Abstract Since Darwin and Humboldt, researchers have tried to understand how species adapt to different elevations. Tropical reptiles are typically diverse in warm, lowland environments, yet many reptile lineages have colonized high elevation environments on both islands and the mainland. Nonetheless, the frequency with which these environments have been colonized remains unclear. The occurrence of high elevation species on multiple mountain ranges could reflect a single lowland-to-highland transition followed by subsequent divergence into multiple species or, alternatively, could result from more than one colonization event with limited within-lineage diversification. Here, we test these alternatives for anole lizards which, though predominantly found in tropical lowlands, also occupy multiple mountain ranges in Central and South America and the Caribbean. Analyzing extensive climatic and distributional data for 303 species and thermal physiology data (cold tolerance or CTmin) for 64 species, we found that colonization of high-elevation regions has occurred many times in anoles, that the frequency of such occupation is lower than the opposite, and that biogeographic dispersal across mountains and shifts in climatic niche are distributed non-randomly across the phylogeny. Additionally, transitions between lowland and highland habitats do not coincide with shifts in the rate of stochastic trait evolution for either cold tolerance or minimum thermal niche. Instead, highland lineages show stronger selection toward a colder optimum for minimum ambient temperature, consistent with climatic niche conservatism in montane environments. Cold tolerance itself shows no such shift, suggesting a decoupling between the climatic environment lineages experience and the evolution of a physiological trait that should, in principle, track it. Together, these results show that repeated mountain colonization has reshaped climatic niche evolution in Anolis, while physiological cold tolerance has followed a comparatively stable, elevation-independent trajectory.
Abstract Aposematic phenotypes advertise their unprofitability to predators by means of colorful warning signals. The Neotropical family Dendrobatidae comprises some of the prime examples of aposematism in amphibians but with pronounced intraspecific variation in some species, particularly in the genus Oophaga. We herein compare the skin spectral reflectance, pigment composition and gene expression of individuals with aposematic (red) and cryptic (green) phenotypes of Oophaga granulifera from Costa Rica. Our findings reveal that accumulation of keto-carotenoids, xanthophylls, and β-carotene in the skin are responsible for the red aposematic phenotype in this species. Several differentially expressed pigmentation genes, particularly some in the carotenoid metabolism pathway, are strongly associated with the distinction between red and green skin phenotypes. Green frogs also show pronounced up-regulation of the bco1 gene which has been associated to ketocarotenoid-based polymorphisms in other species and represents a strong candidate for additional enzymatic studies. We found no clear candidate ketolase gene but the ketolation enhancer ttc39b was upregulated in the liver of red O. granulifera, aligning with previous studies that underscore the importance of this ancillary gene for keto-carotenoid metabolism. Gene ontology enrichments indicate that, along with the carotenoid metabolism genes, red frogs upregulate the metabolism of amino acids, lipids and the mitochondrial energy production, markedly in the liver but also in the skin. These results suggest a close association between increased keto-carotenoid accumulation and a higher metabolic rate in the red frogs which is congruent with macroevolutionary patterns in the family and behavioral observations in this species.
Environmental boundaries shape genetic diversity through the interacting effects of geographic distance, local adaptation, and constraints on gene flow. The ochre sea star (Pisaster ochraceus), an intertidal keystone predator, has long been considered to have limited spatial genetic structure along the North American Pacific coast, likely due to its extended larval dispersal period and high potential for gene flow. Here, we characterize spatial genomic variation in Pisaster ochraceus using whole-genome sequencing data from individuals spanning nearly 3000 kilometers of coastline from Alaska to southern California. Analyses of putatively neutral SNPs demonstrate considerable mixing across the latitudinal range, but also reveal substantial structure between outer Pacific coast populations and those within the semi-enclosed Salish Sea, suggesting restricted gene flow and demographic divergence between these regions. Genomic divergence is further supported by evidence of selection, with outlier loci highlighting extended regions of low diversity in the Salish Sea, consistent with recent selective sweeps and potential local adaptation to distinct estuarine conditions. These findings support the role of oceanographic barriers and environmental heterogeneity in shaping population structure in Pisaster ochraceus, challenging earlier expectations of range-wide homogeneity and providing insight into the persistence of this keystone marine species in a rapidly changing world.
About one hundred subterranean catfish species have been described, resulting from repeated colonization of cave environments by multiple surface lineages. Most cave-dwelling species are found in the Americas, in particular in South America, but a few species also live in Central and North America. Despite the availability of high-quality genome assemblies for two cave species, the Mexican blind catfish Prietella phreatophila and the Colombian blind catfish Trichomycterus rosablanca, genomic approaches to investigate genetic changes associated with subterranean life or to estimate cave colonization times remain largely unexplored. To fill this gap, we additionally sequenced the genomes of four blind and depigmented subterranean catfishes from Peru (three Trichomycterus and one Astroblepus), as well as the genomes of four close surface relatives. We first extracted a large set of light-related genes, such as phototransduction and crystallin genes, and found contrasting decays of these sequences in different cave species, from 1% of pseudogenes in T. rosablanca to 48% in P. phreatophila. Two independent molecular dating methods gave congruent ages, indicating that these catfishes colonized subterranean habitats at different times, ranging from Early Pliocene to Late Pleistocene, supporting the hypothesis that surface catfishes repeatedly and rapidly adapted to subterranean habitats. The oldest cave species, P. phreatophila, appears to have been thriving in the dark for over 3.5 million years. Moreover, a genome-wide analysis of protein-coding genes suggests weaker purifying selection on mildly deleterious mutations in this cavefish than in other catfish lineages, likely reflecting a long-term small effective population size.
We report the consequences of >330 generations of experimental evolution under larval undernutrition for male postcopulatory success and traits thought to mediate it in Drosophila melanogaster, comparing them to phenotypically plastic responses. Males from populations evolved on standard diet showed a >30% plastic reduction in the size of accessory glands (AG) when raised on a nutrient-poor larval diet. Experimental evolution on the poor diet led to a further reduction that was more pronounced in smaller individuals, changing the allometric slope between AG and wing size. Rather than the expected reduction in seminal fluid protein expression, we observed a plastic increase on poor diet in investment in Acp36DE and Acp62F at the expense of Acp26Aa and SP, and an evolutionary shift in the time course towards lower virgin and higher post-mating SFP expression. Surprisingly, neither the plastic nor evolved reduction in AG was associated with impaired performance in reproductive output from matings with excess females, the ability to induce female oviposition or performance in sperm competition ("sperm defense"), except when poor diet-adapted males were raised on standard diet. Thus, larval nutrient shortage favors reduced investment in AG development, but this is compensated for by other mechanisms, minimizing consequences for postcopulatory success.
Species coexistence is critical to the assembly of biodiverse communities. When closely related species come into secondary contact, competitive and reproductive interactions can both influence the potential for coexistence. We tested whether ecological and/or evolutionary factors affect coexistence dynamics in a pair of closely related honeyeaters that have come into secondary contact in the Solomon Islands. Myzomela cardinalis colonized the island of Makira and established a population in sympatry with the endemic M. tristrami. These taxa are ecologically similar and hybridize. If ecological factors are promoting coexistence, we expect species to partition where they forage for resources or defend breeding territories. In addition, evolutionary pressures may facilitate coexistence if species mate assortatively, avoiding production of potentially low-fitness hybrid offspring. Using data on foraging locations, nest locations, and mate pairing, we find support for partitioning of space use, specifically in the context of nest placement. Phenotypic pairs of the recently arrived species nested significantly closer to the coastline than did endemic species pairs. We also find strong evidence of assortative mating based on phenotype. Thus, both ecological and evolutionary factors appear to contribute to the coexistence of these closely related hybridizing species.
Testis morphology may act as a determinant of sperm size, and the evolutionary pressure to produce longer sperm may impose functional constraints on testicular architecture. Postcopulatory sexual selection, particularly sperm competition, is widely recognised as a primary driver of the remarkable interspecific variation in sperm size and number across animals. Theoretical hypotheses predict that longer sperm require wider seminiferous tubules and that intense sperm competition favours an increased proportion of sperm-producing (seminiferous) tissue relative to non-spermatogenic components, independent of overall testis size. Using a phylogenetic comparative approach across 78 anuran species, we tested these two predictions. Our analyses revealed that the cross-sectional area of the seminiferous tubules was significantly and positively correlated with sperm length, thereby supporting the proposed morphogenetic constraint. Furthermore, relative testis size, which was used as a validated proxy for sperm competition intensity, was positively associated with the proportion of seminiferous tissue. In contrast, absolute testis size did not predict this tissue proportion. Our findings suggest that sperm competition shapes anuran testicular architecture through two distinct evolutionary pathways: indirect selection for wider tubules mediated by longer sperm, and direct selection for increased investment in seminiferous tissue. This tissue optimisation extends beyond simple testicular enlargement and reveals sophisticated evolutionary adaptations to postcopulatory sexual selection.
In temperate climates, dormancy enables organisms to survive winter, with timing often tied to environmental cues, such as daylength, that differ along latitudinal gradients. Adaptation to these gradients is crucial during range expansion. Clark et al. (2026) found that in the introduced northern tamarisk beetle (Diorhabda carinulata), populations from the range core were locally adapted in dormancy timing to core environments, while newly arrived edge populations showed heterogeneous responses to daylength, consistent with adaptation to seasonal timing. Genetic variation and high heritability in dormancy traits in the core populations likely drive range expansion potential through rapid evolution of dormancy traits.
Insects produce a vast diversity of sex pheromone compounds despite strong stabilizing selection on species-specific signals. In multiple insect lineages, these pheromones chemically resemble the volatiles produced by plants. Here, I propose that adaptation of insect sensory systems to plant chemistry biases the origin and diversification of insect pheromones. Repeated independent recruitment of plant-like compounds, either through sequestration or de novo biosynthesis, suggests that pheromone evolution can be shaped by ecological interactions. Receptors with dual roles in host detection and pheromone detection may be functionally constrained, further influencing signal diversification and receptor specialization. This framework links sensory biases with macroevolutionary patterns, generating testable predictions about how sensory biases shape insect pheromone evolution.
Environmental shifts often dictate Arthropod morphological evolution, yet certain lineages maintain remarkably conserved body plans across diverse habitats. Whip spiders (Amblypygi) emerged over 300 Ma and exhibit striking morphological conservatism; nonetheless, what drives this apparent conservatism remains an open question. Here, we analyzed how body size and shape evolved in response to climate and habitat by examining the contributions of bioclimatic variables and habitat type to morphology, alternative macroevolutionary models, estimating the strength of the phylogenetic signal, and testing whether evolutionary rates differ. Habitat was the strongest predictor of body size, with cave-dwelling species approximately 22% larger than surface species, while climatic gradients accounted for almost none of the shape variation. The evolution of both body size and shape was best described by a single-peak Ornstein-Uhlenbeck model, suggesting stabilizing selection toward a shared adaptive peak. Body size exhibited a moderate phylogenetic signal consistent with a Brownian motion process, whereas body shape lacked a clear phylogenetic signal, indicating stronger stabilizing selection on shape. Together, our findings suggest that the morphological conservatism of whip spiders is maintained by a "jack-of-all-trades" strategy, in which stabilizing selection favors a versatile phenotype that facilitates the occupation of diverse ecological niches without marked morphological divergence.
Environmental heterogeneity can favor phenotypic plasticity, but whether evolutionary responses in one environment predict trait expression after environmental change remains unclear for threshold traits. Polyphenisms-plasticity characterized by discrete alternative morphs-rely on developmental thresholds, and as a consequence, are often expected to permit partial evolutionary decoupling among alternative phenotypes. Using replicated experimental evolution and artificial selection of a resource polyphenism in the nematode Pristionchus exspectatus, which develops either a predatory morph or a microbivorous morph, I tested whether evolutionary changes in morph frequency are coupled across environments. Across independent lineages, I asked whether evolutionary increase in predatory morph frequency under selection predicted phenotypic change when populations were reared back in the ancestral environment. I found a strong positive cross-environment coupling: for both sexes, lineages showing larger evolutionary responses during the first 25 generations, and across the full 50-generation experiment, also showed larger increases in predatory morph expression after environmental reversal. Artificial selection on mouth-form produced the same pattern. These results show that even a discrete threshold trait can retain strong and repeatable correlated responses across environments, consistent with morph-frequency evolution being channeled by developmental architecture shared across environments.
Modularity is a pattern whereby traits evolve as interrelated systems, resulting in lower covariation between modules than within. Modularity may facilitate diversification by permitting the phenotype to independently respond to selection. The Appalachian Mountains are a biodiversity hotspot for lungless salamanders (Plethodontidae). Despite their ecological diversity, putative catalysts of their radiation in the Appalachians are poorly understood. We test whether (i) Appalachian salamanders exhibit modularity in functional, morphological characters and (ii) if the rate of evolution-a fundamental macroevolutionary signal of ecological opportunity-varies among modules and if their rates are correlated. We find that Appalachian salamanders exhibit modularity under two different models in which their head, trunk, limbs, and tail or the head, body, and limbs act as separate modules. The three major clades, Plethodon, Eurycea, and Desmognathus, vary in the presence and extent of modularity. Across Appalachian salamanders, modules exhibit non-significant differences in rates of evolution (~1.5-fold), with the trunk and tail modules exhibiting the slowest and fastest rates, respectively. We also find that the rate of modular evolution can be highly correlated, suggesting that modules may respond similarly to ecological opportunity. These results suggest that modularity underlies the morphological diversity of Appalachian salamanders by permitting localized regions of the phenotype to respond independently to selection, but not evolve at different rates.
Anglerfishes (Lophiiformes) have evolved diverse morphological solutions for life in the deep sea (>200 m). Previous studies have shown that the bathypelagic lineage (Ceratioidei) exhibits high evolutionary rates; however, the intrinsic mechanisms underlying this accelerated evolution remained unclear. Here, we examine patterns of modularity and integration, rates of morphological evolution, and evolutionary rate matrices across the skulls of 100 anglerfish species spanning shallow and deep-sea habitats using geometric morphometrics and phylogenetic comparative methods. We find that both deep-benthic and bathypelagic anglerfishes exhibit stronger patterns of integration compared to their shallow-water relatives. The iconic bathypelagic anglerfishes (Ceratioidei) differ from other Lophiiformes by exhibiting an integrated upper-lower jaw system, likely driven by selection for feeding efficiency in resource-scarce environments. Jaw evolution in Ceratioidei, Chaunacoidei, and Ogcocephaloidei exhibits novel evolutionary trajectories that differ from the dominant pattern across Lophiiformes. Our findings suggest that extreme environments promoted morphological innovation in anglerfishes through evolution in novel phenotypic directions and strengthening of evolutionary integration.
While theory has long explained how selection can favor dispersal, we know much less about the capacity for dispersal to evolve in natural populations. One challenge is to identify how heritable genetic variation in multiple dispersal traits aligns with directions of selection on these traits. Therefore, we used an experimental pedigree in the solitary ascidian Molgula occidentalis and constructed Bayesian quantitative genetic models to estimate evolvability of dispersal traits. We compared the evolvability of dispersal traits by: 1) assessing the average evolvability of the G-matrix, 2) considering specific directions of selection hypothesized from biomechanical and life history reasoning, and 3) estimating the predicted response to selection from the observed additive genetic covariance between dispersal traits and fitness components. There was greater additive genetic variation in tail length than in trunk length, as there was for maternal effect and dominance variance. As a result, selection for longer tails (faster swimming) was associated with a higher evolvability compared to selection for shorter tails and longer trunks (energetic efficiency) or shorter tails and trunks (fecundity). The predicted response to selection at hatching and settlement, based on observed additive genetic covariances, was similar for trunk and tail length. Overall, evolutionary change in dispersal distances would occur more rapidly under selection on swimming ability than on energetic economy and fecundity. Furthermore, multiple lineages within Molgulidae have repeatedly diverged along the larval morphology axis in which we measured the highest evolvability. Our results demonstrate the utility of combining estimates of evolvability with hypothesized and observed selection gradients.
Differences in ploidy levels represent a significant barrier to interspecific gene flow, but growing evidence from natural and experimental systems suggests that this barrier may not be as strong as commonly believed. In this study, we aimed to examine patterns of interploidy hybridization between two ecologically similar and partially sympatric wetland perennials in the central Apennines: diploid Cardamine apennina and allotetraploid C. amporitana. Our detailed chromosomal, flow cytometric, and genomic (RADseq) analyses revealed a strikingly high frequency of allotriploids across multiple sites, with no evidence of backcrossing, later-generation hybrids, or higher-level allopolyploids. Contrary to expectations, clonal propagation is not the primary mechanism underlying the observed abundance of triploids. Instead, a high hybridization rate with recurrent, bidirectional, and polytopic hybrid formation, together with the presumed longevity of triploid individuals, appears to explain their persistence. Our findings also raise two key issues: the possible triggers of this apparently recent burst of hybridization, and the potential long-term consequences of frequent allotriploid formation for the survival of the parental (sub)endemic species in the Apennines. From a broader perspective, this study underscores the evolutionary significance and dynamics of species contact zones.
Vertebrates have varied body size distributions. Among these, non-avian dinosaurs have uniquely large minimum and maximum sizes, but the reasons remain unknown. Energetic fitness models provide a potential explanation, by describing how physiological scaling relationships should structure body size distributions under selection to maximize the conversion of energy into offspring. We show that the body size distributions of birds, mammals, and turtles fit the expectations of energetic fitness models, but snakes, lizards, and crocodylians do not. Moreover, no reasonable combination of physiological scaling relationships explains the up-shifted minimum body size of non-avian dinosaurs or flightless birds. We propose that energetic fitness models perform well when body size distributions are governed primarily by intrinsic energetic factors. However, extrinsic constraints imposed by ecological factors such as competition, predation, or ecological niche may also be needed to explain why species body size distributions differ from the model expectations in some groups. The abrupt macroevolutionary shift from non-avian dinosaurs with minimum adult body sizes of 400 g, to birds with modal body size of 30 g cannot be explained by changes in intrinsic physiological factors, and may instead have been caused by an abrupt release of ecological constraints, potentially related to the origin of flight.
Transgenerational immune priming increases the resistance or tolerance of offspring from pathogen-exposed parents. This phenomenon can have substantial ecological and evolutionary consequences, highlighting the importance of understanding its generality both across host taxa and within a host species. Transgenerational immune priming has been reported in multiple invertebrate species, but the robustness and generality of priming in offspring is not clear. For instance, prior studies using Daphnia spp., which are freshwater invertebrates and dominant grazers, found contrasting results for transgenerational immune priming. Some studies found transgenerational immune priming for certain genotypes and in specific contexts while others found no evidence of transgenerational immune priming. Our study addresses multiple questions about transgenerational immune priming using three clones of Daphnia dentifera and three pathogen species varying in their fitness impacts on hosts. We collected offspring from mothers either unexposed or exposed to pathogens and then exposed offspring to either the same pathogen as the maternal exposure (a homologous challenge) or a different pathogen (a heterologous challenge). We measured offspring susceptibility for all treatments and pathogen burden for the two 'obligate killer' pathogens. We did not find any evidence of transgenerational immune priming related to offspring susceptibility. Following a heterologous challenge, one clone showed a reduction in spore burden of one pathogen, which could be an indication of increased tolerance, but no significant reduction in susceptibility. Our results, paired with mixed support from previous studies, suggest that transgenerational immune priming is not a consistent or strong factor influencing disease dynamics in the D. dentifera system.
