ALLOPARENTAL EGG CARE IN THE POLYCHAETE WORM OPHRYOTROCHA-DIADEMA

In the simultaneously hermaphroditic worm Ophryotrocha diadema, eggs a re laid in nesting sites i.e. widenings of mucous trails built by pare nts. Nesting sires where eggs are present represent highly predictable places where other conspecifics, attracted by the mucous trails, tend to congregate. Care for developing embryos is associated with regular alternation of sex functions and reciprocal egg exchange between part ners of the same pair. Generally both parents tend their eggs, but egg s develop equally well if they are cared for by a genetically unrelate d individual (adopter). The aim of this study was to investigate the p ossible evolutionary significance of the adoption of neglected eggs by unpaired worms. Results of our experiments indicate that: 1. Apparent ly there are no direct. cues (e.g. chemical) for kin recognition: cues are only indirect, i.e. only eggs located in the nesting sites elicit parental care by any worm; and 2. In a low-density laboratory populat ion (1 individual per 500 mi) of O. diadema, by tending,eggs of whatev er provenance in the nesting sites, unpaired hermaphrodites increase b y 1.23 times their mating opportunities, compared with hermaphrodites not caring for eggs and seeking for a mate outside the nesting sires. In this sense, in a low-density population, non-parental egg attendanc e can be considered adaptive.