Variation in the mode of reproduction among individuals of the ostracod Candonocypris novaezelandiae

Abstract

This study describes the results of laboratory breeding experiments designed to determine the mode of reproduction of female Candonocypris novaezelandiae from populations with and without males. Two morphological forms of this species were studied: a large-green and small-brown morph. Large-green females from populations without large-green males invariably generated genotypically identical daughters by parthenogenesis, regardless of the presence or absence of males in the laboratory cultures. In contrast large-green females from a population that included large-green males, when they had the opportunity for fertilization, usually produced genotypically diverse offspring of both sexes. These females were probably sexually reproducing. Unmated females from the mixed-sex population did not reproduce. The small-brown morph was collected from a single water body in which it was represented by both sexes and co-occurred with large-green parthenogenetic females. Most of the small-brown females tested reproduced sexually in the presence of males or did not reproduce in the absence of males. One small-brown unmated female, however, reproduced by parthenogenesis. Available evidence indicates that the field population of the small-brown morph includes both sexual and parthenogenetic females and that the relative abundance of the parthenogenetic females is increasing with time. The sexual and asexual forms within and between morphs are probably independent.