Mating and sexual selection in the threatened crayfish, Austropotamobius italicus.

Mating by the threatened crayfish Austropotamobius italicus was studied in the laboratory during October-November 2002. For two hours we observed the interactions occurring in 17 groups composed of three differently-sized adult males and one receptive female and we checked, in the subsequent three days, for spermatophore deposition by males and for spawning by females. Results showed: (1) the “reluctant” and “choosy” behaviour of the females, (2) the large-male size advantage, and (3) the occurrence of a form of “sperm competition”. In our study, we did not find an ultimate explanation for female preference of large males. Indeed, male size is a good predictor of the outcome of intrasexual competition for the access of mates. If males have genes that enable them to attain the larger size, females mating with big males might produce big sons and therefore gain better reproductive success through their sons’ progeny.