This dominant 4.5metre male Estuarine Crocodile (Crocodylus porosus) resides a kilometre or so downstream from my own abode on Cooper Creek; a proximity that we never forget!
It has long been known that crocodile gender is determined by temperature. If the temperature of egg incubation is cool, around 30 degrees C, the hatchlings are all female. Warmer temperatures, around 34 degrees C, hatch all males. There is also strong population bias towards females; often as high as 10 to 1.
For about thirty years, this skewed ratio was thought to provide an evolutionary advantage, whereby sex ratio optimises survivorship considerations.
In a recent News in Science article by Dani Cooper, entitled ‘Sex-change lizards settle a hot topic’, Professor Rick Shine of Sydney University and his former student Dr Daniel Warner, now of Iowa State University, report that they have proven this 30-year-old theory.
Studying the relatively short-lived Jacky dragon (Amphibolurus muricatus), which produces off-spring within one year of hatching and lives no longer than four years, the researchers found that hormonal manipulation of gender determination had no effect on the health and survival of the hatchlings, but the natural males were five to 10 times better in terms of mating and producing offspring, while the natural females produced four to five times more offspring.
It was therefore shown that the incubation temperature that produces that sex in nature optimised reproductive success of each sex.
Jennifer Marohasy BSc PhD is a critical thinker with expertise in the scientific method.
Just how long have these crocodiles been around and how many major swings in Earth’s temperatures have they survived–males and females alike? If we believe global warmers about the future, only male crocodiles will be born and they will be all gay.
Woody,
Some 84-million years, according to http://en.wikipedia.org/wiki/Crocodilia
However, I do wonder what part the female plays in influencing incubation temperature via nest design. It may be more complicated than merely nesting at the same time each year with an identical nest design that allows the external temperature to dictate gender population ratio.
woody,
i think the variability of nest construction by the females would allow for some flexibility in the ratio of male to female. so even if it does get warmer there will still be females hatched. also even if only males crocs are born, i’m not sure they will all be that happy about it.
What are you guys talking about? Doesn’t the research say: “Shine says female Jacky dragons are produced from eggs incubated at low (23°C-26°C) and high (30°C-33°C) temperatures whereas males are produced at intermediate temperatures.” Doesn’t that mean in the middle? That is 26°C > Male < 30°C so all the research is showing is that gender is temperature related. Over 33°C they may not hatch at all! Are cooked crocodile eggs good to eat?