Impact of an insecticide on persistence of inherent antipredator morphology of a small cladoceran, Bosmina.

Pesticides often modify predatory interactions by enhancing (or inhibiting) the development of antipredator morphologies of freshwater cladocerans. In the present study, we assessed the impacts of an insecticide, carbaryl, on the life-history parameters of a polymorphic cladoceran, Bosmina longirostris, and on Bosmina-copepod interaction. In this Bosmina species, all juvenile individuals have the defensive morphology irrespective of presence of predators in juvenile stages, and they lose or maintain such morph compliance with the presence/absence of the predators in adult stages. In the present study, individual somatic growth and population growth rate decreased due to applied carbaryl. Moreover, the animals lost the defensive morphology when their body size was smaller than with no-carbaryl treatment even in the presence of predators, indicating that the insecticide inhibited persistence of the inherent antipredator morphology. Such a chemical disturbance will increase the predation risk to individuals and, in turn, influence the population dynamics of the bosminids through increased mortality.