Sea urchins are usually gonochoristic, with all of their five gonads 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 producedviable gametes, and we identified for the first time a somatic sex-specific marker in this phylum: Doublesex and mab-3 related transcription factor 1 (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.
Summary Sentence
A self-fertile hermaphroditic S. purpuratus sea urchin containing four testes and one ovary/ovotestis is described; the results support a hypothesis of genetic sex determination in this species.
Graphical Abstract
Highlights
A hermaphrodite sea urchin is described containing four testes and one ovary/ovotestis
The hermaphrodite is self-fertile
The ovotestis is largely an ovary with a small segment containing sperm
The Doublesex ortholog, DMRT1, was found to be a sex-specific marker in Strongylocentrotus purpuratus
These results support a genetic basis of sex determination in sea urchins
We find that gonad determination is distinguishable from other somatic tissue organization in the adult
