Heat waves in Florida, United States, are causing a serious gender imbalance in sea turtle populations.

The increased temperature of the sand is causing almost all the turtles that are born to be female.

“The scary thing is that the last four summers in Florida have been the hottest on record,” Bette Zirkelbach, manager of the Turtle Hospital in the Florida Keys town of Marathon, told Reuters.

In some tortoise populations, 99% of hatchlings are female, she added.

Why temperature is key

The sex of sea turtles is not determined during fertilization, but rather depends on the temperature of the developing eggs.

If the eggs are incubated below 27°C, the hatchlings will be male. If the eggs are incubated above 31 ° C, the hatchlings will be female, the United States National Oceanic and Atmospheric Administration, NOAA, notes on its site.

Temperatures that fluctuate between the two extremes will result in a mixture of male and female baby turtles.

“As Earth experiences climate change, rising temperatures could lead to skewed and even lethal hatching conditions, affecting species of turtles and other reptiles,” adds NOAA.

Jose Luis Crespo, veterinarian, responsible for the Conservation Area of ​​the Fundación Oceanogràfic in Valencia, Spain, told BBC Mundo that “by not depending on genetic differentiation and having the same chromosomes, in the case of sea turtles it is the temperature of incubation for a certain period which influences the activity of certain enzymes”.

“A greater activity of the enzymes involved in the metabolism of sexual hormones activates metabolic pathways that lead to the determination of females. This is a very brief way of explaining it, but in essence that happens, it is mainly influenced by temperature, although it is thought that other aspects such as humidity could also have a lesser influence”.

Also in other parts of the world

The problem of disproportionate birth of female turtles is not limited to Florida beaches.

“Today and due to global warming, it is a widespread problem worldwide, with a feminization of pups born on the main spawning beaches globally,” said Crespo.

“It is a problem that worries scientists and conservationists from all over the planet and on which they are studying, working and proposing tools to counteract its impact.”

A 2018 study in Australia noted that in one of the largest populations of green turtles on the Great Barrier Reef, 99% of hatchlings were female.

In the southern part of the Great Barrier Reef, with cooler waters, one male was born for every two females. But in the northern part, the ratio was one male for every 116 females, according to the study published in the journal Current Biology.

The big question is what will be the long-term consequences of the drastic imbalance between the number of males and females.

“The real impact is unknown, as the female:male ratio needed for a population to be viable is not known, but it is feared that it may compromise the future of tortoise populations, starting with low gene flow and the impact that it is known that it has this for the health of the populations,” Crespo explained to BBC Mundo.

“This is one of the possible explanations given to the colonization process that is being observed in the western Mediterranean where countries like Italy, France and Spain are seeing an increase in turtles that come to nest on their shores when it has never been considered a nesting area.

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