Segui questo link per vedere altri tipi di pubblicazioni sul tema: Asexuel.
Articoli di riviste sul tema "Asexuel"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 articoli di riviste per l'attività di ricerca sul tema "Asexuel".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi gli articoli di riviste di molte aree scientifiche e compila una bibliografia corretta.
1
Key, Adam. "The Silent A". Journal of Autoethnography 2, n. 4 (2021): 446–65. http://dx.doi.org/10.1525/joae.2021.2.4.446.
Testo completoAbstract (sommario):
This critical autoethnography explores experiences as an asexual cismale and the inherent tensions and struggles experienced in the dialectic between societal expectations of sexual desire as a man and the lack of sex drive characteristic of an asexual orientation. It explores the exclusion asexuals experience, as they occupy a third space between straightness and queerness, leaving them nowhere in either the gender or sexuality roles spectrums to truly call home. As asexuals exist in a space not often considered by heterosexual and queer individuals and asexual men exist between the tension of sexual expectation and orientation, music is utilized as a means of common language. This essay offers this connection through a series of autoethnographic glimpses, each set to a different song or lyric, as a soundtrack to give voice to the silenced experiences of asexuals.
2
Tobler, M., e I. Schlupp. "Expanding the horizon: the Red Queen and potential alternatives". Canadian Journal of Zoology 86, n. 8 (agosto 2008): 765–73. http://dx.doi.org/10.1139/z08-056.
Testo completoAbstract (sommario):
The Red Queen hypothesis (RQH) is one of the most widely accepted hypotheses explaining the persistence of sexual reproduction despite its costs. It posits that sexual species, compared with asexuals, are more adept at countering parasites, because their per-generation recombination rate is higher. Despite theoretical support, current empirical studies have failed to provide unanimous support. Here, we suggest that future tests of the RQH should more thoroughly elucidate its underlying assumptions and potential alternative hypotheses. While the RQH predicts that negative frequency-dependent selection shapes host–parasite interactions, differences between sexuals and asexuals are potentially important. Key assumptions about asexual species and their sexual close relatives include (i) ecological and behavioral traits are similar, (ii) among-individual genetic diversity is greater in sexuals than in asexuals, and (iii) within-individual genetic diversity is similar in asexuals and sexuals. We review current evidence for the RQH, highlight differences between asexual and sexual species and how those differences might translate into differential responses to parasite infections, and discuss how they can influence the results and interpretation of empirical studies. Considering differences between asexual and sexual species in future tests of the RQH will help to refine predictions and eliminate alternative hypotheses.
3
Scheu, S., e B. Drossel. "Sexual reproduction prevails in a world of structured resources in short supply". Proceedings of the Royal Society B: Biological Sciences 274, n. 1614 (27 febbraio 2007): 1225–31. http://dx.doi.org/10.1098/rspb.2007.0040.
Testo completoAbstract (sommario):
We present a model for the maintenance of sexual reproduction based on the availability of resources, which is the strongest factor determining the growth of populations. The model compares completely asexual species to species that switch between asexual and sexual reproduction (sexual species). Key features of the model are that sexual reproduction sets in when resources become scarce, and that at a given place only a few genotypes can be present at the same time. We show that under a wide range of conditions the sexual species outcompete the asexual ones. The asexual species win only when survival conditions are harsh and death rates are high, or when resources are so little structured or consumer genotypes are so manifold that all resources are exploited to the same extent. These conditions, largely represent the conditions in which sexuals predominate over asexuals in the field.
4
Larose, Chloé, Darren J. Parker e Tanja Schwander. "Fundamental and realized feeding niche breadths of sexual and asexual stick insects". Proceedings of the Royal Society B: Biological Sciences 285, n. 1892 (28 novembre 2018): 20181805. http://dx.doi.org/10.1098/rspb.2018.1805.
Testo completoAbstract (sommario):
The factors contributing to the maintenance of sex over asexuality in natural populations remain unclear. Ecological divergences between sexual and asexual lineages could help to maintain reproductive polymorphisms, at least transiently, but the consequences of asexuality for the evolution of ecological niches are unknown. Here, we investigated how niche breadths change in transitions from sexual reproduction to asexuality. We used host plant ranges as a proxy to compare the realized feeding niche breadths of five independently derived asexual Timema stick insect species and their sexual relatives at both the species and population levels. Asexual species had systematically narrower realized niches than sexual species, though this pattern was not apparent at the population level. To investigate how the narrower realized niches of asexual species arise, we performed feeding experiments to estimate fundamental niche breadths but found no systematic differences between reproductive modes. The narrow realized niches found in asexual species are therefore probably a consequence of biotic interactions such as predation or competition, that constrain realized niche size in asexuals more strongly than in sexuals.
5
Riesch, Rüdiger, Ingo Schlupp e Martin Plath. "Female sperm limitation in natural populations of a sexual/asexual mating complex ( Poecilia latipinna , Poecilia formosa )". Biology Letters 4, n. 3 (4 marzo 2008): 266–69. http://dx.doi.org/10.1098/rsbl.2008.0019.
Testo completoAbstract (sommario):
In sperm-dependent sexual/asexual mating systems, male mate choice is critical for understanding the mechanisms behind apparent stability observed in natural populations. The gynogenetic Amazon molly ( Poecilia formosa ) requires sperm from sexual males (e.g. Poecilia latipinna ) to trigger embryogenesis, but inheritance is strictly maternal. Consequently, males should try to avoid or reduce the cost of mating with asexuals. We investigated male mate choice by documenting the presence of sperm in natural populations and found that a higher proportion of sexual females had sperm than asexuals. In addition, among those females that had sperm, sexuals had more sperm than asexuals. Our results hint at a role for male mate choice as a stabilizing factor in such systems.
6
Carranza, Juan, e Vicente Polo. "Sexual reproduction with variable mating systems can resist asexuality in a rock–paper–scissors dynamics". Royal Society Open Science 2, n. 7 (luglio 2015): 140383. http://dx.doi.org/10.1098/rsos.140383.
Testo completoAbstract (sommario):
While sex can be advantageous for a lineage in the long term, we still lack an explanation for its maintenance with the twofold cost per generation. Here we model an infinite diploid population where two autosomal loci determine, respectively, the reproductive mode, sexual versus asexual and the mating system, polygynous (costly sex) versus monogamous (assuming equal contribution of parents to offspring, i.e. non-costly sex). We show that alleles for costly sex can spread when non-costly sexual modes buffer the interaction between asexual and costly sexual strategies, even without twofold benefit of recombination with respect to asexuality. The three interacting strategies have intransitive fitness relationships leading to a rock–paper–scissors dynamics, so that alleles for costly sex cannot be eliminated by asexuals in most situations throughout the parameter space. Our results indicate that sexual lineages with variable mating systems can resist the invasion of asexuals and allow for long-term effects to accumulate, thus providing a solution to the persisting theoretical question of why sex was not displaced by asexuality along evolution.
7
Amat, Isabelle, Jacques J. M. van Alphen, Alex Kacelnik, Emmanuel Desouhant e Carlos Bernstein. "Adaptations to different habitats in sexual and asexual populations of parasitoid wasps: a meta-analysis". PeerJ 5 (12 settembre 2017): e3699. http://dx.doi.org/10.7717/peerj.3699.
Testo completoAbstract (sommario):
BackgroundCoexistence of sexual and asexual populations remains a key question in evolutionary ecology. We address the question how an asexual and a sexual form of the parasitoidVenturia canescenscan coexist in southern Europe. We test the hypothesis that both forms are adapted to different habitats within their area of distribution. Sexuals inhabit natural environments that are highly unpredictable, and where density of wasps and their hosts is low and patchily distributed. Asexuals instead are common in anthropic environments (e.g., grain stores) where host outbreaks offer periods when egg-load is the main constraint on reproductive output.MethodsWe present a meta-analysis of known adaptations to these habitats. Differences in behavior, physiology and life-history traits between sexual and asexual wasps were standardized in term of effect size (Cohen’sdvalue; Cohen, 1988).ResultsSeeking consilience from the differences between multiple traits, we found that sexuals invest more in longevity at the expense of egg-load, are more mobile, and display higher plasticity in response to thermal variability than asexual counterparts.DiscussionThus, each form has consistent multiple adaptations to the ecological circumstances in the contrasting environments.
8
Stelzer, Claus-Peter. "Does the avoidance of sexual costs increase fitness in asexual invaders?" Proceedings of the National Academy of Sciences 112, n. 29 (21 luglio 2015): 8851–58. http://dx.doi.org/10.1073/pnas.1501726112.
Testo completoAbstract (sommario):
The high prevalence of sexual reproduction is considered a paradox mainly for two reasons. First, asexuals should enjoy various growth benefits because they seemingly rid themselves of the many inefficiencies of sexual reproduction—the so-called costs of sex. Second, there seems to be no lack of asexual origins because losses of sexual reproduction have been described in almost every larger eukaryotic taxon. Current attempts to resolve this paradox concentrate on a few hypotheses that provide universal benefits that would compensate for these costs and give sexual reproduction a net advantage. However, are new asexual lineages really those powerful invaders that could quickly displace their sexual ancestors? Research on the costs of sex indicates that sex is often stabilized by highly lineage-specific mechanisms. Two main categories can be distinguished. First are beneficial traits that evolved within a particular species and became tightly associated with sex (e.g., a mating system that involves sexual selection, or a sexual diapausing stage that allows survival through harsh periods). If such traits are absent in asexuals, simple growth efficiency considerations will not capture the fitness benefits gained by skipping sexual reproduction. Second, lineage-specific factors might prevent asexuals from reaching their full potential (e.g., dependence on fertilization in sperm-dependent parthenogens). Such observations suggest that the costs of sex are highly variable and often lower than theoretical considerations suggest. This has implications for the magnitude of universal benefits required to resolve the paradox of sex.
9
Stelzer, Claus-Peter, e Jussi Lehtonen. "Diapause and maintenance of facultative sexual reproductive strategies". Philosophical Transactions of the Royal Society B: Biological Sciences 371, n. 1706 (19 ottobre 2016): 20150536. http://dx.doi.org/10.1098/rstb.2015.0536.
Testo completoAbstract (sommario):
Facultative sex combines sexual and asexual reproduction in the same individual (or clone) and allows for a large diversity of life-history patterns regarding the timing, frequency and intensity of sexual episodes. In addition, other life-history traits such as a diapause stage may become linked to sex. Here, we develop a matrix modelling framework for addressing the cost of sex in facultative sexuals, in constant, periodic and stochastically fluctuating environments. The model is parametrized using life-history data from Brachionus calyciflorus , a facultative sexual rotifer in which sex and diapause are linked. Sexual propensity was an important driver of costs in constant environments, in which high costs (always > onefold, and sometimes > twofold) indicated that asexuals should outcompete facultative sexuals. By contrast, stochastic environments with high temporal autocorrelation favoured facultative sex over obligate asex, in particular, if the penalty to fecundity in ‘bad’ environments was large. In such environments, obligate asexuals were constrained by their life cycle length (i.e. time from birth to last reproductive adult age class), which determined an upper limit to the number of consecutive bad periods they could tolerate. Nevertheless, when facultative asexuals with different sexual propensities competed simultaneously against each other and asex, the lowest sex propensity was the most successful in stochastic environments with positive autocorrelation. Our results suggest that a highly specific mechanism (i.e. diapause linked to sex) can alone stabilize facultative sex in these animals, and protect it from invasion of both asexual and pure sexual strategies. This article is part of the themed issue ‘Weird sex: the underappreciated diversity of sexual reproduction’.
10
Choleva, Lukáš, Apostolos Apostolou, Petr Ráb e Karel Janko. "Making it on their own: sperm-dependent hybrid fishes ( Cobitis ) switch the sexual hosts and expand beyond the ranges of their original sperm donors". Philosophical Transactions of the Royal Society B: Biological Sciences 363, n. 1505 (2 giugno 2008): 2911–19. http://dx.doi.org/10.1098/rstb.2008.0059.
Testo completoAbstract (sommario):
Interspecific hybridization may result in asexual hybrid lineages that reproduce via parthenogenesis. Contrary to true parthenogens, sperm-dependent asexuals (gynogens and hybridogens) are restricted to the range of bisexual species, generally the parental taxa, by their need for a sperm donor. It has been documented that asexual lineages may rarely use sperm from a non-parental species or even switch a host. The available literature reports do not allow distinguishing, between whether such host switches arise by the expansion of asexuals out of their parental's range (and into that of another's) or by the local extinction of a parental population followed by a host switch. The present study combines new and previously collected data on the distribution and history of gynogenetic spined loaches ( Cobitis ) of hybrid origin. We identified at least three clonal lineages that have independently switched their sperm dependency to different non-parental Cobitis species, and in cases incorporated their genomes. Our current knowledge of European Cobitis species and their hybrids suggests that this pattern most probably results from the expansion of gynogenetic lineages into new areas. Such expansion was independent of the original parental species. This suggests that sperm dependence is not as restrictive to geographical expansion when compared with true parthenogenesis as previously thought.
11
Schwander, Tanja, Bernard J. Crespi, Regine Gries e Gerhard Gries. "Neutral and selection-driven decay of sexual traits in asexual stick insects". Proceedings of the Royal Society B: Biological Sciences 280, n. 1764 (7 agosto 2013): 20130823. http://dx.doi.org/10.1098/rspb.2013.0823.
Testo completoAbstract (sommario):
Environmental shifts and lifestyle changes may result in formerly adaptive traits becoming non-functional or maladaptive. The subsequent decay of such traits highlights the importance of natural selection for adaptations, yet its causes have rarely been investigated. To study the fate of formerly adaptive traits after lifestyle changes, we evaluated sexual traits in five independently derived asexual lineages, including traits that are specific to males and therefore not exposed to selection. At least four of the asexual lineages retained the capacity to produce males that display normal courtship behaviours and are able to fertilize eggs of females from related sexual species. The maintenance of male traits may stem from pleiotropy, or from these traits only regressing via drift, which may require millions of years to generate phenotypic effects. By contrast, we found parallel decay of sexual traits in females. Asexual females produced altered airborne and contact signals, had modified sperm storage organs, and lost the ability to fertilize their eggs, impeding reversals to sexual reproduction. Female sexual traits were decayed even in recently derived asexuals, suggesting that trait changes following the evolution of asexuality, when they occur, proceed rapidly and are driven by selective processes rather than drift.
12
BSc, Erin Hampson. "Negotiating (in)visibility: A phenomenological analysis of asexual students’ experiences of university". Psychology of Sexualities Review 11, n. 1 (2020): 26–41. http://dx.doi.org/10.53841/bpssex.2020.11.1.26.
Testo completoAbstract (sommario):
Asexuality research is an emerging topic and understanding gained through the perspectives of asexuals offer insights into how asexuality is experienced within social contexts. This exploratory study sought to understand the everyday experiences of self-identified asexuals within university contexts, the challenges they face and the ways in which these are understood and navigated. Four participants, attending UK universities, were recruited through lesbian, gay, bisexual, trans, queer, intersex and asexual (LGBTQIA+) Facebook groups. Data was collected through photo-elicitation interviews and analysed using interpretive phenomenological analysis, through which three superordinate themes were developed: navigating normative social space, navigating (in)visibility and coming out and creating safer spaces. These, along with their subordinate themes, are outlined and then discussed in relation to existing literature and recommendations for future research are made.
13
Orr, H. Allen. "The Rate of Adaptation in Asexuals". Genetics 155, n. 2 (1 giugno 2000): 961–68. http://dx.doi.org/10.1093/genetics/155.2.961.
Testo completoAbstract (sommario):
Abstract I study the population genetics of adaptation in asexuals. I show that the rate of adaptive substitution in an asexual species or nonrecombining chromosome region is a bell-shaped function of the mutation rate: at some point, increasing the mutation rate decreases the rate of substitution. Curiously, the mutation rate that maximizes the rate of adaptation depends solely on the strength of selection against deleterious mutations. In particular, adaptation is fastest when the genomic rate of mutation, U, equals the harmonic mean of selection coefficients against deleterious mutations, where we assume that selection for favorable alleles is milder than that against deleterious ones. This simple result is independent of the shape of the distribution of effects among favorable and deleterious mutations, population size, and the action of clonal interference. In the course of this work, I derive an approximation to the probability of fixation of a favorable mutation in an asexual genome or nonrecombining chromosome region in which both favorable and deleterious mutations occur.
14
Auld, Stuart K. J. R., Shona K. Tinkler e Matthew C. Tinsley. "Sex as a strategy against rapidly evolving parasites". Proceedings of the Royal Society B: Biological Sciences 283, n. 1845 (28 dicembre 2016): 20162226. http://dx.doi.org/10.1098/rspb.2016.2226.
Testo completoAbstract (sommario):
Why is sex ubiquitous when asexual reproduction is much less costly? Sex disrupts coadapted gene complexes; it also causes costs associated with mate finding and the production of males who do not themselves bear offspring. Theory predicts parasites select for host sex, because genetically variable offspring can escape infection from parasites adapted to infect the previous generations. We examine this using a facultative sexual crustacean, Daphnia magna, and its sterilizing bacterial parasite, Pasteuria ramosa . We obtained sexually and asexually produced offspring from wild-caught hosts and exposed them to contemporary parasites or parasites isolated from the same population one year later. We found rapid parasite adaptation to replicate within asexual but not sexual offspring. Moreover, sexually produced offspring were twice as resistant to infection as asexuals when exposed to parasites that had coevolved alongside their parents (i.e. the year two parasite). This fulfils the requirement that the benefits of sex must be both large and rapid for sex to be favoured by selection.
15
Krois, Nicole R., Anvesh Cherukuri, Nikhil Puttagunta e Maurine Neiman. "Higher rate of tissue regeneration in polyploid asexual versus diploid sexual freshwater snails". Biology Letters 9, n. 4 (23 agosto 2013): 20130422. http://dx.doi.org/10.1098/rsbl.2013.0422.
Testo completoAbstract (sommario):
Characterizing phenotypic differences between sexual and asexual organisms is a critical step towards understanding why sexual reproduction is so common. Because asexuals are often polyploid, understanding how ploidy influences phenotype is directly relevant to the study of sex and will provide key insights into the evolution of ploidy-level variation. The well-established association between genome size and cell cycle duration, evidence for a link between genome size and tissue regeneration rate and the growing body of research showing that ploidy influences growth rate and gene expression led us to hypothesize that healing and tissue regeneration might be affected by ploidy-level variation. We evaluated this hypothesis by measuring the rate of regeneration of antenna tissue of Potamopyrgus antipodarum , a New Zealand snail characterized by frequent coexistence between diploid sexuals and polyploid asexuals. Antennae of triploid and presumptive tetraploid asexuals regenerated more rapidly than the antennae of diploid sexuals, but regeneration rate did not differ between triploids and tetraploids. These results suggest either that ploidy elevation has nonlinear positive effects on tissue regeneration and/or that factors associated directly with reproductive mode affect regeneration rate more than ploidy level. The results of this study also indicate that the lower ploidy of sexual P. antipodarum is unlikely to confer advantages associated with more rapid regeneration.
16
Schön, Isa, Fernando Rodriguez, Matthew Dunn, Koen Martens, Michael Shribak e Irina R. Arkhipova. "A Survey of Transposon Landscapes in the Putative Ancient Asexual Ostracod Darwinula stevensoni". Genes 12, n. 3 (11 marzo 2021): 401. http://dx.doi.org/10.3390/genes12030401.
Testo completoAbstract (sommario):
How asexual reproduction shapes transposable element (TE) content and diversity in eukaryotic genomes remains debated. We performed an initial survey of TE load and diversity in the putative ancient asexual ostracod Darwinula stevensoni. We examined long contiguous stretches of DNA in clones from a genomic fosmid library, totaling about 2.5 Mb, and supplemented these data with results on TE abundance and diversity from an Illumina draft genome. In contrast to other TE studies in putatively ancient asexuals, which revealed relatively low TE content, we found that at least 19% of the fosmid dataset and 26% of the genome assembly corresponded to known transposons. We observed a high diversity of transposon families, including LINE, gypsy, PLE, mariner/Tc, hAT, CMC, Sola2, Ginger, Merlin, Harbinger, MITEs and helitrons, with the prevalence of DNA transposons. The predominantly low levels of sequence diversity indicate that many TEs are or have recently been active. In the fosmid data, no correlation was found between telomeric repeats and non-LTR retrotransposons, which are present near telomeres in other taxa. Most TEs in the fosmid data were located outside of introns and almost none were found in exons. We also report an N-terminal Myb/SANT-like DNA-binding domain in site-specific R4/Dong non-LTR retrotransposons. Although initial results on transposable loads need to be verified with high quality draft genomes, this study provides important first insights into TE dynamics in putative ancient asexual ostracods.
17
Stöck, Matthias, Dmitrij Dedukh, Radka Reifová, Dunja K. Lamatsch, Zuzana Starostová e Karel Janko. "Sex chromosomes in meiotic, hemiclonal, clonal and polyploid hybrid vertebrates: along the ‘extended speciation continuum'". Philosophical Transactions of the Royal Society B: Biological Sciences 376, n. 1833 (26 luglio 2021): 20200103. http://dx.doi.org/10.1098/rstb.2020.0103.
Testo completoAbstract (sommario):
We review knowledge about the roles of sex chromosomes in vertebrate hybridization and speciation, exploring a gradient of divergences with increasing reproductive isolation (speciation continuum). Under early divergence, well-differentiated sex chromosomes in meiotic hybrids may cause Haldane-effects and introgress less easily than autosomes. Undifferentiated sex chromosomes are more susceptible to introgression and form multiple (or new) sex chromosome systems with hardly predictable dominance hierarchies. Under increased divergence, most vertebrates reach complete intrinsic reproductive isolation. Slightly earlier, some hybrids (linked in ‘the extended speciation continuum') exhibit aberrant gametogenesis, leading towards female clonality. This facilitates the evolution of various allodiploid and allopolyploid clonal (‘asexual’) hybrid vertebrates, where ‘asexuality' might be a form of intrinsic reproductive isolation. A comprehensive list of ‘asexual' hybrid vertebrates shows that they all evolved from parents with divergences that were greater than at the intraspecific level (K2P-distances of greater than 5–22% based on mtDNA). These ‘asexual' taxa inherited genetic sex determination by mostly undifferentiated sex chromosomes. Among the few known sex-determining systems in hybrid ‘asexuals', female heterogamety (ZW) occurred about twice as often as male heterogamety (XY). We hypothesize that pre-/meiotic aberrations in all-female ZW-hybrids present Haldane-effects promoting their evolution. Understanding the preconditions to produce various clonal or meiotic allopolyploids appears crucial for insights into the evolution of sex, ‘asexuality' and polyploidy. This article is part of the theme issue ‘Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part II)’.
18
Hörandl, Elvira. "Geographical Parthenogenesis in Alpine and Arctic Plants". Plants 12, n. 4 (13 febbraio 2023): 844. http://dx.doi.org/10.3390/plants12040844.
Testo completoAbstract (sommario):
The term “Geographical parthenogenesis” describes the phenomenon that asexual organisms usually occupy larger and more northern distribution areas than their sexual relatives, and tend to colonize previously glaciated areas. Several case studies on alpine and arctic plants confirm the geographical pattern, but the causal factors behind the phenomenon are still unclear. Research of the last decade in several plant families has shed light on the question and evaluated some of the classical evolutionary theories. Results confirmed, in general, that the advantages of uniparental reproduction enable apomictic plants to re-colonize faster in larger and more northern distribution areas. Associated factors like polyploidy seem to contribute mainly to the spatial separation of sexual and asexual cytotypes. Ecological studies suggest a better tolerance of apomicts to colder climates and temperate extremes, whereby epigenetic flexibility and phenotypic plasticity play an important role in occupying ecological niches under harsh conditions. Genotypic diversity appears to be of lesser importance for the distributional success of asexual plants. Classical evolutionary theories like a reduced pressure of biotic interactions in colder climates and hence an advantage to asexuals (Red Queen hypothesis) did not gain support from studies on plants. However, it is also still enigmatic why sexual outcrossing remains the predominant mode of reproduction also in alpine floras. Constraints for the origin of apomixis might play a role. Interestingly, some studies suggest an association of sexuality with abiotic stresses. Light stress in high elevations might explain why most alpine plants retain sexual reproduction despite other environmental factors that would favor apomixis. Directions for future research will be given.
19
Wilson, Christopher G., e Paul W. Sherman. "Spatial and temporal escape from fungal parasitism in natural communities of anciently asexual bdelloid rotifers". Proceedings of the Royal Society B: Biological Sciences 280, n. 1765 (22 agosto 2013): 20131255. http://dx.doi.org/10.1098/rspb.2013.1255.
Testo completoAbstract (sommario):
Sexual reproduction is costly, but it is nearly ubiquitous among plants and animals, whereas obligately asexual taxa are rare and almost always short-lived. The Red Queen hypothesis proposes that sex overcomes its costs by enabling organisms to keep pace with coevolving parasites and pathogens. If so, the few cases of stable long-term asexuality ought to be found in groups whose coevolutionary interactions with parasites are unusually weak. In theory, antagonistic coevolution will be attenuated if hosts disperse among patches within a metapopulation separately from parasites and more rapidly. We examined whether these conditions are met in natural communities of bdelloid rotifers, one of the longest-lived asexual lineages. At any life stage, these microscopic invertebrates can tolerate the complete desiccation of their ephemeral freshwater habitats, surviving as dormant propagules that are readily carried by the wind. In our field experiments, desiccation and wind transport enabled bdelloids to disperse independently of multiple fungal parasites, in both time and space. Surveys of bdelloid communities in unmanipulated moss patches confirmed that fungal parasitism was negatively correlated with extended drought and increasing height (exposure to wind). Bdelloid ecology therefore matches a key condition of models in which asexuals persist through spatio-temporal decoupling from coevolving enemies.
20
Boyer, Loreleï, Roula Jabbour-Zahab, Pauline Joncour, Sylvain Glémin, Christoph R. Haag e Thomas Lenormand. "Asexual male production by ZW recombination in Artemia parthenogenetica". Evolution 77, n. 1 (8 dicembre 2022): 1–12. http://dx.doi.org/10.1093/evolut/qpac008.
Testo completoAbstract (sommario):
Abstract In some asexual species, parthenogenetic females occasionally produce males, which may strongly affect the evolution and maintenance of asexuality if they cross with related sexuals and transmit genes causing asexuality to their offspring (“contagious parthenogenesis”). How these males arise in the first place has remained enigmatic, especially in species with sex chromosomes. Here, we test the hypothesis that rare, asexually produced males of the crustacean Artemia parthenogenetica are produced by recombination between the Z and W sex chromosomes during non-clonal parthenogenesis, resulting in ZZ males through loss of heterozygosity at the sex determination locus. We used RAD-sequencing to compare asexual mothers with their male and female offspring. Markers on several sex-chromosome scaffolds indeed lost heterozygosity in all male but no female offspring, suggesting that they correspond to the sex-determining region. Other sex-chromosome scaffolds lost heterozygosity in only a part of the male offspring, consistent with recombination occurring at a variable location. Alternative hypotheses for the production of these males (such as partial or total hemizygosity of the Z) could be excluded. Rare males are thus produced because recombination is not entirely suppressed during parthenogenesis in A. parthenogenetica. This finding may contribute to explaining the maintenance of recombination in these asexuals.
21
Przybylo, E., e D. Cooper. "Asexual Resonances: Tracing a Queerly Asexual Archive". GLQ: A Journal of Lesbian and Gay Studies 20, n. 3 (1 gennaio 2014): 297–318. http://dx.doi.org/10.1215/10642684-2422683.
Testo completo
22
Kolarčik, Vladislav, Valéria Kocová, Vlastimil Mikoláš, Lenka Mártonfiová, Nikola Hajdučeková e Pavol Mártonfi. "Variability of Reproduction Pathways in the Central-European Populations of Hawthorns with Emphasis on Triploids". Plants 11, n. 24 (13 dicembre 2022): 3497. http://dx.doi.org/10.3390/plants11243497.
Testo completoAbstract (sommario):
The role of apomeiosis, parthenogenesis, and pseudogamy in the asexual reproduction of some plant groups has not been fully elucidated in relation to species diversification. Quantitative analyses of seed origin may help in gaining better understanding of intercytotypic interactions. Asexual reproduction associated with polyploidy and frequent hybridization plays a crucial role in the evolutionary history of the genus Crataegus in North America. In Europe, the genus represents a taxonomically complex and very difficult species group not often studied using a modern biosystematic approach. We investigated the reproduction pathways in mixed-cytotype populations of selected taxa of Crataegus in eastern Slovakia, Central Europe. The investigated accessions were characterized by seed production data and the ploidy level of mature plants as well as the embryo and endosperm tissues of their seeds determined via flow cytometry. Diploid and polyploid hawthorns reproduce successfully; they also produce high numbers of seeds. An exception is represented by an almost sterile triploid. Diploids reproduce sexually. Polyploids shift to asexual reproduction, but pseudogamy seems to be essential for regular seed development. In rare cases, fertilization of unreduced gametes occurs, which offers opportunity for the establishment of new polyploid cytotypes between diploid sexuals and polyploid asexuals. Opposite to sexual diploids, triploids are obligate, and tetraploids almost obligate apomicts. Apomixis is considered to help stabilize individual weakly differentiated polyploid microspecies. Pseudogamy is a common feature and usually leads to unbalanced maternal to paternal contribution in the endosperm of triploid accessions. Parental contribution to endosperm gene dosage is somehow relaxed in triploids. Our Crataegus plant system resembles reproduction in the diploids and polyploids of North American hawthorns. Our data provide support for the hypothesis that polyploidization, shifts in reproduction modes, and hybridization shape the genus diversity also in Central Europe.
23
Kuttin, E. S., W. Kaplan, H. I. Scholer, H. Burtscher e H. Köhler. "Sexual and Asexual Reproduction of Aspergillus nidulans in vivo: Sexuelle und asexuelle Reproduktion von Aspergillus nidulans in vivo". Mycoses 28, n. 3 (24 aprile 2009): 109–16. http://dx.doi.org/10.1111/j.1439-0507.1985.tb02103.x.
Testo completo
24
Grosberg, Richard K., e Roger N. Hughes. "Asexual Obsessions". Evolution 46, n. 6 (dicembre 1992): 1976. http://dx.doi.org/10.2307/2410050.
Testo completo
25
Shoubridge, Eric A. "Asexual healing". Nature 461, n. 7262 (settembre 2009): 354–55. http://dx.doi.org/10.1038/461354a.
Testo completo
26
MCCONNELL, J. "Asexual cycle". Lancet 344, n. 8914 (luglio 1994): 53. http://dx.doi.org/10.1016/s0140-6736(94)91073-1.
Testo completo
27
Grosberg, Richard K. "ASEXUAL OBSESSIONS". Evolution 46, n. 6 (dicembre 1992): 1976–79. http://dx.doi.org/10.1111/j.1558-5646.1992.tb01188.x.
Testo completo
28
Blichfeldt, Bodil Stilling, e Karina M. Smed. "‘Do it Forever’: Discursive representations of older adults and sexualities in vacation marketing". Journal of Vacation Marketing 25, n. 2 (22 aprile 2018): 264–76. http://dx.doi.org/10.1177/1356766718771421.
Testo completoAbstract (sommario):
In advertising, sex has been ascribed a major role, but mostly in a one-dimensional, uniform, and ageist manner framing sexuality as the privilege of younger people. This has traditionally strengthened stereotyping discourses of older adults as ‘asexual’. However, in recent years, counter narratives emphasizing sex as an integral part of active, healthy, and successful aging have gained momentum. Using the promotional video ‘Do it Forever’ as a relevant case, this article analyzes representations of older adults’ sexualities in vacation marketing and points to how advertising is not ‘innocent’, but discursively positions older adults’ sexualities within an antiaging culture which positions older adults as ‘sexy olders’ in sharp opposition to the discourse of ‘asexsual old age’, potentially leaving older adults with little room to construct (a)sexual identities in-between the two strong and oppositional discourses.
29
Mee, J. A., e E. B. Taylor. "The cybrid invasion: widespread postglacial dispersal by Phoxinus (Pisces: Cyprinidae) cytoplasmic hybrids". Canadian Journal of Zoology 90, n. 5 (maggio 2012): 577–84. http://dx.doi.org/10.1139/z2012-023.
Testo completoAbstract (sommario):
Peculiar reproductive processes that arise during sperm-dependent asexual reproduction may have important roles in allowing coexistence of sperm-dependent asexuals and their sexually reproducing hosts. Though typically clonal, nonclonal reproduction in the hybrid gynogenetic species Phoxinus eos–neogaeus can reestablish sexual northern redbelly dace ( Phoxinus eos (Cope, 1861)) nuclear genomes. These hybrid-derived P. eos biotypes, known as cybrids, have finescale dace ( Phoxinus neogaeus Cope, 1867) mitochondria but are otherwise indistinguishable from “pure” P. eos. Our goal was to determine the extent of the cybrids’ distribution, and hence to evaluate their role in mechanisms of asexual–sexual coexistence. We also set out to determine the geographic origins of P. eos–neogaeus and cybrids. Our sampling revealed that all Phoxinus species and biotypes are widely distributed in North America, but that cybrids have replaced pure P. eos, or preempted postglacial colonization by pure P. eos, in the northern portion of their distribution. Also, all P. eos–neogaeus and cybrids had mitochondrial DNA (mtDNA) sequences closely related to a lineage originating from a Mississippi glacial refugium. No P. eos–neogaeus or cybrids were derived from a divergent P. neogaeus lineage discovered in Atlantic Canada. It is therefore unlikely that P. eos–neogaeus or cybrids originated in any Atlantic glacial refugia. If P. neogaeus mitochondria are better adapted to northern environments, widespread mtDNA introgression may facilitate coexistence in northern areas by reducing the disparity in fitness between P. eos–neogaeus and its sexual hosts.
30
Orr, H. A., e S. P. Otto. "Does diploidy increase the rate of adaptation?" Genetics 136, n. 4 (1 aprile 1994): 1475–80. http://dx.doi.org/10.1093/genetics/136.4.1475.
Testo completoAbstract (sommario):
Abstract Explanations of the evolution of diploidy have focused on the advantages gained from masking deleterious alleles. Recent theory has shown, however, that masking does not always provide an advantage to diploidy and would never favor diploidy in predominantly asexual organisms. We explore a neglected alternative theory which posits that, by doubling the genome size, diploids double the rate at which favorable mutations arise. Consequently, the rate of adaptation in diploids is presumed to be faster than in haploids. The rate of adaptation, however, depends not only on the rate of appearance of new favorable mutations but also on the rate at which these mutations are incorporated (which depends on the population size and on the dominance of favorable mutations). We show that, in both asexuals and sexuals, doubling the mutation rate via diploidy often does not accelerate the rate of adaptation. Indeed, under many conditions, diploidy slows adaptation.
31
Vallejo-Marin, Mario. "Correlation between polyploidy and asexual reproduction". Ecosistemas 23, n. 3 (23 dicembre 2014): 78–82. http://dx.doi.org/10.7818/ecos.2014.23-3.10.
Testo completo
32
李亭萱, 李亭萱, e 李明峰 Ting-Hsuan Lee. "臺灣無性戀身分認同歷程之研究". 中華輔導與諮商學報 67, n. 67 (maggio 2023): 045–82. http://dx.doi.org/10.53106/172851862023050067003.
Testo completoAbstract (sommario):
<p>本研究旨在瞭解臺灣無性戀身分認同歷程，以及情感與性慾樣貌，邀請六位無性戀受訪者進行訪談，資料分析採敘事研究「類別—內容」視無性戀為一主體，進行跨個案資料分析。研究發現六位受訪者雖有共同經驗，但個別差異極大，身分認同之前，可幽微感受「性慾」或「情感」與有性戀存在著些微差異，分別以不在意、保持困惑、合理化與病理化面對差異。認同路徑從「契機」開始區分為二，其一是認同契機經歷「足夠強度的內外在刺激，同時有意識於無性戀一詞展開探究，並浸潤於個人情感與性慾經驗，經過多次來回反覆思辯」，進而有無性戀認同；其二為認同契機經驗「輕輕置入，快快連結，便有意識對無性戀一詞展開探究」，即有無性戀認同。另外，無性戀情感與性慾呈現多元樣貌，情感呈現樣貌包含：（1）對「任何事物」皆無感；（2）我不知道什麼是「忌妒」；（3）我只是很喜歡這個朋友；（4）太靠近的關係讓人窒息；（5）相當非常熱愛一件事。以及性慾呈現樣貌包含：（1）性幻想：無、第三者角度看性互動、虛擬二次元；（2）肢體碰觸：拒絕—接受；（3）關於自慰：純粹生理層次；（4）性行為：抗性—可接受；（5）電影呈現情慾的反應。最後，提出對未來研究與實務建議。</p> <p> </p><p>With the evolution of the times, the issue of "multiple sexuality" (lesbian, gay, bisexual, transgender, queer/questioning, intersex, ally/asexual: LGBTQIA) has gradually received attention from the public. Based on current research results and the public’s understanding of LGBTQIA, we see a gradual decrease of knowledge by each ascending order of abbreviations. "Asexuality" is the fourth sexual orientation trend independent of heterosexuality, homosexuality, and bisexuality. There are fewer than 20 studies on asexuality conducted both domestically and internationally. In Taiwan, the only study that has been published on the subject was Wang’s (2014) "Love without Sex: Asexual Experiences in a Sexualized Society". This suggests that the topic of asexuality has received limited attention from the academic community over the past seven years. The awareness of asexuality has stagnated. This research aims to understand the identity process of Taiwan’s asexual identity, as well as the appearance of romantic attraction and sexual desire. Six asexual interviewees were invited to participate in the interviews. The data analysis adopted a narrative research "category-content" to treat asexuality as a subject and conduct cross-case data analysis. The results showed that although the six interviewees had common experiences, individual differences were significant. Not every interviewee followed a linear journey toward their identity. Before identity, they felt a slight difference in sexuality between "romantic attraction" and "sexual desire." There are four pattern they faced four ways: did not care, remained confused, rationalized, and pathological. Even if they had heard of the term asexuality, it was not easy for them to connect it with their own situation. There were two paths starting from the "turning point." The first path was sufficient internal and external stimuli, while consciously exploring the term asexuality, infiltrating the personal pass of romantic attraction and sexual desire experience, after many back-and-forth debates. The second path was from the turning point to "put in lightly, connect quickly, and then consciously explore the term asexuality." Only "slightly" compares one’s own situation, even in the interview process, "not" describes that comparing past experiences immediately produces belonging, similar to completing an "administrative task," such as "Oh, my vote is based on the neighborhood"; "Vote somewhere" is just an administrative action. The six interviewees actively or passively explored the term "asexuality" at this stage. Most of them searched for online information and joined asexuality clubs. They connected "asexuality" with their own experiences and completed their identity. In addition, asexual romantic attraction and sexual desire presents multiple appearances. The appearance of romantic attractions includes: (1) No feeling for "anything"; (2) I do not know what "jealousy" is; (3) I just like this friend very much; (4) A relationship that is too close is suffocating; and (5) I love one thing very much. The appearance of sexual desire includes: (1) sexual fantasies, nothing, sexual interaction from the third perspective, and virtual people; (2) physical touch: from rejection to acceptance; (3) regarding masturbation, only at the physiological level; (4) sexual behavior: anti-sex to acceptable, and (5) the film presents an erotic reaction: "I feel like I am being harassed, unnecessary erotic clips, just selling sensationalism." Finally, suggestions for future research and practice are presented. Suggestions for future research: (1) heterogeneity in the asexual community is high, and it is necessary to expand each combination in the group or choose a deeper understanding and (2) understanding asexual intimacy from a "relational orientation" or "system theory." Suggestions for counseling: (1) enhance the sensitivity of multicounseling culture and explore the appearance of "romantic attraction" and "sexual desire" in detail; (2) counselors must reflect on the perspective of "sexual values" and the expansion of "sex-related issues" and (3) it is strongly recommended that gender education and sex education textbooks in national and senior high schools should include the concept of asexuality.</p> <p> </p>
33
李亭萱, 李亭萱. "臺灣無性戀現身經驗之初探". 輔導與諮商學報 46, n. 1 (maggio 2024): 025–49. http://dx.doi.org/10.53106/181815462024054601002.
Testo completoAbstract (sommario):
<p>本研究旨在探究臺灣無性戀現身經驗，邀請6位無性戀者進行訪談，不聚焦單一現身對象，以開放地態度蒐集與探究資料，以「敘事研究取向」視框進行資料分析，試圖理解無性戀之現身經驗為何？研究結果有三：（一）無性戀能見度低影響現身經驗，包含需要解釋「什麼是無性戀」、現身是多次反覆全面性的行動、難以被理解；（二）臺灣同性婚姻對於無性戀現身經驗獨具意義，包含評估欲現身對象的酷兒知能與開放度、實踐社會正義、大幅降低被病理化的思維；（三）向伴侶現身尤為挑戰，包含避免錯誤期待、考量現身風險。最後，依據研究結果與文獻對話給予未來研究與實務建議，包含（一）研究建議：聚焦於無性戀像伴侶現身議題；（二）實務建議：在教育或教學現場，提供教師與學生「無性戀」概念，以提升無性戀的能見度；在諮商實務的現場，實務工作者要積極反思自身的「性價值觀」，以及擴展「性相關議題」之視框，除了增加對各個性傾向關注度之外，必須胸懷性少數的多樣性，避免先入為主的刻板印象，才不致在助人工作的成效上陷入盲點與困境，對性少數與臺灣整體社會有所貢獻。</p> <p> </p><p>The purpose of this study is to explore the disclosure experience of Taiwan asexual by interviewing six Taiwanese asexual individuals. Using a narrative research approach, we analyzed the data through the "category-content" method. There are three parts in the results. Firstly, considerations to disclosure their asexuality is influenced by the people they are interacting with. For instance, disclosure to their family is based on the quality of daily relationships, how accepting and open-minded to queer knowledge they are; disclosure to friends and communities is part of the process of identity recognition, increasing common sense of queer individuals, practicing social justice, and challenging old frameworks; disclosure to partners put them into the risks of not being understood and forming false expectations. Secondly, disclosure strategies include starting the discussion with the concept they already known, sharing views and feelings in daily life, and avoiding being put themselves into a difficult situation where everyone knows nothing about asexuality; Thirdly, the challenges include being misunderstood, easy to be pathological, further exploration of related knowledge, and closer to ideal relationships. The most challenging thing to asexual people is disclosure to their partner. Asexual people consider whether the disclosure is good for relationship or not, and the purpose of disclosure is hoping their partner hold no incorrect expectations.</p> <p>This study discusses as follows. (1) the low visibility of asexuality affects the experience of disclosure, and it is a repeated and comprehensive action. To a certain extent, "asexuality comes out" equals "needs to explain what asexuality is". Some Asexual individuals choose not to come out temporarily because of "to avoid trouble". This is not "in the closet" or "go invisible", but a purely interpersonal consideration. (2) Disclosure is related to the contemporary script and telling to their partners is particularly challenging. Asexual men influenced by "masculinity" and asexual women feeling challenged to appear as contemporary women are all making attempt to break away from the traditional sexual scripts (3) Taiwan same-sex marriage plays an unique and meaningful role for asexuality and this facilitates consideration of disclosure and practices social justice. In terms of strategies of disclosure, discussing "same-sex marriage" as a starting point as nowadays people have had a more friendly attitude towards same-sex marriage. In the end of the study, some suggestions are made based on the results and discussions.</p> <p> </p>
34
Whitton, Jeannette, Christopher J. Sears e Wayne P. Maddison. "Co-occurrence of related asexual, but not sexual, lineages suggests that reproductive interference limits coexistence". Proceedings of the Royal Society B: Biological Sciences 284, n. 1868 (6 dicembre 2017): 20171579. http://dx.doi.org/10.1098/rspb.2017.1579.
Testo completoAbstract (sommario):
We used randomizations to analyse patterns of co-occurrence of sexual and apomictic (asexual) members of the North American Crepis agamic complex (Asteraceae). We expect strong asymmetry in reproductive interactions in Crepis : apomicts produce clonal seeds with no need for pollination and are not subject to reproductive interference from co-occurring relatives. However, because they still produce some viable pollen, apomicts can reduce reproductive success of nearby sexual relatives, potentially leading to eventual local exclusion of sexuals. Consistent with this, randomizations reveal that sexuals are over-represented in isolated sites, while apomicts freely co-occur. Incorporation of taxonomic and phylogenetic evidence indicates that this pattern is not driven by local origins of asexuals. Our evidence that patterns of local co-occurrence are structured by reproductive interference suggests an underappreciated role for these interactions in community assembly, and highlights the need for explicit tests of the relative contributions of ecological and reproductive interactions in generating patterns of limiting similarity.
35
Yan, Zhi-Chao, Guang-Yuan Qi, Tian-Yi Yao e Yuan-Xi Li. "Mitochondrial Genomes of Two Asexual Trichogramma (Hymenoptera: Trichogrammatidae) Strains and Comparison with Their Sexual Relatives". Insects 13, n. 6 (16 giugno 2022): 549. http://dx.doi.org/10.3390/insects13060549.
Testo completoAbstract (sommario):
Despite its substantial costs, sexual reproduction dominates in animals. One popular explanation for the paradox of sex is that asexual reproduction is more likely to accumulate deleterious mutations than sexual reproduction. To test this hypothesis, we compared the mitogenomes of two asexual wasp strains, Trichogramma cacoeciae and T. pretiosum, to their sexual relatives. These two asexual strains represent two different transition mechanisms in Trichogramma from sexual to asexual reproduction. Asexual T. pretiosum is induced by Wolbachia, while T. cacoeciae presumably originated from interspecific hybridization. We sequenced and assembled complete mitochondrial genomes of asexual T. cacoeciae and T. pretiosum. Compared to four sexual relatives, we found no evidence of higher mutation accumulation in asexual Trichogramma mitogenomes than in their sexual relatives. We also did not detect any relaxed selection in asexual Trichogramma mitogenomes. In contrast, the intensified selection was detected in Nad1 and Nad4 of the asexual T. pretiosum mitogenome, suggesting more purifying selection. In summary, no higher mitochondrial mutation accumulation was detected in these two asexual Trichogramma strains. This study provides a basis for further investigating mitochondrial evolution and asexual reproduction in Trichogramma.
36
Judson, Olivia P., e Benjamin B. Normark. "Ancient asexual scandals". Trends in Ecology & Evolution 11, n. 2 (febbraio 1996): 41–46. http://dx.doi.org/10.1016/0169-5347(96)81040-8.
Testo completo
37
Meirmans, P. G., H. C. M. Den Nijs e P. H. Van Tienderen. "Male sterility in triploid dandelions: asexual females vs asexual hermaphrodites". Heredity 96, n. 1 (28 settembre 2005): 45–52. http://dx.doi.org/10.1038/sj.hdy.6800750.
Testo completo
38
Cuevas-Cruz, Juan Carlos, Marcos Jiménez-Casas, Jesús Jasso-Mata, Paulino Pérez-Rodríguez, Javier López-Uptón e Ángel Villegas-Monter. "Asexual propagation of Pinus leiophylla Schiede ex Schltdl. et Cham." Revista Chapingo Serie Ciencias Forestales y del Ambiente XXI, n. 1 (aprile 2015): 81–95. http://dx.doi.org/10.5154/r.rchscfa.2014.08.033.
Testo completo
39
Constable, George W. A., e Hanna Kokko. "Parthenogenesis and the Evolution of Anisogamy". Cells 10, n. 9 (18 settembre 2021): 2467. http://dx.doi.org/10.3390/cells10092467.
Testo completoAbstract (sommario):
Recently, it was pointed out that classic models for the evolution of anisogamy do not take into account the possibility of parthenogenetic reproduction, even though sex is facultative in many relevant taxa (e.g., algae) that harbour both anisogamous and isogamous species. Here, we complement this recent analysis with an approach where we assume that the relationship between progeny size and its survival may differ between parthenogenetically and sexually produced progeny, favouring either the former or the latter. We show that previous findings that parthenogenesis can stabilise isogamy relative to the obligate sex case, extend to our scenarios. We additionally investigate two different ways for one mating type to take over the entire population. First, parthenogenesis can lead to biased sex ratios that are sufficiently extreme that one type can displace the other, leading to de facto asexuality for the remaining type that now lacks partners to fuse with. This process involves positive feedback: microgametes, being numerous, lack opportunities for syngamy, and should they proliferate parthenogenetically, the next generation makes this asexual route even more prominent for microgametes. Second, we consider mutations to strict asexuality in producers of micro- or macrogametes, and show that the prospects of asexual invasion depend strongly on the mating type in which the mutation arises. Perhaps most interestingly, we also find scenarios in which parthenogens have an intrinsic survival advantage yet facultatively sexual isogamous populations are robust to the invasion of asexuals, despite us assuming no genetic benefits of recombination. Here, equal contribution from both mating types to zygotes that are sufficiently well provisioned can outweigh the additional costs associated with syngamy.
40
Sun, Yanxia, Xu Zhang, Aidi Zhang, Jacob B. Landis, Huajie Zhang, Hang Sun, Qiu-Yun (Jenny) Xiang e Hengchang Wang. "Population Genomic Analyses Suggest a Hybrid Origin, Cryptic Sexuality, and Decay of Genes Regulating Seed Development for the Putatively Strictly Asexual Kingdonia uniflora (Circaeasteraceae, Ranunculales)". International Journal of Molecular Sciences 24, n. 2 (11 gennaio 2023): 1451. http://dx.doi.org/10.3390/ijms24021451.
Testo completoAbstract (sommario):
Asexual lineages are perceived to be short-lived on evolutionary timescales. Hence, reports for exceptional cases of putative ‘ancient asexuals’ usually raise questions about the persistence of such species. So far, there have been few studies to solve the mystery in plants. The monotypic Kingdonia dating to the early Eocene, contains only K. uniflora that has no known definitive evidence for sexual reproduction nor records for having congeneric sexual species, raising the possibility that the species has persisted under strict asexuality for a long period of time. Here, we analyze whole genome polymorphism and divergence in K. uniflora. Our results show that K. uniflora is characterized by high allelic heterozygosity and elevated πN/πS ratio, in line with theoretical expectations under asexual evolution. Allele frequency spectrum analysis reveals the origin of asexuality in K. uniflora occurred prior to lineage differentiation of the species. Although divergence within K. uniflora individuals exceeds that between populations, the topologies of the two haplotype trees, however, fail to match each other, indicating long-term asexuality is unlikely to account for the high allele divergence and K. uniflora may have a recent hybrid origin. Phi-test shows a statistical probability of recombination for the conflicting phylogenetic signals revealed by the split network, suggesting K. uniflora engages in undetected sexual reproduction. Detection of elevated genetic differentiation and premature stop codons (in some populations) in genes regulating seed development indicates mutational degradation of sexuality-specific genes in K. uniflora. This study unfolds the origin and persistence mechanism of a plant lineage that has been known to reproduce asexually and presents the genomic consequences of lack of sexuality.
41
Chen, Guanhan. "Research on the Development Path of Feminism from an Aromantic Asexual Perspective". Journal of Gender, Culture and Society 4, n. 2 (12 luglio 2024): 34–38. http://dx.doi.org/10.32996/jgcs.2024.4.2.5.
Testo completoAbstract (sommario):
Aromantic asexual is a perspective that has rarely been used in the research of Feminism, and this paper aims to explore the possibility and significance of combining aromantic asexual and feminism to fight against “sexual hegemony” from the perspective of the social identity of aromantic asexual. This paper will carry out research through the following aspects: firstly, analyse the concept of aromantic asexual and clarify its connotation and characteristics; secondly, explore the historical basis of the combination of aromantic asexual and feminism and reveal the links and commonalities between the two; then analyse the reasons why aromantic asexual and feminism can move towards the union, and explore the motivation and possibilities of the combination of the two; finally, explore the reflection on the combination of aromantic asexual and feminism, and conclude that the combination of aromantic asexual and feminism has been a very important factor in the development of the feminist movement. Finally, it discusses the reflection on the combination of aromantic asexual and feminism and concludes that the combination of aromantic asexual and feminism is insufficient in resisting the path of “sexual hegemony.” The research in this paper shows that aromantic asexual and feminism have a certain historical basis and connection and that they share some common concepts and goals. At the same time, the combination of aromantic asexual and feminism is not accidental but may be based on the common resistance to and demand for the phenomenon of “sexual hegemony”. Therefore, the combination of aromantic asexual and feminism to fight against “sexual hegemony” has certain rationality and significance and can bring new inspiration and impetus to the cause of gender equality. However, it is also necessary to note that there may be shortcomings in practice, which need to be further studied and explored in depth. It is suggested that future research should strengthen the exploration of the combination of aromantic asexual and feminism, promote cooperation and development between the two, and provide more possibilities and support for the advancement of the cause of gender equality.
42
Mollet, Amanda L., e Brian R. Lackman. "Asexual Borderlands: Asexual Collegians’ Reflections on Inclusion Under the LGBTQ Umbrella". Journal of College Student Development 59, n. 5 (2018): 623–28. http://dx.doi.org/10.1353/csd.2018.0058.
Testo completo
43
Fine, Julia Coombs. "From crushes to squishes". Journal of Language and Sexuality 12, n. 2 (13 luglio 2023): 145–72. http://dx.doi.org/10.1075/jls.22004.fin.
Testo completoAbstract (sommario):
Abstract Previous research on language, sexuality, and affect has focused primarily on the presence rather than the absence of desire. This analysis investigates the linguistic manifestations of non-desire on two subreddits: r/AskReddit and r/Asexual. Contrasting asexual redditors’ responses to threads such as When and how did you realize you were asexual? with straight, allosexual redditors’ responses to a thread titled Straight redditors, when did you realize you were straight?, I find that allosexual and asexual redditors’ responses differ in agency and emotionality. While straight allosexual redditors attribute their lack of homosexual desire to factors other than themselves, asexual redditors attribute their lack of allosexual desire to their own identity. Additionally, asexual redditors frame their realizations of their asexuality as processual and emotional, using feel and felt more often than straight allosexual redditors’ responses. These results expose the importance of emotionality – including lack of desire – as a resource for asexual identity construction.
44
Dolmatov, Igor Yu. "Asexual Reproduction in Holothurians". Scientific World Journal 2014 (2014): 1–13. http://dx.doi.org/10.1155/2014/527234.
Testo completoAbstract (sommario):
Aspects of asexual reproduction in holothurians are discussed. Holothurians are significant as fishery and aquaculture items and have high commercial value. The last review on holothurian asexual reproduction was published 18 years ago and included only 8 species. An analysis of the available literature shows that asexual reproduction has now been confirmed in 16 holothurian species. Five additional species are also most likely capable of fission. The recent discovery of new fissiparous holothurian species indicates that this reproduction mode is more widespread in Holothuroidea than previously believed. New data about the history of the discovery of asexual reproduction in holothurians, features of fission, and regeneration of anterior and posterior fragments are described here. Asexual reproduction is obviously controlled by the integrated systems of the organism, primarily the nervous system. Special molecular mechanisms appear to determine the location where fission occurs along the anterior-posterior axis of the body. Alteration of the connective tissue strength of the body wall may play an important role during fission of holothurians. The basic mechanism of fission is the interaction of matrix metalloproteinases, their inhibitors, and enzymes forming cross-link complexes between fibrils of collagen. The population dynamics of fissiparous holothurians are discussed.
45
Howard, Russell J. "Asexual deviants take over". Nature 357, n. 6380 (giugno 1992): 647–48. http://dx.doi.org/10.1038/357647a0.
Testo completo
46
Vielle Calzada, J. P., C. F. Crane e D. M. Stelly. "Apomixis--The Asexual Revolution". Science 274, n. 5291 (22 novembre 1996): 1322–23. http://dx.doi.org/10.1126/science.274.5291.1322.
Testo completo
47
Martinez, D. E., e J. S. Levinton. "Asexual metazoans undergo senescence." Proceedings of the National Academy of Sciences 89, n. 20 (15 ottobre 1992): 9920–23. http://dx.doi.org/10.1073/pnas.89.20.9920.
Testo completo
48
TRIPP, Erin A. "Is asexual reproduction an evolutionary dead end in lichens?" Lichenologist 48, n. 5 (settembre 2016): 559–80. http://dx.doi.org/10.1017/s0024282916000335.
Testo completoAbstract (sommario):
AbstractClassical hypotheses in lichenology predict pairs of species in which sexual lineages are ancestral and long-lived evolutionarily and that these give rise to derived, evolutionarily transient asexual lineages. Extensive phylogenetic information generated over the last 20 years regarding relationships within and among various groups of lichens makes possible an investigation of polarity and lability in reproductive mode across diverse clades. To test the long-held hypothesis of asexual reproduction as an evolutionary dead end in lichens, existing phylogenetic data from 23 studies were utilized to reconstruct gains and losses of sexual and asexual reproduction in a model-based statistical framework. Summed across all studies, between 26–44 origins of asexual reproduction from sexual ancestors (forward transitions) and 14–25 origins of sexual reproduction from asexual ancestors (reverse transitions) were identified. However, the higher number of gains of asexual reproduction was concentrated in a relatively low number of clades (e.g. Dirina). The greater number of forward compared to reverse transitions is consistent with dogma in both lichenology and evolutionary biology, but nonetheless this study documents numerous reverse transitions, suggesting that asexual lineages represent a source for evolutionary innovation.
49
Hall, Scott, David Knox e I. Joyce Chang. "Out of the Shadow and Into the Light: New Data Comparing Asexual and Sexual Undergraduates". Journal of Positive Sexuality 7, n. 2 (1 dicembre 2021): 63–77. http://dx.doi.org/10.51681/1.722.
Testo completoAbstract (sommario):
Drawing from a large dataset of over 13,000 college students, this research compared 75 self-identified asexual individuals with heterosexual, bisexual, and gay/lesbian undergraduates. The results revealed that asexual individuals were less likely to have engaged in sexual behaviors (oral sex, anal sex, friends with benefits, sexual intercourse, hooking up) than heterosexual, bisexual, and gay or lesbian individuals. Asexual and heterosexual individuals were similar in endorsing absolutist sexual values, having a lower willingness to cohabit, and reporting less likelihood of having masturbated. Asexual individuals were similar to other sexual minorities in being less religious and having more positive attitudes toward LGB issues. A multinomial logistic regression analysis using all the variables with significant differences at the bivariate level revealed similar findings, though asexual individuals differed most dramatically in their lower levels of sexual experience when compared to gay/lesbian individuals. Future researchers are encouraged to consider reframing asexuality as more sex positive so as to recognize diversity and empower asexual individuals.
50
Nelson, Amanda E., e Maurine Neiman. "Persistent Copulation in Asexual Female Potamopyrgus antipodarum: Evidence for Male Control with Size-Based Preferences". International Journal of Evolutionary Biology 2011 (10 aprile 2011): 1–7. http://dx.doi.org/10.4061/2011/439046.
Testo completoAbstract (sommario):
Transitions from sexual to asexual reproduction provide a useful context for investigating the evolutionary loss of nonfunctional traits. It is often assumed that useless behaviors or structures will degrade, but this process is poorly understood. Potamopyrgus antipodarum is an ancestrally sexual New Zealand freshwater snail characterized by numerous independent transitions to asexual all-female lineages. The availability of multiple independently-derived asexual lineages of various time since derivation from sexual ancestors means that the P. antipodarum system is well-suited for the study of trait loss related to mating behavior and copulation. Here, we asked whether mating behavior in asexual female P. antipodarum degrades with increasing asexual lineage age. While copulation frequency did not differ in females from old versus young asexual lineages, post hoc analyses indicated that it was instead positively associated with mean lineage female size. We observed that female P. antipodarum take a passive physical role in copulatory interactions, indicating that female behavior may not be a useful variable for detection of sex-related vestigialization in this system. Instead, males seem to be in proximate control of copulation frequencies, meaning that male mating behavior may be a primary determinant of the expression of mating behavior in asexual female P. antipodarum.