Heritable differences in sexual signaling and morphology between urban and forest túngara frogs

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.