Males and females can exhibit differences in body size, producing sexual size dimorphism (SSD). Both body size and SSD vary markedly across taxa, providing a framework to examine whether male and female body sizes are coupled and to identify general versus lineage-specific patterns. Using evolutionary models, we compared rates and disparity patterns to evaluate whether male and female body size evolve in tandem and how SSD diverges across four speciose lizard families (Anolidae, Chamaeleonidae, Liolaemidae, and Phrynosomatidae) and a broader dataset encompassing 2476 Squamata species. Male body size evolved faster than female body size in all families except Liolaemidae, which exhibited the highest overall rates of evolution. Male and female body size displayed similar disparity patterns, contrasting with those of SSD. Our findings underscore the importance of analyzing male and female traits independently, as such analyses revealed differences in the trajectories of disparity in body size and SSD across taxa, and highlighted the distinct evolutionary dynamics of body size and dimorphism in the Andean Liolaemidae radiation. Overall, our study highlights the role of sex-specific evolution in shaping broader patterns of morphological diversity, offering insights into the macroevolutionary divergence of sexually dimorphic traits.
Abstract Urbanization drastically changes our planet, and persistence in urban areas requires species to adapt. Sexual signaling has been argued to be a driver of population divergence between urban and non-urban populations, but it is often unclear whether population divergence is adaptive and caused by plastic and/or genetic processes. Calling behavior of urban and forest túngara frogs (Engystomops pustulosus) provides a well-known example of urban adaptation. However, we lack insight into the underlying genetic divergence between populations and heritability of calling behavior. Our aim was to examine the relative contributions of plastic and genetic components to urban-forest differences in sexual signaling and associated morphological traits. We reared frogs of urban and forest descent in a common garden using a paternal half-sib breeding design and used quantitative genetic approaches informed by whole-genome sequencing to estimate heritability. We show heritable urban-forest differences in call rate and amplitude (depending on the social environment), and in body size and condition. Moreover, behavioral as well as morphological traits had low to moderate heritability estimates. Our study provides insights into the underlying mechanisms of urban versus forest phenotypic divergence and suggests that sexual signaling and associated morphological traits in túngara frogs have the potential to adaptively evolve.
Abstract Why are some birds louder than others? Menezes and Podos (2026) examined vocal amplitude across 123 bird species, revealing substantial variation in how loudly different bird species communicate. Vocal amplitude was primarily associated with body size and beak gape width, whereas ecological factors showed no significant relationships. Despite the potential role of loud calls in attracting mates, the analyses found no clear relationship between vocal amplitude and polygamy.
Abstract A central goal in evolutionary biology is to understand how species boundaries are maintained despite gene flow. Two North American wildflower species with divergent floral syndromes, Penstemon davidsonii (bee syndrome) and P. newberryi (bird syndrome), have formed hybrid zones in the eastern Sierra Nevada for at least 85 years. We combined multiple approaches to test whether divergent floral syndromes enforce reproductive isolation as predicted by classic models of pollinator-driven ecological speciation. The two parent species exhibited strong divergence across multivariate trait space and have maintained genomic differentiation despite persistent hybridization. Floral hue, a key component of pollination syndrome, mapped to a single genomic region containing two candidate genes with large effects on anthocyanin pigment composition. Pollinator visual models indicated that genetic variation at this region affects detectability to hummingbirds, but not bees. Genomic cline analyses identified many significantly steep clines, suggesting a polygenic basis to reproductive isolation. Surprisingly, these barriers appear unrelated to floral isolation; the major floral hue locus exhibits a strikingly shallow genomic cline and elevated heterozygosity, suggesting pervasive gene flow. Our results reveal that conspicuous trait divergence can be decoupled from reproductive barriers, challenging assumptions about how reproductive isolation is maintained in hybridizing populations.
