Imagine if temperature were to determine the sex of humans. If your mom wanted a girl, she would have to stay in a warm place during her pregnancy. Congratulations because she hit the jackpot in the Philippines! However, if she wanted a boy, she would have to flee our tropical country to find a cooler place. Global warming would certainly put a damper on the latter. That may not be the case for us, but for sea turtles, this is a reality because of temperature-dependent sex determination.
The sex of developing sea turtles all boils down to temperature. According to the National Oceanic and Atmospheric Administration, the temperature threshold for determining the sex of sea turtles is 81.9 degrees Fahrenheit (27.7 degrees Celsius) which generally means turtles incubated below 81.9 F would hatch as male, whereas turtles incubated above 81.9 F would hatch as female. Temperature-dependent sex determination or TSD is a type of environmental sex determination in which temperatures experienced during embryonic development determine the sex of the offspring.
One prime reason for TSD is the increase of the enzyme aromatase (the enzyme that converts the male hormone testosterone into the female hormone estrogen), which can alter depending on temperature. This is in contrast with humans whose sex is determined by the X and Y sex chromosomes, hence a 50-50 chance of either sex occurring typically. This phenomenon, however, isn’t just limited to sea turtles but can be visible to a variety of other fish and reptiles such as crocodiles, lizards, etc. This allows mothers to control the sex of one’s offspring by laying eggs in cooler or warmer spots depending on whether the population needs more males or females.
Although scientists have yet to be certain why some animals’ sexes are temperature-dependent while others aren’t, a biologist at the National Autonomous University of Mexico claimed in an interview by Live Science in 2021 that temperature-dependent sex determination could stem from the fact that reptiles do not have parental care, unlike mammals. Because of this, their eggs closely interact with the environment around them. According to the NOAA, climate change is responsible for raising the temperatures of nesting sands, as this area is where most turtle eggs incubate. This places these animals at risk of local extinction if there would be too many females and not enough males to reproduce.
However, while the imbalance of males and females could be threatening for sea turtle populations, having more females than males isn’t necessarily unnatural. According to a report from Insider, sea turtle nests that are 90% female aren’t uncommon, since only a few males are needed to fertilize eggs. Nevertheless, males are already outnumbered by around 10 to 1, as the amount of male turtles continuously drops.
But more than affecting the sex of sea turtles, climate change in general causes more storms, which can wipe out thousands of incubating nests in one go, as well as cause rising sea levels that could flood nests and kill the eggs. With this, we can clearly see that climate change has an effect on the future of biodiversity, whether it be having fewer males due to TSD that could lead to poor genetic diversity or the destruction of habitats.
This puts us in a position to be responsible for mitigating climate change. We have to recognize that we not only have the future of sea turtles in our hands but also the rest of the world’s.
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