Why don’t animals seem to favour sex change?

February 4th, 2009 - 2:22 pm ICT by IANS  

Toronto, Feb 4 (IANS) The sex of humans and animals remains unchanged - but some species do switch genders, in a phenomenon called sequential hermaphroditism. It occurs naturally from plants to fishes. Following four decades of research that established why sex change is advantageous, the question remains why it is rare among animals.

“An intuitive, yet rarely studied, explanation is that the considerable time or energy it takes to change sex make hermaphroditism unfeasible for most animals,” said Suzanne Alonzo, assistant professor of evolutionary biology at Yale University. She supervised graduate student Erem Kazancioglu’s study.

Researchers built theoretical models of the hermaphrodite and separate-sex life histories. In their “game” models, sex change “players” vary the age of their sex change, while the separate-sex strategy responds by altering the number of male and female offspring it produces.

“We were surprised to see that a hermaphrodite could spend 30 percent of its lifetime in the process of changing sex, and still persist in a population,” said Kazancioglu. “This suggests that only huge costs can disfavour sex change.”

So, why is sex change so rare? And, why does one species of fish reproduce strictly as separate sexes, while another very closely related species flexibly changes sex?

A comparative study of hermaphroditic and separate-sex mating systems, which the authors are currently performing, may provide a clue, a Yale release quoting Kazancioglu said.

These findings will appear in the March issue of The American Naturalist.

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