Sea turtles' friends may do them in
Farmers who raise alligators or conservationists who breed sea turtles should watch the temperature of their hatcheries. Eggs that are a little too cool or too warm can produce animals predominantly, or even totally, of one sex.
That is a strategy for rapid extinction, as two recently published studies suggest.
In April, Mark W. J. Ferguson of the Queen's University of Belfast and Ted Joanen of the Louisiana Wildlife and Fisheries Commission published a paper in Nature describing the sex-temperature effect in an alligator species (Alligator mississippiensis). They speculated that such temperature-sensitive reproduction may even have contributed to the extinction of dinosaurs in a period of climatic change.
Then, in June, a different research team reported a similar effect in Green sea turtles (Chelonia mydas). The team included Stephen J. Morreale, James R. Spotila, and Edward A. Standora of State University College at Buffalo, N.Y., and Georgita J. Ruiz of both the Universidad Nacional Autonoma de Mexico and Rutgers University. In a paper published in Science, they warn that conservationists trying to breed endangered sea turtles may defeat their purpose by neglecting incubation temperatures.
Such findings match similar effects seen in a few other reptile species, including some freshwater turtles. They suggest that sex determination for an undetermined number of reptiles may depend critically on egg incubation temperatures. For the alligator, temperatures 30 degrees C. and lower produced all females, while temperatures 34 degrees and above yielded all males, Ferguson and Joanen report. The turtle researchers found an opposite tendency. Nest temperatures below 28 degrees C. produced 90 to 100 percent males. Temperatures above 29.5 degrees produced yields of 95 to 100 percent females.
These researches raise a warning for reptile breeders, whether they are farmers or conservationists. The sex-temperature sensitivity for each species involved should be determined, if not already known. Then incubation should be carefully controlled.
The turtle researchers go so far as to suggest that, if this sensitivity is not known, then conservationists should not try to breed that species artificially, even in a natural beach habitat. It would be better, they say, to locate wild nests and protect those.
They add that, when the temperature sensitivity is known, detailed care is needed to produce a natural sex ratio in hatchlings. Since a turtle mother probably knows what is best for its eggs, they urge that a beach hatchery ''duplicate as closely as possible the depth, the amount of shading, and egg chamber dimensions of natural nests.''
Nature's ways are intricate and subtle. The surprising findings on reptile reproduction illustrate that scientists have scarcely begun to understand the system of organic life on this planet. They are yet another warning that it is dangerous to upset that system carelessly and without adequate knowledge of the biological consequences.