Evolution最新文献

Several empirical examples and theoretical models suggest that the greenbeard effect may be an important mechanism in driving the evolution of altruism. However, previous theoretical models rely on assumptions such as spatial structure and specific sets of pleiotropic loci, the importance of which for the evolution of altruism has not been studied. Here, we develop a population-genetic model that clarifies the roles of extrinsic assortment (e.g., due to population structure) and pleiotropy in the maintenance of altruism through the greenbeard effect. We show that, when extrinsic assortment is too weak to promote the evolution of altruism on its own, the greenbeard effect can only promote altruism significantly if there is a pleiotropic locus controlling both altruism and signaling. Further, we show that indirect selection via genetic associations is too weak to have a noticeable impact on altruism evolution. We also highlight that, if extrinsic assortment is strong enough to promote the evolution of altruism on its own, it also favors the spread of alleles encoding the other functions of a greenbeard trait (signaling and discriminatory behavior), as well as genetic associations. This occurs despite the fact that the greenbeard effect did not favor the evolution of altruism in the first place. This calls for caution when inferring the causality between greenbeard traits and the evolution of altruism.

In constant environments, the coexistence of similar species or genotypes is generally limited. In a metapopulation context, however, types that utilize the same resource but are distributed along a competition-colonization trade-off can coexist. Prior work used a generic trade-off between within-deme competitive ability and between-deme dispersal ability. We show that sporulation in yeasts and other microbes can create a natural trade-off such that strains that initiate sporulation at higher rates suffer in terms of within-deme competition but benefit in terms of between deme dispersal. Using chemostat dynamics within patches, we first show that the rate of sporulation determines the colonization ability of the strain, with colonization ability increasing with sporulation rate up to a point. Metapopulation stability of a single strain exists in a defined range of sporulation rates. We pairwise invasability plots to show that coexistence of strains with different sporulation rates generally occurs, but that the set of sporulation rates that can potentially coexist is smaller than the set that allows for stable metapopulations. We also show how a continuous set of strains can coexist and verify our conclusions with numerical calculations and stochastic simulations. Stable variation in sporulation rates is expected under a wide range of ecological conditions.

Galapagos giant tortoises are endemic to the Galapagos Archipelago, where they are found in isolated populations. While these populations are widely considered distinguishable in morphology, behavior, and genetics, the recent divergence of these taxa has made their status as species controversial. Here, we apply multispecies coalescent methods for species delimitation to whole-genome resequencing data from 38 tortoises across all 13 extant taxa to assess support for delimiting these taxa as species. In contrast to previous studies based solely on divergence time, we find strong evidence to reject the hypothesis that all Galapagos giant tortoises belong to a single species. Instead, a conservative interpretation of model-based and divergence-based results indicates that these taxa form a species complex consisting of a minimum of 9 species, with most analyses supporting 13 species. There is mixed support for the species status of taxa living on the same island, with some methods suggesting multiple populations of a single species per island. These results make clear that Galapagos giant tortoise taxa represent different stages in the process of speciation, with some taxa further along in that evolutionary process than others. Our study provides insight into the complex process of speciation on islands, which is urgently needed given the threatened status of island species around the world.

Divergence in gametic traits can play a key role in reproductive isolation. Lifjeld et al. (2025) examined the evolution of sperm length in pairs of songbird populations at various stages along the speciation continuum. Their analyses demonstrated that sperm length diverges more rapidly in species with higher levels of female promiscuity, likely due to stabilizing selection favoring sperm cells that fit within female sperm storage structures. This divergence in sperm length may kickstart speciation in promiscuous songbirds.

Are differences between species the long-term consequence of microevolution within species, or does speciation involve fundamentally different processes? We analyzed the brain and body sizes of present-day primate species using a novel phylogenetic comparative method that decomposes the phenotypic covariance of these traits into speciational and anagenetic components. We estimated that approximately half of speciation events are accompanied by accelerated phenotypic change. Equivalent in magnitude to approximately 7 million years of gradual microevolution, such speciational changes in brain and body size account for about 58% of the phenotypic variation among extant species. Interestingly, speciational changes in brain and body size appear significantly less correlated (r ≈ 0.83) than gradual, microevolutionary changes in these same traits (r ≈ 0.97). This indicates that the strong allometric constraint that dictates microevolution in brain and body sizes is relaxed at speciation events. These results suggest that phenotypic evolution is not only accelerated during speciation but also involves events that seldomly occur at microevolutionary timescales.

Feathers are complex structures exhibiting structural/functional disparity across species and plumage. Flight was lost in >30 extant lineages from ~79.58 Ma-15 Ka. Effects of flight loss on senses, neuroanatomy, and skeletomusculature are known. To study how flightlessness affects feathers, we measured 11 feather metrics across the plumage of 30 flightless taxa and their phylogenetically closest volant taxa, with broader sampling of primaries across all orders of crown birds. Our sample includes 27 independent flight losses, representing nearly half of extant flightless species. Feather asymmetry measured by barb angle differences between trailing and leading vanes decreases in flightless lineages, most prominently in flight feathers and weakest in contour feathers. Greatest changes in feather anatomy occur in older flightless lineages (penguins, ratites). Comparative methods show some microscopic feather traits are not dramatically modified after flightlessness compared to body mass increase and relative wing and tail fan reduction, but changes toward greater symmetry are stronger. Relaxing selection for flight does not rapidly modify feather flight adaptations, apart from asymmetry. Feathers of recently flightless lineages resemble their volant relatives. Developmental constraints and relaxed selection for novel feather morphologies may explain some observed changes. Macroscopic changes to flight apparati (skeletomusculature, airfoil size) are more evident in recently flightless taxa and could more reliably detect flightlessness in fossils, with increased feather symmetry as a potential microscopic signal. We observed apical modification in later stages of feather development (asymmetric displacement of barb loci), while morphologies arising during early developmental stages are only altered after millions of years of flightlessness.

In functional systems composed of many traits, selection for specialized function can induce trait evolution by acting directly on individual components within the system, or indirectly through networks of trait integration. However, strong integration can also hinder diversification into regions of trait space that are not aligned with axes of covariation among traits. Thus, non-independence among traits may limit functional expansion. We explore this dynamic in the evolution of fin shapes in 106 species from 38 families of coral reef fishes, a polyphyletic assemblage that shows exceptional diversity in locomotor function. Despite expectations of a strong match between form and function, we find subtantial fin shape disparity across species that share a swimming mode. The evolution of fin shape is weakly integrated across the four functionally dominant fins in swimming and integration is weakened as derived swimming modes evolve. The weak integration among fins in the ancestral locomotor condition provides a primary axis of diversification while allowing for off-axis diversification via independent trait responses to selection. However, the evolution of novel locomotor modes coincides with a loss of integration among fins. Our study highlights the need for additional work on the functional consequences of fin shape in fishes.

A contemporary interpretation of Dollo's Law states that the evolution of a specialized structure is irreversible. Among land plants, reproductive specialization shows a trend toward increasing complexity without reversion, raising questions about evolutionary steps and the irreversibility of reproductive complexity. Ferns exhibit varied reproductive strategies; some are dimorphic (producing separate leaves for photosynthesis and reproduction), while others are monomorphic (where one leaf is used for both photosynthesis and spore dispersal). This diversity provides an opportunity to examine the applicability of Dollo's Law in the evolution of reproductive leaf specialization. We analyzed 118 species in Blechnaceae and Onocleaceae, applying quantitative morphometrics and phylogenetic comparative methods to test the pillars of a modernized interpretation of Dollo's Law. The evolution of dimorphism in Blechnaceae is neither stepwise nor irreversible, with direct transitions from monomorphism to dimorphism, including several reversions. In contrast, Onocleaceae exhibits an irreversibility to monomorphism only upon further specialization of fertile leaves for humidity-driven spore dispersal; this suggests that additional specialization, not dimorphism alone, may facilitate irreversibility. These results provide insight into the canalization of fertile-sterile leaf dimorphism in seed plants, where the addition of traits like heterospory and integuments lead to further specialization and potential irreversibility. These findings suggest that as new specialized traits evolve alongside preexisting ones, reversion may become increasingly unlikely.

Under current climate change patterns, rapidly changing environments can impose strong selection on traits. Costly traits that require heavy investment and strongly affect fitness may be particularly vulnerable to such changes. Despite organisms experiencing dynamic environments, our knowledge of costly trait response is limited as longitudinal studies across generations are rare. Using a long-term 11-generation dataset, we examined how fine-scale spatial and temporal variation in ecological and demographic conditions modify costly traits, specifically positive allometry in morphological traits under different selection pressures, in Psammophilus dorsalis, a short-lived socially polygynous lizard. We comprehensively measured males and females across non-overlapping generations and space and quantified fine-scale variation in key ecological and demographic parameters. Positive allometry in male head width (under sexual selection) varied dramatically over generations and space. Limited rainfall, harsh temperatures, and greater competition promoted positive allometry in male head width. In stark contrast, positive allometry in female interlimb length (under fecundity selection) only weakly correlated with environmental conditions. We demonstrate that costly traits are sensitive to changing environments depending on the underlying selection pressure, with sexually selected traits showing larger effects in tropical lizards. Future climatic predictions, indicating accelerated warming and altered rainfall, can strongly impact phenotypes in tropical lizards.