SEX ALLOCATION IN THE SIMULTANEOUSLY HERMAPHRODITIC POLYCHAETE WORM OPHRYOTROCHA-DIADEMA

Pairs are formed preferentially between 2 simultaneous hermaphrodites, which reciprocally change sex roles and trade eggs. Allocation of reproductive effort during simultaneous hermaphroditic and protandrous phases was evaluated. Efficiency of fertilization in the protandrous phase is low but positively correlated with body length. A fertilization ratio of 95% is obtained only at the simultaneous hermaphoroditic stage. This explains why protandrous males are generally not selected as mates in the reproductive strategy. Self-fertilization is avoided by behavioral constraints. The observed female bias in reproductive effort suggests that hermaphroditism should be evolutionarily stable, as the male investment in reproductive effort follows the law of diminishing returns. -from Author