Evolution; International Journal Of Organic Evolution[JOURNAL]
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200 papers
"Nesting assistance": a new hypothesis for the evolution of polyandry and a test in an African foam-nesting treefrog.
Byrne PG, Whiting MJ, Silla AJ … +1 more , Keogh JS
Evolution · 2026 Jun · PMID 42229500 · Publisher ↗
Why polyandry evolves remains a compelling evolutionary question. While numerous material benefits of polyandry have been demonstrated, there has been limited attempt to link the fitness of polyandrous females to nesting...
Why polyandry evolves remains a compelling evolutionary question. While numerous material benefits of polyandry have been demonstrated, there has been limited attempt to link the fitness of polyandrous females to nesting behavior. Here, we introduce the "nesting-assistance" hypothesis as a new explanation for the evolution of polyandry. We theorize that in species where females are primarily responsible for nest construction, and males display some form of nesting assistance, that mating with multiple males leads to the production of more viable nests and improved offspring survival or performance. We provide an initial test of the "nesting-assistance" hypothesis in the African gray foam-nest treefrog (Chiromantis xerampelina), a species where multiple males commonly join females to construct arboreal foam nests. Field observations revealed that individuals involved in polyandrous matings synchronize the timing of bouts of leg churning, a conspicuous reproductive behavior essential for foam-nest construction. Moreover, matings involving more males produced bigger nests that were more resistant to desiccation. Paternity analysis revealed that males involved in polyandrous matings gained a share of paternity, suggesting a direct fitness benefit from nesting assistance. Our findings support the "nesting assistance" hypothesis and provide evidence for a new yet potentially widespread benefit of polyandry.
Digest: Longitudinal striping in rodents.
Ayers H
Evolution · 2026 May · PMID 42208494 · Publisher ↗
Why do some rodents exhibit longitudinal dorsal stripes rather than the much more common monochromatic pelage coloration? Caro et. al (2026) investigated this question by matching pelage patterning with socioecological v...
Why do some rodents exhibit longitudinal dorsal stripes rather than the much more common monochromatic pelage coloration? Caro et. al (2026) investigated this question by matching pelage patterning with socioecological variables placed on a phylogenetic tree. Their findings hint at striping being a form of predator defense that works particularly well against aerial predators, but no evidence was found for a communicative function.
Digest: Between Yellow and Orange: Genomics of Hybridization in Colias Butterflies.
Buckley SJ
Evolution · 2026 May · PMID 42208492 · Publisher ↗
How does hybridization shift over time, and what are its consequences on phenotypic variation? Using genomics, Jahner et al. (2026) show how hybridization between Colias butterflies has shifted over a five-year period, w...
How does hybridization shift over time, and what are its consequences on phenotypic variation? Using genomics, Jahner et al. (2026) show how hybridization between Colias butterflies has shifted over a five-year period, with complex impacts on phenotype (wing colour). While most hybrids had intermediate phenotypes, relatively few butterflies with intermediate wing colours were themselves hybrids. These results highlight not only the fluctuating role of hybridization but also demonstrate its subtle and complex impacts on phenotypes.
Relaxed selection diminishes social memory and expression of host defenses against cuckoos.
Tolman D, Rönkä K, Kluen E … +5 more , Jolkkonen J, Bari PD, Ientile R, Campobello D, Thorogood R
Evolution · 2026 May · PMID 42206823 · Publisher ↗
Behavioral defenses are a key adaptation across animals, but confirming decay under relaxed selection is challenging. If expression involves decision-making, then defenses may only be expressed when the right environment...
Behavioral defenses are a key adaptation across animals, but confirming decay under relaxed selection is challenging. If expression involves decision-making, then defenses may only be expressed when the right environmental cues are available (i.e., cryptic plasticity). Even if defenses wane, they could be quickly restored once selection resumes as animals can learn by observing others (i.e., social memory). Here we tested cryptic plasticity and social memory under relaxed selection in a cuckoo host, the Common Reed Warbler, by manipulating perceived parasitism risk with social information in geographically-distinct areas differing in allopatry (100 to 1000 years). Despite predicting social information of a cuckoo vs. a control would elicit otherwise cryptic behavioral defenses, only birds that mobbed model cuckoos prior to manipulation upregulated this defense, and only in the recently allopatric population. Social information also had no effect on low-to-absent rates of foreign egg rejection, a second line of defense common to cuckoo host species. These results contrast with parasitized locations where similar methods provoke mobbing and increase egg rejection ten-fold. Our study therefore suggests that, even when manipulating information to account for reaction norms, behavioral defenses may degrade rapidly under relaxed selection, demonstrating a process facilitating a geographic mosaic of coevolution.
How do mate-finding Allee effects affect evolutionary rescue?
Deraje P, Uecker H
Evolution · 2026 May · PMID 42190236 · Publisher ↗
In sexually reproducing populations, the challenge of finding mates at low densities can impose a strong demographic Allee effect. Environmental change can cause a population to fall below its Allee threshold by reducing...
In sexually reproducing populations, the challenge of finding mates at low densities can impose a strong demographic Allee effect. Environmental change can cause a population to fall below its Allee threshold by reducing the population size or by increasing the threshold if the latter depends on affected life-history traits. Evolutionary rescue then relies on overcoming the Allee effect, which gets increasingly difficult as the population declines. Despite mate-finding Allee effects being common, most models of evolutionary rescue assume that mating is assured even at low densities. Here, we set up a population genetic model to study the potential for evolutionary rescue of a population below its Allee threshold. For the analysis, we combine stochastic computer simulations with mathematical arguments. As expected, mate limitation can severely impede rescue, but the extent differs across sexual systems. We further show that it shifts the optimal sex ratio for dioecious but not for androdioecious populations, alters optimal evolutionary routes when there are trade-offs between increasing mate-finding efficiency and fecundity, and enhances the importance of standing genetic variation relative to de novo mutants. Overall, our results highlight the importance of accounting for positive density dependence in the assessment of a population's scope for evolutionary rescue.
Taxonomic context and genomic architecture jointly shape expression divergence across animals.
LaBoone PA, Piya AA, Assis R
Evolution · 2026 May · PMID 42176354 · Publisher ↗
Gene expression divergence is a major source of phenotypic variation, yet the factors that shift regulatory optima remain incompletely understood. In particular, it is unclear how broad taxonomic differences and local ge...
Gene expression divergence is a major source of phenotypic variation, yet the factors that shift regulatory optima remain incompletely understood. In particular, it is unclear how broad taxonomic differences and local genomic architecture interact to shape the tempo and mode of expression evolution. Here, we analyze single-copy orthologs between species pairs in Drosophila and mammals to compare rates and magnitudes of expression divergence, assess the influence of genome architecture, and evaluate tissue-specific and functional patterns. Using a computational framework that predicts expression divergence and species-specific expression optima, we identify markedly higher divergence rates in Drosophila than in mammals, consistent with theoretical expectations and prior empirical work. Contrary to expectations, genes located in nested structures, in which one gene lies entirely within the intron of another, were no more likely to diverge than unnested genes in either taxon. However, when divergence occurred in Drosophila, nested genes exhibited larger shifts in expression optima, with the strongest effects among internal genes. Divergence rates were also higher among young than old nested genes in both taxa, although magnitudes of expression shifts were indistinguishable, suggesting that nesting contributes to early regulatory instability but does not typically trigger large regulatory changes. Tissue-level and functional analyses further revealed taxon- and architecture-specific signatures of expression divergence, including contrasting patterns across reproductive and neural tissues, as well as enrichment of core regulatory processes among unnested genes and enrichment of drug and xenobiotic metabolism among nested genes in Drosophila. Collectively, these findings highlight how taxonomic context and genome architecture can shape expression evolution in distinct and measurable ways, giving rise to contrasting patterns of regulatory divergence.
Biomechanical trade-offs and the evolutionary dynamics of weapon morphology: phylogenetic comparative evidence from scorpion pincers.
Foerster SÍA
Evolution · 2026 May · PMID 42175900 · Publisher ↗
Pincer-like appendages are multifunctional structures that have evolved repeatedly within Arthropoda. In scorpions, they appear in the form of pedipalp chelae, providing an excellent example of form-function integration...
Pincer-like appendages are multifunctional structures that have evolved repeatedly within Arthropoda. In scorpions, they appear in the form of pedipalp chelae, providing an excellent example of form-function integration in evolutionary biology. Performance traits such as pinch force, closing speed, and mechanical resistance can be reliably predicted from chela morphology and directly influence fitness through a wide range of interactions. Despite of this, the evolutionary trajectories underlying the morphological diversity of the scorpion chelae remains poorly understood. Phylogenetic comparative analyses were conducted on chela measurements from 547 species (ca. 19% of all known scorpion species) to examine evolutionary allometry and to test whether chela length, width, and height were characterized by similar evolutionary rates and stabilizing regimes. Positive allometry was detected across all dimensions, with height scaling most steeply with body size. Ornstein-Uhlenbeck models revealed distinct evolutionary dynamics: chela length exhibited the highest instantaneous evolutionary rate while simultaneously experiencing the strongest stabilizing selection, whereas height and width displayed comparable long-term variance despite differing rates, consistent with coordinated functional constraints on robustness. These findings demonstrate that high rates of phenotypic evolution do not necessarily imply weak selection but rather indicate the magnitude of stochastic forces that selection must counteract to maintain functional integrity.
Convergence, stability, and thermal adaptation of the rubisco large subunit in plants.
Leung A, Chang BSW, Sage RF
Evolution · 2026 May · PMID 42172107 · Publisher ↗
Enzymes are adapted to perform optimally in different thermal regimes that would otherwise alter kinetics and stability. Whether adaptive evolution in the photosynthetic enzyme ribulose-1,5-bisphosphate carboxylase/oxyge...
Enzymes are adapted to perform optimally in different thermal regimes that would otherwise alter kinetics and stability. Whether adaptive evolution in the photosynthetic enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) also compensates for thermal variation remains uncertain. We examined molecular evolution and modelled the change in folding free energy (ΔΔG, where negative values indicate stabilization) of the rubisco large subunit (RbcL) in four phylogenetically distant plant genera: wood ferns (Dryopteris), sea lavenders (Limonium), pines (Pinus), and viburnums (Viburnum). Using codon evolutionary models in each genus, we observed widespread positive selection and parallel substitution in the catalytic α/β barrel domain. Species with warmer growing seasons had derived amino acids with stronger hydrogen bond contributions to ΔΔG. Protein structure-based modelling showed that the hydrogen bond contribution to stability tracked the growing season temperature of species carrying the derived amino acid. Stronger hydrogen bonds were offset by weaker contributions from hydrophobic solvation interactions, such that total ΔΔG showed no relationship with growing season temperature. In Viburnum, the strength of positive selection differed among biomes, with cold temperate and cloud forest clades showing stronger positive selection. These patterns are consistent with environmental tuning of non-covalent interactions within the enzyme. However, modest effect sizes indicate that other components of the rubisco holoenzyme likely also contribute to its thermal evolution.
Genomic architecture of the developing forelegs of Drosophila prolongata; an exaggerated weapon and ornament.
Audet T, Perdigón Ferreira J, Meena A … +10 more , Abass M, Torabi-Marashi A, Yeom J, Zaghloul F, Zaghloul N, Mizrahi A, Novikov J, Xi E, Lüpold S, Dworkin I
Evolution · 2026 May · PMID 42172094 · Publisher ↗
Elaborate secondary sexual traits are among the most striking phenotypes in nature. Functional genetic studies of these phenotypes generally focus on within-species analyses of candidate signalling pathways. These provid...
Elaborate secondary sexual traits are among the most striking phenotypes in nature. Functional genetic studies of these phenotypes generally focus on within-species analyses of candidate signalling pathways. These provide insight into mechanisms of trait expression, but not necessarily genetic differences contributing to evolutionary change. Drosophila prolongata offers an exceptional model to explore the evolution of trait exaggeration, as the only known species with male-specific foreleg size exaggeration in the melanogaster species group. We performed sex-specific RNA-seq in developing fore- and midleg tissues (imaginal discs) sampled at both the onset, and just after initiation of, sexually dimorphic growth in D. prolongata, D. carrolli (∼4MYA divergence) and D. melanogaster (∼35MYA). We observed a positive relationship between number, but not magnitude of differential expressed, sex-biased genes, with the extent of adult phenotypic dimorphism. Using genes identified from our differential expression analysis, we used RNAi knockdown in D. melanogaster to test their potential role in growth in the leg. Knockdown of several genes had quantitative impacts, whole one gene, grain, caused D. prolongata-like leg phenotypes. We also observed modest changes in magnitude and direction of expression differences, in signalling pathways previously implicated in sexually dimorphic evolution in other species. Our results are consistent with the evolution of sex-specific phenotypes being jointly mediated by few genes with large, and many more genes with modest impacts on sex-biased gene expression.
Digest: Directional selection in human limb evolution.
Tecel D
Evolution · 2026 May · PMID 42159316 · Publisher ↗
How has limb morphology diversified across the hominoid phylogeny, and does this divergence reflect natural selection or genetic drift? Cooper et al. (2026) apply a quantitative genetic framework to test evolutionary pro...
How has limb morphology diversified across the hominoid phylogeny, and does this divergence reflect natural selection or genetic drift? Cooper et al. (2026) apply a quantitative genetic framework to test evolutionary processes across multiple limb elements. While most lineages exhibit stabilizing selection or neutrality, strong directional selection is detected on the branch leading to Homo sapiens, indicating that human limb evolution represents a distinct departure from broader hominoid trends.
Reexamining the evolutionary history of the mammalian medial pterygoid muscle.
Schultz JA, Weaver LN, Jäger KRK … +1 more , Grossnickle DM
Evolution · 2026 May · PMID 42104962 · Publisher ↗
In stem mammals, feeding and hearing are closely linked due to jaw bones being involved in both functions. Osteological changes during the evolutionary separation of these systems are well documented in the fossil record...
In stem mammals, feeding and hearing are closely linked due to jaw bones being involved in both functions. Osteological changes during the evolutionary separation of these systems are well documented in the fossil record, but changes to soft tissue anatomy are less certain. The medial pterygoid muscle is a jaw adductor that develops medial to Meckel's cartilage, inserting on the mandibular angular process in therians (placentals and marsupials). Likewise, in stem mammaliaforms, the medial pterygoid is often assumed to have passed medial to the ossified Meckel's cartilage, inserting on the dentary 'angular' (i.e., pseudangular) process, a plesiomorphic pattern of muscle attachment also assumed to be present in some derived cynodonts. Thus, the traditional interpretation is that the medial pterygoid remained medial to Meckel's cartilage through the evolution from early cynodonts to therians. We highlight a pattern that contrasts with that interpretation: the medial pterygoid inserts lateral (not medial) to Meckel's cartilage in monotremes. Further, fossil evidence suggests that this pattern was also present in stem therian eutriconodontans and spalacotherioids, which lack the pseudangular process, suggesting that the muscle is either 1) evolutionarily labile in terms of its relative position to Meckel's cartilage, or 2) did not insert on the pseudangular process of early cynodonts. We support the latter hypothesis, proposed by Patterson (1956), which indicates that the medial pterygoid did not shift medial to Meckel's cartilage until the complete ear-jaw separation in cladotherians (therians and close relatives), with the shift linked to the evolution of the therian angular process as an insertion site.
Phylogenetics, Trait Covariance Analysis, and the Evolution of Fin and Body Shape in the Surgeonfishes.
Lungstrom LL, Farjo M, Isdonas R … +2 more , George AB, Westneat MW
Evolution · 2026 May · PMID 42104957 · Publisher ↗
Insights into ecomorphology are enriched when investigating evolutionary correlations between ecologically and functionally important traits. However, tools currently available to model patterns of shape covariation limi...
Insights into ecomorphology are enriched when investigating evolutionary correlations between ecologically and functionally important traits. However, tools currently available to model patterns of shape covariation limit researchers to either assume that trait covariances between taxa are independent of, or completely described by, their shared evolutionary history. Using a novel Pagel's λ adjustment to incorporate phylogenetic signal in trait covariance analysis, we aim to solve this long-standing problem in phylogenetic comparative methods and investigate ecological associations and evolutionary shape covariation in the ecologically and morphologically diverse case study of surgeonfishes (Acanthuridae). By revising acanthurid phylogenetic relationships and analyzing the geometric morphometrics of their body, head, and fins, we found that head and body shape were significantly associated with dietary ecotype. Surgeonfishes showed a significant negative correlation between caudal fin and pectoral fin shape; high/low aspect ratio (AR) tails are associated with low/high AR pectoral fins, respectively, suggesting locomotor tradeoffs. With our new approach to estimate the influence of phylogeny on trait covariances between taxa, we found the caudal fin covaried with both the body and pectoral fin due to dietary and locomotor demands, respectively and exhibited the highest evolutionary variance along the primary axis of integration in all trait covariance comparisons.
Surviving ancestors, hard polytomies, and seed plant evolution.
Renner SS, Grimm G, Sokoloff DD
Evolution · 2026 May · PMID 42101906 · Publisher ↗
Forty years of phylogenetic analysis have failed to resolve the relationships among the major groups of seed plants. From the fossil record it is clear that more seed plant groups have gone extinct than are extant, thoug...
Forty years of phylogenetic analysis have failed to resolve the relationships among the major groups of seed plants. From the fossil record it is clear that more seed plant groups have gone extinct than are extant, though some direct ancestors of today's clades could have survived. Here we reanalyze morphological matrices relevant to seed plants, applying two underutilized visualization tools: Networks for displaying incompatible phylogenetic signal and Romerograms (spindle diagrams) for depicting alternative relationships, suspected budding speciation, and surviving ancestors. Surviving ancestors give rise to hard polytomies, and networks may help pinpoint them as suggested by experiments in which we added simulated ancestors to our matrix. Romerograms - whose reproducible construction we illustrate - offer a heuristic means of representing phylogenetic hypotheses, and we argue that the field's near-exclusive focus on identifying sister groups and representing them in cladograms may have driven phylogenetics into an impasse. Identifying true evolutionary polytomies warrants further methodological research, but broadening the repertoire of data visualization approaches may help overcome the field's entrenched bias toward strictly dichotomous trees.
Lifetime fitness and annual survival are heritable and highly genetically correlated in a wild primate population.
Tuliozi B, Archie EA, Tung J … +1 more , Alberts SC
Evolution · 2026 May · PMID 42101905 · Publisher ↗
The additive genetic variance (VA) of fitness quantifies the expected response to selection. Lifetime reproductive success (LRS) is an effective metric of lifetime fitness in animal population, while time-limited fitness...
The additive genetic variance (VA) of fitness quantifies the expected response to selection. Lifetime reproductive success (LRS) is an effective metric of lifetime fitness in animal population, while time-limited fitness metrics such as annual survival or fertility can help to identify which fitness component - e.g., annual survival or fertility - harbor the most VA in fitness. Here we estimated the VA and heritability (h2) of LRS and three time-limited fitness metrics in a wild female baboon population in Kenya. The most heritable metrics were LRS (h2=0.25 [0.18, 0.34]) and annual survival (h2=0.23 [0.15, 0.33]). By further partitioning LRS, we were able to show that nearly all the VA for LRS was attributable to survival to first successful reproduction. Furthermore, all fitness metrics examined were highly genetically correlated with each other, supporting the use of time-limited metrics when LRS data are limited. Our analyses predicted faster phenotypic evolution than we have observed, raising the possibility that environmental or social variables masked responses to selection or inflated estimated VA. Overall, our findings reveal a substantial genetic contribution to variation in survival, and in turn, to fitness and contemporary evolution in a long-lived animal.
Unmasking black and yellow in a common garden: genetic and environmental drivers of urban colour divergence.
Sandmeyer L, Grégoire A, Caro SP … +5 more , Fargevieille A, Chenet B, Romans M, Charmantier A, Doutrelant C
Evolution · 2026 May · PMID 42101890 · Publisher ↗
Communication signals of many taxa, such as colouration, differ in urban areas compared to natural habitats. However, the mechanisms shaping these divergences-genetic or environmental-remain unclear. We studied urban and...
Communication signals of many taxa, such as colouration, differ in urban areas compared to natural habitats. However, the mechanisms shaping these divergences-genetic or environmental-remain unclear. We studied urban and forest great tits (Parus major) from populations where carotenoid-based colouration is reduced in urban habitats compared to forest, and first examined whether they differed in their melanic patches. We then used a common garden experiment to determine if the colour differences were maintained when birds were raised from the unincubated egg stage in a common environment. In the wild, urban males showed smaller black ties than forest males, and along an urbanisation gradient within urban habitat. Common garden birds of urban origin exhibited reduced chromatic yellow breast and smaller ties compared to forest-origin birds. In contrast, common garden birds from both habitats did not differ in yellow brightness or ultraviolet chroma. These results suggest that divergences in carotenoid saturation and melanin patch are primarily driven by genetic changes or early maternal investment in eggs, whereas yellow brightness or ultraviolet chroma are more environmentally determined. These findings provide information on the mechanisms driving phenotypic divergence in urban birds, with potential implications for mate choice, social dynamics, and evolutionary trajectories in anthropogenic landscapes.
Digest: Evidence for incipient hybrid speciation in the Black-cheeked Gnateater.
Ottenburghs J
Evolution · 2026 May · PMID 42101882 · Publisher ↗
Homoploid hybrid speciation continues to be debated, particularly regarding the role of hybridization in generating reproductive isolation. Lima et al. (2026) present genetic evidence for an admixed lineage in the Black-...
Homoploid hybrid speciation continues to be debated, particularly regarding the role of hybridization in generating reproductive isolation. Lima et al. (2026) present genetic evidence for an admixed lineage in the Black-cheeked Gnateater (Conopophaga melanops). Notably, patterns of isolation-by-distance, clinal plumage variation, and discordant signals in mitochondrial and nuclear markers complicate this interpretation. These findings highlight the difficulty of distinguishing hybrid speciation from secondary gene flow and underscore the reticulated nature of evolution.
Diversification and divergence in Myioborus warblers: insights into evolutionary relationships and plumage genetics.
Arias LNC, Bennett KFP, Campagna L … +6 more , Wood AW, Bonaccorso E, Cuervo AM, Cadena CD, Lovette IJ, Toews DPL
Evolution · 2026 May · PMID 42096496 · Publisher ↗
Genomic data can provide valuable insights into the evolutionary history of rapidly diversifying groups and the genetic basis of phenotypic traits. We performed whole-genome resequencing of the warbler genus Myioborus to...
Genomic data can provide valuable insights into the evolutionary history of rapidly diversifying groups and the genetic basis of phenotypic traits. We performed whole-genome resequencing of the warbler genus Myioborus to investigate the dynamics of its recent diversification in Neotropical mountains. Mitochondrial and nuclear DNA produced mostly concordant tree topologies and revealed a pattern of north-to-south and low-to-high elevation colonization. Within a young tropical Andes clade (M. albifrons, M. ornatus, and M. melanocephalus), we found topological incongruence between our phylogenies. In general, relationships coincided with plumage types; however, three taxa with striking plumage differences exhibited low mitochondrial divergence. The hybridizing taxa M. ornatus chrysops and M. melanocephalus bairdi showed very shallow genomic differentiation, with most divergence peaks across the genome shared with other parulid warbler pairs, pointing to shared genomic architecture shaping these regions. However, a unique differentiated region included the gene CCDC91, which is associated with melanin-based plumage differences in other birds. We also identified a large region of elevated differentiation on the Z chromosome showing strong signals of reduced recombination. Together, these results highlight the interplay of deep ancestral divergence, recent hybridization, and shared genomic architecture in shaping the evolution of phenotypic and genomic diversity in Myioborus.
History of divergence and gene flow shaping geographic variation in Andean warblers (Myioborus).
Arias LNC, Cuervo AM, Cadena CD … +4 more , Bonaccorso E, Witt C, Lovette I, Campagna L
Evolution · 2026 May · PMID 42089468 · Publisher ↗
Studying how genetic variation is structured across space, and how it relates to divergence in phenotypic traits relevant to reproductive isolation, is important for our understanding of the speciation process. We used d...
Studying how genetic variation is structured across space, and how it relates to divergence in phenotypic traits relevant to reproductive isolation, is important for our understanding of the speciation process. We used ddRAD-seq data to examine genetic variation across the distribution of an Andean warbler species complex (Myioborus ornatus-melanocephalus), which includes a known hybrid zone between two taxa with striking plumage differences. Genetic structure reflects geographic variation in head plumage, with some breaks coinciding with major topographic barriers in the Andes. We found that M. o. chrysops and M. m. bairdi, the two hybridizing taxa, were characterized by low overall genetic divergence. Based on our cline analyses of plumage and genomic hybrid indices, this hybrid zone extends for approximately 250 km, where advanced generation hybrids are likely most common. We also identified a slight difference in the geographic centers of the plumage and genetic ancestry clines, potentially suggesting asymmetric introgression of chrysops-like plumage traits. By studying genetic variation in a phenotypically diverse group distributed across a topographically complex area that includes a hybrid zone, we show how both geographic features and plumage traits potentially relevant to mate choice may contribute to species formation and maintenance in tropical mountains.
Founder effects drive high mitochondrial dN/dS in island rails.
Wanders K, Oğuzhan Z, Stervander M … +10 more , Kimball RT, Braun EL, Dreyer S, Øksnebjerg DB, Graves GR, Rahbek C, Chen G, Feng S, Zhang G, Hosner PA
Evolution · 2026 Jun · PMID 42089461 · Publisher ↗
Insular (island-limited) populations typically show signatures of weak purifying selection, indicating high genetic load and reduced fitness compared with mainland populations. However, the source of this pattern is ofte...
Insular (island-limited) populations typically show signatures of weak purifying selection, indicating high genetic load and reduced fitness compared with mainland populations. However, the source of this pattern is often unclear-it may reflect residual signatures from a temporary period of small effective population size (Ne) associated with island colonization (founder effects), persistently small Ne due to the lower carrying capacity of islands (range limitations), or relaxed selective constraints unrelated to Ne. Here, we disentangle these hypotheses by analyzing the drivers of variation in evolutionary rates of nonsynonymous (dN) and synonymous (dS) sites in nine mitochondrial genes (8001 bp) from 40 rail species (Aves: Rallidae). We find that insular species with short terminal branches (indicating recent island colonization) have highly elevated mitochondrial dN/dS across multiple mitochondrial genes. In contrast, rails representing more ancient island colonizations have dN/dS ratios that are indistinguishable from mainland/widespread species. Furthermore, we find that island size is unrelated to dN/dS among island species. These results indicate that insular rails suffer a high initial cost of island colonization and undergo a period of inefficient selection due to founder effects, but that there is little impact from longer-term range limitations or relaxed selection.
Determinism and contingency in the evolution of giant filter-feeding vertebrates.
López-Galán J, Ferrón HG, Botella H
Evolution · 2026 May · PMID 42089459 · Publisher ↗
Giant suspension feeders have evolved repeatedly across vertebrates, but the relative roles of deterministic factors and phylogenetic contingency remain unclear. To test this, we integrate new selachian data with publish...
Giant suspension feeders have evolved repeatedly across vertebrates, but the relative roles of deterministic factors and phylogenetic contingency remain unclear. To test this, we integrate new selachian data with published pachycormiform and cetacean datasets to reconstruct phylomorphospaces from standardized cranial, dental, and jaw metrics (gape, orbit size, mechanical advantage, mandibular aspect ratio), evaluate convergence using quantitative metrics, and fit alternative multivariate evolutionary models. Independent lineages evolve from distinct macrophagous ancestors but follow roughly parallel trajectories into a shared morphospace region linked to efficient capture of small planktonic prey. Overlap is limited: pachycormiforms and filter-feeding selachians occupy adjoining areas, while mysticetes extend to a distinct endpoint along the same functional continuum. Convergence is strongest across clades, particularly between pachycormiforms and selachians, and comparatively weak within clades. Evolutionary modeling favors multiregime Ornstein-Uhlenbeck processes over Brownian or single-regime alternatives, identifying either three clade-specific optima or a shared optimum for pachycormiforms and selachians distinct from cetaceans. These results reveal repeated convergence on analogous functional designs stabilized around lineage-specific adaptive peaks. Giant filter-feeders thus illustrate how selective pressures can guide evolutionary direction, while historical constraints shape trajectories-showing determinism and contingency as complementary forces.
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