Tesi sul tema "Reproductive"
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1
Clayton, Thompson J. "Law, rights and reproduction : reproductive autonomy in ethical rationalism". Thesis, University of Westminster, 2016. https://westminsterresearch.westminster.ac.uk/item/9y598/law-rights-and-reproduction-reproductive-autonomy-in-ethical-rationalism.
Testo completoAbstract (sommario):
As medical technology has advanced, so too have our attitudes towards the level of control we can expect to hold over our procreative capacities. This creates a multi-dimensional problem for the law in terms of access to services which prevent conception, access to services which terminate a pregnancy and recompensing those whose choices to avoid procreating are frustrated. These developments go to the heart of our perception of autonomy. In order to evaluate these three issues in relation to reproductive autonomy, I set out to investigate how the Gewirthian theory of ethical rationalism can be used to understanding the intersection between law, rights, and autonomy. As such, I assert that it is because of agents’ ability to engage in practical reason that the concept of legal enterprise should be grounded in rationality. Therefore, any attempt to understand notions of autonomy must be based on the categorical imperative derived from the Principle of Generic Consistency (PGC). As a result, I claim that (a) a theory of legal rights must be framed around the indirect application of the PGC and (b) a model of autonomy must account for the limitations drawn by the rational exercise of reason. This requires support for institutional policies which genuinely uphold the rights of agents. In so doing, a greater level of respect for and protection of reproductive autonomy is possible. This exhibits the full conceptual metamorphosis of the PGC from a rational moral principle, through an ethical collective principle, a constitutional principle of legal reason, a basis for rights discourse, and to a model of autonomy. Consequently, the law must be reformed to reflect the rights of agents in these situations and develop an approach which demonstrates a meaningful respect of autonomy. I suggest that this requires rights of access to services, rights to reparation and duties on the State to empower productive agency.
2
Singh, Navsharan. "Contesting reproduction, gender, the state and reproductive technologies in India". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0003/NQ37055.pdf.
Testo completo
3
Weis, Christina Corinna. "Reproductive migrations : surrogacy workers and stratified reproduction in St Petersburg". Thesis, De Montfort University, 2017. http://hdl.handle.net/2086/15036.
Testo completoAbstract (sommario):
Surrogacy is an arrangement whereby a woman conceives in order to give birth to child or children for another individual or couple to raise. This thesis explores how commercial gestational surrogacy is culturally framed and socially organised in Russia and investigates the roles of the key actors. In particular it explores the experiences of surrogacy workers, including those who migrate or commute long distances within and to Russia for surrogacy work and the significance of their origin, citizenship, ethnicity and religion in shaping their experience. Ethnographic fieldwork was carried out in St Petersburg between August 2014 and May 2015 and involved semi-structured interviews, (participant) observations, informal conversations and ethnographic fieldnotes with 33 surrogacy workers, 7 client parents, 15 agency staff and 11 medical staff in medical and surrogacy agency facilities. Data were analysed using inductive ethnographic principles. A reflexive account, which includes a consideration of the utility of making one’s own emotional responses a research tool, is also included. Drawing on and expanding on Colen’s (1995) conceptual framework of stratified reproduction and Crenshaw’s (1989) analytical framework of intersectionality, this research shows that surrogacy in Russia is culturally framed and therefore socially organised as an economic exchange, which gives rise to and reinforces different forms of intersecting reproductive stratifications. These stratifications include biological, social, geographic, geo-political and ethnic dimensions. Of particular novelty is the extension of Colen’s framework to address geographic and geo political stratifications. This was based on the finding that some women (temporarily) migrate or commute (over long distances) to work as gestational carriers. The thesis also demonstrates how an economic framing of surrogacy induced surrogacy workers to understand surrogacy gestation as work, which influenced their relationships with client parents. Given the rapid global increase in the use of surrogacy and its increasingly internationalised nature, this research into the social organisation of commercial gestational surrogacy in Russia is timely and has implications for users, medical practitioners and regulators, as well as researchers concerned with (cross-border) surrogacy and reproductive justice.
4
Millbank, Jenni. "Reproductive outsiders". Thesis, University of Kent, 2015. https://kar.kent.ac.uk/50009/.
Testo completoAbstract (sommario):
This body of work examines law’s response to non-genetic families. I have always centred the experience of family formation and family life such that I have traversed and linked distinct legal sites and doctrines, examining access to family formation avenues, models for legal recognition of families once formed and, latterly, legal responses to information sharing and broader kinship practices among genetically related individuals in childhood and later life. In doing so I have made a major contribution to a body of scholarship centring ‘lived lives’ in the exploration of family, relationship and reproduction law at its broadest, incorporating comparative analysis across closely related jurisdictions, attention to and integration of sociological data, and a focus on responsive practical reform outcomes. As an important part of my focus upon lived lives I have brought a continual awareness of gender to the unpacking of ‘gay and lesbian’ equality claims and reform movements to analyse the differential position of women and men in relation to parenting and paid labour, and latterly to build a framework of analysis that bridges heterosexual/same-sex family formation issues (papers 1, 2, 3) to examine links and resonances across ‘reproductive outsiders’ or non-genetic family forms (papers 3, 4). The sweep and reach of this approach makes an original contribution by stepping out of doctrinal and jurisdictional silos to examine the impact of law upon, and the unmet legal needs of, non-genetic families through the life cycle. Throughout these works I have contributed to analysis and debate about the role of ‘the eternal biological family’ in law, specifically engaging in the inter-relation of developing social notions of genetic essentialism, father’s rights and recognition of non-genetic family forms, in legal regimes governing family relationships. I have been one of the leading thinkers in the area of ‘functional family’ developing a clear articulation of how these ideas, drawn from psychology and sociology were mapped across into legal regimes recognising informal relationships (paper 1), examining the limitations of ‘functionality’ when in conflict with genetic parenthood (paper 2) and going on to build a framework for understandings of legal parenthood in non-genetic families as involving a dynamic interaction of intentionality and functionality (paper 2 and 3). In my work on ART and surrogacy I have built upon a body of feminist work on relational theory, agency and resonant choice. I have applied this approach to argue for the centring of an understanding of the interests and needs of parties in ART as part of a web of relationships rather than as isolated and oppositional rights (papers 6, 7, 8). In particular I have made original contributions to understandings of the human embryo in law not as an entity worthy of recognition in its own right, but as an object of unique value to the woman who created it, including on occasion as an imagined relation (paper 6); in directing attention to lateral rather than simply linear genetic links in ART law and policy (paper 6, 7, 8); in looking at how the views of parents shape and interact with those of offspring in seeking information on genetic relatives (paper 8) and in understandings of the significance of the numbers of potential genetic relatives (paper 7). In this area I have made important contributions to unpacking policy rationales and examining the largely ignored evidence base concerning family numbers and identity disclosure regimes (papers 7, 8) and concerning the experiences of surrogates in the development of laws governing surrogacy parentage and payment (papers 4, 5). I have argued for a nuanced and attentive notion of relatedness in law, incorporating the diverse and changeable understandings of the significance of genetic links (traversing a wide range of meanings from information source to family member) that individuals in non-genetic families formed through ART have expressed (papers 4, 5, 6,7, 8). Taken together, this is a body of feminist socio-legal work on the regulation of family relationships, assisted reproduction, genetics, kinship in law. Through this work I have made an original contribution to both scholarly thinking and legislative and policy frameworks responding to the needs of non-genetic family forms.
5
Tang, Shiu-wai. "Reproduction has never been natural the social construction of reproduction in the age of new reproductive technologies /". Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B22331888.
Testo completo
6
Mills, Lesley Judith. "Effects of endocrine-disrupting chemicals on fish reproduction and reproductive indicators /". View online ; access limited to URI, 2006. http://0-digitalcommons.uri.edu.helin.uri.edu/dissertations/AAI3248238.
Testo completo
7
Jolly, Nicole. "Racial Reproductive Control Logics and the Reproductive Justice Movement". ScholarWorks@UNO, 2012. http://scholarworks.uno.edu/td/1449.
Testo completoAbstract (sommario):
The reproductive justice movement gives a voice and representation to women of color whose experience of reproductive control is impacted by intersecting layers of oppression. This thesis uses an intersectional approach to develop the concept of racial reproductive control logics, which describes the relationship between racial logics and racial patterns of reproductive control. The study uses qualitative interviews and content analysis of organizational material to explore how the reproductive justice movement is influenced by racial reproductive control logics.
8
Jacobs, Marc. "Between reproductive rights and access to reproductive healthcare services: narratives of reproductive rights activists in South Africa". Thesis, Rhodes University, 2017. http://hdl.handle.net/10962/17707.
Testo completoAbstract (sommario):
The motivation behind the research paper, “Between reproductive rights and access to reproductive healthcare services: Narratives of reproductive rights activists in South Africa” stems from the notion that civil society groups have often played a critical role in addressing social justice issues concerning women’s rights. Since 1996 after implementation of the Choice on Termination of Pregnancy (CTOP) Act, South Africa has frequently been praised for its progressive abortion laws that formally recognises women’s need for reproductive autonomy and equality. However, ineffective implementation has resulted in many women facing a combination of barriers to accessing reproductive healthcare services. Thus, resulting in some women opting for unsafe, illegal abortion services and placing their health and lives in danger. The purpose of the study, therefore, is to capture the perceptions of contemporary South African based reproductive rights activists and NGOs who engage in campaigns that seek to highlight the complex relationship between reproductive rights and access to such rights. Data for the study was collected through open-ended questionnaires in which participants provided their unique opinions as activists who regularly engage with the abortion and access issues in South Africa. Results from the study suggest that ineffective implementation of the CTOP Act can be attributed to a lack of political will to prioritise women’s sexual and reproductive rights, thereby further marginalising women in society. Results also point to the need for widespread support from civil society on women’s rights matters so that the State can more effectively be held accountable for catering to the most marginalised women in South African society.
9
Bowers, Janice E. "Reproductive Potential and Minimum Reproductive Size of Ferocactus wislizeni (Cactaceae)". University of Arizona (Tucson, AZ), 1998. http://hdl.handle.net/10150/554307.
Testo completo
10
Batty, Lynne Patricia. "Assisted Reproductive Technology: The Aotearoa/New Zealand Policy Context: A thesis submitted in fulfilment of the requirements for the degree of Master of Arts in Sociology in the University of Canterbury". Thesis, University of Canterbury. Sociology, 2002. http://hdl.handle.net/10092/912.
Testo completoAbstract (sommario):
The focus of this thesis is the current policy situation in relation to assisted reproductive technologies (ART) in Aotearoa/New Zealand. I explore how government policies (and lack of policy) have shaped access to ART. I also explore the policy initiatives of funding agencies, the National Ethics Committee on Assisted Human Reproduction (NECAHR), managers, healthcare professionals, and interest groups. My investigation into ART policy issues critically examines the various formal mechanisms and policies used to regulate and control ART in Aotearoa/New Zealand. Drawing on my analysis of policy-focused documents and material from in-depth interviews with key actors in the policy debate, I demonstrate how the ad hoc and contingent approach to ART developments, practices, funding, and access has contributed to inconsistent and inequitable access to ART services. I argue that the lack of an ART-specific policy organisation contributes to fragmented, and possibly discriminatory, policy decisions. I examine how the use of restrictive access criteria to manage the increasing demand for publicly funded ART services disadvantages certain groups wishing to use these services. By investigating the influence of rationing strategies on the allocation of resources and regulation of access, I provide some appreciation of the 'messy reality' of policy creation, interpretation, and implementation. I argue that the criteria used to limit access to public ART services obscure the use of social judgements and provider discretion. Likewise, they succeed in limiting publicly funded ART treatments to those who conform most effectively to the normative definition of family. My analysis of the ART policy discourse identifies silences and gaps in relation to specific ART practices, particularly the use of ART by Maori. I highlight the invisibility and marginalisation of Maori within the ART policy debate. After examining the broader issues concerning Maori access to health services, I explore how these may affect Maori using ART services to overcome infertility. I argue that the gathering of information about the utilisation of ART services is crucial for the accurate identification of the needs of Maori. It is also fundamental for effective monitoring of state health policy decisions and outcomes.
11
Grabinski, Eva K. (Eva Kristine). "Women's reproductive choice, struggles to define and shape women's reproductive experiences". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ54455.pdf.
Testo completo
12
Dutney, Luke. "Reproductive Biology and Controlled Reproductive Development of Captive Cobia (Rachycentron canadum)". Thesis, Fisheries Research and Development Corporation, 2016. http://era.daf.qld.gov.au/id/eprint/8755/.
Testo completoAbstract (sommario):
Cobia aquaculture began in Australia in 2007; however, expansion of commercial production has been limited, due in part to low and inconsistent supply of seed stock for ongrowing. This study aimed to address the constraints of reproductive performance of cobia in captive conditions and investigate strategies to improve the efficiencies of broodstock management in commercial and research facilities.
In a study evaluating the growth of three cohorts of captive reared cobia, to determine the existence and extent of sexually dimorphic growth, intersex development in cobia was identified and recorded for the first time. There was no sexually dimorphic growth in the first two cohorts of fish. In contrast, females from third cohort were significantly larger than males once mean body weight exceeded 2 kg. It is proposed that the observed variations in growth and gonad malformations observed in cohorts 1 and 2 were the result of exposure to endocrine disruptors, the type and source of which remains unknown.
In order to quantify the ovarian development of cobia, there was a need to develop an accurate method of assessing and quantifying ovarian maturation in the presence of asynchronous development. A simple, commercially applicable methodology was devised that used the proportional distribution of different oocyte stages to describe the developmental state of the ovary.
Two trials were conducted to examine the effect of repeated injections of luteinising hormone releasing hormone analogue (LHRHa) and human chorionic gonadotropin (hCG) on stimulating vitellogenesis, supporting ovarian maturation and levels of circulating 17βestradiol (E2). Ovarian development was highly variable within treatments and those fish that initiated vitellogenesis continued to develop regardless of treatment with exogenous hormones. There was no change in E2 concentrations as a result of LHRHa injections and limited evidence to suggest a change in plasma E2 in response to hCG injection. While iv hormonal therapy is effective in inducing spawning in cobia, the results suggest that hormone therapy is not an effective approach to initiating or supporting early stage ovarian development in cobia.
Two cohorts of cobia broodstock were assessed to examine ovarian development and circulating E2 in response to photothermal manipulation. In each study, broodstock were subjected to either a temporally compressed regime or an ambient regime. In the first study ovarian development was generally limited, irrespective of the phototherm regime and there was no significant difference in development between treatments. At the completion of the second trial there was no significant difference in ovarian development between the compressed and ambient phototherm; however, fish in the compressed phototherm were found to develop earlier in the season than those in ambient conditions. Fish in the first trial showed sporadic development in which ovarian samples contained low numbers of late stage oocytes amongst a large percentage of previtellogenic oocytes, possibly due to exposure to endocrine disruption in the early life history of the cohort.
Two cohorts of captive reared cobia were progressively examined as pre- and postpubescent fish to examine the suitability of identifying gender by analysing the androgen 11-ketotestosterone (11KT) in blood and fin clip samples. The gender of individual cobia could be identified by analysing plasma 11KT between the months of October and March, provided the mean population weight was 2 kg or above. The measurement of 11KT concentrations in fin clip samples did not provide an accurate indication of plasma 11KT and as such, was not suitable for predicting gender in cobia. Overall the relative cost, infrastructure and equipment required to conduct steroid analysis limits the application of this methodology in commercial cobia production in comparison to the traditional method of gonadal biopsy.ref:68ga4
13
Ragúz, María. "Sexual and reproductive health and women development from a gender perspective: The role of men". Pontificia Universidad Católica del Perú, 2013. http://repositorio.pucp.edu.pe/index/handle/123456789/101096.
Testo completoAbstract (sommario):
Women's health, particularly, sexual and reproductive health, and development are here approached from a gender and human rights perspective, underlying the need to address these problems from a relational and comprehensive point of view. The issue of how sexual and reproductive health is approached and the "men's as partners" strategy is discussed. Adult women-centered, female-only family planning reproduction and contraception are criticized. Gender violence eradication is stressed as an entry to sexual and reproductive health programs. The case of Peruvian urban and rural women in poverty from Amazonian and Andean communities is taken as an example. Obstacles and achievements in working with men are reviewed but a gender transversal perspective is highlighted. Finally, women's sexual and reproductive health is related to development and seen as a standpoint for addressing health.Se discute como se tratan los problemas de la salud sexual y reproductiva y el desarrollo de la mujer desde una perspectiva transversal de género y de derechos, subrayando la necesidad de trabajarlos desde una perspectiva integral. Se critican los programas y servicios centrados en la mujer adulta, en la reproducción y en la planificación familiar femenina. Asimismo, se señala la necesidad de trabajar en la erradicación de la violencia de género como una entrada para el trabajo en este ámbito. Como ejemplo, se presenta el caso de la salud sexual y reproductiva en comunidades andinas y amazónicas rurales y en extrema pobreza del Perú. Las dificultades y logros en el trabajo con hombres son analizados, subrayándose la necesidad de una perspectiva transversal de género en el trabajo. Finalmente, se relaciona la salud de la mujer con desarrollo y se concluye en la necesidad de trabajar siempre en este sentido.
14
Tedder, Amanda. "Impact of Reproductive Mode on Skeletal Development in a Reproductively Bimodal Squamate Species". Digital Commons @ East Tennessee State University, 2018. https://dc.etsu.edu/etd/3468.
Testo completoAbstract (sommario):
Viviparity has evolved multiple times within squamates. Eggshells are reduced in viviparous forms, which reduces calcium available to embryos during development. This study tested the hypothesis that reduced calcium impacts neonates of viviparous forms. Developmental series from oviparous and viviparous populations of Zootoca vivipara (reproductively bimodal) were cleared & stained to reveal bone development. Photographs (high magnification, calibrated to size) were used to obtain measurements of lengths of the body, humerus, femur, skull and lower jaw, and of ossified portions of limb bones. Percent ossification was scored for targeted skull bones. Results were analyzed using general linear models and revealed no differences in ossification in either limbs or skull. Overall size of oviparous neonates was significantly larger. Findings do not support our hypothesis and indicate that reduction in eggshell calcium in embryos of viviparous populations does not negatively impact limb or skull ossification during development but may influence overall size.
15
Morgan, Jonathan J. "State Regulation of Assisted Reproductive Technology". BYU ScholarsArchive, 2010. https://scholarsarchive.byu.edu/etd/2206.
Testo completoAbstract (sommario):
State regulation of assisted reproductive technology (ART) has been occurring since the inception of earlier technological advances such as artificial insemination to aid human reproduction. I provide a brief overview of the current regulation of ART in the U.S. and the literature on state regulation. Unlike previous studies of ART regulation which use content analysis or case studies of individual state laws I estimate ART regulation for the entire U.S. by using a series of random effects logistic regression models for the time period 1995-2006. To my knowledge this is the first quantitative analysis of ART regulation. I test the hypothesis that the demand for ART is an important predictor of ART legislation in the U.S. Other hypotheses derived from the ART literature were also tested in the analysis. Results indicate that demand for ART is the most influential factor in predicting ART legislation from 1995-2006. Additionally, educational attainment of a state's population and the percentage of married couple households with children in each state may have a direct effect on the demand for ART and an indirect effect on ART regulation.
16
Alvarez, Mora Bruna. "Las (ir)racionalidades de la maternidad en España: Influencias del mercado laboral y las relaciones de género en las decisiones reproductivas". Doctoral thesis, Universitat Autònoma de Barcelona, 2017. http://hdl.handle.net/10803/454824.
Testo completoAbstract (sommario):
El contexto reproductivo español ha sido descrito como de “infertilidad estructural” (Marre, 2009), a causa del descenso de la fecundidad desde mediados de los años 70, debido principalmente a las condiciones del mercado laboral (Marre, 2009), los discursos feministas que vinculaban la libertad de las mujeres con la no-maternidad (Marre, 2012 a Briggs et al., 2012) y a la falta de políticas públicas de apoyo a la maternidad (Comas d’Argemir et al., 2016). A pesar de esta situación, la mayoría de mujeres tienen hijos/as, aunque tengan menos de los que quisieran (Bernardi, 2005) y más tarde.
A través de cincuenta y nueve entrevistas presenciales y de una etnografía digital (Murthy, 2008), se han analizado las condiciones del mercado laboral y las relaciones de género como mecanismos de gobernanza reproductiva (Morgan y Roberts, 2012), para comprender los procesos de decisiones reproductivas de las parejas heterosexuales que tuvieron hijos/as a través de relaciones sexuales en un contexto de infertilidad estructural y, por lo tanto, a priori, desfavorable.
Los principales resultados de la investigación que aquí se presenta apuntan a que los regímenes morales (Morgan y Roberts, 2012) del mercado laboral y las relaciones de género producen “verdades” que enfatizan la dicotomía entre la feminidad – asociada a los trabajos reproductivos- y la masculinidad –asociada a los trabajos productivos-. Así, la madre es considerada la principal cuidadora de sus hijos/as y, en consecuencia, es una mala trabajadora. A pesar del aumento de la participación de los hombres en las tareas domésticas y de cuidados, las mujeres continúan siendo las principales responsables. El hecho de tener hijos/as sitúa a las mujeres como madres y, por lo tanto, se les asigna la responsabilidad de los trabajos reproductivos (enculturación, crianza y cuidados) en un tiempo indefinido, que sobrepasan los procesos biológicos (embarazo, parto y lactancia) temporalmente acotados.
Paralelamente, la maternidad es explicada como una opción donde las mujeres, supuestamente, pueden escoger. Pero las mujeres que tienen más hijos/as y más jóvenes son aquellas que entienden la maternidad como una etapa de su ciclo vital, sin plantearse otra opción que la de tener hijos/as. Para estas mujeres, la necesidad y las ganas de tener hijos/as aparece cuando se encuentran alrededor de los treinta años, tienen pareja, perciben una cierta estabilidad laboral y económica y tienen una vivienda.
En cambio, las mujeres que tienen hijos/as como un estilo de vida, tienen menos y más tarde. El énfasis en explicar la maternidad como una decisión influye en su intensificación (Hays, 1996; O’Reilly, 2004a), porqué se convierte en una opción elegida. Si no se quieren asumir las responsabilidades que se le asocian, supuestamente se puede escoger no tener hijos/as.
Las condiciones del mercado laboral, las relaciones de género y el hecho de explicar la maternidad como una elección, contribuyen a la bajada de la fecundidad en España. Mientras por un lado, cada vez es más difícil encontrar las condiciones adecuadas para tener hijos/as, por el otro, las madres serán consideradas automáticamente, las principales responsables de los cuidados y el ámbito doméstico.Spanish reproductive context has been described as “structural infertility” (Marre, 2009), because of the fertility declining occurred since the 70’s. The main reasons are the labour market conditions (Marre, 2009), feminist discourses that entangle woman freedom with non-motherhood (Marre, 2012 in Briggs et al., 2012), and the lack of public policies to support motherhood (Comas d’Argemir et al., 2016). However, most women have children in Spain, but later and fewer children than they would like to have (Bernardi, 2005). Through fifty-nine interviews and digital ethnography (Murthy, 2008), conditions in the labour market and gender relations at home have been analysed as mechanisms of reproductive governance (Morgan and Roberts, 2012). The main aim of this research is to understand the reproductive decision-making of heterosexual couples who have children through sexual intercourse in a structural infertility context. Results show that moral regimes (Morgan and Roberts, 2012) of the labour market and gender relations produce “truths” that focus on the femininity –reproductive work- and masculinity –productive work- dichotomy. The mother is considered the main carer of their children, consequently becoming a bad worker. Although men have increased their participation in caring and household, women still are the main responsible for it. Through having children, women become mothers. That means, through the biological events temporarily bounded (pregnancy, birth and breastfeeding) women become responsible for reproductive work (socialize, rear and care children) for indefinite time. Motherhood is explained as a question of choice, considering that women could choose to have or not to have children. However, women who understand motherhood as a step in the life course, without considering any other option, have more children and younger. The need and the wiling of having children appear when women are around thirty years old, they have a stable partner, economic or labour stability and have a place to live in. Otherwise, women who understand motherhood as a life style have fewer children and later. Explaining motherhood as a choice helps to the intensification of motherhood (Hays, 1996; O’Reilly, 2004a), because it is something that women choose. If women do not want to be responsible for reproductive work, they could choose not having children. Labour conditions and gender relations at home, together with the consideration of motherhood as a choice, make difficult to find the appropriate moment to have children, and if women have them they will be responsible for reproductive work. This situation helps to the fertility declining in Spain.
17
Wilson, Poe Emma. "Vitrification of day 5/6 human morulas/blastocysts: A 10 year retrospective study in a private assisted reproductive techniques [ART] clinic". Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/96876.
Testo completoAbstract (sommario):
Thesis (MMed)--Stellenbosch University, 2015.ENGLISH ABSTRACT: This study was designed to retrospectively evaluate the established embryo vitrification/warming programme currently implemented at Drs Aevitas Institute for Reproductive Medicine and to look at factors that might play a role in optimizing the pregnancy outcomes thereof. Vitrification is the achievement of a “state of suspended animation” wherein molecular translational motions are arrested without structural reorganization of the liquid. In embryo vitrification it involves placement of the embryo in a very small volume of vitrification medium that must be cooled at extremely high cooling rates. The vitrification medium contains cryoprotectants to prevent any cryoinjury from occurring to the embryo. This process was initially proposed to effectively manage supernumerary embryos, but it has also provided a viable method of reducing costs for additional embryo transfers as well as the reduction of the incidence of multiple births. Patients who are at risk of ovarian hyper stimulation syndrome (OHSS) can also have all of their embryos vitrified in advance to reduce the likelihood of adverse clinical symptoms if a pregnancy is established. Throughout the period in which vitrification has been in practice, there have been advances in technology as well as continual research being conducted to establish whether newly suggested techniques do, in fact, optimize the outcomes of vitrification. Focus has subsequently been applied to the carrier device used for vitrification, the day on which the embryos are vitrified and stored, as well as the number of embryos transferred in each respective cycle, all to ensure the most favourable outcome. This retrospective study confirmed the use of the Cryotop® as the most viable carrier device for successful survival and pregnancy outcomes. Transfer of day 5 vitrified embryos resulted in significantly higher pregnancy rates compared to day 6 vitrified embryos. Results also indicated that the number of embryos transferred does indeed have a significant effect on the pregnancy outcome and consequently we can possibly argue against the implementation of single embryo transfer in the vitrification programme. Investigation into the effect of female age, specifically oocyte age, on each of these categories indicated that reduced age can be associated with optimal outcomes; however this could not be proven statistically in this cohort of patients. To further look at optimization of the vitrification/warming programme, a Literature Survey was conducted to ascertain the results after Assisted Hatching in frozen/warmed human embryos. Assisted Hatching has been proposed as a solution to Zona Pellucida hardening, which has been found to occur during vitrification. The need for further studies and a meta-analysis of the literature is confidently proposed, as well as a Prospective Study to evaluate the effect of Laser Assisted Hatching in the human blastocyst vitrification/warming programme at Drs Aevitas Institute for Reproductive Medicine.
AFRIKAANSE OPSOMMING: Hierdie studie is ontwerp om die gevestigde embrio vitrifikasie/ontdooi program by Drs Aevitas Instituut vir Reproduktiewe Medisyne, retrospektief te evalueer en die faktore te optimaliseer wat swangerskap uitkomste kan beïnvloed. Vitrifikasie is die proses waardeur die molekulere aktiwiteit binne die embrio in ‘n staat van arres gehou word sonder om die strukture binne die sitplasma te versteur. Dit behels die plasing van ʼn embrio in 'n klein hoeveelheid vitrifikasie medium wat teen 'n hoë tempo afgekoel word. Die vitrifikasie medium bevat kriobeskermmiddels wat die embrio tydens die vitrifikasie proses teen moontlike skade beskerm. Hierdie proses is aanvanklik voorgestel om oortollige embrio’s doeltreffend te bestuur. Dit bied ʼn koste effektiewe metode vir embrio terugplasing, en verlaag die insidensie van veelvoudige swangerskap. Vitrifikasie bied pasiënte met ʼn hoë risiko vir ovariale hiperstimulasiesindroom (OHSS) ‘n alternatief om nadelige kliniese simptome te vermy indien ʼn swangerskap bereik word. Tegnologiese vordering en voortdurende navorsing ondersoek voortdurend nuwe tegnieke vitrifikasie uitkomste te optimaliseer. Fokus word geplaas op die draertoestel wat gebruik word vir vitrifikasie, die dag waarop die embrio's gevitrifiseer en gestoor word, sowel as die aantal embrio’s wat met elke vitrifikasie siklus teruggeplaas word. Hierdie retrospektiewe studie het bevestig dat die gebruik van die Cryotop® die mees suksesvolle toestel vir oorlewing en swangerskap uitkomste is. Die terugplasing van dag 5 gevitrifiseerde embrios het beduidende hoër swangerskapsyfers as dag 6 embrios tot gevolg gehad. Die resultate het ook aangedui dat die aantal embrio's wat teruggeplaas word 'n beduidende uitwerking op die swangerskapsyfer het. Daar kan dus moontlik teen die implementering van 'n enkel embrio-terugplasing neiging in die vitrifikasie program geargumenteer word. Resultate het ook getoon dat optimale uitkomste verwant is aan ʼn laer oösiet ouderdom, alhoewel dit nie in die groep pasiente statisties bewys kon word nie. 'n Literatuurstudie oor AH (Assisted Hatching) op gevitrifiseerde/ontdooide menslike embrio’s is uitgevoer om die vitrifikasie/ontdooi program verder te optimaliseer. AH bied ‘n oplossing vir Zona pellucida verharding, wat tydens vitrifikasie plaasvind. Verdere studies, 'n meta-analise van die literatuur, sowel as 'n prospektiewe studie om die effek van laser AH in gevitrifiseerde/ontdooide menslike blastosiste by Drs Aevitas Instituut vir reproduktiewe medisyne te evalueer, word voorgestel.
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Timlin, Claire Lourdine. "Strategies for Improving Reproductive Efficiency of Beef Cattle with Assisted Reproductive Technologies". Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/98841.
Testo completoAbstract (sommario):
Reproductive efficiency in beef cattle can be improved with reproductive technologies at the herd, individual cow, and embryonic levels. Decreasing the bull:cow ratio for natural service after fixed time artificial insemination (FTAI) can alleviate economic burden associated with FTAI. In experiment 1, the total number of cows exposed per bull was negatively correlated with pregnancy rate to natural service on first return to estrus after FTAI in fall herds. The number of open cows per bull in fall herds using one natural service sire was negatively correlated with pregnancy rate on first return to estrus. There was no correlation between number of cows exposed per bull and pregnancy rates in fall herds with multiple sires or in spring herds. However, bull:cow ratio accounted for only 5–11% of the variation in pregnancy rates, thus we conclude that a reduced bull:cow ratio did not affect natural service return to estrus pregnancy rate. Experiment 2 examined how supplementing calcium salts of soybean oil (CSSO) improves beef cow fertility. Non-pregnant cows received supplement with either saturated fat or omega-6 rich CSSO. There were no changes in dominant follicle diameter, corpus luteum volume, plasma progesterone, or endometrial gene expression (PTGES and AK1B1, PPARA, PPARA, PPARD) between treatments. Plasma and follicular fluid fatty acid compositions were altered between treatments. Experiment 3 examined if size parameters of zygotes have potential as a non-invasive, objective embryo selection method. The outer diameter, area of ooplasm, and thickness of zona pellucida (ZP) was digitally measured on individual artificially activated oocytes and in-vitro fertilized (IVF) zygotes. Larger outer diameter increased probability of development to the blastocyst stage by days 7 and 8 for activated oocytes and tended to by day 8 for IVF zygotes. Thinner ZP increased probability of development to blastocyst stage on days 7 and 8 for oocytes, and to day 8 for IVF zygotes. Area did not affect development but was positively correlated with blastomere number on day 8. An interaction between diameter and ZP thickness was observed in zygotes, but not activated oocytes, suggesting oocyte activation is not always a suitable replacement for in-vitro fertilization.Doctor of Philosophy
We need to improve reproductive efficiency in beef cows if we are to combat the challenges of producing more food while using less resources due to limited land availability and concerns with greenhouse gas emissions from agriculture. In cow-calf production systems, this means producing one healthy calf per cow per year. Cattlemen can implement a variety of assisted reproductive technologies to achieve this goal. Achieving maximal reproductive efficiency will require using technologies that are incorporated into herd management, individual animal care, and in vitro embryo production. Fixed time artificial insemination (FTAI) allows cattlemen to maximize the number of cows becoming pregnant and calving earlier in the season to increase efficiency. Unfortunately, use of FTAI is uncommon in cow-calf production systems because of labor and economic restraints. In order to improve economic feasibility of FTAI, bull-related costs need to be reduced, which can be done through increasing the number of cows serviced per bull (decreasing the bull:cow ratio). This study retrospectively examined correlations between the bull:cow ratio and pregnancy rate on first return to estrus after FTAI. There was little to no correlations between bull:cow ratio and pregnancy rates, and if they were significant, there was much variation in the data. With this we concluded that a reduced bull:cow ratio does not affect pregnancy rate on first return to estrus, allowing producers to increase the number of cows serviced by a single bull and reduce bull related costs. Supplementing calcium salts of soybean oil (CSSO) that are rich in omega-6 fatty acids can enhance beef cow fertility, but it is unclear why this happens. Using non-pregnant cows as a model, we studied the effects of either saturated fat or CSSO on reproductive parameters such as ovarian structures, hormone concentrations, and uterine gene expression. There were no changes in any of these parameters between treatments, but there were changes in the concentrations of certain plasma and follicular fluid fatty acids. There was also reduced activity of lipid metabolism enzymes. We were unable to pinpoint how CSSO supplementation improves reproduction, but the altered fatty acid content of tissues and altered enzyme activity likely plays a key role, thus ultimately impacting fatty acid utilization and growth of the embryo. In-vitro embryo production can increase the number of offspring produced from a single female and accelerate the incorporation of animals with high genetic merit into herds. To obtain optimal pregnancy rates with in vitro embryos, we should develop non-invasive, objective methods for identifying the most viable embryos. This study examined if size parameters of activated and fertilized oocytes are indicative of successful development. We discovered that oocytes with large diameters and those with thin zona pellucida were most likely to develop to the blastocyst stage, and that the area of the cell was positively correlated with blastocyst total cell number. An interaction between diameter and ZP thickness was observed in zygotes, but not activated oocytes, suggesting oocyte activation is not always a suitable replacement for in-vitro fertilization. This suggests that digital measurements of fertilized oocytes may have potential as objective selection criteria Addressing issues of reproductive inefficiency in beef cows requires a comprehensive approach, as there is not one ideal solution. Management techniques can alleviate the cost of FTAI by reducing the number of bulls used without affecting pregnancy rates. Supplementing CSSO can alter tissue fatty acids to enhance fertility. Finally, the efficiency of in vitro embryo production can be improved by selecting better embryos for transfer without compromising the embryo. Combinations of all these techniques can create more reproductively efficient animals.
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Timlin, Claire. "Strategies for Improving Reproductive Efficiency of Beef Cattle with Assisted Reproductive Technologies". Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/98841.
Testo completoAbstract (sommario):
Reproductive efficiency in beef cattle can be improved with reproductive technologies at the herd, individual cow, and embryonic levels. Decreasing the bull:cow ratio for natural service after fixed time artificial insemination (FTAI) can alleviate economic burden associated with FTAI. In experiment 1, the total number of cows exposed per bull was negatively correlated with pregnancy rate to natural service on first return to estrus after FTAI in fall herds. The number of open cows per bull in fall herds using one natural service sire was negatively correlated with pregnancy rate on first return to estrus. There was no correlation between number of cows exposed per bull and pregnancy rates in fall herds with multiple sires or in spring herds. However, bull:cow ratio accounted for only 5–11% of the variation in pregnancy rates, thus we conclude that a reduced bull:cow ratio did not affect natural service return to estrus pregnancy rate. Experiment 2 examined how supplementing calcium salts of soybean oil (CSSO) improves beef cow fertility. Non-pregnant cows received supplement with either saturated fat or omega-6 rich CSSO. There were no changes in dominant follicle diameter, corpus luteum volume, plasma progesterone, or endometrial gene expression (PTGES and AK1B1, PPARA, PPARA, PPARD) between treatments. Plasma and follicular fluid fatty acid compositions were altered between treatments. Experiment 3 examined if size parameters of zygotes have potential as a non-invasive, objective embryo selection method. The outer diameter, area of ooplasm, and thickness of zona pellucida (ZP) was digitally measured on individual artificially activated oocytes and in-vitro fertilized (IVF) zygotes. Larger outer diameter increased probability of development to the blastocyst stage by days 7 and 8 for activated oocytes and tended to by day 8 for IVF zygotes. Thinner ZP increased probability of development to blastocyst stage on days 7 and 8 for oocytes, and to day 8 for IVF zygotes. Area did not affect development but was positively correlated with blastomere number on day 8. An interaction between diameter and ZP thickness was observed in zygotes, but not activated oocytes, suggesting oocyte activation is not always a suitable replacement for in-vitro fertilization.Doctor of Philosophy
We need to improve reproductive efficiency in beef cows if we are to combat the challenges of producing more food while using less resources due to limited land availability and concerns with greenhouse gas emissions from agriculture. In cow-calf production systems, this means producing one healthy calf per cow per year. Cattlemen can implement a variety of assisted reproductive technologies to achieve this goal. Achieving maximal reproductive efficiency will require using technologies that are incorporated into herd management, individual animal care, and in vitro embryo production. Fixed time artificial insemination (FTAI) allows cattlemen to maximize the number of cows becoming pregnant and calving earlier in the season to increase efficiency. Unfortunately, use of FTAI is uncommon in cow-calf production systems because of labor and economic restraints. In order to improve economic feasibility of FTAI, bull-related costs need to be reduced, which can be done through increasing the number of cows serviced per bull (decreasing the bull:cow ratio). This study retrospectively examined correlations between the bull:cow ratio and pregnancy rate on first return to estrus after FTAI. There was little to no correlations between bull:cow ratio and pregnancy rates, and if they were significant, there was much variation in the data. With this we concluded that a reduced bull:cow ratio does not affect pregnancy rate on first return to estrus, allowing producers to increase the number of cows serviced by a single bull and reduce bull related costs. Supplementing calcium salts of soybean oil (CSSO) that are rich in omega-6 fatty acids can enhance beef cow fertility, but it is unclear why this happens. Using non-pregnant cows as a model, we studied the effects of either saturated fat or CSSO on reproductive parameters such as ovarian structures, hormone concentrations, and uterine gene expression. There were no changes in any of these parameters between treatments, but there were changes in the concentrations of certain plasma and follicular fluid fatty acids. There was also reduced activity of lipid metabolism enzymes. We were unable to pinpoint how CSSO supplementation improves reproduction, but the altered fatty acid content of tissues and altered enzyme activity likely plays a key role, thus ultimately impacting fatty acid utilization and growth of the embryo. In-vitro embryo production can increase the number of offspring produced from a single female and accelerate the incorporation of animals with high genetic merit into herds. To obtain optimal pregnancy rates with in vitro embryos, we should develop non-invasive, objective methods for identifying the most viable embryos. This study examined if size parameters of activated and fertilized oocytes are indicative of successful development. We discovered that oocytes with large diameters and those with thin zona pellucida were most likely to develop to the blastocyst stage, and that the area of the cell was positively correlated with blastocyst total cell number. An interaction between diameter and ZP thickness was observed in zygotes, but not activated oocytes, suggesting oocyte activation is not always a suitable replacement for in-vitro fertilization. This suggests that digital measurements of fertilized oocytes may have potential as objective selection criteria. Addressing issues of reproductive inefficiency in beef cows requires a comprehensive approach, as there is not one ideal solution. Management techniques can alleviate the cost of FTAI by reducing the number of bulls used without affecting pregnancy rates. Supplementing CSSO can alter tissue fatty acids to enhance fertility. Finally, the efficiency of in vitro embryo production can be improved by selecting better embryos for transfer without compromising the embryo. Combinations of all these techniques can create more reproductively efficient animals.
20
Webb, Robert. "Control of reproductive function". Thesis, University of Edinburgh, 2012. http://hdl.handle.net/1842/27629.
Testo completoAbstract (sommario):
My research has focused on the control of reproductive function, particularly ovarian function in farm animal species. It has included the study of the mechanisms controlling follicular growth, ovulation rate control and corpus luteum function. Experimental approaches have included comparisons between mono- and poly-ovular species, between breeds of sheep with differing ovulation rates and utilising genetically selected lines of sheep. The work has included the development of a novel ovarian transplantation approach in large animal species for maintaining fertility after low temperature freezing. As well as providing an excellent large animal model to study the recruitment of primordial follicles and follicle development to ovulation, it is currently being extended to the development of whole ovary cryopreservation and transplantation. The research has involved the delineation of the importance and roles of gonadotrophins, metabolic hormones and locally-produced growth factors in follicular growth and development. The results demonstrated the interaction between extraovarian hormones and intra-ovarian growth factors, including the importance of growth hormone and related hormones and growth factors on follicular development. These studies required the development and detailed validation of a range of hormone assays and physiologically relevant cell culture systems for follicular cells. The importance of environmental factors, such as nutrition, was investigated. This included the demonstration of the direct effects of nutrition on gene expression within follicular cells to influence oocyte quality and embryo survival. Subsequent work investigated the underlying mechanisms of action, demonstrating the differing impact of various metabolic factors necessary for either follicular growth or the maintenance of oocyte quality. This research enabled the formulation of diets and feeding strategies that significantly improved pregnancy rates in dairy cattle and which are now being used by the industry. This work is of particular relevance in halting the decline in fertility, since selection of dairy cows on the single trait of milk production was shown to result in a continuing reduction in conception rates at approximately 1% per annum.
21
Flanagan, Kate Elizabeth. "Reproductive strategies in parasitoids". Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244765.
Testo completo
22
Varndell, Nigel Philip. "Reproductive strategies in insects". Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430060.
Testo completo
23
Madgwick, Suzanne. "Reproductive development in calves". Thesis, University of Newcastle Upon Tyne, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401845.
Testo completo
24
Smith, Keith Charles. "Reproductive abnormalities in ewes". Thesis, University of Bristol, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319129.
Testo completo
25
Guinnee, Meghan A. "Plasticity in reproductive traits". Thesis, University of Edinburgh, 2005. http://hdl.handle.net/1842/16998.
Testo completoAbstract (sommario):
In this thesis, I explore how an individual’s environment, or the environment of its mother, affects its reproductive life-history characteristics (age at maturity, size at maturity, offspring size, offspring number). I attempt to explain observed responses using adaptive reasoning and/or mathematical modelling. I find that mean egg size decreases with increasing clutch size in Daphnia, and explore possible causes of this using a mathematical model. This pattern could be an adaptive response, if larger offspring have greater fitness advantages in food-limited environments. However, such a pattern can also result from a minimum viable egg size that is similar to the optimal egg size. I also empirically test the fitness effects of hatching from a small or large egg in Daphnia. I find that offspring from food-limited mothers are larger, but that they mature later, produce less offspring per clutch, do not produce larger offspring and produce fewer offspring per unit time. I find that the nematode parasites Strongyloides ratti and Nippostrongylus brasiliensis mature at different rates depending on the efficacy of the host immune response, but that differences are species-dependent. In addition, female N. brasiliensis suffer decreased fecundity at higher densities, but only in hosts with fully-functioning immune systems; in hosts with no thymus-based immune system, there is no density-dependent fecundity effect. This suggests that the density-dependent effects often observed in parasitic nematodes are mediated by the host immune system. This thesis reminds us that small differences in an individual’s surroundings, or even its mother’s surroundings, can profoundly affect when, how, and how successfully an animal reproduces. Often, these effects can be explained using adaptive reasoning, and/or mathematical modelling. When and how an animal reproduces is certain to have consequences for its fitness. Implications and future research directions are also discussed.
26
Vincent, Amanda Claire Jane. "Reproductive ecology of seahorses". Thesis, University of Cambridge, 1990. https://www.repository.cam.ac.uk/handle/1810/283668.
Testo completo
27
Fujita, Shiho. "Reproductive Biology in Wild Female Primates : Variability in Hormonal Profiles, Behavior and Reproductive Parameters". 京都大学 (Kyoto University), 2003. http://hdl.handle.net/2433/149150.
Testo completo
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Rivera, Gutiérrez Priscila. "En Busca de la Donante Perfecta. Narrativas en torno a la ovodonación". Doctoral thesis, Universitat Autònoma de Barcelona, 2021. http://hdl.handle.net/10803/673341.
Testo completoAbstract (sommario):
A la recerca de la donant perfecta analitza com el mercat reproductiu permea les experiències de les dones que acudeixen a les clíniques per donar els seus òvuls. A partir dels seus narratives, en aquesta dissertació, exploro la forma en què està organitzat el sistema de ovodonació a Barcelona. Alhora que pretén visualitzar les seves reflexions, motivacions, vivències i temors al voltant de l'acte de donar, però també el paper que adquireixen les substàncies i els cossos reproductius a l'interior de la biotecnologia.En busca de la donante perfecta analiza cómo el mercado reproductivo permea las experiencias de las mujeres que acuden a las clínicas para donar sus óvulos. A partir de sus narrativas, en esta disertación, exploro la forma en que está organizado el sistema de ovodonación en Barcelona. A la vez que pretende visualizar sus reflexiones, motivaciones, vivencias y temores en torno al acto de donar, pero también el rol que adquieren las sustancias y los cuerpos reproductivos al interior de la biotecnología.
Looking for a Perfect Donor analyzes how the reproductive market permeates the women's experiences who come to clinics to donate their eggs. Based on their narratives, in this dissertation, I explore the way the egg donation system is organized in Barcelona. At the same time, it intends to visualize their reflections, motivations, experiences, and fears around the act of donating and the role that substances and reproductive bodies play within the biotechnology of women who come to clinics to donate their eggs.
Universitat Autònoma de Barcelona. Programa de Doctorat en Antropologia Social i Cultural
29
Hardy, Ian Charles Wrighton. "Reproductive strategies in parasitic wasps". Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/46805.
Testo completo
30
Foy, Robbie. "Promoting effective reproductive health care". Thesis, University of Edinburgh, 2005. http://hdl.handle.net/1842/29108.
Testo completoAbstract (sommario):
This thesis is concerned with approaches used by the Scottish Programme for Clinical Effectiveness in Reproductive Health (SPCERH) to improve quality of care. The work embraces two main themes: understanding factors that influence clinical practice; and evaluating strategies to improve practice. Many factors influence practice, such as the nature of targeted behaviours, professionals and organisations (Chapter 1). An observational study, of practice related to 42 audit recommendations in 16 gynaecology units, found that attributes of recommendations independently modified the effects of a national audit and feedback project (Chapter 2). Four evaluations of dissemination and implementation strategies were conducted. The first, a telephone survey of 201 obstetricians and midwives, highlighted gaps in awareness of national recommendations on the prevention of material mortality (Chapter 3). The second, a before-and-after postal survey of 92 obstetricians, found mixed changes in self-reported practice following the dissemination of four national obstetric guidelines (Chapter 4). The third, an interrupted time series analysis, evaluated trends in the care of 1263 women in four maternity units related to of these guidelines, on mild, non-proteinuric hypertension in pregnancy (Chapter 5). No improvements in the appropriateness of initial investigations and subsequent clinical management were found. The fourth study, a cluster randomised trial involving all 26 gynaecology units in Scotland, evaluated a strategy to promote a guideline on induced abortion care. The strategy, delivered under the auspices of SPCERH, comprised audit and feedback, educational meetings, dissemination of a structured case record, and promotion of patient information. The strategy was refined in the light of barriers identified following a pre-intervention case record review, interviews with gynaecologists and a theoretically-derived survey of 151 clinical staff (Chapter 6). Post-intervention compliance with guideline recommendations was assessed by a review of 1474 case records and a survey of 1028 patients. No intervention effect was observed, possibly related to high pre-intervention compliance with selected recommendations and the appropriateness of the implementation strategy (Chapter 7).
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McLeod, Carolyn. "Self-trust and reproductive autonomy". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0018/NQ49281.pdf.
Testo completo
32
West, Stuart Andrew. "Reproductive strategies in parasitic Hymenoptera". Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309736.
Testo completo
33
Waters, Brent. "The family and reproductive technologies". Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312634.
Testo completo
34
Read, Andrew F. "Comparative analyses of reproductive tactics". Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.256378.
Testo completo
35
Coello, Segundo. "Reproductive biology of Atlantic mackerel". Thesis, Bangor University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276820.
Testo completo
36
Sourbut, Elizabeth M. "Property in reproductive body parts". Thesis, University of York, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.533474.
Testo completo
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Wilson, Ann Margaret. "Reproductive allocation in flowering plants". Thesis, University of Plymouth, 1986. http://hdl.handle.net/10026.1/2206.
Testo completoAbstract (sommario):
The proportion of resources which an organism devotes to reproduction has been assumed to be of great evolutionary and ecological significance. However, in previous studies of reproductive allocation (RA) in plants, there has been no consensus of precisely what is being measured nor how it should be measured. An attempt was made to determine the 'best' method of measuring RA and then apply this to a range of species with differing ecological strategies. Under nutrient stress caused by a low N treatment Taraxacum officinale and Poa annua were found to maintain their RA despite up to 4 fold reductions in biomass. Under K and P deficient conditions there was a preferential allocation of these elements to reproductive structures in Taraxacum. Ruderal plants therefore, seem to maintain biomass RA and seed quality despite nutrient stress. Although the nutrient RA in Taraxacum was found to be significantly different from biomass RA (KRA = 71% PRA = 66% BRA= 51.7%) the extent of the difference varied between treatments. There was therefore no obvious alternative currency to biomass. The evolutionary consequences of reproduction may also be measured through a reproductive cost which may take the form of reduced future reproduction, survival or growth. Prevention of flowering in Digitalis purpurea resulted in an increase in the number of axillary buds produced, Similarly in Plantago lanceolata removal of flowers resulted in a 3 fold increase in production of buds. In both species realisation of a reproductive cost was prevented. The importance of individual variability was noted. The importance of plant morphology was evident and was used to explain some of the anomalous RA values in the comparative experiment. RA values were collected for 40 species of Gramineae. RA was a useful ecological index which emphasised the ruderal element of a plant's strategy. When used in conjunction with other parameters particularly Rmax, RA produced a meaningful classification of species in terms of their ecological strategy.
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Jones, Katherine M. G. "Reproductive decisions in monogamous birds". Thesis, University of Glasgow, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368524.
Testo completo
39
Newson, Lesley. "Kin, culture and reproductive decisions". Thesis, University of Exeter, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273006.
Testo completo
40
Francis, Anne Julia. "Chemical impairment of reproductive functions". Thesis, University of Surrey, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293344.
Testo completo
41
Reynolds, Louis Percy. "Reproductive bud development in pears". Thesis, Stellenbosch : Stellenbosch University, 2004. http://hdl.handle.net/10019.1/50079.
Testo completoAbstract (sommario):
Thesis (MScAgric)--University of Stellenbosch, 2004.ENGLISH ABSTRACT: Reproductive bud development is the first step of sexual reproduction of plants and is a major factor determining yield. For consistent yields in pears, knowledge of the development of the reproductive bud is required. The development of the reproductive bud with emphasis on the primordial bourse shoot was studied. The bourse shoot is important because of the ability of a bourse shoot to become reproductive, which can lead to bourse-overbourse bearing. The progression of reproductive bud development in 'Forelle' and 'Rosemarie' was studied from primordial bourse shoot initiation until dormancy the following season. The primordial bourse shoot was initiated in January 2003. The primordial bourse shoot progressed during dormancy with a plastochron length of 60 days in June. The rate of preformed leaf formation increased rapidly until August when the plastochron was 5 days. 'Rosemarie's' primordial bourse shoot development was more advanced at full bloom, which is a possible reason for the higher bourse-aver-bourse bearing habit of the cultivar. The number of leaves of the bourse shoot was more than with the 'Forelle', which has a low tendency for bourseover- bourse bearing. Flower initiation of the terminal bourse shoot bud was 56 and 77 d.a.f.b. for the 'Forelle' and 'Rosemarie', respectively. Initiation was well correlated with bourse shoot growth cessation. An increase in mitotic activity occurred during flower differentiation of the terminal bourse bud with a peak of floral appendage formation during December and January. From February until dormancy enlargement of the floral parts took place. The influence of severe dormant pruning and the quality of 2- year-old wood, on reproductive bud sink strength of 'Packham's Triumph' trees were investigated. The sink strength of primary growth increased by 40 % for short bearing units (SBU's) and 140 % for thick bearing units (BU's) as compared to long bearing units (LBU's) and thin BU's respectively. The increase in primary growth was due to better fruit set and larger fruit in the SBU's and the thick BU's. Since the increase in primary growth is less for SBU's compared to thick BU's the conclusion, which can be made, is that branch diameter influenced sink strength more than branch length. With increase in branch diameter the size of the xylem transport system increases more than that of the phloem. The increase in xylem transported metabolites, in particular root derived cytokinin seems to predominantly influence the magnitude of the sink strength. The influence of scoring and 6-benzyladenine (BA) application, during the flower induction phase on 'Doyenne du Cornice' and 'Rosemarie', were studied. Scoring caused a 50 % increase in fruit number of 'Doyenne du Cornice', which resulted in a 38 % increase in yield compared to the control. The increase in fruit number was due to higher percentage reproductive buds and improved bud quality. For the 'Rosemarie' scoring at the correct time resulted in a 40 % increase in reproductive buds. Scoring disrupts basipetal transport in the phloem, which results in the removal of apical dominance and an increase in root derived cytokinin's. More meristems can respond to inductive conditions and high quality reproductive buds develop. The combination of BA and scoring, lead to more flowers per inflorescence in 'Doyenne du Cornice'.
AFRIKAANSE OPSOMMING: Reproduktiewe knopontwikkeling by die peer Reproduktiewe knopontwikkeling is die eerste fase van reproduktiewe voortplanting in plante en is belangrik, want dit bepaal die oesgrootte. Vir konstante oeste in peerproduksie moet reproduktiewe knopontwikkeling verstaan word. Die ontwikkeling van die reproduktiewe knop, meer spesifiek die primordiale beursloot is bestudeer. Die beursloot is belangrik a.g.v. die beurs-oorbeurs drawyse. Die ontwikkeling van die reproduktiewe knop van 'Forelle' en 'Rosemarie' is gevolg. Die primordiale beursloot is Januarie 2003 geinisieër en ontwikkel tydens die boom se dormante fase met 'n plastochron van 60 dae gedurende Junie. Preformeerde blaarvormingstempo neem toe tot Augustus waar die plastochron 5 dae is. 'Rosemarie' se primordiale beursloot ontwikkeling was meer gevorderd teen volblom, met meer beurslootblare reeds teenwoordig. Dit is dalk die rede vir die hoër tendens van beurs-oor-beurs drag van die kultivar in vergelyking met 'Forelle'. Die terminale beurslootknop is 56 en 77 dae na volblom geïniseer vir 'Forelle' en 'Rosemarie' respektiewelik. Inisiasie was goed gekorreleerd met beeïndiging van beurslootgroei. Blomdifferensiasie het inisiasie gevolg met 'n toename in mitotiese aktiwiteit, blomaanhangsel vorming het 'n piek bereik III Desember en Januarie. Vanaf Februarie tot dormansie het ontwikkeling hoofsaaklik in vergroting van blomorgane plaasgevind. Die invloed van strawwe dormante snoei en die kwaliteit van 2-jaar-oue dra-eenhede op sinksterkte van reproduktiewe knoppe van 'Packham's Triumph' pere is ondersoek tydens die 2002/03 seisoen. Die sinksterkte van primêre groei het 40 % toegeneem vir kort dra-eenhede en 140 % vir dik dra-eenhede in vergelyking met lang dra-eenhede en dun dra-eenhede respektiewelik. Die toename in primêre groei vir kort en dik dra-eenhede kon toegeskryf word aan beter vrugset en groter vrugte. Omdat die toename in sinksterkte minder is vir kort dra-eenhede in vergelyking met dik dra-eenhede kan die afleiding gemaak word dat dra-eenheiddikte sinksterkte meer beïnvloed as dra-eenheidlengte. Met 'n toename in dra-eenheiddikte, neem xileemvaatweefsel meer toe as floeëmvaatweefsel. 'n Toename in xileem getranslokeerde metaboliete, meer spesifiek wortel vervaardigde sitokiniene beïnvloed die sinksterkte van die reproduktiewe knoppe. Die invloed van ringelering (ringsnit deur floeëm sonder bas verwydering) en 6-bensielaldenien (BA) toediening tydens reproduktiewe knopinduksie van 'Doyenne du Cornice' en 'Rosemarie' is ondersoek. Ringelering het 'n 50 % toename in vrugaantal veroorsaak wat die oes met 38 % laat toeneem het in vergelyking met die kontrole, vir 'Doyenne du Cornice'. Die toename in vrugte was a.g.v. 'n hoër persentasie reproduktiewe knoppe en toename in blomkwaliteit. By 'Rosemarie' het ringelering 'n 40 % toename in reproduktiewe knoppe bewerkstellig. Ringelering onderbreek die basipetale vervoer in die floeëm, verwyder dus apikale dominansie, met die gevolg dat daar 'n toename in wortel geproduseerde sitokiniene is. Meer meristeme reageer op induktiewe toestande en reproduktiewe knoppe van hoë kwaliteit vorm. Die kombinasie van ringelering en BA -toediening het meer blomme per reproduktiewe knop veroorsaak.
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Fontes, Sónia Alexandra de Jesus. "Reproductive management in captive elephants". Master's thesis, Universidade de Lisboa, Faculdade de Medicina Veterinária, 2017. http://hdl.handle.net/10400.5/14044.
Testo completoAbstract (sommario):
Dissertação de Mestrado Integrado em Medicina VeterináriaElephants have been widely used by Humans for several centuries: for meat, as warriors through several kingdoms, for their heavy work power, for public entertainment, and for their unique tusks, leading them to be poached for the ivory trade. Nowadays we face the reality of a decreasing number of elephants in most of their range countries, leading them to be considered endangered (Asian) or vulnerable (African) to extinction. Being charismatic mega-vertebrates, made them one of the most desired wildlife to keep and show in zoological collections. Interdiction to the importation of wildlife was an important step, but with no more importation of individuals from the wild, the need to preserve the captive population became mandatory, and the zoological institutions make great efforts to maintain these animals in their collection and extend the conservation of these species. The inability to produce sufficient captive offspring and the continuous declining number in their natural habitat has urged research on elephant reproduction physiology. Asian and African elephants reproduce well in the wild but due to historically poor reproductive performance under human care, most captive populations face the possibility of local extinction. Besides logistical issues, elephant breeding in captivity faces management problems due to diseases, like ovarian and uterine pathologies and bull infertility. Therefore, it is important to understand the anatomy, physiology and all associated pathologies which can lead to reproduction failure, and for the future management of captive elephant populations is fundamental to ensure that professional decisions are made. Recent advances in endocrine monitoring and ultrasound imaging techniques allow researchers to understand the complex mechanisms that control reproduction in elephants, unique in several features. In this thesis, I reviewed all relevant studies from 2000 to nowadays, with special emphasis to the African elephant. Reproductive breeding management considerations to the captive population of the Lisbon Zoo were derived. Finally, four clinical cases in elephant reproduction that were followed and assisted by the author are analysed and discussed.
RESUMO - Maneio reprodutivo de elefantes em cativeiro - Por muitos séculos, os elefantes têm sido utilizados pelo Homem: como produto de caça, soldados de guerra de diversos reinos, pela sua capacidade de trabalho pesado e pelas suas presas, levando a que sejam abatidos para o mercado de marfim. Atualmente, na maior parte da sua distribuição, o número de elefantes continua a decrescer o que levou à sua corrente classificação em “Vulnerável” (Africano) e em “Ameaça de Extinção” (Asiático). Devido ao carisma destes mega vertebrados, os elefantes são um dos mais desejados animais para manter e exibir em Zoos. A interdição à importação de mais indivíduos do meio selvagem foi um passo importante para a conservação destas espécies, mas tornou a manutenção das populações cativas existentes uma prioridade e grandes esforços foram tomados pelas instituições de cativeiro. Um ponto fulcral tem sido o estudo da fisiologia reprodutiva dos elefantes, para que seja atingido um número de descendentes suficientes para manter estas populações. Tanto os elefantes asiáticos (Elephas maximus) como os elefantes africanos (Loxodonta africana) conseguem reproduzir-se com sucesso no meio selvagem mas, devido a uma história de baixa performance reprodutiva sob cuidados humanos, muitas das populações cativas correm o risco de extinção local. Para além de problemas logísticos, a reprodução de elefantes em cativeiro debate-se com questões de maneio devido a enfermidades, como patologias ováricas e uterinas e infertilidade no macho. Compreender e tornar disponível as novas descobertas no ramo da anatomia, fisiologia e as mais comuns patologias associadas a falha reprodutiva tornou-se então uma prioridade para garantir que decisões ponderadas possam ser tomadas no maneio de elefantes cativos. Avanços recentes em monitorização hormonal e em técnicas de ultrasom permitiu aos investigadores perceber os mecanismos complexos que controlam a reprodução nos elefantes, que apresentam variadas características únicas. Posto isso, nesta tese, foram recolhidos e compilados todos os resultados relevantes publicados desde o ano 2000, com especial ênfase em dados relativos ao elefante africano. Considerações sobre o maneio reprodutivo da população de elefantes Africanos existente no Jardim Zoológico de Lisboa são também abordadas. Por fim, quatro casos clínicos, auxiliados e seguidos pelo autor são analisados e debatidos.
N/A
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Pirk, Christian Walter Werner. "Reproductive conflicts in honeybee colonies". Thesis, Rhodes University, 2002. http://hdl.handle.net/10962/d1005443.
Testo completoAbstract (sommario):
In advanced eusocial hymenopteran societies workers have ovaries and can lay eggs, but are unable to mate. Workers are more related to their own offspring than to every other member of the colony. So worker reproduction contains both worker-worker and worker-queen conflict. The queen- worker conflict is discussed elsewhere, but if the queen mates with more than two males, worker policing should be selected to lower potential conflicts. However in the Cape honeybee it was predicted that worker policing is absent or less expressed than in other honeybee subspecies, because workers produce female offspring thelytokously. So laying workers and their offspring are nearly genetically identical, which results in the fact that other workers are as related to workers derived from eggs laid by the queen as laid by a worker. However, worker reproduction may be costly and therefore worker policing could be an evolutionary adaptation in the Cape honeybee to lower the costs derived from laying worker activity. Indeed, Cape honeybee colonies show efficient egg removal behaviour, suggesting that other factors like colony efficiency could favour egg removal behaviour. Since egg removal behaviour is a colony phenomenon, factors that affect colony performance could also affect egg removal behaviour. Egg removal behaviour was considerably affected by environmental changes, indicating that other tasks have a higher priority than egg removal behaviour. Thousands of queenright colonies of the neighbouring subspecies (A. m. scutellata) were taken over by laying A. m. capensis workers, showing that A. m. capensis workers are facultative social parasites. These observations strongly indicate that laying workers of A. m. capensis are able to evade worker policing and the inhibitory effects of the queen pheromones, but what potential strategies could these laying workers use to increase the survival of their eggs and evade the queen? On the one hand, egg removal behaviour is variable. One behavioural strategy of laying workers to achieve successful reproduction could be that they lay during periods with low egg removal behaviour. On the other hand, the inhibitory effect of the queen’s pheromones diminishes with distance. Maybe the level of egg removal also depends, like the inhibitory effect of the queen pheromones, on the distance from the queen. Indeed, further away from the queen the effect of the queen pheromone and the level of egg removal is reduced, making successful worker reproduction possible. In both subspecies, A. m. capensis and A. m. scutellata, egg removal behaviour is reduced further away from the queen. In the case of A. m. scutellata egg removal is lacking further away from the queen. This explains why colonies of scutellata are so prone to takeovers by laying Cape honeybee workers. One question in the context of parasitic Cape honeybees is how they manage to get into the host colony. One way could be that they get into the colonies during a natural colony merger which is common in African bees. Two unrelated colonies merged and it took them only 24 hours to show effective integration. Because both colonies are unrelated, the potential reproductive conflict among workers should be more strongly expressed than in a normal colony, which is not the result of a merger. Therefore, the effect of nestmate recognition for eggs on the egg removal behaviour was investigated. The results suggest that workers recognise the origin of an egg and that the standard policing experiments overestimate the level of egg removal and only represent relative values. Moreover, the results show that colony specific components on the eggs are more important than a postulated queen egg marking pheromone. Finally, for the first time empirical evidence from a population of the parasitic laying Cape honeybee workers, invading thousands of colonies of A. m. scutellata in northern South Africa, for a short-sighted selection theory is presented.
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Whitekettle, Richard W. "Studies in Levitical reproductive impurity". Theological Research Exchange Network (TREN), 1994. http://www.tren.com.
Testo completo
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Tortosa, Christina Suzanne. "Reproductive diseases of dairy cattle /". Click here to view, 2009. http://digitalcommons.calpoly.edu/dscisp/6.
Testo completoAbstract (sommario):
Thesis (B.S.)--California Polytechnic State University, 2009.Project advisor: Edwin Jaster. Title from PDF title page; viewed on Jan. 21, 2010. Includes bibliographical references. Also available on microfiche.
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Tshiswaka-Kashalala, Gauthier. "Reproductive Health and Labour Outcomes". Thesis, University of Pretoria, 2014. http://hdl.handle.net/2263/45867.
Testo completoAbstract (sommario):
This thesis formalizes the interaction between income and fertility outcomes using a
fertility model taking account of mediation. Despite the diversity of studies concerned
with the determinants of fertility, one consistent nding is that the timing and the
number of children born to a couple are ultimately determined by the interaction
between a couple's fecundity and their contraceptive behaviour. For example, fecund
individuals may or may not be sexually active, may or may not be using contraception,
which would in
uence their degree of risk for pregnancy. In this context, fecundity
is a necessary but insu cient cause of fertility. The two variables, fecundity and
contraception, are mediator variables in the causal path between income and fertility
(Baron and Kenny, 1986). It follows that, understanding the interaction between
biological and behavioural determinants of fertility holds the key to understanding
fertility trends in any society.
With our understanding of causal-mediation in place, this thesis extends the health
investment model to develop a model of the sequential nature of the human reproductive
process. Because reproductive health is commonly understood as the capability
to procreate and the freedom to decide if, when and how often to do so, poor reproductive
health outcomes have long been acknowledged as a main cause of economic
hardship for women and their children, accounting for 18% of the total global burden
of disease and representing 32% of the burden among women of reproductive age.
Thus, the presented theoretical model of the demand for reproductive health services is a derived demand for reproductive health (with adjustment costs). Our theory
suggests that the relationship between family planning services, their marginal costs,
the stock of reproductive health capital and the woman's earnings volatility is essentially
nonlinear. The theoretical predictions arising from the model are empirically
supported from individual level South African data.
Because a number of the health costs are associated with `mistakes', in the sense
that childbearing might be ill-timed, because the reproduction process cannot be
completely controlled, at least yet, the previous model is extended to account for
uncertainty in the process. In other words, an assumption that contraception gives
women perfect control over their fertility outcomes is considered to be too simplistic.
Therefore, the focus remains on the e ectiveness of contraceptive use in controlling
fertility, but in a setting of uncertainty. The model developed ts nicely into the analysis
of the sequential nature of the human reproductive process, as it makes use of the
continuation or option value of contraception, which is assumed to depend on potential
future labor market prospects, and the uncertainty inherent in the reproduction
process. The model naturally leads to a mixed hitting time (MHT) empricial model;
a woman becomes pregnant when the underlying stochastic reproductive health process
rst crosses a threshold in zero. We nd empirical support for our theoretical
analysis.Thesis (PhD)--University of Pretoria, 2014.
tm2015
Economics
PhD
Unrestricted
47
Bjursell, Alice. "Identifying the reproductive state of female Julia Creek dunnarts (Sminthopsis douglasi) by behavioural observations". University of Southern Queensland, Faculty of Sciences, 2006. http://eprints.usq.edu.au/archive/00004243/.
Testo completoAbstract (sommario):
[Abstract]: The Julia Creek dunnart (Sminthopsis douglasi) is an endangered carnivorous marsupial. A recovery plan for the species has been initiated by Queensland Parks and Wildlife Service, which includes captive breeding.An important factor in breeding S. douglasi is the identification of oestrus. The current method to identify oestrus consists of examining urine samplesfor presence of cornified cells. To collect urine, the animals have to be removed from their cages and restrained. This method is stressful for theanimals, as well as time consuming. The aim of this study was to identify specific behaviour of S. douglasi associated with oestrus, which could be readily observed without the need for handling the animal. This wouldprovide a non-invasive way of identifying oestrus, which would facilitate breeding the species in captivity and planning conservation programs.Behaviour of S. douglasi was observed throughout the night by video recording. The most striking result was the increase in activity of the female when she was in oestrus compared to non-oestrus. The most informativebehaviour to observe was entry by the female into the nest box and the frequency with which she entered the area closest to the wall of the enclosure. A discriminant function analysis generated an equation with anover-all predictive power (OPP, the probability of making an accurate identification of reproductive state) of 89%. This result was obtained by watching two random five-minute periods of activity. The equation was tested and verified with new individuals and attained a similar level of OPP. However, the equation was less accurate when the observed female’s social context was changed from being housed adjacent to a male, to being accompanied by another female or housed singularly. Consistent with thesensitivity of activity levels as an indicator, the distance run in an exercise wheel was also a good predictor of oestrous state. Females ran a significantly longer distance in their exercise wheel when in oestruscompared to non-oestrus (p<0.001).
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Graham, Jessica Lynn. "Reproductive Timing in a Changing World: Understanding Mechanisms and Costs Associated With Reproductive Timing Decisions". Diss., North Dakota State University, 2018. https://hdl.handle.net/10365/27478.
Testo completoAbstract (sommario):
Organisms in temperate zones time reproduction to occur when conditions are optimal for raising offspring. However, individuals of many taxa vary in precise timing of breeding. The mechanisms underlying the existing variation are not well understood, particularly in females. I hypothesized that individual variation in daily (i.e., circadian) rhythms, which are highly conserved across taxa, are related to variation in reproductive timing. By measuring activity onset in two species of songbirds, we found that females beginning their day earlier also breed earlier. I further asked if sex-steroid hormones were related to onset of daily activity in free-living individuals. My results show that maximal levels of estradiol are correlated with onset of activity in free-living females. This suggests that circadian rhythms may influence much of the variation seen in timing of breeding and individual physiology influences circadian behavior. In addition to mechanisms underlying reproductive timing, I also investigated potential selective pressures that could act on timing decisions. Early breeding females often produce more and larger offspring, however, most of the population breeds later than this optimum, suggesting there are costs associated with early reproduction. To determine if early breeding females are better able to handle an additional energetic challenge, I injected incubating females with a mild antigen and monitored nest survival in early and late breeders. The immune challenge caused a significant increase in nest failure compared to controls and success did not differ between early and late breeders. Next, using a long-term dataset I asked whether females who breed early experience accelerated rates of aging via telomere loss. I found that early breeding females experience higher telomere attrition compared to females breeding later. Annual change in telomere length was not related to reproductive output, but females experiencing cooler temperatures during egg laying and incubation (i.e., laying earlier in the season) had higher telomere attrition. With telomere loss and length being important determinants of lifespan and longevity, higher telomere attrition in early breeders may be linked with reduced overwinter survival. A better understanding of mechanisms and costs will help determine how populations will adjust to, or suffer from, a changing climate.NSF; ND EPSCoR; Sigma Xi; Mountain Lake Biological Station; Department of Biological Sciences; Environmental and Conservation Sciences Program; American Ornithologists Union; Wilson Ornithological Society
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Ruhlen, Rachel L. "Diets, estrogen environment of the fetus, and development of the reproductive tract and other systems /". free to MU campus, to others for purchase, 2003. http://wwwlib.umi.com/cr/mo/fullcit?p3091965.
Testo completo
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Larkin, Katelyn. "Effects of polyploidy and reproductive mode on life history trait expression". Thesis, University of Iowa, 2015. https://ir.uiowa.edu/etd/1673.
Testo completoAbstract (sommario):
Although genomes are perhaps the single most important element of living systems, why they feature such striking variation and how this variation is maintained within and across natural populations remains unclear. One of the most common and important means by which genomic variation is generated is ploidy elevation. While polyploidy has been implicated in the remarkably successful radiations of angiosperms, teleost fish, and amphibians, the phenotypic consequences of changes in ploidy level are poorly understood, especially in animals. I use a large, multi-year common garden experiment to identify potential life history costs and benefits of polyploidy and asexual reproduction, a trait often associated with polyploidy, in Potamopyrgus antipodarum. This snail is well suited for studying ploidy variation and sex because diploid sexuals and triploid and tetraploid asexuals frequently coexist, allowing us to use comparisons of sexuals to asexuals and triploid to tetraploid asexuals to study both the effects of ploidy elevation and sex. I detected a strong negative correlation between growth rate and time to maturity and found that sexual P. antipodarum grew and matured significantly more slowly than the polyploid asexuals. Sexual P. antipodarum were also more likely to die before achieving reproductive maturity than their asexual counterparts. By contrast, there were no apparent life history differences between triploid and tetraploid asexuals, indicating that direct phenotypic benefits of ploidy elevation are unlikely to explain the relatively rapid growth and maturation of asexuals. My results suggest that ploidy elevation does not inevitably confer phenotypic consequences, that reproductive mode influences life history trait expression, and that sexual P. antipodarum persist in many natural populations in spite of substantial life history disadvantages.