SEXUALLY DIMORPHIC FREE-SWIMMING BEHAVIOR IN THE AMPHIPOD CRUSTACEAN AMPELISCA-ABDITA

This paper describes a novel sexually dimorphic pattern of behaviour in the tube-building amphipod Ampelisca abdita (Mills). Mature males and females enter the water column at night. However, while males enter the water column every night, females enter it only when they moult. Since female amphipods only mate shortly after they moult, it is hypothesized that this sexually dimorphic pattern of free-swimming behaviour is an adaptation that permits males and receptive females to locate each other during the brief period when copulation can occur, while reducing the time that females are exposed to pelagic predators.