Journal of Evolutionary Biology最新文献

The universality of the trade-off between fecundity and longevity in life-history theory is sometimes contested. Social insects present the arguably strongest challenge, as (i) queens not only monopolize reproduction, but also live much longer than workers, and (ii) within a caste, those individuals that lay more eggs are also observed to live longer. Positive fecundity-longevity relationships can appear in observational data even though an underlying trade-off exists, as individual variation in resource acquisition (e.g., variation in habitat quality) can mask the trade-off. Here, we demonstrate theoretically that the fecundity-longevity trade-off in social insects can be easily masked even without differences in individual quality. Demographic stochasticity, caused by variable worker lifespans, leads to self-reinforcing dynamics (equivalent to the well-known Matthew effect), where "lucky" colonies exhibit healthy growth and long-lived, productive queens, while "unlucky" colonies show the opposite combination of traits. Allocation variation between individual queens, if present, can unmask the trade-off in principle, but the trade-off remains commonly concealed not only when measuring fecundity as a cumulative total (a strongly confounded measure as longer-lived queens have more time to produce eggs), but also when measuring fecundity as a rate. Our results help align superorganismal fitness components with general life-history principles, and highlight the necessity of experimental manipulations when making statements regarding trade-offs or the lack thereof.

Genomic differentiation usually accompanies speciation, but that differentiation is often highly heterogeneous across the genome. Understanding what parts of the genome are more prone to differentiation can inform us about genomic regions and evolutionary processes that may be central to the speciation process. Here, we study genomic variation among 3 hybridizing species of North American woodpecker: red-breasted, red-naped, and yellow-bellied sapsuckers (Sphyrapicus ruber, S. nuchalis, and S. varius). We use whole genome resequencing to measure genetic variation among these species and to quantify how the level of differentiation varies across the genome. We find that regions of high relative differentiation between species (FST) tend to have low absolute nucleotide distance between species (πB), indicating that regions of high relative differentiation often have more recent between-population coalescence times than regions of low relative differentiation do. Most of the high-FST genomic windows are found on the Z chromosome, pointing to this sex chromosome as being particularly important in sapsucker differentiation and potentially speciation. These results are consistent with a model of speciation in which selective sweeps of globally advantageous variants spread among partly differentiated populations, followed by differential local adaptation of those same genomic regions. We propose that sapsucker speciation may have occurred primarily via this process occurring on the Z chromosomes, resulting in genetic incompatibilities involving divergent Z chromosomes.

Although sexual selection is a well-established part of evolutionary biology, controversies remain about the roles of males and females. For instance, despite clear evidence of male mate choice across a very broad range of species, traditional views of male and female sex roles-the former competitive, the latter choosy-are still common. In addition, studies looking at mate choice in natural populations, especially in terms of male mate choice, remain limited. Here, we consider body size, an important phenotype in mate choice in many species, and its association with patterns of non-random mating in wild populations of two species of seed bugs, Spilostethus pandurus and Lygaeus creticus. We found strong directional pre-copulatory sexual selection for larger females in both species. On the other hand, patterns of selection on male size differed between the two species. There was directional sexual selection for larger individuals in L. creticus, and stabilizing selection for intermediate-sized males in S. pandurus. Our results suggest that while males and females in both species mate non-randomly with respect to the body size of their partner, male pre-copulatory mate choice may be an important component of selection on females in the wild.

Populations are often spread across a spatially heterogeneous landscape, connected by migration. Consequently, the question arises whether divergent selective forces created by spatial heterogeneity can overcome the homogenizing force of migration and loss of diversity through genetic drift to favour different traits across space. The resulting population differentiation due to divergent selection is known as local adaptation. While local adaptation has been studied in a variety of settings, it remains unclear under what conditions local adaptation of certain life-history traits can arise. Life-history traits, such as those determining an organism's fecundity (the parameter r) and ability to compete for resources (the parameter K) demonstrate unique eco-evolutionary feedback loops due to their direct relationship to individual fitness. Classic ecological theory holds that in a constant environment, long-term evolution maximizes the population's competitive ability. Divergent selective pressures on life-history traits requires complex environmental differences, such as heterogeneous patterns of seasonality. We consider life-history evolution in a Lotka-Volterra model with three types of seasonal perturbations: repeated sudden crashes in population size, fluctuating death rates, and fluctuating resource levels. We show that fluctuating resources cannot change the evolutionary outcome, but that sufficiently harsh population crashes or fluctuating death rates favour increased fecundity over competitive ability. Our results quantify what we expect qualitatively based on early life-history theory. Finally, we apply deterministic and stochastic modelling to study local adaptation of an island population to periodic population crashes in an island-mainland model. We find that local adaptation favouring r-selected individuals again arises when conditions are sufficiently harsh, but not so harsh that the island population cannot be sustained in the absence of migration.

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.