PRIOR RESIDENCE EFFECTS IN SHELTER DEFENSE IN ADULT SIGNAL CRAYFISH (PACIFASTACUS-LENIUSCULUS (DANA)) - RESULTS IN SAME-SEX AND MIXED-SEX DYADS

In a variety of taxa, the initial resident in a spatial area enjoys a dominance advantage over a subsequent intruder. In decapod crustaceans this ''prior residence effect'' has been demonstrated in lobsters, pr awns, and crabs. However, there is scant evidence for the effect in cr ayfish. In the present series of experiments, individual signal crayfi sh (Pacifastacus leniusculus) were introduced into one side of divided aquaria, which contained a shelter. Another crayfish was put into the opposite side. Twenty-four hours later the divider was removed. In sa me-sex encounters 76% of female residents retained shelter possession, as did approximately 70% of male residents, both sexes demonstrating a significant territorial prior residence effect. In mixed-sex encount ers, female residents retained shelter possession against male intrude rs in 80% of them. However, male residents retained shelter occupancy in only 33% of the encounters with female intruders. These findings de monstrate the existence of a prior resident effect in P. leniusculus. The contest advantage of females over males is consistent with previou s research showing female dominance over males in social dominance hie rarchies in this species.