FEMALES INHIBIT MALES' PROPENSITY TO DEVELOP INTO SIMULTANEOUS HERMAPHRODITES IN CAPITELLA SPECIES I (POLYCHAETA)

¹ Biology Department, University of Pennsylvania, Philadelphia, Pennsylvania 19104

The propensity for a male of Capitella species I to develop into a simultaneous hermaphrodite is shown to be inhibited by the presence of females. However, even when females are rare, males which develop into hermaphrodites do so nearly as quickly as males held in all male cultures or in isolation. When held in isolation males which do not switch are smaller than their male siblings which do. The maternal parent has no effect on the propensity of switching; no differences are found between male offspring which are derived from either females or hermaphrodites. It has been suggested that hermaphroditism in Capitella is an adaptation to low density. Yet females do not become hermaphroditic, hermaphrodites do not self-fertilize, and hermaphrodites function primarily as females. It seems much more likely that hermaphroditism in Capitella is an adaptation to living in small local populations which experience local mate competition.