Mating behavior and a behavioral assay for female receptivity in the red-claw crayfish Cherax quadricarinatus

Females of the red-claw crayfish Cherax quadricarinatus do not undergo external changes that may indicate receptivity. To study mating behavior and develop a behavioral assay for female receptivity, pairs of size-matched males and females were housed in aquaria each divided in two by a transparent partition, with a tube-shelter on each side. Observations on shelter occupation were conducted daily at 30-min intervals. In addition, each pair was allowed to interact daily for 10 min after lifting the partition. The female almost invariably initiated the mating activity. Though infrequently observed prior to copulation in this study, the male performed a stereotyped courtship action, namely, sudden thrusts of his chelipeds toward the female. Unlike most crayfishes, the male did not use the claws to grasp, position, or hold the female during copulation, and positioned himself on his dorsum underneath the female. The percentage of observations in which the female was outside the shelter was much higher on the day of mating than on any other day prior to, or following, mating. No behavioral clues for female receptivity were detectable during the daily en counters prior to the day of mating. The level of shelter occupation by females reliably indicates receptivity; it is limited, however, to the day of mating.