Comparing phylogeographic patterns across different biogeographic regions can illuminate how different types of landscapes promote the formation and persistence of incipient species, providing insights into the evolutionary mechanisms underlying broadscale biodiversity gradients. The Neotropics are a global biodiversity hotspot, and the megadiverse Andes-Amazonia system exhibits elevational gradients in both species richness and speciation rates. Using whole genomes from a congeneric set of eight habitat-generalist canopy frugivore birds (Tangara tanagers), we compare the phylogeography of tropical Andean versus lowland Amazonian species to characterize intraspecific diversification dynamics associated with these distinct but adjacent biomes. We found that all species exhibited low genetic structure consistent with their dispersive ecology, but Andean species have relatively greater population genetic structuring across their ranges than Amazonian species. Additionally, populations separated by prominent geoclimatic barriers showed lower gene flow and higher differentiation in montane versus lowland Tangara. Lastly, all Andean species have lower genetic diversity, a proxy of effective population size. Together, these results support greater incipient speciation in the mountains owing to stronger allopatry and smaller populations, while the larger, more diverse, and well-connected populations of the lowlands may foster enhanced persistence. We discuss potential implications for the origin and maintenance of regional biodiversity gradients.

It has been proposed that female ornaments are less likely to evolve because females face a steeper trade-off between offspring production and ornamentation than males. In their study, Pärssinen et al. (2025) show that direct benefits provided by males during reproduction are associated with the presence of female ornamentation in dance flies, probably because such benefits allow females to offset the costs that may arise from producing these traits.

At macroevolutionary scales across species, sexual dimorphism often covaries with body size, generating allometric trends. Such patterns are most evident for body size dimorphism, while trends in sexual shape dimorphism remain underexamined. Additionally, how small body sizes (miniaturization) affects such patterns is largely unknown. We evaluated allometry in sexual shape dimorphism in two families of geckos to determine whether changes in body size associate with changes in shape dimorphism. Using surface scans of head shape from nearly 600 individuals across 99 species, we found considerable variation in levels of sexual shape dimorphism across taxa, with some species displaying little dimorphism and others exhibiting large sexual differentiation. Interspecific trends differed between the two families, with strong negative allometry in Sphaeorodactylidae (a family with many small-bodied species), while Phyllodactylidae (a family containing few small-bodied species) displayed isometry and no discernible trend. Notably, greater sexual shape dimorphism was displayed in small-bodied sphaerodactylid species, and corresponded with females exhibiting more robust heads; consistent with sex-specific foraging strategies and dietary differences observed in this group. Our study reveals that interspecific allometry in traits other than body size can have a pervasive influence on patterns of phenotypic diversity across the tree of life.

Nests are primarily shaped by natural selection, but are also subject to sexual selection. Here, we investigated the potential role of sexual selection in shaping nest visual patterns, focusing on scale-invariance, a property describing how patterns remain similar across spatial scales. In humans, it has been documented that visual patterns are more attractive when their scale-invariance resembles natural habitats, likely because they are more efficiently processed. The underlying mechanism, called processing bias, extends the sensory drive hypothesis from colors to patterns. Applied to birds, processing bias predicts that nests whose scale-invariance matches natural habitats could be sexually selected. We tested this using a comparative analysis of weaverbirds. We quantified the deviation of nest scale-invariance from a range of putative selection optima, then evaluated whether interspecific variation in this deviation is explained by mating system and sexual size dimorphism, two proxies for sexual selection. For both proxies, effect sizes were largest for the same putative optimum, aligning with scale-invariance values in natural habitats. Sexual selection may thus favour nest designs that are efficiently processed, such as those with habitat-like features. Our findings also highlight the challenge of designing a specific test for this hypothesis and call for further research linking pattern perception and sexual selection.

Do caecilians retain some degree of vision? Navarrete Méndez et al., (2025) used an integrative approach to show that the long-wavelength-sensitive (LWS) opsin gene is present and that retinal morphology remains intact across all eight caecilian families investigated. This finding suggests that caecilians maintain some visual capacity, likely enabling day-night or color discrimination. More broadly, this study highlights key aspects of sensory adaptation in subterranean tetrapods.

A key insight of evolutionary genetics is that the evolvability of a population depends crucially on the amount and distribution of heritable phenotypic variation across traits. Because this insight focuses on segregating variation, the traits that don't vary among individuals but differ among higher taxa are ignored. Slowly evolving traits, like body plan organization and homologs, are nevertheless essential because they set the phenotypic boundary conditions within which variation segregates. Therefore, understanding long-term evolutionary change requires understanding the principles that control variation in varying AND conserved traits, in addition to understanding how drift and selection influence segregating population variation. In this perspective, I propose that this understanding is attainable if we acknowledge that different processes, which map sequence variation to phenotypic variation, have different capacities to produce variation and evolve. I suggest decomposing the GP map according to types of processes with different variational properties. For vertebrates, these are: morphogenesis, growth, and maintenance. This perspective allows us to focus on how these processes interact under the influence of natural selection and delineate the conditions leading to different patterns of evolutionary change.

Whether the same genes underlie parallel adaptive trait evolution remains an open question in biology. The degree of genetic parallelism is expected to increase at higher genetic hierarchical levels (i.e., single nucleotide polymorphisms [SNPs] to genes to pathways to phenotype) due to the hierarchical nature of the genetic basis of traits, which genomic approaches can help elucidate. Previous research shows a large degree of variation in the extent to which phenotypic parallelism shares the same genetic mechanisms in nature. Here we analyzed the degree of genetic parallelism underlying repeated divergence in bill morphology of island scrub-jays (Aphelocoma insularis), across three naturally replicated pine-oak ecotones on Santa Cruz Island, California, USA. We analyzed 66,503 SNPs generated using restriction site-associated DNA sequencing (RADseq) in 161 island scrub-jays to identify candidate SNPs associated with environmental variation and divergence in bill morphology. We then examined signatures of parallelism in genomic regions containing candidate SNPs and the associated genetic pathways. We found little evidence for parallelism at the SNP or gene level, but substantial parallelism at the pathway level. Our results support the view that the degree of genetic parallelism underlying repeated phenotypes depends on the genetic level of organization being analyzed.

Many pathogenic organisms, including malaria parasites, produce specialized life stages for within-host multiplication (asexual) versus onward transmission (sexual reproduction). Restrained investment into transmission stage production-by allowing faster multiplication-is predicted to curtail the lifespan of infection via faster host recovery or mortality, a classic tradeoff between the rate and duration of transmission. In contrast, under a reproduction-survival tradeoff, restraining investment into reproduction should extend survival (for parasites, infection duration). To distinguish between these predictions, we develop a within-host mathematical model incorporating immunity to track dynamics across infection age (time since start of blood-stage infection) for human malaria infections. When transmission investment is constant across infection age, increased investment reduces infection duration and parasite fitness. Optimal transmission investment occurs at a lower value (around 5%) than predicted by models lacking feedback between transmission investment and immunity. When strategies vary with infection age, our model shows that malaria parasites benefit from delaying transmission investment to allow for faster within-host multiplication. We show that adaptive immunity can impose a survival-reproduction tradeoff, an emergent property of the model. Our theoretical framework provides a basis for understanding the timing and duration of infectiousness, with implications for parasite evolution in response to control efforts.

Buzz pollination, where some species of bees vibrate flowers to release pollen, is easily disrupted by rain. Sperotto et al. (2025) show that in the Neotropical clade Miconieae, small flowers often evolve acuminate "drip-tip" petals in humid regions and wet seasons. These petals, resembling leaf drip-tips, repeatedly arose across the phylogeny and are strongly associated with wetter habitats. By draining water away from reproductive organs, drip-tip petals may promote effective pollination, highlighting how floral evolution is shaped by both pollinator interactions and environmental pressures.

Models of optimal offspring size and bacterial aging share the same underlying mathematical problem: how should a parent optimally distribute limited resources among its offspring? Optimal offspring size theory has long explored the trade-off between offspring number and size in higher organisms. Meanwhile, the emerging field of bacterial aging examines whether and under what conditions cells evolve unequal sharing of old cellular components. Despite addressing similar problems, these models remain constrained by field-specific assumptions. We unify them in a generalized resource-distribution framework that yields insights and predictions unreachable by either field alone. Our central finding is that the convexity of the function relating resources to offspring survivorship determines whether equal or unequal distribution of resources is the optimal strategy. We show that these optimal strategies evolve, characterize their robustness to fluctuating environments, and uncover the conditions that select for producing a "runt of the litter."

Explaining variation in the extent of division of labour remains a major problem for our understanding of how complex life evolved. Ants show remarkable variation in their extent of reproductive division of labour, from workers who can reproduce sexually and are approximately the same size as queens, to workers that are completely sterile and 300x smaller than their queens. Examining data from 546 species of ant, we found that: (i) the ancestral ant worker likely had full reproductive potential, though was effectively sterile in the presence of a queen; (ii) the loss of worker reproductive potential generally followed a sequential step-by-step process, via reduced capacity for sexual reproduction, then the production of males only, and finally complete sterility; (iii) the independent evolution of complete sterility has occurred approximately 17 times, with only 42% of ant species having sterile workers; (iv) reproductive size dimorphism has increased to higher levels around 9 times. Exploring potential causality, we found support for the size-complexity hypothesis, that increased colony size has favoured increased division of labour between queens and workers, examining both queen-worker size dimorphism and the loss of reproductive capacity in workers.

Male harm occurs when traits in males that increase their reproductive success incidentally reduce female fitness. In Drosophila melanogaster, many lab studies have revealed the presence of male harm, but recent work has shown that its expression can be dramatically reduced, even eliminated, when sexual interactions and mating occur in an environment that differs from traditional lab rearing vials. Here we follow up on this to separately test the effect of fly density and structural complexity of the mating environment in mediating the expression of male harm. We performed separate two-way factorial assays that measured the fitness of females while manipulating their exposure to males and the density of flies or the structural complexity of the environment during exposure. Male harm, quantified as the relative reduction in female fitness under increased male exposure, was not affected by density, but was significantly reduced -essentially eliminated- by increased structural complexity. Our results demonstrate that seemingly simple choices, like the environment used in a laboratory model system, can have profound impacts on the expression of harm and hence views on the prevalence of sexual conflict. This is noteworthy because conflict can shape other fundamental evolutionary processes including adaptation, purging, and speciation.

Asexual lineages are rare in social animals with biparental care, where successful reproduction typically requires coordinated behavior between two individuals of opposite sex. Male-less lineages of the termite Glyptotermes nakajimai provide a unique opportunity to unravel how sexual reproduction can be lost in such animals. Here we show that modification of the mate-pairing process predated the evolution of the asexual populations. Termite colonies are typically initiated by a mating pair that searches for a nest site through a tandem courtship behavior. Our comparative analysis of tandem running in Glyptotermes termites revealed that two related species, G. fuscus and G. satsumensis, exhibited both female-leader and male-leader tandem runs. However, tandem running was rare and ephemeral in both sexual and asexual lineages of G. nakajimai. Furthermore, our comparative studies indicated typical monogamous pairing was uniquely lost in G. nakajimai, while pairs initiate nests in G. fuscus and G. satsumensis. Our study evidenced that a clear disruption of termites' classic reproductive behavioral sequence, coupled with an alternative mode of colony foundation, was likely a precondition for the evolution of asexuality in species with biparental care.

Accelerating climate change and extreme temperatures urge us to better understand the potential of populations to tolerate and adapt to thermal challenges. Interspecific hybridization can facilitate adaptation to novel or extreme environments. However, predicting the long-term fitness effects of hybridization remains a major challenge in evolutionary and conservation biology. Experimental evolution with microbes provides a powerful tool for tracking adaption, across generations and in real time. We investigated the thermal adaptation dynamics of four species of budding yeast (Saccharomyces) and their interspecific F2 hybrids, for 140 generations under cold (5°C) and warm (31°C) conditions. We found significant variation in the evolutionary potential of species and hybrids, strongly determined by their natural temperature tolerance. The largest fitness improvements occurred in hybrids, with some populations nearly quadrupling in fitness in the cold environment, exceeding both parents in thermal adaptive potential. While adaption rates in some hybrid populations were high, their absolute fitness by the end of evolution was comparable to that of their parents. Reciprocal transplanting of evolved populations from the endpoint of evolution into opposite temperatures revealed that hybrids had greater resilience when challenged with sudden temperature shifts. Our results highlight that hybridization alters the fitness outcomes of long-term adaptation to extreme environments and may render populations more resilient to sudden environmental change, presenting both opportunities and challenges for conservation and sustainable agriculture.

Phenotypic plasticity is widespread and evolutionarily important, but genomic consequences of new plastic traits remain unclear. Here, we explore patterns of molecular evolution linked to the repeated evolution of Cephalotes turtle ant worker plasticity, in which smaller minor workers and distinct larger soldiers are produced from a single genomic blueprint through developmentally plastic mechanisms. We integrate developmental transcriptomics with comparative genomic approaches to test the relative relationships of selection on genes, selection on regulatory sequences, and the emergence of lineage-specific genes with the repeated evolution of the soldier morph. We find that phenotypic plasticity shields protein-coding genes from selection, whereas it imposes a strong selective constraint on the evolution of gene regulatory loci. The development of a soldier morph disproportionately involves the activity of evolutionarily ancient genes. Moreover, our data link three pathways- nutrition via insulin signaling, imaginal disc development, and for the first time Hippo signaling- which allow for the differential development of soldiers and workers from a single genomic background in turtle ants. Taken together, our results provide evidence that plasticity leads to relaxed selection on genes, but imposes selective constraint on regulatory elements, during the repeated evolution of the turtle ant soldier morph.

Weiss and Berv (2025) proposed and tested a resource longevity hypothesis on marine invertebrates in deep-sea ecosystems. They found that organisms in ephemeral environments have faster substitution rates, whereas those in stable environments have slower rates. The study confirmed that evolutionary rates differ across habitat types, a pattern the authors attributed to habitat longevity. Notably, there was no significant association between species body size and evolutionary rate. This suggests that resource variability drives evolutionary rates in these extreme environments.

Spatial network structure impacts the ecological and evolutionary dynamics of species interactions. Previous work on host-parasite systems has shown that parasite virulence is driven by dispersal rates and spatial structure, assuming that dispersal is an ecologically fixed parameter. However, dispersal is also a trait under selection and can evolve. In this context, we develop an individual-based eco-evolutionary model, in which both parasite virulence and host dispersal can evolve in representative terrestrial (random-geometric graphs; RGGs) and riverine aquatic (optimal channel networks; OCNs) landscapes. We find that in riverine aquatic landscapes, evolutionarily stable (ES) dispersal rates are lower and ES virulence is greater relative to terrestrial landscapes when dispersal mortality is low. When dispersal mortality is high, both dispersal and virulence evolve to lower values in both landscape types. Diverging co-evolutionary patterns between landscapes are explained by differences in network topology. Specifically, the highly heterogeneous degree distribution in riverine aquatic landscapes 1) leads to low parasite relatedness allowing for the evolution of greater virulence and 2) leads to spatial heterogeneity in host densities that constrains the evolution of dispersal to lower values. Our work highlights the importance of considering the concurrent and co-evolution of dispersal when studying trait evolution in complex landscapes.

Why has sperm gigantism evolved, and how do subcellular allocations scale with size? Schalkowski & Cutter (2025) addressed these questions with transmission electron microscopy of Caenorhabditis sperm, finding that a species with giant sperm disproportionately invests in mitochondria, consistent with energetic demands of motility and persistence. Here, the results are interpreted through anisogamy theory, highlighting how ecological conditions can favor sperm gigantism, why such costly sperm remain rare, and how new data invite mechanistic models of gamete evolution.

Organismal color and pattern is important to numerous aspects of animal fitness, and may impact species divergence. Whether different environmental conditions may impact rates of color diversification, and the subsequent impacts on lineage diversification, has not been well studied. We investigated the evolution of color and pattern in Darters (Etheostomatinae; Percidae), a species-rich clade of freshwater fishes showing a remarkable diversity in color. Using recently developed approaches in color and pattern analysis we quantified color and pattern attributes in 122 species. We applied multivariate and phylogenetic comparative methods to investigate the relationship between river habitat (drainage area, elevation, slope, substrate, etc) and darter color characteristics and changes in the rate of color evolution. We found color attributes were significantly related to river habitat, and rates of color evolution differed between macro- and micro-habitat categories; smaller streams and riffles in particular were associated with the rapid evolution of conspicuous and complex color patterns. We suggest that these differences are consistent with tradeoffs in predator abundance and photic environment. Small river habitats may facilitate rapid evolution of species-specific color patterns and reinforce divergence in secondary sympatry.

Sociability, defined as individuals' tendencies to affiliate with conspecifics, has positive associations with fitness in animals as well as with health, well-being and longevity in humans. Despite its importance, we still have limited information about natural genetic variation in sociability. As part of a long- term initiative to address this knowledge gap, we quantified changes in allele frequencies in adult fruit flies (Drosophila melanogaster) from lineages that we artificially selected to diverge in sociability. Based on our genomic analyses, we generated a short list of 226 SNPs representing 169 candidate genes influencing variation in sociability. We also made a shorter list of 41 SNPs from 36 genes that showed the largest average divergence between the low and high sociability lineages. Experiments using knockdowns of 19 of the candidate sociability genes revealed that 18 of them significantly affected sociability, though some effects were sex-specific. Our results provide important insights into a quantitative trait central to the lives of many animals including humans.