Safely telling she- from he-turtles.

Safely telling she- from he-turtles

The endangered Kemp's ridley sea turtle makes its home off Mexico's Gulf Coast, near Rancho Nuevo. Some 500 miles north, at the National Marine Fisheries Services in Galveston, Tex., researchers working on a capital breeding project hope to repopulate native waters with egg-laying ridley females. That effort, however, has posed a dilemma for biologist Charles Caillouet and his Fisheries Service colleagues: Although a harmless radioimmunoassay for testosterone can reveal the gender of prepubescent ridley sea turtles with 90 percent accuracy, the most reliable method of identifying the sex of newly hatched turtles would require killing them. Waiting the necessary two years for the turtles to come of age for the radioimmunoassay would slow repopulation efforts; releasing hatchling of undetermined gender would leave researchers unable to guarantee an ample supply of females.

Now, scientists from the University of Tennessee at Memphis have developed a promising alternative based on genetic fingerprinting techniques. After fragmenting DNA extracted from a small blood sample, Suzanne Demas and her co-workers apply a genetic probe that selectively binds to gender-specific DNA fragments. The proble, a DNA sequence first isolated in a highly poisonous Asian snake, can distinguish sexes even in hatchlings, Demas says. It also works in the green sea turtle--a ridley relative -- and Demas thinks it may assist gender identification in other reptiles as well.

In a study of 30 ridleys whose sex had been determined by others using a different method, Demas and her colleagues accurately identified the gender of 15 females and 14 males. They also identified the gender of nine of 10 green sea turtles, the researchers report in a forthcoming EXPERIMENTAL ZOOLOGY.

The DNA probe may also lead to a more precise determination of the relationship between gender and incubation temperature for ridley eggs. The Galveston group has observed that a relatively warm incubation environment produces predominantly female hatchlings, while temperatures just 5[degrees]C to 8[degrees]C cooler produce mostly males. The probe "should aid researchers in determining whether turtles raised in hatcheries for release into the wild interfere with the normal ratio of male to female animals," Demas says.

Saving ridleys from extinction may depend on precisely controlled repopulation. Demas asserts. She notes that the creatures face several dangers in the wild: They often feed near drilling platforms, where underwater shock waves can kill them, and many drown when entangled in shrimpers' nets.