A condition-dependent male sexual signal predicts adaptive predator-induced plasticity in offspring

Abstract

The possibility that sexual selection promotes adaptive evolution in variable environments remains controversial. In particular, where the scale of environmental variation results in parents and their offspring experiencing different environmental conditions, such variation is expected to break down associations between adult sexual traits and adaptive offspring traits. However, when adaptive offspring plasticity in nonsexual traits acts as an indirect benefit of mate choice, then mate choice for males that produce more plastic offspring could promote adaptation to variable environments. This hypothesis assumes that male sexual signals predict offspring plasticity, which has rarely been tested. To test this assumption, we used spadefoot toads (Spea multiplicata) to investigate whether variation in male sexual signals predicts the expression of tadpole tail-fin plasticity in response to predation cues. Such plasticity has been shown to be adaptive in numerous amphibian taxa. We found that condition-dependent male call characteristics predicted offspring plasticity. Generally, both phenotypic plasticity and female mate choice are ubiquitous in nature; therefore, adaptive associations between male sexual signals and offspring plasticity such as the one reported here might be common. Sexual signals can indicate individuals’ capacity to sire high-quality offspring, which provides a mechanism by which sexual selection can contribute to adaptive evolution. Whether this occurs in variable environments is unclear, however, because variable environments can expose parents and their offspring to different selection pressures. To address this uncertainty, we investigated the possibility that sexual signals can signal the capacity to sire offspring that express adaptive phenotypic plasticity in response to prevailing selective pressures. Using spadefoot toads, we found that condition-dependent male sexual signals predict the expression of tadpole tail-fin plasticity in response to predation cues. Because this form of plasticity has been demonstrated to be adaptive in several amphibian taxa, our results suggest that associations between sexual signals and adaptive offspring plasticity can allow sexual selection to promote adaptive evolution in variable environments.