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Climate change could leave sea turtles without mates

Sea turtles might be facing an unusual problem: too many girls.

Unlike a human baby, whose X and Y chromosomes determine whether it will be born a boy or a girl, a sea turtle's sex is defined during egg incubation periods. Warmer temperatures lead to a higher proportion of females while cooler conditions result in more males.

A new Florida Atlantic University study published by Endangered Species Research finds that conditions such as heavier rains and temperature shifts are impacting loggerhead sea turtle sex ratios, potentially influencing future reproduction rates for the species.

Over the past four years, study authors Alexandra Lolavar and Jeanette Wyneken examined the nesting beaches for loggerhead turtles in Boca Raton, in south Florida.

"There are several takeaways from this research. The first one is that rising sea levels and changing climates affect more than human cities. In the case of sea turtles, they impact these animals' main resource in that they must nest on beaches, and beaches are vulnerable (to the effects of climate change)," Wyneken, a professor of biological sciences at the university, told CBS News.

Wyneken said that beaches have a temperature that is very specific to turtle incubation - they are cool, but not too cool, essentially. That delicate balance is changing, and she said that these shifts in weather and temperature are "shifting the outcomes of developments in sea turtles."

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The nesting beaches along Florida's coast are important, because they produce the majority of the loggerhead hatchlings entering the northwestern Atlantic Ocean. Florida Atlantic University

"If an animal has this system when the egg is laid in which it is not destined to be male or female, but will instead be directed one way or another by the incubation environment, then that environment is really important," Wyneken said. "If that environment becomes altered too much, then you could be left with too many of one sex and not enough of the other."

Wyneken stressed that what is troubling for the longevity of the species is that the majority of the hatchlings that were sampled were female.

While researchers have long known that a turtle's sex determination is dependent on temperature, Wyneken said that this research gave a clearer sense of just how delicate the balance is between temperature and an even division of the sexes.

Even without climate change factors, survival rates for individual sea turtles are pretty bleak on their own. Only about one in 2,500 to 7,000 infant sea turtles reach adulthood. Those who do make it can live 50 years or more.

For this study, the researchers sampled nests during the 2010 through 2013 nesting seasons. The loggerhead nesting season goes from April through October, and Wyneken and Lolavar broke the season up into three categories -- April to mid-June, mid-June through July, and then August through September.

Female loggerheads between about age 17 to 33 nest at intervals of about two to four years. While the average loggerhead female has about three to six nests in a season and produces roughly 105 eggs per nest, a mother turtle would need to lay eggs over the course of 10 seasons, or nearly 30 years, in order to simply replace herself and potentially one mate.

"These animals have been around for 40 to 60 million years and we know that there have been ice ages and hotter periods and the Earth has gone through its ice house and hot house periods - this has definitely all happened before, but definitely not at the rate that we see now," she said. "There has been resilience in these animals and changes in their biology, so we started to look at the question of, 'Well, OK, temperature is a nice director for sex determination, so what else could modify the sex of the embryos?'"

Wyneken said she and Lolavar examined different weather constraints impacting turtle incubation. They examined local rainfalls and the temperature of the sand, the temperatures of the nests, and then sex ratios for the hatchlings. Wyneken said that she and the team inserted temperature data loggers in the sand during the nesting season at three locations and at three different sand depths to understand how the above sand column would directly impact the eggs.

The results showed some irregularities in typical incubation patterns.

"We would see eggs incubated in hot wet seasons that would yield more males, which is not keeping with the 'hot chicks, cool dudes' model that my students jokingly refer to. We'd be left with - and this sounds accidentally inappropriate - 'hot wet guys,' " Wyneken added. "It basically made us re-think where there's resiliency in these animals, where the mechanisms are? Our paper sets up the question of, 'Well, if we have animals that are resilient to climate change, where is the resilience, where does it come from, what is it?'"

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The majority of hatchlings in the sampling were female, suggesting that across the four seasons most nest temperatures were not sufficiently cool to produce males. Florida Atlantic University

What's next for the research? Wyneken said that a deeper study would involve examining the genetics of the embryos - what genes are "turned on" by temperature changes and which ones are "turned off."

"People are starting to look at embryos as little worlds with their own ecosystem," she said. "That isn't my area of expertise, I myself am focused on the nest conditions, but some of my students and colleagues are trying to get at the genetic mechanisms behind all of this."

Wyneken said that one big-picture impact of this kind of research is that it essentially gives a cute, nonthreatening face to the importance of combating the negative effects of climate change.

"There is this need for a big effort to cut down on our greenhouse gas emissions not just in the U.S. but worldwide," she said. "I mean you have these babies with big brown eyes and big feet and they bring on the cute factor. It certainly has forced me to think about how I make my own footprint on the world."

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