Chemical signal divergence among populations influences behavioral discrimination in the whiptail lizard Aspidoscelis lineattissimus (squamata: teiidae)

Too much information? Males convey parasite levels using more signal modalities than females utilise

Elaborate sexual signals are thought to have evolved and be maintained to serve as honest indicators of signaller quality. One measure of quality is health, which can be affected by parasite infection. Cnemaspis mysoriensis is a diurnal gecko that is often infested with ectoparasites in the wild, and males of this species express visual (coloured gular patches) and chemical (femoral gland secretions) traits that receivers could assess during social interactions. In this paper, we tested whether ectoparasites affect individual health, and whether signal quality is an indicator of ectoparasite levels. In wild lizards, we found that ectoparasite level was negatively correlated with body condition in both sexes. Moreover, some characteristics of both visual and chemical traits in males were strongly associated with ectoparasite levels. Specifically, males with higher ectoparasite levels had yellow gular patches with lower brightness and chroma, and chemical secretions with a lower proportion of aromatic compounds. We then determined whether ectoparasite levels in males influence female behaviour. Using sequential choice trials, wherein females were provided with either the visual or the chemical signals of wild-caught males that varied in ectoparasite level, we found that only chemical secretions evoked an elevated female response towards less parasitised males. Simultaneous choice trials in which females were exposed to the chemical secretions from males that varied in parasite level further confirmed a preference for males with lower parasites loads. Overall, we find that although health (body condition) or ectoparasite load can be honestly advertised through multiple modalities, the parasite-mediated female response is exclusively driven by chemical signals.

Chemical signaling glands are unlinked to species diversification in lizards

Sexual selection has long been thought to increase species diversification. Sexually selected traits, such as sexual signals that contribute to reproductive isolation, were thought to promote diversification. However, studies exploring links between sexually selected traits and species diversification have thus far primarily focused on visual or acoustic signals. Many animals often employ chemical signals (i.e., pheromones) for sexual communications, but large-scale analyses on the role of chemical communications in driving species diversification have been missing. Here, for the first time, we investigate whether traits associated with chemical communications-the presence of follicular epidermal glands-promote diversification across 6,672 lizard species. In most analyses, we found no strong association between the presence of follicular epidermal glands and species diversification rates, either across all lizard species or at lower phylogenetic scales. Previous studies suggest that follicular gland secretions act as species recognition signals that prevent hybridization during speciation in lizards. However, we show that geographic range overlap was no different in sibling species pairs with and without follicular epidermal glands. Together, these results imply that either follicular epidermal glands do not primarily function in sexual communications or sexually selected traits in general (here chemical communication) have a limited effect on species diversification. In our additional analysis accounting for sex-specific differences in glands, we again found no detectable effect of follicular epidermal glands on species diversification rates. Thus, our study challenges the general role of sexually selected traits in broad-scale species diversification patterns.