Some interesting new research. The paper is, unfortunately, behind a paywall but they made a video, so it is worth posting.
Here's the press release for the paper:
Scientists know that temperature determines sex in certain reptiles—alligators, lizards, turtles, and possibly dinosaurs. In many turtles, warm temperatures during incubation create females. Cold temperatures, males. But no one understands why.
A recent study sheds further light on this question. The findings of researchers Kayla Bieser, assistant professor at Northland College, and Thane Wibbels, professor of reproductive biology at the University of Alabama at Birmingham, will be published this month in the primary research journal “Sexual Development,” and is now available online.
This study represents the most comprehensive, simultaneous evaluation of the chronology of how sex-determining genes express themselves during embryonic development and and looks at the impacts of estrogen.
Bieser and Wibbels followed five different genes and what was going on in the exact same turtle. To date, scientists have looked at a number of turtles and pooled the data but Bieser is the first to follow individual turtles. She wanted to know when and how they “express” themselves. For an example, Bieser describes expression as the physical manifestation of those genes such as blue or brown eye color.
She looked at turtle eggs incubated at male and female temperatures and documented what the genes were doing while sex is being determined. “Which genes ‘turn on’ and when, could be an indication of what is triggering sex,” Bieser said.
According to Bieser, temperature-dependent sex determination species may be unable to evolve rapidly enough to offset the increases in temperature, which may ultimately result in their extinction.
“It’s critical that we understand the genetic mechanisms for which temperature acts and incorporate this knowledge into management plans for the conservation of these vulnerable species.”
Secondly, Bieser applied estrogen to eggs at a male-producing temperature. The purpose she said is to help determine the triggers for sex determination and how hormones, such as estrogen, can override the temperature signal.
In other words, would temperature or estrogen win out in deciding sex? The answer: in short, neither. What she found — and this is new information — is when estrogen is applied to eggs incubating at a male temperature, gonads—or sexual parts—do not develop. Or, if they do, they barely develop.
Why? “We don’t know yet,” Bieser said.
Scientists have been doing this experiment for some time but never reported these results. She suspects the reason is because scientists did not dissect the gonadal area specifically and that they took the general area but may have not analyzed the gonads to the same detailed level. In fact, this was a sticking point for one of the reviewers of this study—so Bieser provided photos of her findings.
“This research provides a critical understanding of how temperature acts on and above the genes in species where temperature determines sex—this is particularly critical in light of global climate change,” Bieser said.
Here's the video:
The original paper:
Bieser K.L. · Wibbels T. 2014. Chronology, Magnitude and Duration of Expression of Putative Sex-Determining/Differentiation Genes in a Turtle with Temperature-Dependent Sex Determination. Sexual Development 8(6).