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

TL;DR

Male geckos use both visual and chemical signals to show their parasite levels, but females only respond to the chemical signals.

Contribution

This study shows that while males use multiple signals to indicate parasite levels, only chemical signals influence female behavior.

Findings

Ectoparasite levels are negatively correlated with body condition in both male and female geckos.

Male geckos with higher parasite loads have less vibrant gular patches and chemical secretions with fewer aromatic compounds.

Females prefer males with lower parasite loads based on their chemical signals, not visual ones.

Abstract

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.

Summary: In a diurnal gecko species, ectoparasite level and overall health are honestly advertised through multiple modalities, yet females assess males based only on their chemical signals, raising questions about redundancy in signals that are not used.

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