Maternal Aggression in Red Swamp Crayfish (Procambarus Clarkii, Girard): the Relation Between Reproductive Status and Outcome of Aggressive Encounters With Male and Female Conspecifics

Abstract

Abstract A series of experiments investigated intraspecific aggression by maternal (carrying eggs and/or hatched young) and non-maternal female red swamp crayfish (Procambarus clarkii) residents against intrusions by non-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 determined, as well as the pair member that initiated the aggressive interaction, and the relation between the initiation of aggression and contest outcome. The results showed that: (1) Maternal female residents were 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 non-maternal female intruders. The maternal residents also initiated aggression in a significantly higher proportion of the encounters than the non-maternal intruders. (3) Non-maternal female residents lost 77% of the encounters with non-maternal intruders. Also, the non-maternal intruders initiated aggression in a significantly higher proportion of the encounters than did the non-maternal residents. (4) Non-maternal female residents lost all of their encounters with male intruders. However, there was no significant difference in the proportion of the encounters in which aggression was initiated by residents or intruders. (5) For all experiments combined, maternal residents won a significantly higher proportion of their encounters than did non-maternal residents, regardless of whether the intruders were males or non-maternal females. (6) For the three experiments combined, the initiation of aggression reliably predicted contest outcome (i.e. the initiator of aggression ultimately won). The present results provide the first empirical demonstration, with appropriate non-maternal controls, of maternal aggression in decapod crustaceans. Also, the direct relation between reproductive status and contest outcome in both ovigerous and post-hatch P. clarkii are the first such data reported in crustaceans, in general. Finally, the findings of these experiments bear notable similarities to the results of maternal aggression research in other taxonomic groups.