The outcome of sperm competition is mediated largely by the relative numbers of sperm from competing males. However, substantial variation in features of sperm morphology and behaviour, such as ...length, longevity and motility, exists and researchers have suggested that this variation functions in postcopulatory sexual selection. Recent studies have determined the effect of these sperm-quality traits on fertilization success and a synthesis of this literature reveals that they are important in both sperm competition and cryptic female choice. To understand how postcopulatory sexual selection influences sperm traits, future research should determine sex-specific interactions that influence paternity, identify genetic correlations between ejaculate characters, quantify the relative costs of producing different sperm traits, and test assumptions of models of sperm quality evolution. Such research will shed light on what evolutionary pressures are responsible for the diversity in sperm morphometry and behaviour.
The Impact of Climate Change on Fertility Walsh, Benjamin S.; Parratt, Steven R.; Hoffmann, Ary A. ...
Trends in ecology & evolution,
03/2019, Letnik:
34, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Rising global temperatures are threatening biodiversity. Studies on the impact of temperature on natural populations usually use lethal or viability thresholds, termed the ‘critical thermal limit’ ...(CTL). However, this overlooks important sublethal impacts of temperature that could affect species’ persistence. Here we discuss a critical but overlooked trait: fertility, which can deteriorate at temperatures less severe than an organism’s lethal limit. We argue that studies examining the ecological and evolutionary impacts of climate change should consider the ‘thermal fertility limit’ (TFL) of species; we propose that a framework for the design of TFL studies across taxa be developed. Given the importance of fertility for population persistence, understanding how climate change affects TFLs is vital for the assessment of future biodiversity impacts.
Extreme temperatures can severely impact fertility in animals, plants, and fungi.
Climate change may render populations extinct due to fertility losses.
To understand these risks, we need a cross-species measure of thermal fertility loss.
We propose researchers investigate the ‘thermal fertility limit’ (TFL) of organisms.
Standardised measures of TFLs may help to predict species at risk under climate change.
Continued and accelerating change in the thermal environment places an ever-greater priority on understanding how organisms are going to respond. The paradigm of 'move, adapt or die', regarding ways ...in which organisms can respond to environmental stressors, stimulates intense efforts to predict the future of biodiversity. Assuming that extinction is an unpalatable outcome, researchers have focussed attention on how organisms can shift in their distribution to stay in the same thermal conditions or can stay in the same place by adapting to a changing thermal environment. How likely these respective outcomes might be depends on the answer to a fundamental evolutionary question, namely what genetic changes underpin adaptation to the thermal environment. The increasing access to and decreasing costs of next-generation sequencing (NGS) technologies, which can be applied to both model and non-model systems, provide a much-needed tool for understanding thermal adaptation. Here we consider broadly what is already known from non-NGS studies about thermal adaptation, then discuss the benefits and challenges of different NGS methodologies to add to this knowledge base. We then review published NGS genomics and transcriptomics studies of thermal adaptation to heat stress in metazoans and compare these results with previous non-NGS patterns. We conclude by summarising emerging patterns of genetic response and discussing future directions using these increasingly common techniques.
Considerable evidence exists for local adaptation of critical thermal limits in ectotherms following adult temperature stress, but fewer studies have tested for local adaptation of sublethal heat ...stress effects across life‐history stages. In organisms with complex life cycles, such as holometabolous insects, heat stress during juvenile stages may severely impact gametogenesis, having downstream consequences on reproductive performance that may be mediated by local adaptation, although this is rarely studied. Here, we tested how exposure to either benign or heat stress temperature during juvenile and adult stages, either independently or combined, influences egg‐to‐adult viability, adult sperm motility and fertility in high‐ and low‐latitude populations of Drosophila subobscura. We found both population‐ and temperature‐specific effects on survival and sperm motility; juvenile heat stress decreased survival and subsequent sperm motility and each trait was lower in the northern population. We found an interaction between population and temperature on fertility following application of juvenile heat stress; although fertility was negatively impacted in both populations, the southern population was less affected. When the adult stage was also subject to heat stress, the southern population exhibited positive carry‐over effects whereas the northern population's fertility remained low. Thus, the northern population is more susceptible to sublethal reproductive consequences following exposure to juvenile heat stress. This may be common in other organisms with complex life cycles and current models predicting population responses to climate change, which do not take into account the impact of juvenile heat stress on reproductive performance, may be too conservative.
Sex differences in dioecious animals are pervasive and result from gene expression differences. Elevated sexual selection has been predicted to increase the number and expression of male-biased ...genes, and experimentally imposing monogamy on Drosophila melanogaster has led to a relative feminisation of the transcriptome. Here, we test this hypothesis further by subjecting another polyandrous species, D. pseudoobscura, to 150 generations of experimental monogamy or elevated polyandry. We find that sex-biased genes do change in expression but, contrary to predictions, there is usually masculinisation of the transcriptome under monogamy, although this depends on tissue and sex. We also identify and describe gene expression changes following courtship experience. Courtship often influences gene expression, including patterns in sex-biased gene expression. Our results confirm that mating system manipulation disproportionately influences sex-biased gene expression but show that the direction of change is dynamic and unpredictable.
Environmental change frequently drives morphological diversification, including at the cellular level. Transitions in the environment where fertilization occurs (i.e., fertilization mode) are ...hypothesized to be a driver of the extreme diversity in sperm morphology observed in animals. Yet how fertilization mode impacts the evolution of sperm components-head, midpiece, and flagellum-each with different functional roles that must act as an integrated unit remains unclear. Here, we test this hypothesis by examining the evolution of sperm component lengths across 1103 species of vertebrates varying in fertilization mode (external vs. internal fertilization). Sperm component length is explained in part by fertilization mode across vertebrates, but how fertilization mode influences sperm evolution varies among sperm components and vertebrate clades. We also identify evolutionary responses not influenced by fertilization mode: midpieces evolve rapidly in both external and internal fertilizers. Fertilization mode thus influences vertebrate sperm evolution through complex component- and clade-specific evolutionary responses.
Increasing temperature and thermal variability generate profound selection on populations. Given the fast rate of environmental change, understanding the role of plasticity and genetic adaptation in ...response to increasing temperatures is critical. This may be especially true for thermal effects on reproductive traits in which thermal fertility limits at high temperatures may be lower than for survival traits. Consequences of changing environments during development on adult phenotypes may be particularly problematic for core traits such as reproduction that begin early in development. Here we examine the consequences of developmental thermal plasticity on subsequent adult reproductive traits and its genetic basis.
We used a panel of Drosophila melanogaster (the Drosophila Genetic Reference Panel; DGRP) in which male fertility performance was previously defined as either showing relatively little (status = ‘high’‐performing lines) or substantial (‘low’‐performing lines) decline when exposed to increasing developmental temperatures. We used a thermal reaction norm approach to quantify variation in the consequences of developmental thermal plasticity on multiple adult reproductive traits, including sex‐specific responses, and to identify candidate genes underlying such variation.
Developmental thermal stress impacted the means and thermal reaction norms of all reproductive traits except offspring sex ratio. Mating success declined as temperature increased with no difference between high and low lines, whereas increasing temperature resulted in declines for both male and female fertility and productivity but depended on line status. Fertility and offspring number were positively correlated within and between the sexes across lines, but males were more affected than females.
We identified 933 SNPs with significant evolved genetic differentiation between high and low lines. In all, 54 of these lie within genomic windows of overall high differentiation, have significant effects of genotype on the male thermal reaction norm for productivity and are associated with 16 genes enriched for phenotypes affecting reproduction, stress responses and autophagy in Drosophila and other organisms.
Our results illustrate considerable plasticity in male thermal limits on several reproductive traits following development at high temperature, and we identify differentiated loci with relevant phenotypic effects that may contribute to this population variation. While our work is on a single population, phenotypic results align with an increasing number of studies demonstrating the potential for stronger selection of thermal stress on reproductive traits, particularly in males. Such large fitness costs may have both short‐ and long‐term consequences for the evolution of populations in response to a warming world.
Exposing an insect population to increasing heat stress during development, the authors show significant variation in the population for consequences on some, but not all, subsequent adult reproductive traits. This variation is used to identify candidate genes that may underlie thermal fertility limits.
There is debate in the literature regarding the magnitude, nature, and influence of cognitive impairment in individuals with relapsing-remitting multiple sclerosis (RRMS). Therefore, we conducted a ...meta-analysis that quantified the overall magnitude of cognitive impairment in individuals with RRMS and identified the domains of cognition and clinical/demographic variables that were moderators of the overall effect. We included 57 studies with 3891 participants that yielded a total of 755 effect sizes. Overall, there was a moderate decline in cognitive functioning in individuals with RRMS compared with healthy controls. Larger effects were observed in cognitive domains of motor functioning, mood status and memory and learning. Regarding demographic and clinical variables, age and gender were moderators of cognitive impairment in all cognitive domains, whereas neurological disability and disease duration primarily moderated performance on tasks assessing memory and learning.
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