Journal of Evolutionary Biology最新文献

Transparency provides benefits to prey animals as it makes them less detectable by predators. Transparent animals are often thin, which raises the question of their fragility. In clearwing Lepidoptera, the wing thickness is the evolutionary result of conflicting optical and mechanical needs. All else being equal, a thinner membrane lets light better go through, can still sustain the reduced scales it often bears, it has a low stiffness, which is advantageous for flight, but it resists less to fatigue and failure, a crucial point. An evolutionary way out of these conflicting needs can be spatial heterogeneity in stiffness, with thicker opaque patches compensating for thinner transparent ones, especially when transparency covers a great wing surface proportion. We tested these predictions in Ithomiine butterflies, a tribe comprising closely-related opaque and transparent unpalatable species. We found that species with partially transparent wings have a thinner membrane in the transparent zone than in the opaque one, which likely helps light getting through and agrees with the lighter weight wings have to support in the transparent zone. Despite this difference between opaque and transparent zones, among transparent species the more transparent ones surprisingly have a thicker membrane in their transparent zone. We find no relationship between membrane thickness and scale density, ruling out a predominant role of membrane thickness as a mechanical support for scales. Finally, species with a higher wing proportion occupied by transparency have thicker membranes on their transparent patch, and a greater ratio in thickness between opaque and transparent zones. These latter two results support the hypothesis that clearwing butterflies with larger transparent patches are potentially more fragile and that this frailty is offset by thicker surrounding opaque patches offering higher mechanical resistance, like tubules framing a kite sail. In clearwing butterflies, wing membrane thickness has likely evolved under optical and mechanical selective pressures and further research should experimentally measure the costs, if any, of thinner transparent membranes.

Spontaneous mutation underlies all genetic variation, and thus influences the evolutionary dynamics of complex traits. Although much work has estimated mutation rates for fitness or at molecular scales, we have comparatively little information about mutational influences on other complex phenotypes. We conducted four mutation accumulation experiments with independent clones of Daphnia pulex, and then measured the effect of spontaneous mutation on size at birth, a complex trait whose connection to fitness depends on ecologically-mediated tradeoffs. Therefore it is unclear whether mutations, which are usually neutral or deleterious, should decrease or increase size at birth. In two experiments, individual instances of increased size at birth were common, whereas in the other two experiments, instances of decreased size at birth were common. Together, our data show that genetic background is an important determinant of the consequences of mutation for complex traits, and that mutation rates and direction can vary within species.

Chemical communication is a key mechanism for modulating social and reproductive behaviours. Among the most studied chemical signals are the sodefrin precursor-like factors (SPFs), a group of pheromones that enhances reproduction receptivity in salamanders and frogs. The origin of these pheromones is inferred to date back to the last common ancestor of amphibians. Despite being extensively investigated, the diversity and evolutionary history of the SPF gene family remain incomplete, as the third extant amphibian order, caecilians (order Gymnophiona), has been overlooked. Here, I revisited the molecular evolution of SPF pheromones in amphibians by including candidate SPF sequences from caecilian transcriptome data. To uncover gene duplication events, I inferred the orthology relationships of amphibian SPFs from 35 salamanders, five frogs, and eight caecilians. I performed phylogenetic comparative analyses to describe the evolution of pheromone delivery, linking transmission environment with SPF gene duplication events. SPFs comprised several orthologous groups, potentially revealing multiple ancestral gene duplications during the evolution of this gene family. Several candidate caecilian SPFs were clustered with two types of well-known SPFs (Alpha and Beta SPFs). Importantly, one of these types (Alpha SPFs) has previously been documented only in salamanders. The last common ancestor of amphibians could have delivered their pheromones in terrestrial environments, with derived aquatic courtships associated with SPF gene expansions in salamanders, but not in caecilians. These findings highlighted the importance of including the neglected order of caecilians to study amphibian biology and the evolution of pheromone systems.

Antagonist interactions, such as predator-prey interactions, are widespread in nature and drive both ecological and evolutionary outcomes. Coevolutionary outcomes of antagonistic interactions have been shown to be influenced by environmental conditions, yet the role of abiotic stress in modifying these outcomes remains insufficiently understood. Here we explored how the addition of temperature stress altered evolutionary trajectories of traits of both species in the Pseudomonas fluorescens - Tetrahymena pyriformis (bacteria- ciliate) predator prey system. We found that temperature stress impeded the evolution of traits important for antagonistic interactions in both species. Prey defense levels as well as predators' ability to eat prey were limited under temperature stress. We also found that the addition of temperature stress altered growth rate evolution in evolving populations of both species. Taken together, our results show that temperature stress not only alters the evolutionary trajectories of both predator and prey traits but also hinders their coevolution. These findings suggest that environmental stressors may weaken reciprocal coevolution which could have important consequences for the stability and persistence of ecological communities.

Ecotypes often occupy an environmental gradient, which can lead to divergence in physiological traits between ecotypes. We tested the hypothesis that alligators from inland and coastal environments have physiologically and genetically diverged from one another by exposing coastal and inland alligators to hypo-osmotic (0 PSU), iso-osmotic (10 PSU) and hyper-osmotic (20 PSU) salinities. For each alligator, we measured natremia before and after exposure, one behavioral trait, 10 histological traits, and gene expression levels in the liver and kidney. We found little evidence supporting population genetic differentiation between coastal and inland alligators yet found significant physiological divergence between the two ecotypes. Coastal alligators exhibited slightly elevated natremia across salinity treatments both pre- and post-trial and there were large structural differences between the ecotypes in both the kidney and liver tissues. Broadly, the metabolic features of the liver were decreased and the osmoregulatory abilities of the kidney were increased to a greater extent in the coastal alligators than in the inland alligators, especially at high salinities. This was also reflected in the gene expression data, where most DEGs were involved in metabolic pathways. Together, these findings suggest that coastal alligators maintain sodium balance through a combination of increased renal processing capacity and a slightly elevated natremia set point. Overall, we found that the salinity gradient used in our study elicited contrasting physiological responses between alligators from coastal and inland environments.

Social interactions mediate the phenotypic expression of fitness-relevant traits. The expression of such labile social traits includes three distinct components: an individual's mean trait value (direct effect), its social responsiveness, and its social impact (indirect effects). Traditional methods, such as variance-partitioning or trait-based models, usually only partition individual variation into direct and indirect effects. However, individual variation in social responsiveness and its covariation with direct effects and social impact will affect responses to selection. To date, no studies have explored the performance of models that allow the decomposition of responsiveness from impact. Here, we describe a model for studying variation in phenotypic expression caused by social interactions, and we use simulations to explore its performance under various experimental designs. Our analyses show that with adequate total sample sizes (≥3200), variance components are estimated accurately across all study designs. In contrast, covariance estimation would benefit most from including more unique individuals, followed by more unique social partners per individual, whereas repeated interactions with the same partners added the least improvement to the covariance estimation. We also found that failing to model individual variation in responsiveness, and neglecting measurement error, increases bias and imprecision in trait-based approaches. Hence, disregarding individual variation in responsiveness would ignore a key component of social behaviour, and hamper our ability to acquire unbiased estimates of indirect genetic or social effects.

Phenology and the timing of development are often under selection. However, the relative contributions of genotype, environment, and prior developmental transitions to variance in the phenology of wild plants is largely unknown. Individual components of phenology (e.g., germination) might be loosely related with the timing of maturation due to variation in prior developmental transitions. Given widespread evidence that genetic variation in life history is adaptive, we investigated to what degree experimentally measured genetic variation in Arabidopsis phenology predicts phenology of plants in the wild. As a proxy of phenology, we obtained collection dates from nature of 227 naturally inbred Arabidopsis thaliana accessions from across Eurasia. We compared this phenology in nature with experimental data on the descendant inbred lines that we synthesized from two new and 155 published controlled experiments. We tested whether the genetic variation in flowering and germination timing from experiments predicted the phenology of the same lines in nature. We found that genetic variation in phenology from controlled experiments significantly predicts day of collection from wild individuals, as a proxy for date of flowering, across Eurasia. However, local variation in collection dates within a region was not explained by genetic variance in phenology in experiments, suggesting high plasticity across small-scale environmental gradients or complex interactions between the timing of different developmental transitions. While experiments have shown phenology is under selection, understanding the subtle environmental and stochastic effects on phenology may help to clarify the heritability and evolution of phenological traits in nature.

Darwin argued that natural selection leads organisms to appear as if they are striving to maximize their fitness. This idea is readily recognized at the individual cell or body level, but such adaptive design may also manifest at some higher levels of biological organization. Previous work has formalized the idea that social groups can be viewed as adaptive individuals in their own right-i.e., "superorganisms"-under the assumptions that within-group selection is absent and that there is no class structure. However, the original and most common biological use of the term "superorganism" is in reference to insect colonies in which members exhibit striking class structure in the form of reproductive division of labour. Accordingly, although obligately eusocial colonies are regularly conceptualized as having the capacity for colony-level adaptation, current formalisms are unable to support this idea. Here, we develop a formal theory of group-level adaptation for obligately eusocial colonies by establishing mathematical correspondences that connect the dynamics of natural selection-as described by Price's equation-to the mathematics of optimization-wherein the colony is considered a fitness-maximizing agent-under a range of assumptions as to which members of the colony control its phenotype and the degree to which they are genetically related.

Drosophila bipectinata and D. malerkotliana are two closely related species that share common ecological niches throughout their distribution zone which comes under Oriental-Australian zoogeographical regions. These two species have been found to share several common genetic characteristics and due to this, they may experience interspecific mating under laboratory conditions and produce hybrid progeny. The population genetical work on these two species has been inadequately done by considering inversions and enzyme polymorphisms. We decided to consider the genetic polymorphism involving commonly persistent chromosomal inversions, allozymes, and microsatellite variants of the two species to envisage genetic differentiation among the natural populations of these two species sampled from distant localities of Indian cities. The results of this study indicate that Indian populations of both the species are genetically structured. There exists graded variation (clinal variation) in the level of heterozygosity from north to south as an increase in the observed heterozygosity prevailed from north to south. This trend was observed in the populations of both the species that hints towards similar genetic changes being experienced by its members all along their distribution area. The phylogenetic trees based on the extent of genetic identity between the paired populations of these two species portray two distinct clusters, one for the two populations of north and the other for the remaining populations of south. Further, through this study, it can be stated with certainty that there exists "isolation by distance" as the north and south populations of both the species genetically significantly vary from each other.

The additive genetic variance of a quantitative trait usually is interpreted as a measure of its evolvability, i.e., its capacity for adaptive evolution. However, in populations with overlapping generations, evolvability is also affected by the parental age at reproduction because genotypes that reproduce earlier evolve faster than genotypes with later reproduction. I show here that directional selection of a phenotypic trait inevitably links it with relative age at reproduction and thus developmental timing, whether or not age at reproduction affects reproductive success. In turn, the evolved genetic covariance between the selected trait and reproductive age accelerates the evolutionary response of the trait mean, unless counteracted by strong selection for late reproduction. Hence, not only the genetic variance of the trait but also the genetic variance in age at reproduction contributes to a trait's evolvability, even if the trait was initially unrelated to age at reproduction. I further show that stable generation time requires selection of intermediate strength for later reproduction and that episodes of strong selection tend to shorten average generation time. After a proof of principle by individual-based simulations, I present a formalization of this theory in a quantitative genetic framework, leading to a relatively simple extension of the breeder's equation. Finally, I discuss empirical evidence and implications for senescence and life history evolution.