Does climate change spell doom for sea turtles only because of the way they determine their sex?
Sea turtles may be on their way to extinction because of the mechanism they use to determine their sex. Sea turtles don't use sex chromosomes like we do, but they use the ambient temperature of the sand in which the eggs are deposited by the mother to determine whether the egg will develop as male or as female. When the sand is cooler mostly males will develop, when the sand is warmer mostly females will develop. The temperature range at which the sex determination cascade will switch from male to female really narrow and at the moment, with global warming happening around us, the temperature of the sand is set to female most of the time.
Researchers have now indeed discovered that the ratio of male to female is extremely female-biased in one of the biggest sea turtle populations (Jensen et al. 2018). As the warming did not happen overnight, the adult population still contains quite some males but especially the juvenile and sub-adult populations contain more than 99% females. With the current global warming, the researchers believe that in the near future this population may be completely feminized. It doesn't take long to realize that this means extinction for this turtle population unless they quickly evolve a mechanism to reproduce asexually.