Predicting evolutionary outcomes remains a central challenge in biology. Using three replicate hybrid zones in the Western Andes of Colombia, Castaño et al. (2026) assessed the repeatability of introgression between Lemo...Predicting evolutionary outcomes remains a central challenge in biology. Using three replicate hybrid zones in the Western Andes of Colombia, Castaño et al. (2026) assessed the repeatability of introgression between Lemon-rumped and Flame-rumped Tanagers. Genomic cline analyses revealed heterogeneous patterns of neutral introgression, but deterministic introgression at a plumage-associated locus on chromosome 22. Together, these patterns show that introgression reflects a balance of chance and necessity, with selection generating predictable outcomes amid substantial genomic contingency.
Why natural populations harbor high additive genetic variance for fitness remains an evolutionary puzzle. Connallon and Czuppon (2026) show that balancing selection, long considered irrelevant for additive variance at eq...Why natural populations harbor high additive genetic variance for fitness remains an evolutionary puzzle. Connallon and Czuppon (2026) show that balancing selection, long considered irrelevant for additive variance at equilibrium, can maintain substantial fitness variance when realistic features such as genetic drift and environmental fluctuations are considered. Their models demonstrate that even a small number of balanced polymorphisms can rival thousands of loci at mutation-selection balance, reshaping how fitness variation is interpreted across taxa.
What neural changes underlie the evolution of novel behaviour? Does behavioural innovation require enhanced sensory input, or can it arise through reorganisation of existing neural circuits? Hodge et al. (2026) show that...What neural changes underlie the evolution of novel behaviour? Does behavioural innovation require enhanced sensory input, or can it arise through reorganisation of existing neural circuits? Hodge et al. (2026) show that the enlarged mushroom bodies associated with specialised foraging in Heliconius butterflies reflect localised circuit restructuring, while peripheral sensory pathways remain largely conserved. These findings suggest that cognitive innovation can emerge through changes in integrative brain centres without expansion of sensory systems.
We focus on the evolution of behavioral sexual isolation through the empirical study of two marine isopod species. The males of Jaera albifrons and Jaera praehirsuta engage females in tactile courtship by brushing the fe...We focus on the evolution of behavioral sexual isolation through the empirical study of two marine isopod species. The males of Jaera albifrons and Jaera praehirsuta engage females in tactile courtship by brushing the female's back, but they do so with divergent sets of specialized setae, and female choice results in strong reproductive isolation. Using RADseq-derived genotypes of individuals from natural populations and controlled crosses, we found that secondary contacts between J. albifrons and J. praehirsuta resulted in different levels of heterospecific gene flow. Comparison of the genomic landscapes of differentiation in the two most contrasted situations (extremely low heterospecific gene flow in one geographic region, but strong introgressive hybridization in another) allowed us to conclude that genomic regions resistant to interspecies gene flow are primarily located on the sex chromosomes or on rearranged chromosomes (several fusion-scissions and one reciprocal translocation). These genomic regions show low recombination, and in two cases quantitative trait locus analyses found genetic variation associated with male courtship traits. These results suggest that a period of allopatry may have allowed the divergent coevolution of male traits and female preferences, with genetic bases located at least in part in nonrecombining regions on sex chromosomes and rearranged chromosomes.
Thermal performance curves (TPCs) capture how population growth depends on temperature. When temperatures increase, such as during global change, TPCs may evolve to match new environmental temperatures. While previous st...Thermal performance curves (TPCs) capture how population growth depends on temperature. When temperatures increase, such as during global change, TPCs may evolve to match new environmental temperatures. While previous studies mostly focus on population growth rate TPCs, evolution can also be strongly trait-dependent and require a multi-trait analysis. Here, we empirically tested how TPCs and multiple demographic, life-history and movement traits evolve by selecting four freshwater protist species at increased temperatures starting from clonal populations. After ten months of selection, populations showed a signature of evolutionary responses to the highest selection temperatures in different traits depending on the species. Particularly, we found consistent evolutionary reductions in body size in the three species having the largest cells and evolved changes in movement behaviour in all species. In contrast, we observed few modifications in population growth rate TPCs. These results suggest that adaptation, via evolution of TPCs, might involve the concurrent evolution of several traits. However, this may be species-specific and difficult from de-novo mutation alone, suggesting that natural populations that do not have sufficient standing genetic variation might have to rely on other means of mitigating the effects of climate change, such as dispersal.
Climate change is reshaping environments, raising questions about how species will endure. Pinto and Stelkens (2026) investigate whether hybridization aids adaptation using four yeast species and their interspecific F2 h...Climate change is reshaping environments, raising questions about how species will endure. Pinto and Stelkens (2026) investigate whether hybridization aids adaptation using four yeast species and their interspecific F2 hybrids exposed to extreme temperature stress. While the parental species and their hybrids adapted to temperature extremes, hybrids exhibited unique evolutionary trajectories. These findings highlight the adaptive potential of hybrids and the importance of considering genetic background when determining how organisms will respond to rapid climate change.
Using data from 546 ant species, Turner et al. (2026) address why some ant workers retain reproductive capacity while others evolve complete sterility. They show that increases in colony size consistently favor worker st...Using data from 546 ant species, Turner et al. (2026) address why some ant workers retain reproductive capacity while others evolve complete sterility. They show that increases in colony size consistently favor worker sterility and greater queen-worker size dimorphism. Across the phylogeny, reproductive specialization evolves gradually and has arisen repeatedly. This study causally links colony size to caste differentiation, strengthening the size-complexity hypothesis and clarifying how social groups transition toward greater biological integration.
Allopatric speciation in riverine fishes is often assumed to be ecologically neutral, with divergence driven primarily by geographic isolation and genetic drift. However, recent work on darters from the Central Highlands...Allopatric speciation in riverine fishes is often assumed to be ecologically neutral, with divergence driven primarily by geographic isolation and genetic drift. However, recent work on darters from the Central Highlands of the United States reveals that ecological divergence during allopatry is highly variable and context-dependent. By integrating phylogenomics, morphology, diet, and environmental data, Stokes et al. (2026) demonstrate that phenotypic divergence can arise in allopatrically distributed riverine fish species. However, the degree of phenotypic disparity is not predicted by divergence time, genomic isolation, or geographic distance, highlighting a contingent role for ecology in shaping evolutionary outcomes under allopatry.
Global temperatures are rising and inbreeding is increasingly common in wild animals as populations decline. There is extensive research on inbreeding and temperature stress, but little is known about how they interact t...Global temperatures are rising and inbreeding is increasingly common in wild animals as populations decline. There is extensive research on inbreeding and temperature stress, but little is known about how they interact to affect sexually selected traits. We therefore investigated how developmental temperature (26°C or 30°C) and inbreeding affect male guppies (Poecilia reticulata). We reciprocally cross-bred full-siblings to create inbred and outbred fish, then measured traits under either pre-copulatory (i.e., coloration, gonopodium length, sexual attractiveness, and mating behavior) or postcopulatory (i.e., sperm number, and velocity) sexual selection for ∼120 adult males. There was no evidence that temperature and inbreeding interact to affect trait expression; instead, their effects were additive. Males reared at 30°C were significantly less attractive to females, and made fewer sigmoid mating displays, than males reared at 26°C. Inbred males were also less attractive, but their mating behavior did not differ from that of outbred males. Sperm number and velocity were unaffected by inbreeding or developmental temperature. Unexpectedly, males reared at 30°C and inbred males both had significantly more orange coloration. Our results show that inbreeding and developmental temperature independently influence some sexually selected male traits, suggesting that climate change and habitat fragmentation might alter evolution under sexual selection.
Phylogenetic eigenvector regression (PVR) is widely used in ecology and evolution by representing phylogenetic structure through separable eigenvectors (EVs). Despite this flexibility, its implementation faces three key...Phylogenetic eigenvector regression (PVR) is widely used in ecology and evolution by representing phylogenetic structure through separable eigenvectors (EVs). Despite this flexibility, its implementation faces three key challenges: (1) the selection of EVs, (2) the reduced robustness of ordinary least-squares (OLS) regression under shift-like evolutionary heterogeneity, and (3) the applicability of conventional model complexity rules such as the "samples-per-variable (SPV) ≥ 10" guideline. Here, we propose an optimized PVR framework that addresses these limitations. First, we show that trait-specific selections of EVs often diverge, sometimes producing inconsistent results, and that using their union offers stronger control of phylogenetic nonindependence. Second, we evaluate robust regression estimators within PVR, demonstrating that PVR-MM-and in most cases PVR-L2, the standard OLS estimator-maintains high accuracy under nonstationary evolutionary shifts, where other nonrobust methods fail. Third, through simulation, we reassess the SPV ≥ 10 rule, showing that PVR tolerates EV counts well beyond this threshold, offering greater flexibility while requiring attention to potential overfitting. Extensive simulations across diverse trees and evolutionary scenarios confirm that the optimized framework improves accuracy and robustness. By addressing key aspects of EV selection, regression, and model complexity, our findings strengthen the reliability and applicability of PVR.
Biodiversity is structured in nested Retrospective Reproductive Communities (RRCs) reflecting different levels of information about evolutionary processes. Ranking species involves deciding which level to emphasize, base...Biodiversity is structured in nested Retrospective Reproductive Communities (RRCs) reflecting different levels of information about evolutionary processes. Ranking species involves deciding which level to emphasize, based on a trade-off in information gain and loss. Modeling the selective processes that maintain RRCs along distinct evolutionary paths can inform these trade-offs in species delimitation. We illustrate this approach using the Brazilian wandering spiders (Phoneutria). Integrating genetic markers, geometric morphometrics, color patterns, and environmental data, we applied both established and novel approaches to test divergence through historical natural and sexual selection. We found evidence that selection on ecological niche and ventral abdominal coloration contributed to the formation of 4 distinct RRCs. Two of these RRCs also showed evidence of a lock-and-key mechanism influencing genital morphology evolution. Despite the distinct cohesive forces, gene flow modeling revealed incomplete reproductive isolation, with potential hybrid individuals. We evaluate the implications of lumping versus splitting these lineages and argue that recognizing all 4 RRCs as distinct species would better preserve evolutionary information and minimize downstream impacts on other research fields such as pharmacology, public health, and conservation. Our approach provides a quantitative basis to ponder the implications of choosing between different species hypotheses.
Net selection on a trait reflects the association of phenotype to fitness across an entire life cycle. This longitudinal selection estimate can be viewed as the summation of selection episodes across time, each character...Net selection on a trait reflects the association of phenotype to fitness across an entire life cycle. This longitudinal selection estimate can be viewed as the summation of selection episodes across time, each characterized by a cross-sectional estimate. Selection may be consistent in direction and strength across episodes for some traits, fluctuating in others, and for some, concentrated in a single intense event. While selection on plant reproductive traits is predicted to be stronger through male fitness than female fitness, male fitness remains less studied. We investigated how selection on flowering traits in Brassica rapa varies across a season by measuring male reproductive fitness in four experimental populations. To estimate longitudinal and cross-sectional selection, we introduced plants at successive intervals within a single reproductive season. We genotyped over 3,000 plants and calculated selection on flowering time, duration, and total flowers. Cross-sectional analyses revealed directional selection was common, but patterns were masked by longitudinal estimates. Manipulation of spatial arrangement within populations further revealed to significantly impact pollen movement. Our experiment demonstrates that breeding timing and spatial aggregation interact to create complex evolutionary dynamics.
Divergent selection on coloration and patterning can drive diversification among closely related species. In a recent study, Schroth-Sanchez et al. (2026) used Darter fish to identify specific habitat variables that infl...Divergent selection on coloration and patterning can drive diversification among closely related species. In a recent study, Schroth-Sanchez et al. (2026) used Darter fish to identify specific habitat variables that influence color evolution. They found that smaller, rocky streams with fewer predators and high-light environments contribute to greater rates of diversification and brighter, bolder patterns. This work suggests that certain habitats may foster greater diversification and speciation through an interplay of ecological and sexual selection.
Principal component analysis (PCA) is one of the most widely used approaches for multivariate datasets. Biologists use PCA to visualize data, identify patterns in large datasets, determine independent axes of variation,...Principal component analysis (PCA) is one of the most widely used approaches for multivariate datasets. Biologists use PCA to visualize data, identify patterns in large datasets, determine independent axes of variation, and reduce dimensionality for further statistical analyses. Phylogenetic PCA is an extension of regular PCA that seeks to identify the major axes of variation independent of the phylogeny. We extend these methods by estimating PCA parameters using an explicit probability modeling framework. We implement multiple models of trait evolution (Brownian motion, Ornstein-Uhlenbeck, Early Burst, and Pagel's λ) and use the Akaike information criterion for model selection. We also introduce a probabilistic approach to select the number of principal components to retain from a PCA. We demonstrate the advantages of probabilistic PCA, such as incorporating the error, or noise, arising from dimensionality reduction, which is ignored in regular PCA. We use extensive simulations and an empirical dataset with 35 traits to show the method's performance. We implemented the new approach in the R package "do3PCA" available from the RCran repository.
Eusociality, the highest level of social organization, is rare among vertebrates and is best exemplified by two African mole-rat species (Bathyergidae). The lifetime monogamy hypothesis suggests that monogamy enhances ge...Eusociality, the highest level of social organization, is rare among vertebrates and is best exemplified by two African mole-rat species (Bathyergidae). The lifetime monogamy hypothesis suggests that monogamy enhances genetic relatedness within colonies, favoring the evolution of cooperative behaviors and eusociality. While strongly supported in eusocial insects, its role in vertebrates remains unclear. We evaluated this hypothesis in the Bathyergidae to determine the role of monogamy in the evolution of eusociality in vertebrates. We evaluated two predictions: (1) eusociality should be restricted to monogamous lineages, i.e., monogamy is a precondition of eusociality; and (2) factors additional to monogamy are required for eusociality to evolve. To test these predictions, we inferred a time-calibrated phylogeny for most species of Bathyergidae and combined it with mating system and sociality data to estimate ancestral states and assess evolutionary correlations. We inferred an ancestral monogamous state for social and eusocial African mole-rats. One of the evolutionary transitions with the highest rate of change was from monogamy + solitary to monogamy + social. Our results are consistent with monogamy representing a necessary prerequisite for the evolution of obligate eusociality, while also indicating that additional ecological and life-history factors are required for eusociality to evolve and intensify.
Recent studies have revealed bacterial genome-wide evolution to be complex and dynamic even in a constant environment, characterized by the emergence of new clades competing or temporarily coexisting as each clade underg...Recent studies have revealed bacterial genome-wide evolution to be complex and dynamic even in a constant environment, characterized by the emergence of new clades competing or temporarily coexisting as each clade undergoes evolutionary change. Previous studies on predator-prey dynamics tracking simple ecological and phenotypic metrics have shown predation to fundamentally alter prey evolution, facilitating defense evolution followed by coevolution and frequency dependent selection between defended and undefended prey genotypes. Here we sought to consolidate these fields by examining genome-wide evolution in five bacterial prey species separately subjected to long-term evolution under ciliate predation. We hypothesized that the presence of predation could change the pattern of clonal dynamics, for example, by more frequently producing selective sweeps if predation-defense-related mutations are under strong selection. For all species, we found mutational signals of prey adaptation, with phenotypic data and genomic mutation targets demonstrating changes in composition between the experimental treatments. Intriguingly, despite higher variant counts, overall temporal clade dynamics across the coevolved prey species were strikingly similar to those of bacteria evolving alone, with constant emergence, competition and quasi-stable coexistence of clades. This study shows that long-term molecular evolution in bacterial prey under predation is more interesting and less predictable than we might expect based on existing coevolutionary theories.
Evolutionary theory predicts that variation in longevity persists due to trade-offs between early-life fitness traits (e.g., growth or fecundity) and long-term somatic maintenance. However, such trade-offs can be difficu...Evolutionary theory predicts that variation in longevity persists due to trade-offs between early-life fitness traits (e.g., growth or fecundity) and long-term somatic maintenance. However, such trade-offs can be difficult to detect and may often become apparent only under certain conditions. For instance, developing in novel or atypical environments may alter the genetic architecture of traits, revealing trade-offs that are otherwise hidden under normal conditions. To test this, we compared full-sibling families of the Mexican spadefoot (Spea multiplicata) reared across two larval diets: a typical detritus diet and an atypical live shrimp diet, which they are competitively excluded from in nature. The shrimp diet significantly increased broad-sense genetic variance and heritability for larval growth rate, whereas heritability for post-metamorphic telomere length-a known longevity correlate-remained similar across diets. Moreover, only on the shrimp diet did families with faster growth exhibit shorter telomeres, consistent with a diet-dependent trade-off between growth and somatic maintenance. Overall, our study shows that developing under atypical dietary conditions exposes previously cryptic genetic variation in growth, thereby revealing a trade-off with somatic maintenance. These findings have implications for understanding how environmental change, such as rapid dietary shifts, can shape aging processes and vulnerability to age-related disease.
Pigmentation has been widely studied by evolutionary biologists due to both ease of measurement and relationship to fitness. Drosophila melanogaster pigmentation has represented a particularly useful avenue of investigat...Pigmentation has been widely studied by evolutionary biologists due to both ease of measurement and relationship to fitness. Drosophila melanogaster pigmentation has represented a particularly useful avenue of investigation, as extensive genetic tools have enabled the characterization of the trait's complex architecture. Drosophila pigmentation also varies predictably across space and time in wild populations, suggesting pigmentation is a component of adaptation to local environmental conditions. Despite this, the impact of D. melanogaster pigmentation on fitness, and the environmental factors that drive the evolution of pigmentation, are not well understood. To address this gap, we experimentally evolved replicated D. melanogaster populations in field mesocosms to determine whether and how pigmentation evolves in response to environmental variation. We found that pigmentation rapidly and predictably adapted to a direct manipulation of temperature, supportive of melanization playing a role in thermoregulation. However, we also determined that pigmentation responded adaptively to direct manipulations of numerous additional factors, including intraspecific competition, diet, and the microbiome. These findings suggest that the selective landscape acting on pigmentation is complex and multifaceted, and that patterns of melanization may be driven, at least in part, by indirect selection due to correlations with other fitness-related traits.
Animal venoms vary greatly in compositional complexity, where complex venoms are hypothesized to be maintained by greater dietary breadth. Beyond explaining venom composition, the dietary breadth hypothesis predicts that...Animal venoms vary greatly in compositional complexity, where complex venoms are hypothesized to be maintained by greater dietary breadth. Beyond explaining venom composition, the dietary breadth hypothesis predicts that these more complex venoms should show greater functional breadth in terms of overall toxicity and by disrupting multiple prey physiological processes. We evaluate these predictions with six distinct physiological assays of cardiac and blood clotting functions and compared the effects of venoms from snake species with a range of taxonomic dietary diversity levels. We compared the taxonomic dietary generalists Agkistrodon piscivorus and Sistrurus miliarius to taxa with varying taxonomic specialization, namely Ag. contortrix and Crotalus adamanteus, and Azemiops feae. Comparing fish thrombocyte and mammal platelet aggregation and fibrin clot formation, only species with broader diets disrupted both fish and mammal hemostatic function. Venom of Ag. piscivorus, a uniquely fish-eating species, was the most disruptive of zebrafish heart rate, thrombocyte activation, vascular permeability, and clotting after injury. Sistrurus miliarius was also highly toxic, whereas mammal-specialists' venoms scarcely altered zebrafish physiology. Our results support the hypothesis that dietary breadth selects functionally complex venoms. Understanding venom gene evolution, snakebite symptoms, and searching for therapeutics in venom should be guided by evolutionary ecology.
The role of isolation by distance in shaping population structure across space is well understood, and the same principles should operate over time. Allochrony, the isolation of populations due to separation in time, can...The role of isolation by distance in shaping population structure across space is well understood, and the same principles should operate over time. Allochrony, the isolation of populations due to separation in time, can be a source of genetic differentiation, but remains infrequently documented between yearly asynchronous populations. In this study, we investigate divergence between 2 putative sympatric populations of the alpine butterfly Oeneis chryxus ivallda at Castle Peak, CA, USA. We find clear genetic differentiation between butterflies collected in odd and even years, with limited instances of admixture. The observed GST of 0.05 between the two populations is approximately equivalent to 26 km based on pairwise GST values observed between O. chryxus populations across space. These results demonstrate a potential source of population differentiation in systems that promote multiple-year development in insects, often found in high-elevation and high-latitude environments.