Journal of Evolutionary Biology最新文献

Sperm length is highly variable within ejaculates, between males, among populations, and across species. While theory makes strong predictions about expected mean sperm size, there is less clarity on variation in sperm, although studies have reported sperm-length variation consistent with some theoretical expectations. Typically, the coefficient of variation (CV) is used in these investigations to control for mean-variance scaling. However, a key assumption for this metric to be appropriate in controlling for mean sperm size is that the standard deviation in size scales linearly with the mean. Unfortunately, sperm-length mean-variation relationships are rarely reported making it hard to assess the validity of using CV as a way to compare mean-corrected sperm variation. Here, we investigate mean-variation relationships using 19,873 sperm length measures from 54 species and find little evidence of a consistent relationship between mean sperm-length and sperm-length variation among males within species, meaning CV is not appropriate for comparing relative (mean corrected) variation in sperm size at this level. We also find significant scaling of sperm-length variation with mean sperm-length across species, but the scaling exponent is consistently less than one, the exponent required by analyses using CV to control for sperm size. Our assessment shows that sperm mean-variation scaling relationships are rare within species and strong across species, but that neither supports the uncritical use of CV in studies of relative variation in sperm length.

Protective microbes are known for their service to hosts. While they allow hosts to survive infection, microbes, too, benefit from successful inhibition of incoming pathogens. Under constant pathogen exposure, protective symbionts should thus be selected for. Yet, it is less clear if, and how, microbe-mediated protection is maintained in symbionts in the absence of pathogen pressure. Addressing the stability of protective symbiosis during bacterial adaptation to healthy hosts, we studied microbe-mediated protection of Pseudomonas lurida MYb11 against pathogenic Bacillus thuringiensis Bt247 in its natural host Caenorhabditis elegans MY316. Specifically, we assessed host protection and in vitro inhibition of the pathogen for a collection of derived MYb11 isolates, which were previously evolved during serial passaging in healthy C. elegans hosts. We found that all evolved MYb11 isolates continued to inhibit the pathogen in vitro, while most, albeit not all, continued to protect hosts. We focused on two of these isolates, MT5 and MT11, one with and one without protection, and found that intact protection is associated with high symbiont colonization and resulting lower pathogen proportions. In sum, our study dissects the stability of a natural protective symbiosis and suggests that high colonization ability ensures microbe-mediated protection, even if microbes adapt to host association in the absence of pathogen selection.

Delayed offspring dispersal, the prolonged residence in the natal territory after reaching independence and before dispersing to breed elsewhere, is an important aspect of the evolution of cooperative breeding. By applying a path analysis approach to the long-term Seychelles warbler (Acrocephalus sechellensis) dataset, we studied whether and how delayed dispersal is affected by territory quality, the presence of helpers and non-helping subordinates, maternal breeding status, age and fecundity, and offspring sex ratio. We found that offspring are more likely to disperse when their genetic mothers are co-breeders, helpers are absent, and territory quality is high, highlighting that a complex interplay of ecological and social factors shapes dispersal decisions. In contrast to earlier findings, our analysis does not support the idea that the offspring sex ratio is affected by territory quality and helper presence. Collectively, this study underscores the importance of considering proximate factors in understanding cooperative breeding dynamics, and it shows that path analyses offer valuable insights into dissecting the intricate relationships influencing dispersal in wild populations.

Human-induced environmental changes can have major impacts on how individuals communicate. Species using sexual signals may experience especially rapid shifts in their interactions with both intended receivers (mates) and eavesdroppers (predators). Artificial light at night and anthropogenic noise represent 2 major environmental features of human-dominated habitats which may alter selection pressures imposed on sexual signalers. In this study, we used a full factorial design to investigate individual and combined effects of experimentally added light and noise pollution on the attraction of female frogs and bat predators to speakers broadcasting male túngara frog (Engystomops pustulosus) calls. We conducted 2-choice tests in the field to examine whether predatory and mating preferences for signals differing in conspicuousness change in response to noise and light pollution. Light pollution reduced the number of approaches from predators and mates attracted to our playbacks. The addition of noise pollution enhanced this effect on predators but decreased it for female frogs. Light also lowered female frog preference for conspicuous calls, but this effect was counteracted when noise pollution was added. Reduced numbers of predators and female frogs found under lit conditions suggest light pollution can both reduce natural selection and increase sexual selection pressures on male signals. These findings indicate that light pollution could be responsible for the reduced numbers of predatory bats and female frogs found in urban environments, providing a causal explanation for more conspicuous and attractive sexual signalling in males from urban populations.

Microorganisms are essential for the normal functioning of most vertebrates. Hence, identifying and measuring the factors that shape host-associated microbial communities is necessary to understand the ecological and evolutionary implications of host-microbiota associations. We propose a framework, built on the so-called "metagenomic space" concept, which incorporates multiple definitions and quantifiable features relating to the variation of microbial communities that are associated with vertebrate hosts. By drawing on diverse theories and concepts developed in different fields of biology, our framework sets a conceptual landscape that transcends the mere characterization of microbial communities. This provides the basis to study more complex attributes, such as "potential metagenomic space" and "fundamental metagenomic space," "metagenomic plasticity," and "metagenomic evolvability," which we argue are essential for understanding the microbial contribution to vertebrate host ecology and evolution-and hold considerable promise for advancing applied research and innovation. In doing so, we hope to contribute to an improved understanding of the impact of spatiotemporal variation of vertebrate host-microbiota associations, and inspire new approaches to address testable hypotheses related to ecological, evolutionary, and applied processes.

Most birds are socially monogamous, but extra-pair paternity (EPP) is widespread. EPP can increase variance in male reproductive success and the opportunity for sexual selection, potentially leading to sexual dichromatism. While the link between EPP and sexual dichromatism is well established, over two decades ago, Owens and Hartley suggested that this relationship is mainly driven by structural colours, that is, colours that are created by the interaction between light and the feather microstructure, presumably because of their role in active sexual displays. However, this conclusion was based on a small sample of species. Here, we expand these analyses investigating the relationship between EPP and male and female colouration produced by three colour-producing mechanisms-melanin-based, carotenoid-based, and structural colouration-across over 400 bird species. Our results reveal that EPP relates to colouration across all three mechanisms. In species with high EPP levels, males tend to have more black and less light brown, whereas females are often more cryptically coloured, with less red and blue. Species with high EPP levels also exhibited more colour-producing mechanisms. Our study suggests that EPP can enhance sexual dichromatism by favouring conspicuous male and cryptic female colouration.

Parasitoids are important natural enemies of insects, imposing strong selection for the evolution of resistance. In aphids, the heritable endosymbiont Hamiltonella defensa is a key determinant of resistance, making symbiont-conferred defence a potential target for specific adaptation by parasitoids. We tested this hypothesis in the aphid parasitoid Lysiphlebus fabarum and four of its host species, Aphis fabae fabae, A. hederae, A. urticata, and A. ruborum. The parasitoids show host-associated genetic differentiation indicative of host specialization, and each of these aphid species harbours their own 1-3 distinct strains of H. defensa. We introduced eight H. defensa strains from all four aphid species into a common host background (a laboratory strain of symbiont-free A. fabae fabae) and then tested the ability of 35 field-collected L. fabarum lines from the same four hosts to parasitize the H. defensa-carrying aphids. The origin of symbionts affected parasitism success, with strains from A. fabae fabae and A. hederae conferring strong protection, and strains from A. urticata and A. ruborum providing virtually no protection. For one strain each from A. fabae fabae and A. hederae, we found a signature of specific adaptation by parasitoids, as parasitoids able to overcome their protection mostly came from the same hosts as the symbiont strains. Two other strains were so strongly protective that they permitted very little parasitism independent of where parasitoids came from. While not fully conclusive, these results are consistent with specialized parasitoids adapting to certain defensive symbionts of their host species, supporting the notion of symbiont-mediated coevolution.

Spermatozoa exhibit striking morphological variation across the animal kingdom. In passerine birds, sperm exhibit considerable variation in size, yet the basic sperm phenotype is highly conserved; sperm are filiform, the head is corkscrew-shaped, and the midpiece is elongated and twisted around the flagellum. A significant departure from this typical sperm morphology has been reported in the sister species, the Eurasian bullfinch (Pyrrhula pyrrhula) and Azores bullfinch (P. murina). Here, we report a second evolutionary shift in passerine sperm phenotype in the nominate subspecies of the red-browed finch (Neochmia temporalis temporalis); sperm are nonfiliform, with an ellipsoid head and an extremely short midpiece restricted to the nuclear-axoneme junction. Additionally, we show that the sperm phenotype of the red-browed finch is similar to the putatively neotenous sperm described in the two bullfinch species. Using whole-genome data, we found no evidence that the unusual sperm phenotype of the red-browed finch is associated with reduced genetic variation or a population bottleneck. In contrast, using data on relative testes size, we find some support for the hypothesis that relaxed postcopulatory sexual selection, via a lack of sperm competition, may, at least in part, explain the unusual sperm of the red-browed finch. We also discuss the possible roles of mutation, genetic drift, and genetic hitchhiking in the evolutionary origins and maintenance of neotenous sperm phenotypes. Finally, we suggest that these dramatic evolutionary shifts in sperm phenotype warrant further investigation and highlight the need for a greater understanding of the developmental and genomic basis of sperm phenotype.

Sex differences in cooperation are widespread, but their evolution remains poorly understood. Here, we use comparative analyses of the cooperatively breeding birds and mammals to formally test the leading Dispersal Hypothesis for the evolution of sex differences in cooperation. The Dispersal Hypothesis predicts that, where both sexes delay dispersal from their natal group, individuals of the more dispersive sex should contribute to natal cooperation at lower rates (either because leaving the natal group earlier reduces the downstream direct benefit from natal cooperation or because dispersal activities trade-off against natal cooperation). Our comparative analyses reveal support for the Dispersal Hypothesis; sex biases in dispersal predict sex biases in helper contributions to cooperative care within the natal group across cooperative birds and mammals. Strikingly, in every species that showed significant sex biases in both dispersal and natal helping, the direction of sex bias in dispersal predicted that in natal helping in the manner predicted by the Dispersal Hypothesis. Our analyses also suggest that these patterns cannot be readily attributed instead to alternative hypothesized drivers of sex differences in cooperation (kin selection, heterogamety, paternity uncertainty, patterns of parental care, or differences between birds and mammals). These findings help to clarify the evolutionary drivers of sex differences in cooperation and highlight the need for single-species studies to tease apart whether sex differences in dispersal predict sex differences in natal cooperation because dispersal impacts the direct benefits of natal cooperation (as is often proposed) or because activities that promote dispersal trade off against natal cooperation.

Predator-prey systems often feature periodic population cycles. In an empirical system with a heritable prey defence trait, ecological oscillations were previously shown to cause evolution of prey defence on the timescale of the population cycles. In this paper, we develop a phenotypically structured model comprising partial differential equations to investigate the evolutionary dynamics of prey defence during population cycles for a clonally reproducing prey species. We reveal that ecological population cycles induce evolutionary oscillations not only of the mean prey defence trait but also of trait variance. We show that both eco-evolutionary oscillations and stable dynamics lead to high trait variance for a wide range of parameters. For stable dynamics, we show that this is caused by a mutation-selection balance whose impact is larger than in the absence of predators. For oscillatory dynamics, we show that high trait variance is caused by perpetual changes in the direction of selection. Finally, we highlight that switches between stable and oscillatory dynamics depend on the functional form of the cost and efficiency functions of prey defence.