The aggressive and territorial behaviour of the mantis shrimp Gonodactylus bredini manning (crustacea: stomatopoda).

Abstract

In the stomatopod Gonodactylus bredini when two individuals of the same sex encounter each other, they exhibit marked aggressive interaction. One animal usually becomes dominant over the other in approximately 10-20 minutes, and the frequency of aggressive acts declines steadily during the course of an hour. Dominance is influenced, although not necessarily determined, by size, stage in the reproductive cycle (females), stage in the moult cycle, and individual differences in level of aggressiveness. Aggressive behaviour involves a variety of fixed motor actions including spreading of the raptorial meri, antennular flicking, lunging with the meri spread, coiling of the body, and attacking and striking with the raptorial second maxillipeds. The meral expansion reveals conspicuous white spots on the inner surfaces of the raptorial meri and also silver streaks along the borders of the small first maxillipeds while the remaining maxillipeds are extended to form a rosette. This posture seems to serve as a threat. Because of structural modifications of the cuticle, especially on the dorsal surface of the telson, and of the frequent assumption of a coiled position during aggression, the strikes of attacking animals are seldom severely injurious. In nature G. bredini occupies cavities in rocks in shallow water from just below low tide line, and the aggressive behaviour is well suited to the defence of these cavities. The meral spread, for example, effectively fills the entrance and hence blocks encroachment by an intruder. The occupant may leave briefly to strike another animal or attack prey, but quickly returns to its home. The behaviour with respect to cavities thus seems to be territorial with the territory including the occupied rock plus a small area surrounding it. A resident animal undertakes several housekeeping activities including cleaning its chamber and closing the entrances at night with small bits of debris and reopening them the following morning. Only a particularly aggressive and dominant animal is capable of dislodging a cavity occupant, but eviction takes place rapidly when it does ocrur. Aggressive displays from outside alone seem insufficient to cause a def ender to leave a chamber ; takeover occurs when the attacker enters the cavity and drives the defender out.