Reciprocation, Reproductive Success, and Safeguards Against Cheating in a Hermaphroditic Polychaete Worm, Ophryotrocha diadema Akesson, 1976

Ophryotrocha diadema, a simultaneous her maphroditic polychaete worm, forms pairs in which both partners regularly alternate sex roles and trade eggs. Since 0. 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 mdi vidual per day) ofhermaphroditcs paired with males was significantly lower than the reproductive success of her maphrodites paired with hermaphrodites. This indicates that 0. diadema is able to time spawning activity accord ing 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 ofclutchcs and the short inter val between successive spawnings could be considered a form ofegg parcelling, which would prevent exploitation of hermaphroditic individuals by partners unable to re ciprocate.