Digametic sex determination in the marine polychaete, capitella capitata (Species type i)

Abstract

Sex determination in the polychaete, Capitella capitata (species type I), is thought to be a polygenic trait. Since males can be induced to develop into hermaphrodites, crosses were done to examine the effect of the maternal parent on sex ratio. Female × male crosses produce a 50:50 sex ratio while hermaphrodite × male crosses produce 97 per cent to 100 per cent males. Differences in sex ratio cannot be explained by sex-specific mortality, and crosses between individuals from different geographical areas give similar results. Sex in this species appears to be determined by digamety with females as the heterogametic sex. Thus hermaphrodite × male matings should produce all males since hermaphrodites arise from males and are the same genotype (i.e. ZZ). Female (ZW) × male (ZZ) matings would produce a 50:50 sex ratio. The few females that were produced from a hermaphrodite × male mating were found to be protogynous hermaphrodites. © 1985 The Genetical Society of Great Britain.