Evolution最新文献

There is increasing recognition that the process of species divergence is not uniform across the tree of life, and that newly diverged taxa may differ in their levels of phenotypic and genetic divergence. We investigate the relationship between phenotypic and genetic differentiation across the speciation continuum using sister pairs from a large ecologically diverse radiation of Australian skinks, the Tribe Eugongylini, a high-quality alignment of genomic sequence data, and morphometric data for 90 lineages across the radiation. Based on the framework proposed by Struck et al. (2018) for comparative study of species divergence, we used latent class regression to test for multiple speciation "trajectories". We found evidence for multiple relationships between genetic divergence and morphological disparity for recently diverged sister taxa, which we summarise into two broad patterns. One of these patterns is characterised by relatively rapid morphological differentiation for pairs with greater disparity in environmental variables, consistent with expectations of ecological speciation. The second pattern shows accumulation of both morphological and genetic differences in proportion to each other, consistent with gradual speciation. Our study shows how heterogeneity in speciation processes can be captured in a comparative framework.

Kin selection theory predicts that individuals should evolve to help relatives, either by helping indiscriminately in a population where they do not move very far from their relatives, or by discriminating kin and conditionally helping them. It has been argued that, because kin discrimination enables individuals to reduce how helpful they are with some social partners as well increase how helpful they are with others, this could lead to an increase or a decrease in the overall level of helping. Specifically, it was argued that kin discrimination would increase the overall level of helping if the function relating the optimal level of help and genetic relatedness is convex, but kin discrimination would decrease the overall level of helping if the function relating the optimal level of help and genetic relatedness is concave. However, this prediction was based on a model in which individuals were not able to choose their social partners but only adjust how helpful they should be towards those social partners they have been allocated. Here, we perform a mathematical analysis showing that being able to choose social partners increases the overall level of helping. Consequently, if kin discriminators are allowed to choose whom they help, kin discrimination is more likely to increase the overall level of helping than previously anticipated. We obtained these results in two complementary theoretical settings: one more general, which makes few demographic assumptions, and the other more specific and concrete, which assumes a patch-structured population with complete dispersal.

Mutations are the ultimate source of genetic variation for natural selection to act upon. A major question in evolutionary biology is the extent to which new mutations can generate genetic variation under natural conditions to permit adaptive evolution over ecological time scales. Here we collected fitness data for chemically induced (ethylmethane sulfonate, EMS) mutant lines descended from two Arabidopsis thaliana ecotypes that show differential adaptation to the local environment of our common garden plot. Using a novel nonparametric Bayesian statistical approach, we found that both ecotypes accumulated substantial proportions of beneficial mutations. The poorly adapted ecotype exhibited higher mean mutational effects and higher variance in the fitness effects of mutations compared to the well-adapted ecotype. Furthermore, we predict that it takes less than 4000 generations for the fitness space of the two ecotypes to overlap through mutation accumulation, and that a single founder, through mutation accumulation, is able to achieve the species-wide genetic variation in less than 10,000 generations. Our results provide evidence for relatively rapid local adaptation of Arabidopsis thaliana in natural conditions through new mutations, as well as the utility of a nonparametric Bayesian method for modeling the distribution of fitness effects for field-collected data.

Urban phenotypic divergences are documented across diverse taxa, but the underlying genetic and environmental drivers behind these phenotypic changes are unknown in most wild urban systems. We conduct a common garden experiment using great tit (Parus major) eggs collected along an urbanization gradient to: 1) determine whether documented morphological, physiological, and behavioural shifts in wild urban great tits are maintained in birds from urban and forest origins reared in a common garden (N = 73) and 2) evaluate how different sources of genetic, early maternal investment, and later environmental variation contributed to trait variation in the experiment. In line with the phenotypic divergence in the wild, common garden birds from urban origins had faster breath rates (i.e., higher stress response) and were smaller than birds from forest origins, while wild differences in aggression and exploration were not maintained in the experiment. Differences between individuals (genetic and environmentally induced) explained the most trait variation, while variation among foster nests and captive social groups was limited. Our results provide trait-specific evidence of evolution in an urban species where genetic change likely underlies urban differences in morphology and stress physiology, but that urban behavioural divergences are more strongly driven by plasticity.

Understanding how cooperation evolves in microbial populations, particularly under environmental stress such as antibiotic exposure, remains a key topic in evolutionary biology. Here, we investigate cooperative interactions between antibiotic-resistant and antibiotic-sensitive strains of Escherichia coli. Under antibiotic stress, a small number of antibiotic-sensitive strains rapidly evolve into antibiotic-resistant strains. Resistant E. coli produce indole, which induces a protective response in sensitive cells, enabling them to survive in antibiotic stress conditions. In turn, antibiotic-sensitive E. coli could help reduce toxic accumulation of indole, indirectly benefiting the resistant strain. Indole is harmful to the growth of the antibiotic-resistant strain but benefits the antibiotic-sensitive strain by helping turn-on the multi-drug exporter to neutralize the antibiotic. This mutual exchange leads to increased fitness for both strains in cocultures, demonstrating a mechanism by which mutually beneficial cooperation can evolve in bacterial communities. Our findings provide insight into how mutualism can emerge under antibiotic pressure through metabolic byproduct exchange, revealing new dynamics in the evolution of bacterial cooperation.

Theory predicts that selection against maladaptive hybridization leads to divergence of sexual characters in co-occurring closely related species. Consequently, signal disparity should be greater between sympatric versus allopatric lineage pairs. However, this pattern may also result from species sorting or the greater evolutionary age of sympatric pairs. We used species pairs comparisons to examine the existence of acoustic divergence in a Neotropical montane radiation, the Rhinocryptidae, whose members tend to occupy different elevational ranges. Most rhinocryptids exhibit conservative morphology and are only differentiated by song attributes. Our results show that sympatric species pairs that overlap in elevation exhibited overall greater song divergence compared to allopatric species pairs after controlling for morphological differences, age and phylogenetic effects. Song divergence decreased when excluding sympatric pairs that do not overlap in elevation, suggesting that selection for improved species identification between co-occurring (syntopic) species accentuates signal differentiation. Comparative evolutionary models of signal differentiation over time revealed a similar pattern which suggests that sexual selection in syntopy might have driven reproductive character displacement in this radiation. We conclude that selection against the production of unfit hybrids could favor acoustic traits that reliably signal species identity in tropical environments where many taxa are poorly differentiated by visual attributes.

Understanding evolutionary rescue mechanisms in fragmented populations is crucial in the context of rapidly changing environments. This study employs analytical derivations and simulations within a two-deme metapopulation model using Fisher's geometric model (FGM) framework. We explore the impacts of abrupt environmental changes on two subpopulations that lead to distinct phe- notypic optima. We determine the probability density of distances between these optima through analytical derivations. This enables us to calculate the inter- section volume of the rescue domains of two subpopulations in the phenotypic space. This approach also allows us to assess the fixation probability of muta- tions that concurrently rescue both subpopulations and identify the domain of one-step rescue mutations. Our findings reveal that the likelihood of joint evolu- tionary rescue diminishes with increasing dimensionality of the phenotypic space, posing significant challenges for species with complex trait configurations. The study underscores the importance of genetic variation due to de novo mutations, local adaptation, and migration rates. These insights enhance our understanding of the factors that govern the adaptive potential of fragmented populations in response to severe environmental disturbances.

Many organisms live in predictable environments with periodic variation in growth condition. Adaptation to these conditions can lead to loss of nonessential functions, which could be maladaptive in new environments. Alternatively, living in a predictable environment can allow populations to accumulate cryptic genetic variation that may have no fitness benefit in that condition, but can facilitate adaptation to new environments. However, how these processes together shape fitness of populations growing in predictable environments remains unclear. Through laboratory evolution experiments in yeast, we show that populations grown in a nutrient-rich environment for 1000 generations generally have reduced fitness and lower adaptability to novel stressful environments. These populations showed metabolic remodeling and increased lipid accumulation in rich medium which seemed to provide osmotic protection in salt stress. Subsequent adaptation to stressors was primarily driven by de novo mutations, with very little contribution from the mutations accumulated prior to the exposure. Thus, our work suggests that without exposure to new environments, populations might lose their ability to respond effectively to these environments. Further, our findings highlight a major role of exaptation and de novo mutations in adaptation to new environments, but do not reveal a significant contribution of cryptic variation in this process.

In species with separate sexes, selection on males causes evolutionary change in female traits values (and vice versa) via genetic correlations, which has far-reaching consequences for adaptation. Here, we utilise a sex-specific form of Robertson's Secondary Theorem of Natural Selection to estimate the expected response to selection for 474 organismal-level traits and ~28,000 gene expression traits measured in the Drosophila Genetic Reference Panel (DGRP). Across organismal-level traits, selection acting on males produced a larger predicted evolutionary response than did selection acting on females, even for female traits; while for transcriptome traits selection on each sex produced a roughly equal average evolutionary response. For most traits, selection on males and females was predicted to move average trait values in the same direction, though for some traits, selection on one sex increased trait values while selection on the other sex decreased them, implying intralocus sexual conflict. Our results provide support for the hypothesis that males experience stronger selection than females, potentially accelerating adaptation in females. Furthermore, sex-opposite responses to selection appear to exist for only a small proportion of traits, consistent with observations that the inter-sex genetic correlation for fitness is positive but less than one in most populations so far studied.

The prevalence and strength of antibiotic resistance has led to an ongoing battle between the development of new treatments and the evolution of resistance. Combining multiple drugs simultaneously is a potential solution for combating antibiotic resistance. However, this approach introduces new factors that must be considered, including the influence of drug interactions on the rate of resistance evolution. When antibiotics are used in combination, their effects can be additive, synergistic, or antagonistic. In this study, we investigated the effect of higher-order interactions involving three drugs on resistance evolution in Staphylococcus epidermidis. Previous studies have shown that synergistic interactions can increase the adaptation rate. However, the effects of higher-order interactions on rates of adaptation are unclear. We investigated the adaptation of Staphylococcus epidermidis to single-, two-, and three-drug environments to assess how interactions within drug combinations influence the rate of adaptation. We analyzed both the overall interaction and emergent interaction, the latter being a unique interaction that occurs in three-drug combinations due to the presence of all three drugs, rather than simply strong pairwise interactions. Our results show that neither the overall interactions nor the emergent interactions affect adaptation rates.