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Glen, Then Glenda: Mollusk is Born Male, Transitions to Female With Age

Lissarca miliaris is not exactly a glamorous or remarkable creature. The small, dull, clam-like creatures are filter feeders living a typically less than exciting life beneath the cold waves and icy sheets of Antarctica. The tiny mollusk is getting some time in the spotlight, though, as it was just revealed to have one of the stranger life cycles known to science. All specimens of Lissarca miliaris are born males. As they age and grow, though, they develop female sexual organs, transitioning to a fully female form capable of bearing young by the end of their lifespan.

Researchers were surprised by the discovery, as Lissarca miliaris has been known to science for more than 150 years, but most reproductive research on the species has been done on adult, egg bearing females, which seem perfectly normal until you realize that they were all once juvenile, egg-bearing males. A recent study of those young males found that they were indeed carrying eggs — more, in fact, than their tiny bodies could ever bring to term.

The new thinking is that Lissarca miliaris specimens mate when they are very young, allowing the eggs contained in the juvenile males time to mature while the proud papa grows big enough to support his brood. When it becomes large enough to be a maternal figure, that’s just what it does, developing female sexual organs. Lissarca miliaris also hangs onto its male genitalia for some time during this transition, meaning that the species spends much of its life as a genuine hermaphrodite.

(via PhysOrg, image courtesy of Smithsonian)

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