However, recent research from Duke University reveals that those females also have a higher capability for egg production, even before their sex is decided. It is well known that warmer temperatures cause more turtle eggs to hatch into female hatchlings.
This discovery may help to explain why temperature-dependent sex determination is a trait shared by many animals besides turtles and why the system has survived despite first appearing to be a dangerous tactic. It might also provide us with a frightening preview of what a warmer planet can bring.
Higher incubation temperatures were shown to increase the amount of “germ cells”—pre-eggs—that an embryo carries, according to the research findings, which were published in the journal Current Biology on June 23. In fact, they discovered that those germ cells themselves contribute to the embryo’s gender.
“Sex determination by temperature isn’t just one mechanism,” said senior author Blanche Capel, the James B. Duke Distinguished Professor of Cell Biology at the Duke School of Medicine. “Higher temperatures appear to influence sex determination in the embryo through various cell types in incremental ways.”
Boris Tezak, a postdoctoral researcher in the Capel lab who oversaw this investigation, claimed that the more numerous germ cells themselves appear to be the driving force behind feminization. “The temperatures that produce females are also the temperatures that increase germ cell number,” he claimed.
According to Capel, more germ cells are known to regulate the development of fish females. However, scientists took some germ cells out of red-eared slider embryos grown at an intermediate temperature that should have produced a 50-50 split and found more males than expected to demonstrate the argument that more germ cells result in female turtles.
Since it appears to have evolved multiple times in multiple ways, scientists have known about temperature-dependent sex development for decades and have discovered it in numerous locations throughout the Tree of life.
It appeared everywhere, according to Tezak. Why would this system continue if it seemed like such a dangerous tactic, especially in light of weather changes and climate change?
They postulate that this is due to the reproductive advantage that temperature-dependent sex development confers.
“A female that hatches with more germ cells is presumably more reproductively fit—it increases her reproductive potential to carry more eggs,” explained Tezak. We’ve connected the female pathway to the growth of germ cells; if this does make the female more fertile, it would help to explain why temperature-dependent sex development endures.
What will happen to turtles and other temperature-sensitive breeders if the world’s temperatures continue to rise? Tezak stated, “We’ll be examining how further temperature increases will affect the pool of germ cells. Will it result in less athletic females?
Tezak meticulously raises clutches of red-eared slider eggs acquired from a Louisiana breeder in plastic containers filled with moist medium and maintained at a steady temperature in the lab to find the answers to these issues. At 26 degrees Celsius, one incubator produces more males. Another is at 31 degrees, which is the ideal temperature for increasing female reproduction.
The embryo that was incubated warmer is noticeably larger and more active inside the egg when he removes one of each to examine their development under a very strong light.
We’re speculating that there’s a temperature “sweet spot,” according to Capel. There is a little window where you receive a lot of germ cells, and after that, things start to diminish, according to Capel.
We have incubated several eggs at 33.5 degrees, which is just 2.5 degrees above the ideal temperature for females, according to Tezak. It produced several truly abnormal embryos, including cyclops and two-headed ones. Their germ cells haven’t been counted yet.
To continue the temperature trials, the team is also about to receive several alligator eggs. The opposite pattern from the red-eared slider turtle, alligators are known to produce females at low temps and males at high temperatures. Alligators and turtles both produce females at 31 degrees Celsius since the low temperature for alligators and the high temperature for turtles are the same. The intriguing question, according to Tezak, is if both species exhibit an increase in germ cells at this temperature.