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...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.
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 struct...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.
Organismal color and pattern are 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...Organismal color and pattern are 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 statistics and phylogenetic comparative methods to investigate the relationship between river habitat (drainage area, elevation, slope, substrate, etc), 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.
Many pathogenic organisms, including malaria parasites, produce specialized life stages for within-host multiplication (asexual) versus onward transmission (sexual reproduction). Restrained investment into transmission s...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.
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 nucleot...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, US. We analyzed 66,503 SNPs generated using restriction site-associated DNA sequencing 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.
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 segregatin...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 do not 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.
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 ac...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.
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 Cephal...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 3 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 & 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...Weiss & 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.
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...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."
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 spe...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.
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...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.
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 st...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 single nucleotide polymorphisms (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.
Iris color is a conspicuous and diverse trait across animals, but its evolutionary drivers are poorly understood. In over 1,000 species of Tyranni passerines, we tested hypotheses relating iris color to signaling and cam...Iris color is a conspicuous and diverse trait across animals, but its evolutionary drivers are poorly understood. In over 1,000 species of Tyranni passerines, we tested hypotheses relating iris color to signaling and camouflage, its main putative functions. We expected that, if playing a role in signaling, brighter irises would be positively associated with the strength of social and sexual selection as well as signal conspicuousness, i.e., larger relative eye sizes and contrasting, darker plumage colors around the eyes (contrasting local backgrounds). If aiding in camouflage, darker irises would be associated with higher vulnerability to predation, darker habitats, larger relative eye sizes, and matching, darker plumage colors around the eyes (matching local backgrounds). In support of the signaling hypothesis, we found that brighter irises are associated with darker plumage around the eyes, larger body sizes, territoriality, and sexual size dimorphism. In support of the camouflage hypothesis, we found that darker irises are associated with higher vulnerability to predation (exposed nests, migratory behavior, and terrestrial lifestyles) and larger relative eye sizes, which are associated with darker habitats. Our findings suggest that bright irises are social/sexual signals mostly associated with species under weaker selection favoring camouflage, which has implications for sensory ecology and macroevolutionary patterns of visual signaling.
Understanding how ecological and evolutionary forces shape biodiversity is a core pursuit in macroevolutionary research. Species' dispersal ability significantly impacts their colonization chances and geographic isolatio...Understanding how ecological and evolutionary forces shape biodiversity is a core pursuit in macroevolutionary research. Species' dispersal ability significantly impacts their colonization chances and geographic isolation, profoundly influencing species ecology and evolution. Our study delved into the relationship between dispersal ability and speciation rates within Emberizoidea, a diverse group of passerine birds. We used the Hand-Wing Index (HWI) as a morphological proxy for dispersal ability and phylogenetic data for 749 species of Emberizoidea (∼90% of all recognized species for the clade) using trait-dependent diversification models, including continuous-state (QuaSSE) and hidden-states (SecSSE) models. We also applied the correlated speciation and trait rates simulation (Cor-STRATES) framework to assess correlation between HWI evolution and speciation rates. Our findings revealed that speciation in Emberizoidea was not significantly influenced by dispersal ability as estimated by HWI. While QuaSSE models suggested a peak in speciation rates at intermediate HWI values, the best-fit SecSSE model indicated that speciation was driven by unmeasured trait(s) rather than HWI. Moreover, HWI evolution and speciation rates were not correlated, suggesting that wing shape evolution is unrelated to cladogenetic events in Emberizoidea's evolutionary history. Our study challenges the notion that dispersal ability and wing shape drive diversification in birds, particularly in Emberizoidea.
Phenotypic plasticity is often seen as an alternative adaptive strategy to genetic polymorphism, especially in response to rapid environmental changes. Indeed, a link between plasticity and heterozygosity, i.e., the meas...Phenotypic plasticity is often seen as an alternative adaptive strategy to genetic polymorphism, especially in response to rapid environmental changes. Indeed, a link between plasticity and heterozygosity, i.e., the measure of polymorphism, has previously been dismissed. Here, we compare the thermal plasticity of abdominal pigmentation in eight Drosophila species, four belonging to the melanogaster species group and four to the montium group. Despite a conserved developmental pathway for melanin synthesis, the genetic architecture of its variation has significantly evolved, being polygenic in most species (such as D. melanogaster) and Mendelian or invariable in others. By investigating the thermal plasticity of this trait in species with distinct architectures, we show that the degree of plasticity strongly associates with heterozygosity. Plasticity was resurrected in hybrids between species with no plastic responses but with contrasting melanism, and was higher in heterozygotes in species with simple Mendelian polymorphism. In plastic cases, pigmentation dominance is reversed depending on the developmental temperature. We propose simple genetic models with empirical molecular support to explain this link between phenotypic plasticity and genetic polymorphism. The relationship between these two phenomena, and the impact of each on the evolution of the other, may be more relevant than it is currently appreciated.
Omnivory has been hypothesized to be a macroevolutionary sink. A new study by Ochoa-Sanz et al. (2025) tests this hypothesis in Phyllostomidae, a highly ecologically and species-diverse bat family comprising species with...Omnivory has been hypothesized to be a macroevolutionary sink. A new study by Ochoa-Sanz et al. (2025) tests this hypothesis in Phyllostomidae, a highly ecologically and species-diverse bat family comprising species with different feeding habits, including omnivores and plant specialists. Plant specialists have higher speciation rates than omnivorous bat species, while balanced omnivores have higher speciation rates than plant-predominant ones. Part of the explanation for these differences might be related to the evolution of omnivory during periods of resource scarcity.
Coevolutionary cycling in allele frequencies due to negative frequency-dependent selection-sometimes referred to as Red Queen Dynamics-is a key potential outcome of host-parasite coevolution. While many theoretical studi...Coevolutionary cycling in allele frequencies due to negative frequency-dependent selection-sometimes referred to as Red Queen Dynamics-is a key potential outcome of host-parasite coevolution. While many theoretical studies have focused on understanding the consequences of coevolutionary cycling for the evolution of sex and recombination, little is known about the impact of coevolutionary cycling on the evolution of other life history traits. It is therefore currently unknown how coevolutionary cycling in allele frequencies affects the evolution of key disease characteristics, such as virulence. Here, we combine population genetic and quantitative genetic approaches to theoretically determine the impacts of coevolutionary cycling in allele frequencies on the evolution of virulence in a free-living parasite. By varying the level of genetic specificity required for infection while controlling for the average infection rate, we induce coevolutionary cycles and examine their effects on virulence evolution. We show that coevolutionary cycling does indeed have a strong impact on virulence evolution, with more specific infection genetics and higher allelic diversity generally driving larger and more rapid cycles in allele frequencies, leading to selection for higher virulence. Our research provides new fundamental insights into the relationship between coevolutionary cycling and the evolution of virulence.