Recognition of dominance in the big-clawed snapping shrimp (Alpheus heterochaelis say 1818) part I: Individual or group recognition?

The snapping shrimp Alpheus heterochaelis uses its snapper claw to produce fast water jets in fights. Here we investigate whether these shrimp are able to recognise their opponents (individually or on a group level) in order to reduce fighting costs and risk of injury. Losers meeting familiar or unfamiliar winners differ from those meeting inexperienced opponents by showing immediate escapes after a contact as well as hardly any aggressive behaviours (e.g. water jets). There is a significant decrease in aggressiveness in these losers and this is maintained for days. In contrast, losers meeting inexperienced opponents show a slow stepwise decrease in aggressiveness after losing on several consecutive days. Thus, snapping shrimp can recognise the dominance status of the opponent. The lack of behavioural differences in losers meeting familiar or unfamiliar winners favours recognition on a group level rather than individual recognition.