Evolution; International Journal Of Organic Evolution[JOURNAL]
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200 papers
Specialization of male reproductive tactics corresponds with large gonads and small brains.
Stec H, Zhang GY, Sandkam BA
Evolution · 2026 May · PMID 41618865 · Full text
Sexual selection has strong effects on gonad size, which has been proposed to shift energetic allocations, resulting in concomitant decreases in brain size. However, mixed findings leave it unclear whether negative corre...
Sexual selection has strong effects on gonad size, which has been proposed to shift energetic allocations, resulting in concomitant decreases in brain size. However, mixed findings leave it unclear whether negative correlations reflect direct energetic trade-offs or selection on trait combinations broadly. We tested whether male reproductive tactics impose energetic trade-offs by comparing brain and gonad sizes in Poecilia parae, a fish with discrete alternative male morphs specializing in three reproductive strategies: coercion, display, and sneaking. The obligate sneaker morph had substantially larger gonads and smaller brains than the other morphs, consistent with an energetic trade-off. However, examining individuals within morphs revealed a positive relationship, contradicting the energetic trade-off hypothesis. To resolve which morphs reflect the ancestral tissue state, we also compared gonad and brain sizes of the morphs to two closely related species whose males utilize more flexible reproductive strategies, Poecilia picta and Poecilia reticulata. Again, the P. parae obligate sneaker morph had the largest gonads and the smallest brains. Neuron-to-glia ratio (a proxy for energetic demands) showed no link to gonad size. Our results suggest that reproductive strategies shape brain evolution through correlational selection rather than direct energetic trade-offs, challenging assumptions that sexually selected traits impose constraints through direct resource allocation.
Exploring the stability of sex chromosome systems in Anolis and other iguanas.
Altmanová M, Wouters RM, Batista A … +13 more , Peš T, Antúnez-Fonseca CA, Salguero-Sánchez AJ, Straková B, Kubička L, Rovatsos M, Ariano-Sánchez D, Chinchilla C, Quiroz-Espinoza M, Venkrbec T, Vukić J, Veselý M, Kratochvíl L
Evolution · 2026 Apr · PMID 41614968 · Publisher ↗
Sex determination was once thought to be unstable in ectothermic vertebrates, but several highly diversified groups of non-avian reptiles, such as iguanas sensu lato (Pleurodonta), appear to have conserved sex chromosome...
Sex determination was once thought to be unstable in ectothermic vertebrates, but several highly diversified groups of non-avian reptiles, such as iguanas sensu lato (Pleurodonta), appear to have conserved sex chromosomes. However, this statement has been criticized as being based on a parsimonious conclusion from limited sampling. Here, we tested sex chromosome homology in a further 35 species of pleurodont lizards, mainly of the family Anolidae. We demonstrated sex chromosome homology based on the comparison of the gene dosage of X-specific genes by quantitative PCR. Including these new data, the homology of sex chromosomes has so far been reported in 92 out of over 1,200 recently recognized species of Pleurodonta. The very conserved sex chromosomes in all but one family are at least as old as the basal split of Pleurodonta (estimated over 90 million years). In the case of the family Corytophanidae, all genera share different XX/XY sex chromosomes, which are thus over 25 million years old. We discuss the efficiency and limitations of the approach used for tests of the homology of sex chromosomes, as well as the reasons for the evolutionary stability of sex chromosomes in some lineages. We argue that to obtain a complete picture, all extant species should be tested for homology; however, until we reach this ambitious goal, parsimonious estimates in lineages where fragmentary data suggest stability of sex chromosomes, as in Pleurodonta, are substantiated.
Adaptation at the edge: Patterns of local adaptation and genetic variation during a contemporary range expansion.
Clark EI, Bean DW, Bitume EV … +3 more , Stahlke AR, Hohenlohe PA, Hufbauer RA
Evolution · 2026 Apr · PMID 41614963 · Publisher ↗
During range expansion, differences can evolve between populations at the core and expanding edge of a range. Theory and experiments often focus on range expansions across uniform environments, but in nature, many range...
During range expansion, differences can evolve between populations at the core and expanding edge of a range. Theory and experiments often focus on range expansions across uniform environments, but in nature, many range expansions occur over environmental gradients that present novel selection pressures. We study phenotypic evolution at the core and edge of a range expansion across a gradient, and the expression of genetic variation of core populations in novel environments. We focus on the timing of winter dormancy in a beetle (Diorhabda carinulata), expanding from northern areas with cold winters to southern areas with milder winters. Phenotypes of core populations are consistent with adaptation to northern environments and maladaptation to southern ones. However, phenotypes of edge populations vary, indicating potential adaptation to more variable conditions across the southern sites. Clear shifts in phenotype at the edge relative to the core suggest rapid evolution in response to southern climates. Heritability in a core population was high in a local environment but undetectable in a novel (edge) environment. These results show that core populations have adapted to their local environments, and that long-distance movement into novel environments may reduce heritable genetic variation on which selection can act, and thus hinder adaptation.
Modular reorganization of the trilobite Lonchodomas chaziensis demonstrates mosaic patterns of phenotypic change underlie metamorphosis.
Vargas-Parra EE, Hopkins MJ
Evolution · 2026 Apr · PMID 41614959 · Publisher ↗
Some trilobites underwent drastic morphological transformations through their development. The Ordovician trilobite Lonchodomas chaziensis transformed, in a single molt, from a globular protaspid larva to a drastically d...
Some trilobites underwent drastic morphological transformations through their development. The Ordovician trilobite Lonchodomas chaziensis transformed, in a single molt, from a globular protaspid larva to a drastically different adult-like meraspid juvenile. This metamorphosis may be related to a complete shift in lifestyle from a free-floating planktic life mode into a bottom-dwelling benthic life mode. By focusing on variation between individuals at distinct ontogenetic stages, shifts in covariation patterns through development can be identified to better understand this transformation. Organisms are composed of parts conceptualized in terms of modules, i.e., semi-autonomous packages of highly correlated traits. Modularity is theorized to increase through ontogeny especially in arthropods, which undergo metamorphosis. To test this hypothesis, we examine covariation patterns coincident with the restructuring of the trilobite head. Analyses show a decrease in the structure of modularity during metamorphosis and major shifts in the degree of modularity/integration during and preceding transformation. Further, the part which undergoes the most shape change becomes more integrated with other parts. As shape variation is organized in a mosaic fashion through ontogeny, modularity may have played a role in coordinated ontogenetic change among parts leading up to shifts in form and lifestyle occurring during the "Plankton Revolution" of the early Paleozoic.
Digest: Phenotypic plasticity and the genomic signature of novel castes: insights from soldier evolution in Cephalotes.
Laino L, Neundorf ACA, Feitosa RM … +1 more , Salles MMA
Evolution · 2026 Mar · PMID 41604204 · Publisher ↗
Phenotypic plasticity can alter evolutionary dynamics, but its genomic consequences remain contested. Barkdull & Moreau (2026) combine comparative genomics and developmental transcriptomics in Cephalotes turtle ants to s...
Phenotypic plasticity can alter evolutionary dynamics, but its genomic consequences remain contested. Barkdull & Moreau (2026) combine comparative genomics and developmental transcriptomics in Cephalotes turtle ants to show that the repeated evolution of a soldier morph produces an asymmetric genomic signature: protein-coding genes experience genome-wide relaxed selection and reduced positive selection, whereas conserved noncoding regulatory elements show increased purifying constraint. Worker morph plasticity is driven mainly by co-option of ancient genes and by integration of insulin, imaginal-disc, and Hippo signaling.
High competition and selective extinction: how biotic and abiotic drivers shaped speciation and extinction regimes in carnivora.
Porto LMV, Quental TB
Evolution · 2026 May · PMID 41604196 · Publisher ↗
Understanding the drivers of biodiversity over time is a central goal in macroevolution. Yet, the relative contributions of biotic and abiotic mechanisms remain unclear, especially at broader phylogenetic and spatial sca...
Understanding the drivers of biodiversity over time is a central goal in macroevolution. Yet, the relative contributions of biotic and abiotic mechanisms remain unclear, especially at broader phylogenetic and spatial scales. This study investigates how biotic (competition proxies) and abiotic (temperature) factors shaped Carnivora diversification across North America and Eurasia over the last 45 million years. Using a Bayesian framework, curated fossil data, and an expanded method to assess competition intensity at multiple spatial scales, we quantify speciation, extinction, and diversity patterns across 17 families. Our results show that competition significantly influences diversification on both continents. While competition can hinder speciation by saturating ecological niches, it may also foster diversity via character displacement and niche partitioning, especially under local spatial coexistence. At regional scales, abiotic factors-particularly cooling temperatures and habitat shifts-act as selective extinction drivers, disproportionately affecting specific regions of the body size traitspace and creating gaps. By integrating temporal and spatial perspectives, our study enhances understanding of how biotic interactions and environmental changes jointly shape biodiversity through deep time.
The adaptive significance of polyandry: a meta-analysis.
Yan JL, Dobbin ML, Chen J … +1 more , Dukas R
Evolution · 2026 Apr · PMID 41604172 · Publisher ↗
Polyandry is prevalent, but the optimal patterns of mating for females remain poorly understood despite their importance for our understanding of sexual selection. We therefore performed a meta-analysis on the female fit...
Polyandry is prevalent, but the optimal patterns of mating for females remain poorly understood despite their importance for our understanding of sexual selection. We therefore performed a meta-analysis on the female fitness consequences of mating with multiple males. Across 166 studies spanning 127 arthropod species, we found that mating with more males generally enhanced female fecundity and reduced female lifespan. The net fitness effects of polyandry, however, were small. Moreover, fecundity benefits were not clearly detectable when females mated with more than two males. Additionally, we found first, that studies assessing partial as opposed to lifetime fitness reported greater benefits of polyandry. Second, protocols involving selection bias, where females were afforded some control over mating rates, reported lower costs of polyandry compared to studies without selection bias. Third, polyandry was reported as less beneficial in experiments that involved continuous housing of females with males. Finally, polyandry was more beneficial in species that transfer nuptial gifts. We thus suggest that future polyandry studies aim to measure lifetime fitness while also mitigating selection bias and exposure of females to excessive harassment. Doing so will help us understand how sexual selection operates in both sexes.
Evolutionary history of delayed plumage maturation in manakins (Aves: Pipridae).
Taylor LU, Prum RO
Evolution · 2026 Apr · PMID 41591445 · Publisher ↗
Avian plumage maturation involves replacing feathers, via discrete molts, until reaching an iteratively-regenerated definitive plumage. In most birds, this process takes about one year. In the Neotropical lekking manakin...
Avian plumage maturation involves replacing feathers, via discrete molts, until reaching an iteratively-regenerated definitive plumage. In most birds, this process takes about one year. In the Neotropical lekking manakins (Pipridae), males of most species exhibit delayed plumage maturation (DPM), passing through drab predefinitive plumages for up to three years before reaching a sexually dichromatic, definitive plumage. We used a phylogenetic analysis to investigate the evolutionary history of DPM in manakins. Our unique dataset represents the developmental schedules of individual, colorful plumage patches. We found a single origin of one-year DPM, in which young males spend a year in a drab female plumage. Subsequently, there were three origins of two-year DPM, all of which featured the evolution of an intermediate plumage with colorful patches that distinguish young males from both females and older males. One species evolved three-year DPM by passing through ancestral plumage stages more slowly, and two lineages have secondarily evolved sexual monochromatism by paedomorphic retention of female plumage. By detailing this complex developmental evolutionary history, we show how the iterative regeneration of bird plumages creates multiple distinct levels of ontogenetic homologies and provides new insights into the macroevolution of social signals in young birds.
Spatially structured host genetic diversity leads to the evolution of local specialization.
Visher E, Ali A, Barajas J … +8 more , Masud S, McBride A, Ramos E, Sui M, Villalobos-Heredia C, Walzer N, White PS, Boots M
Evolution · 2026 Apr · PMID 41591439 · Publisher ↗
Host heterogeneity and spatial population structure each influence parasite evolution and may interact when space structures contacts between host types. Here, we experimentally evolve granulosis virus in microcosms of i...
Host heterogeneity and spatial population structure each influence parasite evolution and may interact when space structures contacts between host types. Here, we experimentally evolve granulosis virus in microcosms of its natural Plodia interpunctella (Indian meal moth) host that differ in both spatial structure and host genetic diversity. We control spatial structure by manipulating the viscosity of the food that the larvae live within and host genetic diversity by adding larvae from either one or two non-evolving inbred lines to opposite microcosm ends. We preserve spatial structure across passages and assay virus from different positions within the microcosm on both host genotypes. We find that the lower contact rates between host genotypes resulting from spatial structure can lead to the evolution of locally specialized virus, even when the host population is genetically diverse overall. We also find that spatial structure changes how viruses specialize: viruses evolved in well-mixed environments had lower exploitation rates (proportion infected x virions) on the host they evolved with, while those in spatially structured environments exhibited higher exploitation of familiar hosts. These results demonstrate that spatial structure and host heterogeneity interact to shape pathogen specialization and that the evolutionary consequences of host diversity depend on population structure.
Replicate avian hybrid zones reveal the progression of genetic and trait introgression through time.
Castaño MI, Croyle E, Cadena CD … +1 more , Uy JAC
Evolution · 2026 Apr · PMID 41591390 · Publisher ↗
Replicate hybrid zones between the same taxa provide a unique opportunity to assess the repeatability of the outcome of interspecific matings by uncovering recurrent genomic and phenotypic introgression patterns. Replica...
Replicate hybrid zones between the same taxa provide a unique opportunity to assess the repeatability of the outcome of interspecific matings by uncovering recurrent genomic and phenotypic introgression patterns. Replicates also facilitate exploration of the causes of temporal shifts in hybrid zone structure. We sampled transects along three geographically separate hybrid zones between two avian taxa -the Lemon-rumped (Ramphocelus flammigerus icteronotus) and Flame-rumped (R. f. flammigerus) Tanagers-which hybridize in low passes across the Western Andes of Colombia. We examined environmental, phenotypic and genetic variation using reflectance spectrophotometry and genotype-by-sequencing data mapped to a high-quality de novo genome assembly, aiming to assess the repeatability and progression of introgression after hybridization. We found that all hybrid zones formed independently, showed parallel phenotypic divergence along ecological gradients, low population structure across parental ranges and similar demographic histories. Replicates also exhibited asymmetric introgression of neutral markers from the yellow icteronotus into the hybrid zone. However, the age of the hybrid zones differed, resulting in differences in the extent of geographic and genomic cline displacement from environmental transitions into the red flammigerus range. Despite heterogeneity in locus-specific introgression, the only shared introgression outliers across all hybrid zones were in a genomic region linked to plumage color. Clines for these loci were consistently narrow, suggesting a role in long-term reproductive isolation. Altogether, we showed that locus-specific introgression is largely stochastic, but the magnitude and directionality of neutral introgression can be predictable when demographic conditions are similar and for traits involved in reproductive isolation.
Statistical decomposition of passive and active phenotypic plasticity in traits under homeostatic regulation.
Einum S, Burton T
Evolution · 2026 Apr · PMID 41591379 · Publisher ↗
Traits subject to homeostatic regulation exhibit both active and passive phenotypic plasticity, where trait dynamics are shaped by passive effects of the environment and active physiological regulation. We present a mode...
Traits subject to homeostatic regulation exhibit both active and passive phenotypic plasticity, where trait dynamics are shaped by passive effects of the environment and active physiological regulation. We present a model that decomposes the temporal dynamics of such traits into parameters that describe the passive effect of the environment, the rate at which active regulation is adjusted (i.e., rate of plasticity), and the asymptotic magnitude of active regulation (i.e., capacity for plasticity). We apply this model to a dataset comprising 653 experiments documenting time-course changes in ion concentrations and osmolality of aquatic organisms following salinity shifts. Our model captures the diversity of trait responses, and meta-analyses reveal strong phylogenetic signals in all three parameters. Ray-finned fishes had faster regulatory responses, weaker passive plasticity (i.e., diffusion), and greater magnitude of active regulation than crustaceans. Trait-specific differences were also evident. Active regulation of magnesium was faster and of larger magnitude than the other ions and osmolality, implying strong selection for precise regulation of magnesium, which may play a key role in several physiological pathways. By disentangling the passive vs. active components of homeostatic trait regulation, our approach provides new opportunities for studying novel ecological and evolutionary aspects of phenotypic plasticity.
Female reed warblers in social pairs with low MHC dissimilarity achieve higher MHC dissimilarity through random extra-pair mating.
Halupka L, Strandh M, Sztwiertnia H … +4 more , Klimczuk E, Hasselquist D, O'Connor EA, Westerdahl H
Evolution · 2026 Apr · PMID 41553354 · Publisher ↗
Major Histocompatibility Complex (MHC) polymorphism is maintained by balancing selection through host-pathogen interactions and mate choice. MHC-based mate choice has been investigated across a wide range of vertebrates,...
Major Histocompatibility Complex (MHC) polymorphism is maintained by balancing selection through host-pathogen interactions and mate choice. MHC-based mate choice has been investigated across a wide range of vertebrates, and an established concept is that females should choose a mate with an MHC genotype that is dissimilar to her own to ensure high MHC divergence in her offspring. Here we present evidence from a population of reed warblers, Acrocephalus scirpaceus, that social pairs with extra pair young in their nest have significantly lower MHC dissimilarity than expected by random MHC-based mate choice. Moreover, social pairs with extra pair young in their nest have lower MHC dissimilarity than the potential pairs females could form with other males surrounding the social nest. Therefore, females in pairs with low MHC dissimilarity could improve the MHC divergence of her offspring through extra-pair mating. We propose that when the MHC dissimilarity in the social pair is low, any alternative male represents a better genetic prospect for the female in terms of MHC dissimilarity. This scenario generates a pattern of MHC-disassortative extra-pair mating without requiring active MHC-based mate choice.
Additive genetic variance for fitness maintained by balancing selection.
Connallon T, Czuppon P
Evolution · 2026 May · PMID 41553347 · Publisher ↗
Levels of additive genetic variation for fitness (${{V}_A}( w )$) and its components (e.g., viability and fertility) appear to be high in nature, substantially exceeding levels attributable to deleterious mutations at mu...
Levels of additive genetic variation for fitness (${{V}_A}( w )$) and its components (e.g., viability and fertility) appear to be high in nature, substantially exceeding levels attributable to deleterious mutations at mutation-selection balance. Balancing selection can stably maintain genetic polymorphisms and potentially explain this "excess" fitness variation. Yet, according to classical population genetics theory, balancing selection contributes nothing to ${{V}_A}( w )$ in a population at equilibrium, which has cast doubt on the potential role of balancing selection in maintaining ${{V}_A}( w )$. However, populations are only expected to be at equilibrium when there is no genetic drift and the fitness parameters of balancing selection are completely invariant over time. We explore how violations of these conditions affect the amount of additive genetic variation for fitness maintained by balancing selection. We show that drift and modest temporal fluctuations of balanced polymorphic equilibria each result in substantial ${{V}_A}( w )$, with each balanced polymorphic locus contributing as much to ${{V}_A}( w )$ as thousands of loci at mutation-selection balance. We discuss our results in reference to the surprisingly high levels of ${{V}_A}$ for fitness and life-history traits reported from lab populations of Drosophila and intensively monitored vertebrate populations in the field.
Conservation of sensory pathways implies a localized change in the mushroom bodies is associated with cognitive evolution in Heliconius butterflies.
Hodge EA, Dell'Aglio DD, Couto A … +3 more , McMillan WO, Farnworth MS, Montgomery SH
Evolution · 2026 Apr · PMID 41553341 · Publisher ↗
Evolution of novel behavior is reflected in changes in sensory investment or integration, but the exact nature of these changes is often unclear. The Neotropical butterfly tribe, Heliconiini, offer an attractive system f...
Evolution of novel behavior is reflected in changes in sensory investment or integration, but the exact nature of these changes is often unclear. The Neotropical butterfly tribe, Heliconiini, offer an attractive system for studying how behavioral evolution is facilitated by changes in the neural system. Within the Heliconiini tribe, the genus Heliconius possess fourfold larger mushroom bodies, the insect learning and memory center, than closely related Heliconiini. Mushroom body expansion in Heliconius co-occurred with a dietary innovation, and is associated with systematic spatial foraging and extended lifespan. Heliconius' foraging relies on visual scene memories and, indeed, Heliconius have stable visual long-term memory, and evidence of visual specialization in the mushroom bodies. Here, we explore how vision-specific neuroanatomical and behavioral enhancement in Heliconius impacts sensory pathways upstream of the mushroom bodies by assessing investment across the eyes, sensory neuropils, and projection pathways. Despite evidence of refinement in visually based behavior, we found no increased investment in visual structures, brain areas, or pathways. This suggests that the rapid expansion of the Heliconius mushroom body occurred in a context of conserved detection and processing of visual cues, and that a localized shift within integrative brain centers facilitated the evolution of Heliconius' novel behaviors.
Mosaic evolution and increased integration underpin the evolvability of the dog brain.
Balcarcel AM, Fabre AC, Orliac MJ … +4 more , Verger KL, C Selba M, Hipsley CA, Evin A
Evolution · 2026 Apr · PMID 41553333 · Publisher ↗
How the brains of domestic animals evolved under domestication remains poorly understood. We quantified brain shape variation in domestic dogs (n = 203, 111 breeds) and wolves (n = 40) using endocast-based 3D geometric m...
How the brains of domestic animals evolved under domestication remains poorly understood. We quantified brain shape variation in domestic dogs (n = 203, 111 breeds) and wolves (n = 40) using endocast-based 3D geometric morphometrics. Size, shape, and morphological integration were assessed on the whole brain, and in six morphofunctional subregions. Results demonstrate that domestication and artificial selection significantly restructured brain form and morphological integration patterns in dogs, reflecting mosaic evolution across brain subregions. Dogs exhibit a three-fold increase in brain shape variation relative to wolves, as well as expanded frontal lobes and areas putatively associated with social interaction behavior-these regions are also larger in cooperative vs. independent breeds. Morphological integration is higher in dogs than wolves, and in modern breeds compared to ancient breeds. Thus, rather than constrain, integration appears to facilitate neuroanatomical evolvability under domestication and breeding selection. Ancient dog breeds retain more wolf-like neuroanatomy. Breed function is a poor predictor of brain shape, but brain integration restructures according to breed function, with working breeds displaying the highest integration. These findings reveal the profound impact of domestication on neuroanatomical evolution, emphasizing neuroanatomical features linked to social behavior, and challenging prevailing assumptions about the role of structural integration on evolvability.
Recurrent horizontal gene transfers across diverse termite genomes.
Liu C, Hellemans S, Kinjo Y … +9 more , Mikhailova AA, Aumont C, Weng YM, Buček A, Husnik F, Šobotník J, Harrison MC, McMahon DP, Bourguignon T
Evolution · 2026 Apr · PMID 41543305 · Publisher ↗
Horizontal gene transfer (HGT), the transmission of genetic material across species, is an important innovation source in prokaryotes. In contrast, its significance is unclear in many eukaryotes, including insects. Here,...
Horizontal gene transfer (HGT), the transmission of genetic material across species, is an important innovation source in prokaryotes. In contrast, its significance is unclear in many eukaryotes, including insects. Here, we used high-quality genomes of 45 termites and two cockroaches to investigate HGTs from non-metazoan organisms across blattodean genomes. We identified 289 genes and 2,494 pseudogenes classified into 168 orthologous groups originating from an estimated 281 HGT events. Wolbachia represented the primary HGT source, while termite gut bacteria and the cockroach endosymbiont Blattabacterium did not contribute meaningfully to HGTs. Most horizontally acquired genes descended from recent and species-specific HGTs, experienced frequent duplications and pseudogenizations, and accumulated substitutions faster than synonymous sites of native protein-coding genes. Genes frequently transferred horizontally to termite genomes included mobile genetic elements and genetic information processing genes. Our results indicate that termites continuously acquired genes through HGT, and that most horizontally acquired genes are specific to restricted lineages. Overall, genes acquired by HGT by termites and cockroaches seemed generally non-functional and bound to be lost.
The impact of purifying selection and genetic drift on the distribution of dominance coefficients.
Zeitler L, Gilbert KJ
Evolution · 2026 Mar · PMID 41533661 · Publisher ↗
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 acro...
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.
Persistence of an unusual triple sex chromosome system through allopolyploidization in African clawed frogs (Xenopus, subgenus Silurana).
Premachandra T, Gvoždík V, Anele EU … +7 more , Kučka M, Chan YF, Horb ME, Chifundera ZK, Badjedjea G, Measey J, Evans BJ
Evolution · 2026 Mar · PMID 41489478 · Full text
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-associ...
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.
Commentary: evidence that sexually antagonistic male coloration factors are clustered in a rarely recombining region near the guppy male-determining locus.
Charlesworth D
Evolution · 2026 Mar · PMID 41452323 · Publisher ↗
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 hav...
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.
Digest: Evolution of specialized ant-following behavior across Neotropical birds.
Lagos-Oviedo JJ
Evolution · 2026 Apr · PMID 41439557 · Publisher ↗
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. (2026) show that p...
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. (2026) 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.
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