Sex determination in Hydra: Roles of germ cells (interstitial cells) and somatic cells

Germ cells were exchanged between male and female hydra to determine whether the germ cells or the somatic tissues determine the phenotypic sex of the polyp. Interstitial cells, the precursors of gametes, were removed from male and female Hydra oligactis by gamma irradiation. The resulting polyps, termed “epithelial hydra,” possessed the characteristic morphology of H. oligactis, and could reproduce by budding but could not produce gametes. When these epithelial hydra were repopulated with interstitial cells from normal hydra of the same or opposite sex, their sexual phenotypes were those of the interstitial cell donors. These results indicate that the germ cells, rather than somatic cells, determine the phenotypic sex of hydra.