1,721,011 research outputs found
Male reproductive ageing arises via multifaceted mating-dependent sperm and seminal proteome declines, but is postponable in Drosophila
No full textThese 12 datasets were collected and analysed as part of the paper 'Male reproductive ageing arises via multifaceted mating-dependent sperm and seminal proteome declines, but is postponable in Drosophila'. The datasets give: female egg laying data; insulin mutant proportion alive data; insulin mutant reproduction data; male accessory gland sperm viability data; male cyst number data; male proportion alive data; male reproduction data; male seminal vesicle and accessory gland size data; male seminal vesicle sperm viability data; number of sperm in female storage data; tudor egg laying data; tudor remating data
Characterization and 454 pyrosequencing of major histocompatibility complex class I genes in the great tit reveal complexity in a passerine system.
No full textBACKGROUND: The critical role of Major Histocompatibility Complex (Mhc) genes in disease resistance and their highly polymorphic nature make them exceptional candidates for studies investigating genetic effects on survival, mate choice and conservation. Species that harbor many Mhc loci and high allelic diversity are particularly intriguing as they are potentially under strong selection and studies of such species provide valuable information as to the mechanisms maintaining Mhc diversity. However comprehensive genotyping of complex multilocus systems has been a major challenge to date with the result that little is known about the consequences of this complexity in terms of fitness effects and disease resistance. RESULTS: In this study, we genotyped the Mhc class I exon 3 of the great tit (Parus major) from two nest-box breeding populations near Oxford, UK that have been monitored for decades. Characterization of Mhc class I exon 3 was adopted and bidirectional sequencing was carried using the 454 sequencing platform. Full analysis of sequences through a stepwise variant validation procedure allowed reliable typing of more than 800 great tits based on 214,357 reads; from duplicates we estimated the repeatability of typing as 0.94. A total of 862 alleles were detected, and the presence of at least 16 functional loci was shown - the highest number characterized in a wild bird species. Finally, the functional alleles were grouped into 17 supertypes based on their antigen binding affinities. CONCLUSIONS: We found extreme complexity at the Mhc class I of the great tit both in terms of allelic diversity and gene number. The presence of many functional loci was shown, together with a pseudogene family and putatively non-functional alleles; there was clear evidence that functional alleles were under strong balancing selection. This study is the first step towards an in-depth analysis of this gene complex in this species, which will help understanding how parasite-mediated and sexual selection shape and maintain host genetic variation in nature. We believe that study systems like ours can make important contributions to the field of evolutionary biology and emphasize the necessity of integrating long-term field-based studies with detailed genetic analysis to unravel complex evolutionary processes
Causes and consequences of male reproductive senescence
Full text linkAgeing, a universal phenomenon across all life forms, encompasses changes in a myriad of traits through organismal ontogeny. While senescence, the deterioration of traits with advancing age, is expected to be the most common outcome of ageing, there are exceptions, with some species exhibiting no change or even improvements in traits as they advance in age. Reproductive senescence is a result of declines in traits influencing mating and reproductive success. In my thesis, I address several major open questions pertaining to reproductive senescence: what is the diversity of reproductive senescence patterns across taxa?; what are the evolutionary and proximate causes of male reproductive senescence?; what processes might buffer reproductive senescence?; and what are the fitness consequences of male reproductive senescence? My thesis primarily focuses on males, which are under-represented in reproductive ageing literature compared to females. I use a combination of comparative approaches as well as experiments on the fruit fly Drosophila melanogaster. My thesis has five data chapters (chapters 2 to 6).
My second chapter compares the rates of reproductive senescence in ejaculate traits across non-human animals using meta-analytical approaches. My third chapter systematically reviews across animals, how advancing age influences seminal fluid proteins and oxidative stress. These two comparative chapters combined show that senescence at the level of the ejaculate is ejaculate trait-specific, with seminal fluid traits generally showing senescence, while ejaculate quantity traits rarely showing senescence, across taxa. In my fourth chapter, I use experiments in fruit flies to compare how age-related changes in sperm number and seminal fluid influences male fertility. These experimental results largely support conclusions from my comparative chapters (2 and 3), and suggest that male reproductive senescence is likely a consequence of decline in seminal fluid quality, not sperm number.
In my fifth and sixth chapters, I use fruit flies to study the inter-generational effects of advancing paternal age. Contrary to expectations, I find no evidence for advancing paternal age to affect offspring fitness deleteriously. Instead, my results indicate that advancing paternal age might influence offspring lifespans positively due to viability selection on old fathers. Additionally, I find that paternal age effects are confounded by the effects of paternal sperm storage duration, which studies rarely disentangle.
Overall, my thesis demonstrates that advancing male age can influence male fitness in complex ways. This complexity arises due to differential effects of male age on intra- and inter-generation fitness components, due to various demographic processes modulating senescence, and due to different traits that directly influence reproductive performance varying in their rates of senescence. My thesis has profound implications for reproductive health and understanding population dynamics because it dissects the evolutionary, mechanistic, and demographic causes and consequences of reproductive senescence
The secret in their MHC: variation and selection in a free living population of great tits
Full text linkUnderstanding the genetic basis of fitness differences has been a major goal for evolutionary biologists over the last two decades. Although there are many studies investigating how natural selection can promote local adaptation, few have succeeded to find the link between genotype and fitness of the phenotype. Polymorphic genes of the major histocompatibility complex (Mhc) are excellent candidates for such associations as they are a central component of the vertebrate immune system, playing an important role in parasite resistance, and hence can have direct effects on survival of their bearers. Although associations between Mhc and disease resistance are frequently documented, the epidemiological basis of the host-parasite interaction is often lacking and few studies have investigated the role that Mhc genes play in individual variation in fitness; thus comparatively little is known about the fitness consequences of Mhc in wild populations. Furthermore, the majority of work to date has involved testing associations between Mhc genotypes and disease. However, the mechanism by which any direct selection on the Mhc acts, depends on how genotypes map to the functional properties of Mhc molecules. The aim of this thesis was to characterize Mhc alleles in terms of their predicted functional properties and to investigate whether and how selection operates on Mhc class I functional variation using the great tit (Parus major) population at Wytham Woods as a model host species. Through a comprehensive characterization effort and the use of 454 pyrosequencing platform, I performed a detailed analysis of genetic variation at Mhc class I exon 3 and grouped alleles with similar antigen-binding affinities into supertypes to classify functionally distinct Mhc types. There was extreme complexity at the Mhc class I of the great tit both in terms of allelic diversity and gene number. A total of 862 alleles were detected from 857 individuals; the highest number yet characterized in a wild bird species. The functional alleles were clustered into 17 supertypes; there was clear evidence that functional alleles were under strong balancing selection. To understand the role of Mhc in disease resistance, I examined the linkage between Mhc supertypes, Plasmodium infection and great tit survival, and showed that certain functional variants of Mhc confer resistance to two divergent Plasmodium parasite species that are common in the environment. I further investigated the fitness consequences of functional variation at Mhc, using mark-recapture methods and long-term breeding data; and tested the hypotheses that selection: (i) maximizes Mhc diversity; (ii) optimizes Mhc diversity, or (iii) favours specific functional variants. I found that the presence of three different supertypes was associated with three different components of individual fitness: adult survival, annual recruitment probabilities and lifetime reproductive success. In contrast, there was no evidence for a selective advantage of Mhc functional diversity, either in terms of maximal or optimal supertype diversity. Finally, I explored the role that Mhc plays in female mate choice decisions and examined the reproductive fitness consequences of Mhc-dependent mating patterns. There was little evidence to suggest that functional dissimilarity at Mhc has any influence on female mate choice decisions or that dissimilarity at Mhc affects the reproductive output of the social pair. Overall, this thesis provides strong support for the suggestion that selection favours specific functional variants of Mhc, possibly as a result of supertype-specific resistance or susceptibility to parasites that exert strong selective pressures on their hosts; whereas there is no support for selection favouring maximal or optimal Mhc diversity. More importantly it demonstrates that functional variants of Mhc class I loci are an important determinant of individual fitness in natural populations
Life histories and population dynamics in variable environments
Full text linkEnvironmental variability has broad impacts on the population dynamics of species across the tree of life. Importantly, global climate change is projected to increase environmental variability in regions hosting the highest biodiversity. Therefore, understanding the life history strategies by which populations can evolve to accommodate the often negative effects of environmental variability is critical to understand how global climate change may impact populations across taxa. In this dissertation, I explore one strategy by which populations can accommodate the impacts of environmental variability – i.e., demographic buffering. Specifically, I: (1) identify criteria for determining a buffering mechanism in ecological modelling, (2) demonstrate the utility of “new” perturbation approaches (i.e., the summation of stochastic elasticities of variance and self-second derivatives) when identifying demographic buffering, (3) analyse how environmental autocorrelation and variance impact demographic buffering (as measured by the summation of stochastic elasticities of variance) and the demographic mechanisms that underly these effects, (4) test for efficacy across four measures of demographic buffering (i.e., one correlational method, two methods using terms from Tuljapurkar’s approximation and the summation of stochastic elasticities of variance) and (5) broadly review modern perspectives and suggest new directions regarding where future life history research may lead. Overall, I suggest that the summation of stochastic elasticities of variance is an effective measure of demographic buffering, and that environmental autocorrelation and variance influence this measure through population structure and demographic rate variance, respectively. Furthermore, I outline multiple avenues for future research to better understand how life histories evolve in variable environments
Experimental evolution under varying sex ratio and nutrient availability modulates male mating success in Drosophila melanogaster
No full text(NB: This dataset has been superseded by an updated, final version at https://doi.org/10.5287/bodleian:o1BVXkGQ0) This data was collected between 1 Feb - 11 March 2016 at the Department of Zoology, University of Oxford. It relates to an experiment conducted on fruit flies. Data includes mating data (mating success, mating latency, and mating duration), remating data (remating occurrence, latency, and duration) and offspring data (number of offspring and paternity share of offspring)
The sexually selected ejaculate
Full text linkThe ejaculate is composed of many different parts: proteins, lipids, and much else travels alongside sperm. With so many elements comes the problem of composition. Does the mix matter for male reproductive success? To what extent is the composition fixed? What happens when males lose control over the composition? It is with these questions that this thesis is principally concerned.
I start by testing whether males alter ejaculate composition in relation to the intensity of male-male competition. I find that divergent allocation rules govern the transfer of sperm and seminal fluid proteins (âSFPsâ). While the allocation of both responds to competition, only SFP allocation responds to its intensity. I further show that variation between SFPs in their responsiveness leads to differentially-composed seminal fluid. The resulting ejaculate compositions are each accompanied by distinct costs and benefits for male reproductive performance, some of which appear specific to seminal fluid.
I next demonstrate that loss of BMP-regulated secretions from a seminal fluid-contributing cell-type (âsecondary cellsâ) imparts a syndrome of dysregulation on male and female reproductive performance. Within this, males lose the ability to reduce female receptivity to remating, but gain an advantage in defensive sperm competition. Through a systematic dissection of different episodes influencing sperm competition outcome, I find that loss of these secretions influences sperm entry into storage and potentially enhances their resistance to displacement.
In the following two chapters I show that loss of BMP-regulated secondary cell secretions and the keystone SFP sex peptide affects seminal fluid transfer to females. In both cases, I find clear signals of between-SFP dependencies in the regulation of SFP transfer, which collectively highlight novel mechanisms of seminal fluid organisation. I argue that these organising mechanisms may be used to a maleâs advantage to exercise fine-scale, real-time control over the transfer of ready-made seminal fluid.
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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