VUTURO, S. A.*; SHUSTER, S. M.: Sex change and cannibalism in Gulf of California populations of a commensal polychaete

Most polychaetes are known to be gonochoristic. Hermaphroditism appears to have arisen independently in several families. We have shown that, Ophiodromus pugettensis, a hesionid commensal of sea stars in California, is a simultaneous hermaphrodite with a protandric phase. To examine the relationship between sex change and body size in the Sea of Cortez populations, we sampled worms from four geographically disjunct populations inhabiting four species of sea stars. We found differences in the size of worms and their distribution among host species in the Sea of Cortez. Worms on some host species showed a positive relationship between body size and sexual condition while others do not. Density of worms on sea stars predicted sexual condition on some host species but not in others. We observed cannibalism in the Sea of Cortez populations that has not been observed in California populations. This behavior may be related to observed differences in damage to individuals and the differences in density per host between cannibalistic and non-cannibalistic populations. Our observations suggest that sex change is related not only to body size but is also influenced by the density of worms per star and the sex ratio. Different reproductive strategies among worms on separate host species suggests that worms associating with another host species may be genetically distinct.