Evolution最新文献

African clawed frogs (Xenopus) have a high rate of genome duplication, which may catalyze evolution-including of sex chromosomes. To explore this, for each of four species in the subgenus Silurana, we analyzed sex-associated genetic variation, and in the diploid species X. tropicalis, we explored population structure. We found that the sex-linked regions in all four species are homologous, and we infer that X. calcaratus has an unusual sex determination system with three sex chromosomes, which was previously known only in X. tropicalis. Our results evidence two independent allotetraploidization in Silurana, admixture across ploidy levels, and demonstrate that the most recent allotetraploidization that generated the X. calcaratus lineage occurred after population subdivision arose in X. tropicalis. Thus, this unusual triple sex chromosome system has been maintained independently in two different species for a protracted period and through an allotetraploidization event. Simulations indicate that genetic drift should eliminate one of the sex chromosomes, suggesting that there may be unidentified benefits to maintaining this complex system.

How did size-related evolutionary constraints shape the diversification of craniofacial morphology during the adaptive radiation of Malagasy lemurs? Toyoda (2025) employed geometric morphometrics to investigate craniofacial variation across Madagascar primates. The findings suggest that small-bodied lemurs exhibit a conserved craniofacial form-short rostra and large orbits-driven by mechanical and developmental constraints, yet adapt ecological specialization through rostral modifications. Large-bodied lemurs, in contrast, show greater cranial disparity, indicating a relaxation of size-related constraints. These findings underscore that evolutionary constraints do not merely limit diversification but instead channel morphological evolution along distinct, size-dependent trajectories during adaptive radiation.

The relationship between dominance and selection coefficients is a long-debated topic in evolutionary genetics and important for understanding evolutionary dynamics of populations. How it evolved and how it may vary across species or populations is not fully understood. Using simulations, we investigate how purifying selection and genetic drift affect the distribution of dominance coefficients for segregating deleterious variants. We find that large populations express h-s relationships shaped by efficient selection against highly deleterious and additive mutations, resulting in excess weakly deleterious and recessive mutations. This matches the classic inverse relationship between selection and dominance. Genetic drift in small populations, however, results in a wider range of dominance coefficients for any segregating deleterious variant and reduces or removes the h-s relationship. By investigating allele fixation, we reveal a nuanced dependency on the strength of selection across different simulated selection and dominance distributions. We also compare the combined impact of genetic drift and repeated founder events in simulated range expansions and how these impact the segregating distribution of h, employing differences in effective population size between species core and edge. While dominance patterns in core populations resemble large, constant-size populations, edge populations lack recessive mutations relative to small, constant-size populations. Our findings emphasize the importance of genetic drift and purifying selection in shaping the observed negative relationship between dominance and selection coefficients in large populations. Small populations, however, show an h-s relationship closer to de novo mutations, without the effect of purifying selection. Therefore, it is important to consider population size, genetic drift, and the underlying distribution of dominance coefficients when studying the evolutionary dynamics of deleterious mutations.

We examined the expectation that stronger stabilising selection leads to a decrease in trait variation across species by investigating individual variation in wing length. We hypothesised that species that heavily rely on aerial feeding, as well as long-distance migratory species, show higher canalisation (lower coefficients of variation, i.e., CV values) in wing length than non-aerial feeders and non-migratory species. We collected summary statistics on wing length for males and females from the literature and analysed them using recently developed meta-analytic metrics for integrating phenotypic variance estimates. Our phylogenetic multilevel meta-analysis showed relatively low heterogeneity among CV values, indicating generalisability of the overall CV value (2.6%). Although not all pairwise comparisons were statistically significant, all our analyses consistently showed higher canalisation in aerial compared to non-aerial feeders, and in migratory compared to non-migratory species. We conclude that wing length in bird species relying on their wings more heavily is likely under stronger (stabilising) selection, which in turn would have led to the observed higher canalisation on this trait for those species. Our study showcases how to combine already available descriptive statistics for phenotypic traits with underused meta-analysis of variance approaches to test often-neglected evolutionary predictions.

At macroevolutionary scales across species, sexual dimorphism often covaries with body size, generating allometric trends. Such patterns are most evident for body size dimorphism, while trends in sexual shape dimorphism remain underexamined. Additionally, how small body sizes (miniaturization) affects such patterns is largely unknown. We evaluated allometry in sexual shape dimorphism in two families of geckos to determine whether changes in body size associate with changes in shape dimorphism. Using surface scans of head shape from nearly 600 individuals across 99 species, we found considerable variation in levels of sexual shape dimorphism across taxa, with some species displaying little dimorphism and others exhibiting large sexual differentiation. Interspecific trends differed between the two families, with strong negative allometry in Sphaeorodactylidae (a family with many small-bodied species), while Phyllodactylidae (a family containing few small-bodied species) displayed isometry and no discernible trend. Notably, greater sexual shape dimorphism was displayed in small-bodied sphaerodactylid species, and corresponded with females exhibiting more robust heads; consistent with sex-specific foraging strategies and dietary differences observed in this group. Our study reveals that interspecific allometry in traits other than body size can have a pervasive influence on patterns of phenotypic diversity across the tree of life.

In comparative evolutionary genomics, faster or slower evolution of a particular gene, site, or branch in a phylogenetic tree, when compared to the appropriate average, has been interpreted as evidence of conservation, functional importance, or adaptation. With large consortia generating hundreds of genomes, there is an opportunity to interrogate these datasets for evidence of accelerated or reduced evolutionary rates in protein-coding genes associated with the presence or absence of a given phenotype (e.g., marine vs. terrestrial, nocturnal vs. diurnal). Such rate shifts can reflect the molecular basis of convergent phenotypic adaptation when they occur repeatedly across independent lineages. Here, we introduce an explicit phylogenetic rate test, MoleRate, for acceleration or reduction of nucleotide or protein evolutionary rates in focal lineages vs. the rest of the phylogeny. Compared to existing methods, MoleRate offers execution, explicit likelihood-based hypothesis testing, and the ability to detect and filter out potentially aberrant signal from single lineages. We demonstrate MoleRate's performance on simulated and empirical data, and apply it to several mammalian phenotypes. We also highlight its visualization capabilities, which enable exploration and communication of results. These analyses show that MoleRate detects biologically significant enrichments in selective pressure on specific functions related to the given phenotype, and that enrichments in selective pressure related to the given phenotype, absent when random lineages are tested.

Rensch's rule (RR) is a widespread macroevolutionary pattern describing a positive association between male-biased dimorphism and species size. Applied to sexual size dimorphism, RR is often associated with sexual selection, as larger body sizes may benefit males in competition and courtship. Moreover, the presence of RR in sexual traits further indicates that males reap relative performance benefits beyond large body size alone. Here we describe patterns of elaboration, variation, and sexual dimorphism in tail length in the birds-of-paradise (Aves: Paradisaeidae), which exhibit an extreme diversity in tail lengths, ranging from short-tailed species to the longest-tailed passeriform birds. We found that body size followed RR in polygynous, but not monogamous species, in accordance with the sexual selection hypothesis. However, we found no evidence of RR in tail length, indicating similar evolutionary allometries between males and females. Evolutionary allometries of male and female traits were both strongly positive among long-tailed species, suggesting that the lack of RR results from phenotypic correlations between the sexes, rather than constraints on ornament exaggeration. Our study represents the first integrative test of RR in an ornamental morphological trait and evidences how different aspects of dimorphism interact in a group with a hyperdiverse courtship trait.

The causal role of pollinators in driving the divergence of plant traits is a fundamental tenet of angiosperm evolution, providing hallmark examples of natural selection. However, it remains unclear how geographic variation in pollinator assemblages relates to the divergence of pollination traits in pollination-generalized plants. We characterized pollinator assemblages that interacted with Viscaria vulgaris in southern Sweden, and evaluated, through statistical dimension reduction, whether pollination traits were associated with an inferred main axis of geographic variation in pollinator assemblages. We documented a functionally broad range of pollinators that visited V. vulgaris. Although the most frequent pollinator functional groups were present in most populations, their relative contribution to flower visitation varied across the study area, establishing a geographic mosaic of local pollinator assemblages. We demonstrate that the geographic variation of local pollinator assemblages can predict the divergence of pollination traits in V. vulgaris. The findings of this geographic comparative study are consistent with the hypothesis that geographic variation in pollinator assemblages drives the divergence of pollination traits in pollination-generalized plants. Thus, generalized plant-pollinator interactions do not preclude the divergence of pollination traits, which may maximize the collective contribution of local pollinator assemblages rather than that of a principal pollinator.

Model organisms are powerful tools for discovery in cell and molecular biology, and studies of their natural history have the potential to provide bridges between these fields and ecology and evolutionary biology. The nematode Caenorhabditis elegans is a preeminent model, and recent findings place its center of diversity in the cool, high-elevation forests of Hawaii. To test models of biogeography and species coexistence, we investigated Caenorhabditis on Pohnpei, an island in Micronesia, home to the largest patch of high-elevation forest between Hawaii and Asia. We found nine species of Caenorhabditis, five of them new. Using the distribution of nematodes among habitat patches, we parameterized models of Caenorhabditis population biology that help explain species coexistence patterns. We inferred a phylogeny for 70 species of Caenorhabditis and performed the first quantitative biogeographic analysis for the group. Our analysis suggests that the deep ancestors of the Elegans Supergroup of species lived in the Americas. The Supergroup's subsequent diversification occurred in Oceania, giving rise to a diverse Oceanian fauna and ultimately to multiple lineages that moved into Asia, Africa, Australasia, and back into the Americas. We infer a slow trans-Pacific migration, with the islands of Oceania serving as sources rather than sinks for biodiversity.

Experimental evolution is a powerful method that has been instrumental for revealing core mechanisms of adaptation and coevolution. It has mostly been used in very simple settings of one or two species. Yet, it is now increasingly being employed in more complex community settings that include indirect effects, higher-order interactions, and multidimensional selection typical of natural communities. Here we synthesize the emerging field of experimental evolution in communities and show how community context reshapes selection and evolutionary trajectories, beyond what single-species or pairwise designs predict. We conducted a systematic literature survey targeting multi-species, multi-generation evolution, identifying 100 such studies with the number increasing recently. Despite this progress, most experiments are biased toward microbial systems and competitive interactions, leaving major gaps for predicting evolution in realistic communities. We discuss community ecology concepts in the light of experimental evolution, together with designs that address these concepts. We emphasize three main research areas: indirect and higher-order interactions that make selection multidimensional, eco-evolutionary feedbacks linking trait change to community dynamics, and genetic constraints that shape responses across interaction networks. We then discuss routes to increase ecological realism with field experiments and conclude by outlining key research fronts for experimental evolution in communities.