Evolution of biparental care in the hermaphroditic polychaete worm Ophryotrocha diadema

Abstract

Ophryotrocha diadema is a simultaneously hermaphroditic polychaete worm with a brief adolescent protandrous phase. In the mating system of this worm, pairs are formed preferentially between simultaneous hermaphrodites. Both partners of a pair regularly alternate sex roles, reciprocate egg exchange, and care for developing embryos. Neglected eggs have a 31% probability of dying, but eggs cared for by both parents, by a single parent, or even by an unrelated individual have a 95% probability of developing. In pairs prevented from caring for eggs, intruders succeeded in substituting one of the partners significantly more frequently than in pairs allowed to care for eggs. Thus, the main adaptive value of biparental care would be to guarantee a partner for egg reciprocation. Protandrous males are inefficient brooders, and biparental care becomes fully established only when individuals are able to reciprocate egg exchange, ie they have reached the simultaneously hermaphroditic stage. -Author