Proc. R. Soc. B doi:10.1098/rspb.2008.0675 (2008)

Credit: Y. LOYA

Although many animals can switch from one sex to the other, repeated flip-flopping was thought to be the preserve of one species of fish. But some corals do it too, reveal Yossi Loya at Tel Aviv University and Kazuhiko Sakai at the University of the Ryukyus in Japan.

They collected wild mushroom coral, Ctenactis echinata (pictured), and monitored it in a laboratory over many months. Large coral heads remained female and small ones remained male, but medium-sized corals changed sex bidirectionally and often.

Loya and Sakai note that this coral's size-dependent, labile sexuality is remarkably similar to that of a Japanese tree, Bischofia javanica.