LAUSR

Sea urchins are usually gonochoristic, and each of their five gonads are collectively either testes or ovaries. Here we report an unusual case of hermaphroditism in the purple sea urchin, Strongylocentrotus purpuratus. The hermaphrodite is self-fertile and one of the gonads is an ovotestis; it is largely an ovary with a small segment containing fully mature sperm. Molecular analysis demonstrated that each gonad made bona fide gametes, and we identified for the first time a somatic sex specific marker in this phylum: the Doublesex ortholog, DMRT1. This finding also enabled us to analyze the somatic tissues of the hermaphrodite and we found that the oral tissues (including gut) were out of register with the aboral tissues (including tube feet) enabling a genetic lineage analysis. Results from this study support a genetic basis of sex determination in sea urchins, the viability of hermaphroditism, and distinguish gonad determination from somatic tissue organization in the adult.