Nonrandom mating, mate choice, and male-male competition in the crayfish Austropotamobius italicus, a threatened species.

Under the rationale that behavioral studies may contribute to the conservation of threatened species, we analyzed mating behavior of the crayfish Austropotamobius italicus in the laboratory. Our objectives were to investigate whether nonrandom mating by size occurs in this species and to explore the role exerted by mate choice and male-male competition in inducing mating. We observed 17 "quartets" (one female and three differently sized males), divided into three groups based on the female size. To understand the influence of male-male competition on mating, we compared six quartets with six "duets" (one female and one male). Our results clearly show that mating in A. italicus is nonrandom caused by the clear mating advantage of larger males. In fact, as compared to smaller size categories, large males paired more often and for a longer time, and interrupted the final phase of mating less frequently. Male size-advantage mostly derives from an active female choice for large partners, combined with dominance of big males in intrasexual competition. However, a restricted mating period and the low number of receptive females may make males relatively indiscriminate in their overt behavior towards females. Female selection of big males and male-male competition over mates, also in the form of sperm competition, should result in a skewed reproductive success among males. As a consequence, populations with few big males would be characterized by a low heterozigosity and therefore by little genetic variation upon which selection acts. Our results should warn managers to pay more attention to the size structure of crayfish populations that are used for reintroductions.