marginal growth in some conditions, concluding that asexual cultivation using these parameters is not recommended. The viability of fragments for up to three months in some conditions gives rise to questions of the potential for asexual cultivation in other environments. The optimum conditions across these aquaria were based around a temperature of 21°C, 25μmol photons m-2 s-1 light exposure and holdfast fragments attached to a substrate such as rope. Of particular significance were tip fragments that retained a dark red pigment, which may provide an ideal setting for continued viability and eventual growth due to the reliance of pigment in photosynthesis processes.
Further testing is required to analyse the specific ideal temperature, light exposure and fragmentation origin, alongside other factors such as nutrient levels, to assess if asexual fragmentation is possible for use in commercial cultivation.
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Cordle, Angela Ruth. „Genes involved in asexual sporophyte development in Ceratopteris richardii and Arabidopsis thaliana“. Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/4598.
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The life cycle of land plants alternates between the haploid gametophyte and the diploid sporophyte generations. Asexual reproductive strategies, that bypass meiosis and fertilization, have evolved in diverse land plant taxa. Apogamy is one such strategy that produces a sporophyte directly from a gametophyte cell. The genes that drive the process of apogamy are unknown. Knowledge of these genes and their functions will provide insight into the evolution of asexual reproduction, the sporophyte body plan and the alternation of generations in land plants. My Ph. D. research has focused on identifying the genes function in apogamy commitment, and understanding the functions of their counterparts in angiosperms.
First, I successfully induced apogamy from the fern Ceratopteris richardii and discovered that the gametophytes begin to become committed to apogamy after 10 days of culture on inductive medium. I then created a cDNA library that represents genes with enhanced expression during commitment. Comparison of the Gene Ontology terms mapped to this cDNA library with that of the gametophyte transcriptome of the fern Pteridium aquilinum showed that this library is enriched in genes that function in stress response and metabolism. This library contains many sequences whose homologues in Arabidopsis are specifically expressed or upregulated in flower organs or seed structures, both of which are absent in ferns. One of these genes, UNC93-like, is expressed in the eggs of C. richardii gametophytes, as evidenced by in situ hybridization. Functional egg cells are implicated as necessary for C. richardii gametophytes to undergo apogamy.
In Arabidopsis, an AtUNC93-like mutant, which produces a partial AtUNC93-like transcript, has vegetative and reproductive defects. Embryo abortion and gametophyte lethality contribute to a small seed set in these plants. Reciprocal crosses indicate that the mutant allele does not affect gametophyte function but cause a maternal failure to maintain viability of all gametophytes. Thus, the AtUNC93-like gene is necessary for normal sporophyte vegetative growth and reproductive success, but is dispensable for the direct function of gametophytes.
My research has provided insight into the mechanisms that induce apogamy in a fern. The apogamy library is a valuable resource for future investigations into apogamy.
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Fonseca, da Silva Marques Raquel. „Drivers and fate of jellyfish blooms : The case study of Aurelia coerulea in the Thau lagoon, North Western Mediterranean“. Thesis, Montpellier, 2019. http://www.theses.fr/2019MONTG036.
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Les méduses sont des composants importants des écosystèmes marins. Leurs proliférations spectaculaires ont de graves impacts écologiques et socioéconomiques et sont apparemment renforcées par les pressions anthropiques en milieu marin. Les inquiétudes suscitées par l’accroissement de la fréquence et de l’intensité de ces proliférations, du moins dans certaines régions du globe, appellent à une compréhension plus approfondie de leurs causes. Cependant, la plupart des méduses ont un cycle de vie complexe, comprenant à la fois des stades benthiques et pélagiques, ce qui complique la compréhension des épisodes de proliférations et empêche toute prévision fiable de leur évolution. De plus, le manque de connaissances sur l’avenir de la biomasse générée par les proliférations entrave l'évaluation de leurs impacts. Pour cela, l’écosystème semi-fermé de étang de Thau présente la particularité rare d’abriter une population complète et résidente de la méduse Aurelia coerulea. Il offre donc le cadre idéal pour étudier les multiples processus écologiques qui affectent la dynamique de ses populations benthiques et pélagiques. Ce travail de thèse tire parti de cette opportunité rare afin de préciser l’origine et le devenir des proliférations d’A. coerulea. Cela a été accompli en deux étapes. Premièrement, la dynamique de la population benthique de l’espèce a été étudiée dans l’étang et complétée par une étude de l’écologie trophique des deux stades de vie sur une année. Pour ce faire, des suivis in situ ont été réalisés et complétés par l’analyse de contenus stomacaux et des comparaisons de signatures en isotopes stables. Deuxièmement, le devenir de la biomasse d’A. coerulea dans la lagune a été étudié en évaluant la prédation des poissons sur ses stades benthiques et pélagiques et en suivant la disparition de ses méduses mortes, une fois posées sur le fond. Ceci a été réalisé par analyse moléculaire du contenu des intestins de poisson et par des expériences in situ évaluant les taux de décomposition des méduses et le rôle potentiel de la faune benthiques dans leur disparition. les résultats obtenus mettent en évidence l'interaction complexe de paramètres environnementaux biotiques et abiotiques qui modulent l’intensité des proliférations en influençant conjointement les populations benthiques et pélagiques d'A. coerulea. La température, la salinité, la disponibilité en nourriture et la prédation semblent être les principaux facteurs écologiques contrôlant les proliférations de A. coerulea dans l’étang de Thau, avec quatre périodes critiques dans l’année, où la formation des proliférations est soit facilitée soit minimisée. Enfin, les blooms ont trois principaux devenirs dans la lagune. Les méduses sont avant tout consommées vivantes dans la colonne d’eau par les prédateurs pélagiques (notamment les poissons). Sinon, lorsqu’elles meurent et coulent sur le fond, elles peuvent être consommés par certains organismes benthiques (notamment des gastéropodes) mais sont surtout rapidement reminéralisés par la communauté microbienne locale. Ces résultats apportent des informations précieuses pour prédire l'évolution des proliférations de méduses en réponse aux effets anthropogéniques sur le milieu marin en cours, et anticiper leurs impacts sur le fonctionnement des écosystèmes. Cependant, ils soulignent également la difficulté d’obtenir de telles prévisions et soulignent la nécessité de mener des études approfondies similaires, non seulement pour d’autres méduses mais aussi dans d’autres régions du mondeJellyfish are important components of marine ecosystems. Their spectacular blooms have severe ecological and socioeconomic impacts and are seemingly boosted by anthropogenic pressures on the marine environment. Concerns regarding increases in jellyfish blooms, at least in some areas of the world, call for a deeper understanding of their drivers. However, many jellyfish have complex life cycles, comprising both benthic and pelagic stages, which complicates the understanding of their blooms and predictions on their future evolution. Furthermore, the lack of knowledge regarding the fates of these large accumulations of biomass hampers the assessment of their impacts. With this regards, the semi-enclosed ecosystem of the Thau lagoon presents the rare particularity to harbour a complete resident population of the jellyfish Aurelia coerulea. Therefore, it offers the ideal background to study the multiple ecological processes affecting the dynamics of both its benthic and pelagic populations. This PhD built on this rare opportunity to precise the drivers and fates of the blooms of A. coerulea. This was accomplished in two steps. First, the benthic population dynamics in the lagoon was investigated and complemented with studies on its drivers and on the trophic ecology of both life stages over one year. To do so, in situ monitoring surveys and both stomach content and stable isotope analyses were employed. Second, the fate of A. coerulea biomass in the lagoon was assessed by investigating fish predation on its pelagic and benthic life stages and by studying the degradation of its medusae once dead on the seabed. This was performed by molecular analysis of fish gut contents and in situ experiments evaluating the decay rates of medusae and the potential role of the benthic fauna in their disappearance. The results obtained highlight a complex interaction of biotic and abiotic environmental parameters, which modulate bloom intensity by jointly influencing both the benthic and pelagic populations of A. coerulea. Temperature, salinity, food availability and predation appear to be the main drivers of the blooms of A. coerulea in Thau, with four critical periods, either boosting or lessening local bloom formation each year. Finally, the biomass produced by A. coerulea blooms has three main fates within the lagoon. The medusae can first be consumed alive by several pelagic predators like fish. Otherwise, when they die and sink to the seabed, some can be consumed by benthic scavengers like gastropods, but most are rapidly remineralised by the local microbial community. These findings shed light on the potential evolution of jellyfish blooms in the face of the ongoing anthropogenic forces on the marine environment, and on their impacts on coastal ecosystems functioning. However, they also highlight how intricate jellyfish blooms forecasting is and stress the need for similar comprehensive studies, not only for other jellyfish species but also in many other parts of the world
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Park, Arum. „Parthenogenesis in Hesiod’s Theogony“. Penn State University Press, 2014. http://hdl.handle.net/10150/622192.
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This article examines female asexual reproduction, or parthenogenesis, in Hesiod’s Theogony
and argues that it is a symptom of the unprecedented and unparalleled female presence Hesiod inserts into his cosmos. This presence in turn reflects Hesiod’s incorporation of gender difference and conflict as indispensable both to the creation and, paradoxically, to the stability of the universe. Five of Hesiod’s deities reproduce parthenogenetically: Chaos, Gaea, Night, Strife, and Hera, of whom all but the sexually indeterminate Chaos are female. Hesiod’s male gods have no analogous reproductive ability. The parthenogenetic phases of the early goddesses form much of the fundamental shape and character of the universe, while in the case of Hera, parthenogenesis serves initially as an act of defiance against Zeus but ultimately enforces his reign. Parthenogenesis does not have these functions in either the Near Eastern or other Greek cosmogonic traditions, a difference that reflects Hesiod’s greater emphasis on female participation in his succession myth. Yet Hesiod’s cosmogonic narrative, like others, culminates in the lasting reign of a male god, Zeus. In this context parthenogenesis is a manifestation of female creation, which ultimately reinforces the stability of a male sovereign. The relative prominence of parthenogenesis in the Theogony reflects Hesiod’s emphasis on gender difference and conflict as indispensable to a cosmos in which conflict and concord coexist as equal partners in creation and stability.
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Bode, Susanna Natalia Saskia. „Phylogeny and phylogeography of European sexual and asexual lineages of Eucypris virens (Crustacea:Ostracoda)“. Thesis, University of Sheffield, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531120.
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Phillips, Sarah Wynne. „Asexual overwintering and morph determination in the lettuce root aphid Pemphigus bursarius (L.)“. Thesis, University of Birmingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368424.
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Hanson, Sara Jeanette. „The molecular evolution of reproduction in animals: insights from sexual and asexual rotifers“. Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/1618.
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Sex and meiosis are ubiquitous in eukaryotes as the primary mode of reproduction. This suggests that despite the theoretical energetic advantages of asexual reproduction, organisms capable of sexual reproduction are at a much greater long-term evolutionary advantage. Rotifers, a group of microinvertebrates, offer unique opportunities to examine the evolution of sex due to their extensive proliferation, successful adaptation to a wide variety of ecological niches, and the diversity of reproductive modes represented in the group. The cyclically parthenogenetic monogonont rotifers have overcome constraints on the loss of sexual reproduction in order to frequently transition between sexual and asexual generations, making them a powerful system with which to address the maintenance of sex in animals. Obligately asexual bdelloid rotifers appear to have thrived without sex for tens of millions of years, a period of time much longer than expected given the hypothesized advantages of sexual reproduction. However, the molecular nature of sex and parthenogenesis is poorly understood in any rotifer species.
To expand our knowledge of the molecular mechanisms of monogonont reproduction, we sequenced genomes of two distantly related species, Brachionus calyciflorus and Brachionus manjavacas and identified over 80 homologs for genes involved in meiotic processes. Several of these genes have undergone duplication events specific to the monogonont lineage, including genes with known roles in regulation of cell cycle transitions during meiosis. In addition, global gene expression patterns were determined using obligate parthenogenetic (OP) and cyclical parthenogenetic (CP) strains of B. calyciflorus. Quantitative comparison of expression between these strains revealed differentially expressed genes specific to sexual and asexual reproduction in this species, including genes related to dormancy/resting egg formation, meiosis, and hormone signaling pathways that are thought to be involved in the induction of sexual reproduction in monogononts. Finally, we analyzed gene expression in bdelloid rotifers for evidence of sexual reproduction or the utilization of meiotic genes under conditions inducing high levels of recombination.
Through this work, we have established molecular markers for sexuality and asexuality in monogonont rotifers, and used these markers to evaluate reproduction in bdelloids. The data generated specifically allows for more informed analyses of the evolution of cyclical parthenogenesis and rotifer reproduction. Furthermore, this work extends the use of monogononts as a model system for addressing broader questions regarding the evolution of sexual reproduction.
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Audiffren, Julien. „Etude d'un système d'équations différentielles stochastiques : Le cliquet de Muller“. Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10124.
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Le cliquet de Muller est un modèle mathématiques illustrant l'accumulation de mutations délétères dans une population asexuée. L'idée principale est que l'absence de recombinaison oblige les enfants à avoir au moins autant de mutations nocives que leurs parents, et au bout d'un certain temps, le nombre minimum de mutations délétères de la population, qui est donc un processus croissant, augmente : on dit alors que le cliquet clique. Le modèle du cliquet de Muller qui est étudié dans cette thèse est un système infini d'équations différentielles stochastiques de Fleming-Viot couplées. On montre dans une première partie d'abord que le cliquet s'actionne en temps fini p.s., puis que l'espérance du temps mis pour cliquer est également finie. On utilise pour cela des comparaisons d'équations stochastiques et des changements de temps. Dans une deuxième partie, on démontre que ce modèle est équivalent à un modèle du look-down modifié auquel on a ajouté des mutations et des morts. Puis dans la troisième partie on généralise le résultat de la deuxième à un cadre plus large de systèmes d'équations différentielles stochastiquesMuller's Ratchet is a model from evolutionary theory describing the accumulation of deleterious mutations in asexually reproducing population. The lack of recombination implies that children have all the deleterious mutations of his parent. The minimal number of deleterious mutations carried in the population is an non-decreasing process, and if it increases we say that the Muller's ratchet clicks. The model studied in this thesis is an infinite system of stochastic differential equations. In the first chapter, we first prove that the ratchet clicks in finite time a.s., then that the clicking time has finite expectation. For this we use comparison arguments and time changes. In the second chapter, we prove that this model is equivalent to a modified look-down model with mutation and selection. In the third chapter we generalize the results of chapter 2 to a more general model
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Earnshaw, Diana Mary dos Santos. „Variation in aggressiveness and fungicide sensitivity in sexual and asexual progeny of Phytophthora infestans“. Thesis, Bangor University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409470.
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Riley, Rohan. „Clues of Sexual Reproduction in the 'Ancient Asexual' Fungal Lineage: The Arbuscular Mycorrhizal Fungi“. Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24035.
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Arbuscular mycorrhizal fungi (AMF) represent an ancient and critical symbiotic partner with
the majority of land plants, understood to promote ecosystem productivity and biodiversity and are also important to ecologically sound land management practices. The fungus is thought to be over 400 million years old, and due to a lack of an observable sexual cycle, has been placed into a select group of eukaryotes called 'ancient asexuals', which seemingly defy evolutionary theory by persisting for an extended period of time in the absence of sexual reproduction. Recently however, molecular evidence has accumulated which may suggest AMF harbour a cryptic sexual cycle. In the first chapter of this thesis, entitled "Searching for clues of sexual reproduction in the genomes of arbuscular mycorrhizal fungi",
I review evidence supporting this notion of a cryptic sexual cycle in AMF which includes:
the presence of recombinational events, meiosis-specific genes as well as mating-specific transcription factors called SexM and SexP of the MATA_HMG protein family which are
otherwise found only in the genomes of sexual fungi. In the second chapter, I present the
main research of my MSc work where I used bioinformatic, population genetic, molecular
and experimental approaches to build on this existing evidence of sexuality in AMF. These
findings include the presence of a dramatically expanded family of MAT-HMG genes which are present in several isolates of the Rhizophagus irregularis and also harbour significant allele variation amongst these isolates, some of which resembles variation expected at MAT-genes in other fungi. Q-RT-PCR procedures revealed that at least some of these genes tend to increase in expression during crosses of R. irregularis isolates. We also uncovered the presence of a unique genomic region where at least three of these genes are located in tandem. Finally, several tests of recombination support the presence of intraisolate as well as interisolate recombination events occurring between these MAT-HMG genes.
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Kay, William Tudor. „Novel insights into the asexual life-cycle of the wheat-leaf pathogen Zymoseptoria tritici“. Thesis, University of Exeter, 2017. http://hdl.handle.net/10871/31538.
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Zymoseptoria tritici, the causal agent of Septoria tritici blotch (STB), is the most economically important pathogen of wheat in temperate climates. EU spending on the control of STB is estimated at more than € 1.3 billion per annum, even when tolerant cultivars are used. This thesis comprises 5 data chapters each looking to ascertain reasons for the success of Z. tritici. Using mainly in vitro methods combined with confocal microscopy, this thesis explores asexual spore submergence in rain, epiphytic development, the potential triggers for pycnidiation, low-nutrient ex planta survival, and soil treatments as a novel method of control. Novel findings include that (i) submergence leads to a form of spore dormancy, (ii) epiphytic development is more extensive than previously thought with hyphal growth and sporulation both occurring readily over a 21 day period, (iii) pycnidiation is a rapid, deterministic developmental process, triggered by contents of lysed plant cells, (iv) asexual spores have the capacity to survive for many weeks in low-nutrient environments, and finally (v) that treating soil-borne environmental spores may be a novel way to reduce field inoculum levels before a new crop is sown. Collectively these results provide many new insights in to the behaviour of Z. tritici during its disease cycle. This thesis proposes an updated version of the life cycle for this devastating fungal pathogen and argues that current methods of control are not adequate long-term.
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Kitade, Yuki. „Functional analysis of signaling components regulating pathogenicity and asexual/sexual development in Bipolaris maydis“. Kyoto University, 2019. http://hdl.handle.net/2433/242717.
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Kyoto University (京都大学)0048
新制・課程博士
博士(農学)
甲第21840号
農博第2353号
新制||農||1069(附属図書館)
学位論文||H31||N5212(農学部図書室)
京都大学大学院農学研究科地域環境科学専攻
(主査)教授 田中 千尋, 教授 本田 与一, 准教授 刑部 正博
学位規則第4条第1項該当
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Li, Dan. „A map kinase pathway essential for mating and contributing to asexual development in Neurospora Crassa“. Texas A&M University, 2003. http://hdl.handle.net/1969.1/3936.
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MAP kinases and transcription factors homologous to Saccharomyces cerevisiae
Fus3p/Kss1p and Ste12p have been identified in several plant pathogenic fungi and
found to be required for pathogenicity and sexual reproduction. A gene encoding the
homolog of Fus3p/Kss1p in Neurospora crassa was isolated previously and named mak-
2 (mitogen activated kinase -2). This dissertation describes the isolation of the Ste12p
homolog, pp-1 (protoperithecia-1) and the comparison of the phenotypes of the mak-2
and pp-1 mutants. The similar phenotypes of the mak-2 and pp-1 null mutants suggest
that these proteins are part of the same MAP kinase signaling cascade in N. crassa. In
addition to reduced growth rate, the phenotypes of the mutants demonstrate that this
pathway is required for female fertility, contributes to aerial hyphal development and
repression of conidiophore development. The mak-2 MAP kinase pathway also regulates
several genes putatively involved in secondary metabolism during the mating process.
Among these is a gene cluster that is likely to be involved in the production of a
polyketide secondary metabolite. An orthologous gene cluster was also identified in M.
grisea, and the structural and functional homology of these two related gene clusters was
characterized. Microarray analysis was used to extend the analysis of gene expression in
mak-2 and pp-1 mutants, and a number of downstream target genes of the MAP kinase
pathway were identified and called mak-2 kinase-regulated genes (mkr). A model of this
MAP kinase pathway in N. crassa was developed. Since N. crassa is a saprophytic
fungus but closely related to several plant pathogens, this research may provide an
important perspective on the evolution of a major regulatory pathway governing fungal
pathogenesis.
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Ma, Xiping. „Effects of environmental factors on distribution and asexual reproduction of the invasive hydrozoan, Moerisia lyonsi“. College Park, Md. : University of Maryland, 2003. http://hdl.handle.net/1903/99.
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Thesis (M.S.) -- University of Maryland, College Park, 2003.Thesis research directed by: Marine, Estuarine, Environmental Sciences Graduate Program. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Kownatzki, Dierk. „Asexuelle und sexuelle Reproduktion bei der Vogelkirsche (Prunus avium L.)“. [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=963808451.
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Awah, Nancy. „Studies on Plasmodium falciparum asexual blood stage antigens : RAP-2/RSP-2 and Pf332 in focus“. Doctoral thesis, Stockholms universitet, Wenner-Grens institut, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-57255.
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The life cycle of the malaria parasite is very complex and provides a number of potential targets for vaccination. In this thesis, data on two plasmodial asexual blood stage antigens (RAP-2 and Pf332) are presented. A partial aim of the work presented herein was to investigate the mechanisms responsible for the destruction of erythroid cells in anaemia, and more specifically to define the role of the rhoptry associated protein (RAP)-2 and other members of the RAP complex, RAP-1 and -3 in processes resulting in anaemia. Antibodies to the RAP complex were shown to have the potential to mediate the destruction of RAP-2-tagged erythroid cells by phagocytosis or by complement activation and lysis. In addition, antibodies to RAP-1 and RAP-2 could induce the apoptotic death of RAP-2- tagged erythroblasts. The frequency and functionality of naturally occurring RAP-2 antibodies in the sera of anaemic and non-anaemic Cameroonian children were also investigated. All sera tested contained RAP-2-reactive antibodies by both immunofluorescence and flow cytometry. The anaemic group of children had higher levels of IgG than the non-anaemic ones, while the levels of IgM were similar. With respect to IgG subclasses, higher levels of IgG3 were seen in the non-anaemic individuals as compared to anaemic subjects. The non-anaemic individuals recognised a greater proportion of RAP-2-tagged RBCs and activated complement to a greater extent than the anaemic ones. Earlier studies observed that humans continuously exposed to malaria, recognised Pf332 extensively. Further studies revealed that Pf332 antibodies were able to inhibit parasite growth and cytoadherence in vitro. Making use of Pf332-C231, a sub-fragment of Pf332, we studied the effects/mode of action of C231-specific antibodies on P. falciparum parasite growth and development in vitro. The antibodies appeared to act mainly on late stage parasites by two main mechanisms: 1) through the induction of abnormal/pyknotic parasites, and, 2) RBC lysis (disintegration of RBCs), thus limiting parasite growth and development. The antibody isotype in this context was IgG. Following the removal of immune pressure, parasites resumed growth, albeit at a much slower rate. The results suggest that during natural infections, antibodies to C231 could play a role in parasite control. In summary, these data suggest that antibodies to both antigens could be instrumental in immune responses leading to disease control, but could also mediate pathology.At the time of the doctoral defense, the following publication was unpublished and had a status as follows: Paper 3: Manuscript.
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Blanco, Paananen Adrian, und Johan Storby. „Observing coevolution in simulated bacteria : Using asexual reproduction and simple direct mapped functions for decision-making“. Thesis, KTH, Skolan för datavetenskap och kommunikation (CSC), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-146346.
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In this report we have presented the results of a program which performs simula- tions of artificial bacteria with the ability to evolve different characteristics and behaviours through genetic algorithms. Over time unfit bacteria will die out, and the more fit bacteria will produce offspring with slightly mutated variants of it’s genetic code resembling the evolutionary process. The simulation does not follow the traditional macro-scale hand-picked sexual reproduction often used in genetic algorithms to produce optimal results, but it instead uses individ- ual asexual reproduction which more closely resembles how bacteria reproduce in nature. Furthermore we do not use traditional neural networks for decision making, but simple functions which directly map the bacterias inputs to their decisions. The purpose of this study was to observe whether bacteria with different initial starting populations would coevolve, and specialize into heterogeneous populations. Furthermore we have tried to analyze how the populations inter- act with each other and how changing the different parameters of the simulation would affect the populations. We have performed three separate experiments that differ in their initial conditions, one with pre-created and heterogeneous herbivores and carnivores, one with homogeneous omnivores, and one with bac- teria whose genetic values have been decided at random. The result of our experiments was that we observed coevolution in the bacteria, and that they would despite very different initial starting conditions always grow towards sta- ble heterogeneous populations with very few exceptions.
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Thompson, Faye Laura. „Somatic, genetic and evolutionary trade-offs between sexual and asexual reproduction in a clonal aquatic plant“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2002. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ65650.pdf.
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Piquot, Yves. „Evolution d'un systeme de reproduction mixte sexuee-asexuee approche genetique et ecologique chez sparganium erectum l“. Paris 11, 1996. http://www.theses.fr/1996PA112301.
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Sparganium erectum (le rubanier), comme la majorite des plantes perennes, se reproduit a la fois de facon sexuee et de facon vegetative. Le cout ecologique et genetique de la reproduction secuee, nous a amene a poser la question de la stabilite a l'echelle de l'espece d'un systeme de reproduction mixte sexuee-asexuee par rapport a un mode de reproduction exclusivement vegetatif. Nous avons aborde cette question (1) par l'identification de marqueurs moleculaires et allozymiques permettant de determiner dans quelles mesures les populations naturelles se distinguent par leur diversite genotypique et (2) a travers une etude in situ et en conditions controlees de mettre en relation la valeur des traits d'histoire de vie avec d'une part l'age des populations et d'autre part leur diversite genetique. Nous avons trouve les diversites genetiques les plus eleves (et les investissements les plus eleves a la reproduction sexuee) dans les jeunes populations tandis que les diversites clonales les plus faibles (et les investissements les plus faibles a la reproduction sexuee) ont ete detectes dans les populations anciennes. Ces caracteristiques genetiques et ecologiques refletent la perte de la fonction sexuee a l'echelle de la population. Cette transition pourrait etre le resultat d'une augmentation de la competition entre les clones conduisant a la selection des genotypes favorisant la reproduction vegetative et d'une contre-selection de la reproduction sexuee. Nous suggerons, a partir du modele d'olivieri et al. (1995), qu'un systeme de reproduction mixte peut etre maintenu par l'interaction de deux echelles de selection: une selection intra-population en faveur de la multiplication vegetative et une selection en faveur de la production de graines a l'echelle de la metapopulation
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Crabtree, Sheri Beth. „SEXUAL AND ASEXUAL REPRODUCTIVE CHARACTERISTICS OF THE NORTH AMERICAN PAWPAW [ASIMINA TRILOBA (L.) DUNAL]“. Lexington, Ky. : [University of Kentucky Libraries], 2004. http://lib.uky.edu/ETD/ukypssc2004t00208/etd.pdf.
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Thesis (m.s.)--University of Kentucky, 2004.Title from document title page (viewed Jan. 7, 2005). Document formatted into pages; contains viii, 80p. : ill. Includes abstract and vita. Includes bibliographical references (p. 74-79).
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Widmer, Chad L. „Influences of temperature and salinity on asexual reproduction and development of scyphozoan jellyfish from the British Isles“. Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/6326.
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Jellyfish (Phylum Cnidaria, Class Scyphozoa) play important roles in pelagic ecosystems as predators and prey. Seasonally they form blooms facilitating reproductive success, but that are at times problematic for human enterprise. Medusa abundance has been correlated with environmental variables in several instances. However, the direct mechanisms for changes in medusa abundance are unclear. As global sea surface temperatures continue to change there is increasing concern that warming may enhance conditions favourable for the generation of jellyfish medusae. It is important to understand the ways in which temperature affects all life history stages of jellyfish if we are to begin to understand factors associated with jellyfish bloom formations, but how temperature and salinity affects life history stages of scyphozoan jellyfish from British waters remains largely unknown. In Chapter 1 I provide a general introduction to some key issues important to the formation of jellyfish blooms. In Chapter 2 I present results for experiments testing the effects of temperature on settlement and metamorphosis of planulae larvae of Cyanea capillata, Cyanea lamarckii, Chyrsaora hysoscella, and Aurelia aurita. Chapter 3 reports on the effects of temperature and salinity on survival, and asexual reproduction of scyphistomae of the same species. Chapter 4 reports on the effects of temperature and salinity on growth of newly released ephyrae of each of the above mentioned species, as well as the effects of starvation on survivorship on ephyrae of A. aurita originating from two distinct populations of scyphistomae. In Chapter 5 I provide a brief summary of significant findings for each life history stage, their theoretical implications when taken together, and next steps for future research. I also offer recommendations for ecosystem managers with an eye toward affecting the numbers of near-shore jellyfish medusae generated each season in the waters surrounding the British Isles.