Reciprocation, Reproductive Success, and Safeguards Against Cheating in a Hermaphroditic Polychaete Worm,<i>Ophryotrocha diadema</i>Åkesson, 1976

Abstract

Ophryotrocha diadema, a simultaneous hermaphroditic polychaete worm, forms pairs in which both partners regularly alternate sex roles and trade eggs. Since O. diadema has a protandrous phase, safeguards against cheating by a non-reciprocating partner, either male or hermaphrodite, have evolved. Results of a mate choice experiment indicate that protandrous males are generally discarded as mates because they are unable to reciprocate with eggs. Reproductive success (measured by estimating the mean number of egg masses per individual per day) of hermaphrodites paired with males was significantly lower than the reproductive success of hermaphrodites paired with hermaphrodites. This indicates that O. diadema is able to time spawning activity according to the sexual condition of its partner. On the other hand, oogenesis and the production of multiple batches of mature oocytes is independent of the presence of a partner. Worms did not discard mates with substantially fewer eggs. The small size of clutches and the short interval between successive spawnings could be considered a form of egg parcelling, which would prevent exploitation of hermaphroditic individuals by partners unable to reciprocate.