Researchers Identify Gene for Temperature-Dependent Sex Determination in Snapping Turtles

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In a paper published in the journal Genetics, scientists from the University of North Dakota and the University of Minnesota present multiple lines of evidence linking a gene called CIRBP to temperature-dependent sex determination in common snapping turtles (Chelydra serpentina).

A common snapping turtle (Chelydra serpentina). Image credit: Dakota L. / CC BY-SA 3.0.

A common snapping turtle (Chelydra serpentina). Image credit: Dakota L. / CC BY-SA 3.0.

In crocodiles, alligators, and certain lizard and turtle species, an embryo can become either a male or a female depending on the temperatures it experiences while in the egg.

Rapid climate change may threaten the future of some of these creatures by skewing the sex ratio.

Scientists are trying to understand how these animals will be affected by and adapt to rising global temperatures.

But little is known about how this temperature-dependent switch between ovaries and testes is regulated.

To look for clues to the molecular mechanisms behind this process, the team investigates how genes influence sex determination in snapping turtles.

The advantage of focusing on this turtle species is that sex is determined in a brief five-day window during the 65-day egg incubation: the temperature-sensitive period.

If the incubation temperature during the temperature-sensitive period is changed from a ‘male-producing temperature’ (79.7 degrees Fahrenheit, or 26.5 degrees Celsius) to a ‘female-producing temperature’ (87.8 degrees Fahrenheit, or 31 degrees Celsius), all the eggs will hatch into females.

In previous study, the scientists found that the CIRBP (cold-inducible RNA-binding protein) gene is activated within 24 hours of such a temperature shift. Two days later, several genes known to be involved in ovary or testes development are either activated or repressed.

In the new study, they confirmed that CIRBP is expressed at the right time (very early in the temperature-sensitive period) and the right place (the gonads) to be involved in specifying sex.

“CIRBP seems to play a crucial role in sex determination,” said study lead author Dr. Turk Rhen, from the University of North Dakota.

“The striking part is that we see a consistent association across multiple levels of biology: the variation at the DNA level influences the gene’s activation, which is in turn correlated with whether an individual turtle becomes male or female.”

“That association with sex holds whether we look at individuals or families, and we even see differences at the population level.”

But CIRBP is not the only gene important for specifying sex in snapping turtles, the data show.

“There is a common misconception that there must be a single ‘magic bullet’ gene that determines sex in response to temperature,” Dr. Rhen said.

“Our data suggests that multiple temperature sensors control sex by acting together. We’re trying to identify the other components of this system and to determine how they interact to influence sex.”

“Better understanding variation at these genes may one day allow us to predict how reptile species will evolve under a new climate regime.”

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Anthony L. Schroeder et al. 2016. A Novel Candidate Gene for Temperature-Dependent Sex Determination in the Common Snapping Turtle. Genetics, vol. 203, no. 1, pp. 557-571; doi: 10.1534/genetics.115.182840