How turtles use temperature to figure out their sex

Enlarge / A red-eared slider. (credit: Greg Hume/Wikimedia Commons)

There's a global pandemic happening on a scale that hasn't been seen in roughly a century. So we decided it would be the perfect time to talk about turtle sex. Not turtles having sex, which is undoubtedly an interesting geometry problem, but rather the process by which turtles develop as male or female.

That process is interesting because it seems, at least from our XY chromosomal perspective, to be a bit haphazard: turtles and many other reptiles determine their sex based on ambient temperature. In elevated temperatures, most of the eggs will develop as female; at lower temperatures, most of the eggs will develop as males. We don't really know how they register the temperature and somehow translate it to a complex program of anatomical development. But a new paper in Science fills in some of our gaps.

Sex, of the less interesting sort

If pressed, most of us could remember that human sex determination involves the X and Y chromosomes. But it's often overlooked how things get very complicated downstream of this simple signal. A gene on the Y chromosome turns out to be critical to registering which chromosome combination someone has. A specific tissue interprets the presence or absence of that gene to start a cascade of hormones that reshape how tissues develop and continue to influence things throughout a person's life.

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