ACTIVE BROOD CARE IN AN AMPHIPOD - INFLUENCES OF EMBRYONIC-DEVELOPMENT, TEMPERATURE AND OXYGEN

Female amphipods (Crustacea) carry their fertilized eggs in an externa l brood pouch until the fully formed juveniles emerge (passive brood c are). They may also direct specific maternal activities towards the br ood (active brood care). We show that Crangonyx pseudogracilis, which typically populates freshwaters subject to wide fluctuations in temper ature and dissolved oxygen, engages in a highly responsive form of act ive brood care. This involves a flexing motion by the female that expa nds the brood pouch and increases the suspension of the eggs in the su rrounding medium, accompanied by ventilation of the brood pouch and th e 'cycling' of eggs therein. Females also selectively eject nonviable eggs from their broods. We investigated the expression of this brood c are behaviour in relation to intrinsic and extrinsic factors relevant to the development of broods. The time spent by females in this behavi our initially increased as embryos developed, but decreased once advan ced embryos began to self-ventilate and to have a heart pulse. In addi tion, both increased temperature and decreased oxygen concentration re sulted 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 influe nced by the interaction of embryonic development with temperature/diss olved oxygen regime. In addition, this behaviour may be a key adaptati on facilitating the success of this North American species as an invad er of disturbed and polluted freshwaters in Europe and elsewhere; Evid ence is emerging that other amphipods associated with harsh environmen tal conditions also shaw such active maternal brood care. (C) 1998 The Association for the Study of Animal Behaviour.