Active brood care in an amphipod: influences of embryonic development, temperature and oxygen.

Female amphipods (Crustacea) carry their fertilized eggs in an external brood pouch until the fully formed juveniles emerge (passive brood care). They may also direct specific maternal activities towards the brood (active brood care). We show that Crangonyx pseudogracilis, which typically populates fresh-waters subject to wide fluctuations in temperature and dissolved oxygen, engages in a highly responsive form of active brood care. This involves a flexing motion by the female that expands the brood pouch and increases the suspension of the eggs in the surrounding medium, accompanied by ventilation of the brood pouch and the 'cycling' of eggs therein. Females also selectively eject nonviable eggs from their broods. We investigated the expression of this brood care behaviour in relation to intrinsic and extrinsic factors relevant to the development of broods. The time spent by females in this behaviour initially increased as embryos developed, but decreased once advanced embryos began to self-ventilate and to have a heart pulse. In addition, both increased temperature and decreased oxygen concentration resulted in increased levels of brooding behaviour. We thus propose that this behaviour functions to ameliorate the microclimate of the brood pouch and serves the changing metabolic demand of the brood, as influenced by the interaction of embryonic development with temperature/dissolved oxygen regime. In addition, this behaviour may be a key adaptation facilitating the success of this North American species as an invader of disturbed and polluted freshwaters in Europe and elsewhere. Evidence is emerging that other amphipods associated with harsh environmental conditions also show such active maternal brood care. Copyright 1998 The Association for the Study of Animal Behaviour.