Role of Mechanosensory Stimuli in Intraspecific Agonistic Encounters of the Snapping Shrimp (Alpheus heterochaelis).

Intraspecific agonistic encounters in snapping shrimp (Alpheus heterochaelis) were analyzed using single-frame video analysis. The pair of conspecifics in such an encounter are designated as the snapper, which emits a fast water jet by very rapid closure, or snap, of the large modified snapper claw, and the receiver, which is the target of the water jet. The behavior of both snapper and receiver was evaluated before, during, and after the snap. Interactions between two intact shrimp (experimental series I) were compared with those between an intact shrimp and a "deprived" opponent (one with mechanosensory occlusion produced by coating the setae on the snapper claw with clear lacquer) (experimental series II). The behavior of the receiver is significantly changed by the occlusion, but that of the snapper is not. Intact and deprived opponents usually face each other during snapping, which is often preceded by touching of frontal appendages. The mean duration of claw cocking before snapping is about 500 ms. More than 50% of all snaps (and especially initial snaps) are directed towards the opponent, the water jet usually hitting the snapper claw of the receiver from a mean distance of 0.9 cm. Male shrimp show longer cocking durations, keep a shorter distance, and hit their opponents more often than do females. Intact and deprived snappers usually retreat immediately after snapping, but intact receivers usually approach. In contrast, deprived receivers retreat in most cases and show significantly prolonged latencies compared to intact receivers. Thus, mechanoreceptors on the snapper claw of the receiver play a significant role in intraspecific agonistic encounters.