Burrowing behaviour and species recognition predict colour pattern evolution in freshwater crayfishes

Colour patterns are the spatial arrangements of contrasting colours on an organism's body and can have several non-mutually exclusive functions, including crypsis, species recognition, or as a warning display. Here, I test how colour patterns correspond to ecological and morphological factors across 393 freshwater crayfish species. Using a time-calibrated phylogeny and phylogenetic logistic regression, I examined whether body size, congeneric sympatry, or burrowing behaviour predicts the presence of colour patterning. The best-supported model included additive effects of burrowing ecology and congeneric sympatry, but not body size. Patterned colouration was 7.3 times more likely in aquatic species compared to semi-terrestrial species, consistent with the hypothesis that increased exposure to visually oriented predators correlates to the presence of cryptic colour patterns. Patterning also increased with the number of sympatric congeners, suggesting a role in species recognition. The best-fit model exhibited weak phylogenetic signal, indicating that the relationship between patterning and the ecological predictors were not strongly influenced by shared ancestry. Together, these results suggest that predation pressure and social interactions jointly drive the diversification of colour patterns in crayfishes.