SEX AND THE BEAKED WHALE

See allHide authors and affiliations

Science  19 Dec 2008:
Vol. 322, Issue 5909, pp. 1763
DOI: 10.1126/science.322.5909.1763a
CREDIT: NAN HAUSER, CENTER FOR CETACEAN RESEARCH AND CONSERVATION

The 14 species of rare beaked whales (genus Mesoplodon) sport a wild variety of tusks—some jutting straight up, others curving like scimitar blades from the males' jaws. Scientists have long puzzled over the remarkable diversity. Now an analysis of the whales' DNA suggests that it's all about sex.

When conservation geneticist C. Scott Baker of Oregon State University, Newport, and colleagues drew up the first molecular phylogenetic tree for Mesoplodon, they were surprised to find that species with similarly shaped tusks are not closely related, as had been thought. Nor do closely related species have similar tusks. The pattern is typical of diversification driven by sexual selection, they report in this month's Systematic Biology.

Until now, the only mammals known to have undergone speciation as a result of sexual selection were ungulates with horns and hooves. Just as stags use their horns to fight for females, male beaked whales rake each other with their tusks, says lead author Merel Dalebout, an evolutionary biologist at the University of New South Wales, Kensington, in Australia. “Certain tusks may be shaped better for hitting harder or for sneaky attacks. … Those males win the fights and the females, and then their tusk shape spreads through the population.”

Navigate This Article