Reptiles have been up to this point thought to have two mechanisms of sex determination: a genetic system based off the Z and W sex chromosomes and a environmental mechanism based off of incubation temperature (Known as temperature-sensitive determination or TSD).
Interesting experimental work published in Science this week challenged these "categories". An Australian group took the central breaded dragon, which had been previously shown to use the genetic system and incubated the hatchlings over a range of temperatures. They found that between 72 and 90F that about half appeared male and half were female. This was expected since meiosis would produce an equal amount of Z-containing and W containing ova.
The surprising result came when the researchers looked at the sex ratio of the hatchlings incubated above 93F. They found only two males out of the 35 eggs that hatched. This skewed sex ratio suggested that temperature had trumped genetics at elevated temperatures. The researchers interrogated the situation further. Using a DNA test based off the W chromosome, they showed that 17 of the 33 female hatchlings were genetically male (ZZ). In other words, they ruled out a statistical anomaly and showed that at high temperatures sexual genotypes (ZZ vs ZW) do not really determine gender (sexual phenotype).
You can read more about this work below.
http://www.livescience.com/animalwor...izard_sex.html
http://www.sciam.com/article.cfm?art...9&chanID=sa003
You can also here an interview with Alex Quinn, the main author on the paper at the Science Podcast.
http://podcasts.aaas.org/science_pod...ast_070420.mp3
The story/interview begins at 8:20 of the podcast.
The main author suggested in a 2004 BioEssay that sex wasn't solely genetic vs. TSD-- That these were instead the extremes of a spectrum. This new works seems to provide solid support for his idea.
So global climate change might not solely affect crocs and turtles, it might also affect many more reptiles than previous thought!
Reply With Quote