We’re listening to the sounds of baby crocodiles, freshly hatched from their eggs. You might think that there’d be a fifty-fifty chance that a particular hatchling would be male or a female. But that’s not the case, and we’ll find out why in a moment. I’m Jim Metzner, and this is the Pulse of the Planet, presented by the American Museum of Natural History.
Believe it or not, the sex of baby crocodiles is determined by the temperature of the eggs when they were in the nest — it’s called temperature dependent sex determination.
“Temperature dependent sex determination or what is also known as TSD is a phenomenon that has been studied in a number of reptilian species. And what this means is that the sex of the hatchling is not determined genetically, as it is with human beings and with a lot of other mammalian species, but it actually determined by the average incubation temperature during the middle third of the developmental period.”
Dr. Alison Leslie is a physiological ecologist with the University of Stellenbosch in South Africa. She’s spent the last 4 years studying the Nile crocodile in South Africa’s Lake St. Lucia. Dr. Leslie has observed that St. Lucia’s crocodiles exhibit an unusual form of TSD.
“Turns out that temperatures below 31.7 degrees Celsius produce females. Any temperature above that, in other words, above 31.7, right up until 34.5 degrees Celsius, produce males and then temperatures above 34.5 degrees produce female hatchlings once again. So we have a female, male, female ratio for Nile Crocodiles. Which is pretty interesting.”
So, there’s only about a 3 degree range in which males will occur, which has a major impact on the long-term survival of crocodiles. We’ll hear more in future programs. Pulse of the Planet is presented by the American Museum of Natural History. I’m Jim Metzner.