Evolution最新文献

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.

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.

A recently published genome sequence of a YY guppy male supports long-standing suggestions about the Y-linked region of this fish-that it includes both the male-determining locus and also male coloration factors that have sexually antagonistic effects. Selection against effects of these factors in females is expected to maintain associations with the male-determining locus, and to select for closer linkage in the region, and might lead to suppressed recombination and "evolutionary strata". The new finding that two sequenced Y chromosomes differ specifically in this region suggests that these represent two different Y haplotypes carrying different coloration factors that have been maintained for long enough that their sequences have become differentiated. As theory predicts, such a genome region will show complex peaks and troughs of sequence diversity, and it may be very difficult to locate the individual male-determining and male coloration loci, even when both types of factors have been maintained long-term by frequency-dependent balancing selection.

What factors explain the evolution of specialization in the ant-following behavior across Neotropical birds? By employing ancestral reconstructions and studying the morphofunctional space, Sweet et al. (2025) show that phylogenetic history, rather than functional traits, is the strongest predictor of ant-following specialization. Ant-following behavior showed several reversions but a strong tendency for transitions from facultative to obligate states. This study uncovers the relevance of shared ancestry and niche conservatism in governing the evolution of behavioral specialization.

Sexually selected traits include not only some of the most elaborate phenotypes in nature, but also some of the most diverse and sexually dimorphic. Understanding the interspecific allometric patterns of such traits is key to understanding their evolution. Rensch's rule (RR) represents a widespread macroevolutionary pattern that describes a positive association between male-biased dimorphism and species size. When applied to sexual size dimorphism (SSD), the presence of 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 find that RR in body size is followed by polygynous, but not monogamous species, pointing to sexual selection as a driver of RR. Surprisingly, tail length does not follow RR, indicating similar evolutionary allometries between males and females. However, evolutionary allometries of male and female traits were both strongly positive among long-tailed species, indicating the lack of RR is likely the result of correlations between male and female phenotypes, and not due to 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. Future research on Rensch's rule might benefit from evaluating patterns of allometry in both SSD and dimorphism in secondary sexual characters, as well as from the examination of sex specific allometries.

Do winter conditions drive rapid adaptation in insects, and does prior selection for insecticide resistance constrain it? To test these questions, Prileson et al. (2025) exposed replicate Drosophila populations to an outdoor overwintering period and tracked traits before and after in common gardens. Control populations that had not been previously exposed to insecticides showed consistent shifts in body size and fecundity, indicating rapid adaptation. Resistant populations suffered higher winter mortality, and both control and resistant populations were more susceptible to insecticides after overwintering, indicating a trade-off between resistance and overwintering performance.

Female-producing parthenogenesis is widespread in stick insects. It can be either rare and spontaneous in sexual species, or range from facultative to obligate, the latter sometimes in interspecific hybrids. This review synthesizes current knowledge on its origins, mechanisms, and evolutionary consequences, highlighting the distinction between hybrid and intra-specific origins. Hybrid-derived parthenogens are rare, obligate, and frequently polyploid, producing eggs via endoduplication which maintains heterozygosity. Intra-specific parthenogens are more frequent, typically diploid, and often homozygous due to gamete duplication.Facultative parthenogenesis allows both sexual and asexual reproduction, yet natural populations are usually either sexually reproducing or fully female, with intermediate sex ratios being rare. The mosaic distribution of mixed-sex and female-only populations without clear ecological differences suggests other factors drive the observed patterns. Sexual conflict has been proposed as a driver, but empirical data suggest mating confers fitness benefits to females rather than male-inflicted harm. In the Timema genus, parthenogenesis is linked to reduced selection efficiency and slower adaptation. Multiple obligate parthenogens evolved independently via gamete duplication, paralleling rare spontaneous parthenogenesis in sexual species. This suggests repeated selection for increased parthenogenesis frequencies in different genomic backgrounds. Overall, by providing an update on the current understanding of the phylogenetic distribution, mechanistic diversity, and transitions to parthenogenesis in stick insects, this review establishes Phasmatodea as a model to study the evolutionary significance of asexual reproduction.

Speciation does not always lead to complete reproductive isolation, which can result in hybrid zones with gene flow. In freshwater fishes, secondary contact and hybridization can arise when river courses shift. Shifting river courses can create physical and ecological dispersal barriers, producing fragmented species distributions within the same stream system. Here we investigate a secondary contact zone in western New York (USA) between the Tessellated Darter (Etheostoma olmstedi) and the Johnny Darter (Etheostoma nigrum), integrating double digest restriction site associated DNA sequencing (ddRADseq), low-coverage whole genome sequencing (lcWGS), and mtDNA datasets. Our analyses reveal a complex tri-lineage hybrid zone of E. olmstedi and two divergent E. nigrum lineages. lcWGS and ddRADseq approaches yield similar overall results for population genetic structure; however, the two approaches differ in estimates of the magnitude of population differentiation. Several sites with ongoing admixture are proximate to stream confluences and form a temporally stable mosaic of hybridization across the contact zone. We observe active and apparently stable states of hybridization, supporting the hypothesis that niche partitioning by stream size maintains species identity. The species and populations in the contact zone maintain high levels of genome-wide differentiation across streams. Our study provides insight into the dynamic process of secondary contact and highlights the array of possible genomic outcomes of hybridization.

How did size-related evolutionary constraints shape the craniofacial morphology diversification 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.

What is the probability that autopolyploids establish in a novel, unoccupied habitat, and how is this affected by selfing and assortative mating? Using a modelling approach, Zwaenepoel (2025) found that, following a single migration event, autopolyploids are more likely than diploids to establish under a wide range of circumstances. The author also found that, under continuous migration, the rate of migration, along with factors such as selfing and assortative mating, affect the time to autopolyploid establishment. These findings help to explain how polyploids may colonize more extreme peripheral habitats.