MATERNAL AGGRESSION IN RED SWAMP CRAYFISH (PROCAMBARUS-CLARKII, GIRARD) - THE RELATION BETWEEN REPRODUCTIVE STATUS AND OUTCOME OF AGGRESSIVE ENCOUNTERS WITH MALE AND FEMALE CONSPECIFICS

A series of experiments investigated intraspecific aggression by mater nal (carrying eggs and/or hatched young) and non-maternal female red s wamp crayfish (Procambarus clarkii) residents against intrusions by no n-maternal female and Form I(reproductively active) male conspecifics. Each resident occupied an aquarium containing a shelter for 24 hours prior to the initial intrusion. The winner of each encounter was deter mined, as well as the pair member that initiated the aggressive intera ction, and the relation between the initiation of aggression and conte st outcome. The results showed that: (1) Maternal female residents wer e winners in 92% of the encounters with male intruders, and initiated aggression in a significantly higher proportion of encounters than the male intruders. (2) Maternal female residents were the winners in 75% of the encounters with nonmaternal female intruders. The maternal res idents also initiated aggression in a significantly higher proportion of the encounters than the non-maternal intruders. (3) Non-maternal fe male residents lost 77% of the encounters with non-maternal intruders. Also, the non-maternal intruders initiated aggression in a significan tly higher proportion of the encounters than did the non-maternal resi dents. (4) Non-maternal female residents lost all of their encounters with male intruders. However, there was no significant difference in t he proportion of the encounters in which aggression was initiated by r esidents or intruders. (5) For all experiments combined, maternal resi dents won a significantly higher proportion of their encounters than d id non-maternal residents, regardless of whether the intruders were ma les or non-maternal females. (6) For the three experiments combined, t he initiation of aggression reliably predicted contest outcome (i.e. t ile initiator of aggression ultimately won). The present results provi de the first empirical demonstration, with appropriate nonmaternal con trols, of maternal aggression in decapod crustaceans. Also, the direct relation between reproductive status and contest outcome in both ovig erous and post-hatch P. clarkii are the first such data reported in cr ustaceans, in general. Finally, the findings of these experiments bear notable similarities to the results of maternal aggression research i n other taxonomic groups.