CANBERRA TIMES (Australia) 22 January 08 Jacky or Jill: sex code cracked (Rosslyn Beeby)
Australian researchers have solved an evolutionary mystery of hot reptile sex and survival that's baffled the world's scientists for more than 30 years.
Studying more than 200 Jacky dragons, a common and relatively short-lived lizard found in eastern Australia, University of Sydney biologists Professor Rick Shine and Dan Warner have proved nest temperatures not only determine the sex of reptile hatch-lings but survival of the fittest and most fertile.
In short, there's an optimal incubation temperature for a successful reptile sire that's totally different to the temperature required to produce a fit and fertile female lizard. For mammals and birds, sex is determined by genes, but many reptiles determined the sex of a hatchling during incubation, some time after the egg is laid. Several species, including turtles and crocodiles, have temperature-dependent sex determination, with hotter nests producing females and cooler temperatures producing males.
"We knew nest temperatures affected the likelihood of some reptile species being born male or female, but we didn't know why this occurred," Professor Shine said.
"What we've demonstrated is there's a distinct evolutionary advantage given to males or females incubated at certain temperatures."
The research findings are published this week in the global science journal Nature (*), and provide "the first unequivocal demonstration" of this complex evolutionary process.
"It's been a big one to crack. It's been a problematic area of research and the holy grail of evolutionary biology for over 30 years."
The secret of success for Professor Shine's research team was the Jacky dragon, a 60g lizard which has a lifespan of between two and five years.
"Most research in this field has focused on extremely long-lived reptiles like turtles or crocodiles, so you'd have to be around for 100 years to get conclusive results. We were able to test four different fitness hypotheses with the Jacky dragons and see the results."
Eggs from wild-caught females were incubated at a range of temperatures, and the hatchlings raised in outdoor enclosures.
The researchers also added hormone treatments to nests at different temperatures to override the natural process of sex determination. They compared lizards born in these hormone-enhanced nests to those from nests which hadn't been treated.
"Both the males and females born in the hormone-affected nests in other words, at temperatures their sex are not supposed to be born at were much less fit, and much less likely to have babies, than those born naturally."
The research had benefited from the security of long-term funding provided by the Australian Research Council.
*http://www.nature.com/nature/journal/vaop/ncurrent/abs/nature06519.html;jsessionid=FB41667A2F2A6475086BE25B2CF5DA68
Jacky or Jill: sex code cracked