Substrate use and climate structure chemical signal composition across Australia's most diverse gecko radiation

Scott Andrew Macor , Stephen M Zozaya , Conrad Hoskin, Wesley Read , Craig Moritz , Megan Higgie

Sensory drive theory predicts that communication signals coevolve with sensory systems and the local transmission environment, generating divergence in signals across environmental gradients. Understanding how signalling traits evolve in response to environmental conditions is central to explaining patterns of phenotypic divergence and ecological specialisation, given their role in social interactions, mate choice, and species recognition. Here, we investigate how the abiotic environment shapes the evolution of chemical signalling in Australia’s most speciose gecko genus, Gehyra. We analysed male epidermal pore secretions from 754 individuals, representing 58 species and species-level lineages across climatic gradients spanning the Australian monsoonal tropics and arid zone. Chemical blends were characterised using gas chromatography, and multivariate phylogenetic comparative analyses tested for associations between chemical composition and the abiotic environment. Composition varied along two axes: substrate use, with saxicoline lineages showing blends distinct from arboreal and generalist lineages; and climate, primarily vapour pressure, with some evidence that moisture effects on blend composition are stronger under hotter conditions. Results were robust to sensitivity analyses considering within-lineage variation. These findings are consistent with sensory drive theory and indicate that substrate use and climate are both associated with variation in chemical communication signals at macroevolutionary scales.