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Turtle embryos move inside their eggs to the coolest spots

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A July day in Arizona can get on the warm side



Having recently moved to Arizona, I’m starting to appreciate the need to stay cool for the first time in my life. Here, people employ all kinds of strategies to stay cool. As well as the ones I’ve previously encountered, I’ve now seen people carrying umbrellas when it’s not raining, having wet towels slung around their necks, and crossing the street multiple times to keep in the shade.



This cat may be trying to cool down with this wet towel, but as an endotherm it doesn't have too much to worry about

We can do things to help our bodies cool down or warm up, but for us endotherms (‘warm-blooded’ animals), our bodies do the majority of the work for us. However, ectotherms (‘cool-blooded’ animals) do not control their body temperature internally, and instead have to move themselves around, either into the sun to heat up for the day, or into the shade to cool their body down.




I love this David Attenborough clip showing how marine iguanas in the Galapagos heat up their bodies


The emydid turtle, chinemys reevesii

One thing I had certainly never thought about was whether animals might actively do anything before they are born or hatch to regulate their temperature. One recent study looked at just this. They showed that that embryos of the emydid turtle actually move inside their eggs to the area with the best temperature. To show this, the scientists altered the temperature around some eggs to see what would happen. As they turned up the heat to 29 and 30 °C, the embryo first moved towards it. However, once it reached dangerously high levels (33 °C), then the embryo moved away from it. As a control, the scientists also tested eggs where the embryos were dead: they did not move. This shows that it’s an active mechanism by the animal, and not simply a passive process of fluid movement within the egg.

One interesting possible implication from this finding is for sex-determination, which is determined by temperature in this turtle. This means that individual embryos could have some control over the sex they are at hatching.




Zhao B, Li T, Shine R, Du W-G. 2013 Turtle embryos move to optimal thermal environments within the egg. Biol Lett 9: 20130337.


Photo Credits

Arizona heat: Alan Levine

Cool cat: brianfagan

turtle: Denise Chan

Felicity Muth About the Author: Felicity Muth is an early-career researcher with a PhD in animal cognition. Follow on Twitter @notbadscience.

The views expressed are those of the author and are not necessarily those of Scientific American.

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