It’s getting hot in here: Climate change and sex…determination

When I was 17 and looking at colleges, my parents asked me if I was interested in going to an all-girls school. These schools were known (and still are) for their strong academic reputation. Having grown up with two older brothers though, I was more accustomed to being surrounded by men, so I sought out schools with a higher proportion of men to women.

When I ended up at Carnegie Mellon, with a 60-40 male-female ratio, I thought I had found a community I would feel comfortable in. At the time, though, I didn’t think about what it would be like to go to a school best known for Engineering and Musical Theater. The end result was, yes, more men, but the men were either terrified of women (gasp, you talked to me, was that sex?!?!) or completely not interested (sorry, honey, you’re not a dude).

My husband had the opposite problem going to Sarah Lawrence, a predominantly female school. He imagined it similar to what it was like for a woman at a bar at the end of the night – yeah, you can always go home with someone, but is this really who you want to be going home with?

So let’s just say gender equality in a given population can be useful for creating heterosexual relationships; less pressure and competition for both genders. Of course, this is not only the case for college students, but for other mate-seeking animals as well.

Now there is all sorts of mythology about sex-determination in people. This includes everything from drinking coffee (to stimulate the male sperm!) to cold baths (because girl sperm hate the cold!). As far as I can tell there isn’t much science to this, but in other animals, like some species of lizards, turtles and crocodiles, environment can actually have a strong effect on sex-determination.

If the climate is influencing whether crocodile mommas have little girls or boys, then you bet that climate change could really turn those species upside down.

Let’s take the painted turtles; their offspring’s sex is correlated with summer temperatures (i.e. hotter July equals more girl turtles). As a result, an increase in temperature could eliminate the creation of male offspring all together, leading the world to be overrun with very lonely, really pissed female painted turtles (1). I don’t know about you, but I don’t really want to be swimming around in a pond with a bunch of angry, sexually-deprived lady turtles, do you?

But lest you think that the world will be overrun by little girls, not all species with temperature-dependent sex determination increase the number of females with warmer climate. In fact sometimes, hotter temperature means more male offspring. This is the case for New Zealand’s tuatara, which tend to create more male offspring in a hotter climate.

These lizards are considered living fossils, which means that basically they are the unchanged descendent of lizards that existed 200 million years ago – awesome! The tuatara ancestors were roaming the earth when the earth was one giant super continent – Pangaea – where the weather basically sucked (fluctuating intensely over short periods of time). Because they survived that environment and into our environment, you’d think they were doing something right. But researchers think that the temperature-dependent sex-determination (more boys with warmer temperature) evolved later on in their history. In addition, since previous global climatic changes were much slower than the one we are experiencing now, tuatara had time to evolve as a species to climate shifts back then, whereas now they won’t be able to adapt (2). Basically in the future there will be more boy tuatara, and then there may be no boys or girls or tuatara at all.

So it turns out that your sleazy college roommate was right: the climate you create can really influence the sex you get. In the case of some species of turtles and lizards though, the hotter climate will have a rather cooling effect on their sex life, as it will limit the number and variety of partners they have available to them in the future. As people we should have pity; no matter how sad your sex life is right now, it could be worse. You could be a turtle. Then you might just be doomed.

Minda Berbeco has a PhD in Biology from Tufts University and is a science writer in the Bay area. After reading this article, she thought you might enjoy this delightful video of how the world would be if it were overrun with little girls.

Further Reading:
(1) Climate change and temperature-dependent sex determination in reptiles
(2) Predicting the fate of a living fossil: how will global warming affect sex determination and hatching phenology in tuatara?

3 thoughts on “It’s getting hot in here: Climate change and sex…determination”

  1. Another interesting post about the under-appreciated facts about climate change. I’ll link to this one day next week, probably Wednesday, at SciFact Central.

    I also have some thoughts about this. If the sex balance shifts too far, it will lead to some rather rapid evolutionary changes in the tuatara that favors individuals less influenced by the heat. The surviving females will be the ones most likely to produce eggs that lead to more females. Is anybody studying the genetics of the sex sensitivity to incubation temperature. It would be a difficult but interesting research project.


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