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Saving Turtles Clique by Clique

Loggerhead sea turtles, which feed thousands of miles from their hatching grounds, seem to return to breed with their genetic relatives at sites very close to their births. The finding, in tomorrow's issue of Nature, is the first solid evidence for the turtles' remarkably precise homing instinct, and it strengthens the argument by conservationists that as many nesting areas as possible must be protected to ensure diversity.

>Ecologist and evolutionary biologist Bernd Schierwater of J. W. Goethe University in Frankfurt, Germany, and his colleagues used DNA fingerprinting and sequencing techniques to analyze tissue samples from 81 loggerhead hatchlings found dead at 10 different nesting sites in Greece, Turkey, Crete, and Cyprus. Even on adjacent nesting sites along the Turkish coast, they found evidence of genetic differences in both mitochondrial DNA, which is inherited only from mothers, and genomic DNA, which is inherited from both parents. That finding may suggest that males tend to mate with females from their own nesting site, says Schierwater, which would contradict the prevailing notion that males mate with females from a range of locales.

The new data "complete the half of the picture that's been missing" from earlier studies of mitochondrial DNA differences along the southern Atlantic coast of the United States, says Brian Bowen of the University of Florida. Those studies, which used less precise genetic tests, showed differences between females at beaches thousands of miles apart but provided no data on males.

The latest work suggests that conservation groups must broaden their efforts to protect nesting areas from development. Protecting only a few nesting beaches will save only turtle subpopulations, Schierwater says. Bowen agrees: "If the preservation of genetic diversity is the goal," he says, "it won't be sufficient to protect [only the local] nesting beach."