Colonization, population dynamics, predatory behaviour and cannibalism in Heterocypris incongruens (Crustacea: Ostracoda)

Abstract

We followed the artificial colonization of a temporary pond in Northern Italy by the freshwater ostracod Heterocypris incongruens. The species had not been found in the pond in previous years. In May 2009 we released five laboratory reared, genetically identical, parthenogenetic females and observed the population during colonization and growth until desiccation (MayJuly 2009) and two subsequent hydro-periods (February-March and May-July 2010). High population density was always reached in few weeks, although in late winter 2010 no ovigerous female was observed and in spring 2010 the population was recruited only from resting eggs. In all three hydro-periods swarms formed every day and could be easily seen near the border of the pond to the eye around the median time of the sun path. In laboratory observations, individuals sampled from the swarm forming population showed predatory behaviour: H. incongruens attack, kill and consume live, actively self-defending organisms (Chironomid and mosquito larvae). We also observed cannibalism among adult females. We found low fecundity and high mortality in females sampled from the crowded population and kept in low density laboratory conditions. We discuss how cannibalism, delayed egg hatching, fecundity loss and high mortality by crowding regulate high density populations of H. incongruens, a typical r strategy species.