Journal of Evolutionary Biology最新文献

Inbreeding plays a strong role in shaping life-history traits and behaviours. Supporting evidence for this role often comes from observational studies. Experiments that establish causality and formally test how environmental factors moderate any effects of inbreeding remain underutilized. We ran an experiment to test how developmental temperature and inbreeding influence key life-history traits (growth rate, size and age at maturity, survival, and sex ratio) and locomotor behaviours (boldness and habituation) in juvenile guppies (Poecilia reticulata). We used a controlled breeding design to generate inbred and outbred individuals that were then reared under a control (26 °C) or an elevated temperature (30 °C) until maturity. Developmental temperature strongly affected life-history traits; both sexes matured earlier at 30 °C, but only males exhibited slower early growth and reduced size at maturity. Female growth and size at maturity were unaffected. The higher developmental temperature reduced boldness in both sexes; however, only females at 26 °C habituated to the novel test environment. In contrast, inbreeding had no significant effects on any of the measured traits, nor did it significantly interact with temperature. In sum, under our experimental conditions, developmental temperature is the primary driver of phenotypic plasticity in guppies, generating sex-specific responses in both life-history traits and behaviour, while inbreeding between siblings had no detectable effects on any of the measured traits. Our findings highlight the key role of temperature in shaping developmental and behavioural trajectories, and reveal that a single generation of inbreeding may not always affect life-history traits, even under environmental stress.

The major histocompatibility complex (MHC) is a gene cluster essential for pathogen recognition in jawed vertebrates. It encompasses the MHC class I genes which primarily recognize intracellular parasites, and the MHC class II genes which primarily recognize extracellular parasites. In wild birds, most studies investigating associations between MHC variants and parasites have been carried out in passerines, and have repeatedly shown that specific MHC class I variants provide resistance to intracellular haemosporidian parasites. In contrast, research on the associations between MHC variants and parasites in non-passerine birds remains limited. In this study, we examined the association between MHC-IIB supertypes and the bacterial load of a sexually transmitted bacterium (named C34) in the black-legged kittiwake (Rissa tridactyla), a genetically monogamous seabird. We focused on MHC class II genes because extracellular parasites are particularly prevalent in non-passerines and may therefore exert strong selection on the studied host. We found that females with lower C34 load had better reproductive performance, and higher probability to carry the MHC-IIB supertype SUP6. In contrast, in males, we observed a positive association between C34 load and reproductive performance, but no association between C34 load and MHC-IIB supertypes. While sexually transmitted diseases are not expected to be a strong selective force in genetically monogamous species, our study suggests that C34 might exert a selective pressure on the evolution of the MHC-IIB. Therefore, further research should explore the influence of sexually transmitted diseases on the reproductive biology of genetically monogamous species.

Organisms often face a fundamental trade-off between growth and predator avoidance, where traits that enhance growth-such as higher activity rates-also increase predation risk. While many species reduce activity in response to predators, potentially constraining growth, this trade-off can be mitigated if alternative traits, such as resource digestive efficiency, compensate for reduced activity. Such trait compensation could enable organisms to minimize growth costs while evading predators. To test this idea, we combined a mesocosm experiment with lab-based digestive physiological assays to examine survival selection and plasticity in damselfly larvae exposed to fish predators. We found that selection favoured less active individuals, yet this reduction in activity did not suppress growth. Instead, plastic increases in consumption rate, selection for greater assimilation efficiency, and weaker digestive stress responses allowed individuals to maintain growth despite reduced activity and elevated metabolic rates. Our results reveal that selection on digestive physiology can buffer organisms against the putative costs of predator avoidance, demonstrating how trait networks can decouple growth from predation risk in complex ecological systems.

Male fertility in plants is often controlled by the interaction between mitochondrial and nuclear genes. Some mitotypes confer cytoplasmic male sterility (CMS), making the individual male-sterile, unless the nuclear background contains alleles called restorers, which suppress the effects of CMS and restore the hermaphroditic phenotype. Restorers in cultivated crops are often alleles with strong and dominant effect, but in wild plants, data often suggest more complex systems. Here, we characterized the inheritance and specificity of restoration in a new CMS model, the freshwater snail Physa acuta. We explored two different populations: (i) a naive population, i.e., without contact with CMS in the past 80 generations, and (ii) a non-naive population, where CMS is present and largely restored. Although we found male fertility of individuals with CMS mitogenomes to be heritable in both contexts, this genetic determinism was of a different nature depending on population history. In naive populations not coevolved with CMS, the background variation may include alleles that happen to act as weak quantitative modifiers of the penetrance of CMS, while in populations coevolved with CMS, selection may have favoured, when such variants were available, the emergence of strong alleles with a dominant effect.

Maternal effects (the consistent effect of a mother on her offspring) can inflate estimates of additive genetic variation ($V_{A}$) if not properly accounted for. As they are typically assumed to cause similarities only among maternal siblings, they are often accounted for by modelling maternal identity effects. However, if maternal effects have a genetic basis, they create additional similarities among relatives with related mothers that are not captured by maternal identity effects. Unmodelled maternal genetic variance ($V_{Mg}$) may therefore still inflate $V_{A}$ estimates in common quantitative genetic models, which is underappreciated in the literature. Using published data and simulations, we explore the extent of this problem. Published estimates from 8 species suggest that a large proportion of total maternal variation ($V_{M}$) is genetic ($sim$65%). Both these data and simulations confirmed that unmodelled $V_{Mg}$ can cause overestimation of $V_{A}$ and underestimation of $V_{M}$, the bias increasing with the proportion of non-sibling maternal relatives in a pedigree. Simulations show these biases are further influenced by the size and direction of any direct-maternal genetic covariance. The estimation of total additive genetic variation ($V_{A_t}$; the weighted sum of $V_{A}$ and $V_{Mg}$) is additionally affected, limiting inferences about evolutionary potential from simple maternal effects models. Unbiased estimates require modelling $V_{Mg}$ explicitly, but these models are often avoided due to perceived data limitations. We demonstrate that estimating $V_{Mg}$ is possible even with small pedigrees, reducing bias in $V_{A}$ estimates, and maintaining accuracy in estimates of $V_{A}$, $V_{M}$, and $V_{A_t}$. We therefore advocate for the broader use of these models.

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.