Assessing the role of habitat composition in modulating conflicting selective pressures using a sexually dimorphic lizard: Ctenophorus decresii

Abstract Vegetation structures impose specific selective pressures on animal locomotion strategies, social signalling, and predator avoidance. Species occupying diverse microhabitats may present variation in colouration. For example, different colour hues can arise due to social signalling and predator avoidance: conspicuous colouration for communication and mating, and cryptic colouration for predator avoidance. These opposing functions can result in a trade-off between effective communication and predator avoidance. The Tawny rock dragon ( Ctenophorus decresii ), which occurs across a range of distinct vegetation types and is noted for male-expressed sexually dimorphic colour displays. Here, we investigate correlations between male dorsal colouration and local microhabitat. Specimens were sampled across three distinct habitat types in the Mount Lofty Ranges, South Australia. Male dorsal colouration was quantified using digital photography under standardised light conditions, alongside local vegetation, morphological traits and estimated population densities. Associations between vegetation characteristics and phenotypic traits were then statistically assessed. No differences in morphology or population density were detected between regional site groupings. We found that habitat-specific differences in male C. decresii dorsal colouration were associated with the density of understorey vegetation. Males in dense understorey environments exhibited reduced colour coverage and expressed yellow-oriented hues, while males in sparsely vegetated habitats displayed greater colour coverage with orange-dominated hues. Our study suggests that vegetational structures of microhabitats influence selective pressures and drive phenotypic expression in male dorsal colouration, although the mechanisms driving this relationship remain unresolved.