Intrapopulation variability in coloration is associated with reproductive season in the crayfish <i>Faxonius virilis</i>

Animal coloration has a wide range of biological functions and may be subject to different, sometimes conflicting, selective pressures. In crustaceans, the evolution of coloration is relatively unstudied, despite the broad range of colors and color patterns, which includes variability at multiple levels. Freshwater crayfish are known to show color variability within species and populations, as well as intra-individual variability, but the function, if any, of crayfish coloration is largely unknown. Here, I report on an experiment to understand patterns of color variability in the crayfish <i>Faxonius virilis</i> and show that variation is strongly correlated to ontogenetic changes from a summer non-reproductive form to a fall reproductive form. Crayfish showed comparatively little inter- and intra-individual color variation in their non-reproductive form, but substantial variation at both levels in the reproductive form. Transition to the reproductive form was associated with the development of greener or bluer coloration localized to the chelae on a subset of individuals, but these changes showed no clear correlation with sex or body size. Future investigations should focus on determining whether differences in color between individuals in the mating season are associated with any physiological or behavioral differences, or with differential susceptibility to predation.