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The tortoise and the tortoise

This week's paper is "Embryonic communication in the nest: metabolic responses of reptilian embryos to developmental rates of siblings", published in Proceedings of the Royal Society by Jessica McGlashan and others.

Turtle eggs deeper in a nest are exposed to lower temperatures. Since they don't regulate their own temperature and since the rate of development depends on temperature, you might expect these eggs to hatch later than those above them. If their older siblings leave first, that could reveal the location of the nest to hungry predators. Some turtle species have solved this problem -- all the turtles emerge together, in contrast to what would be predicted by differences in temperatures to which they were exposed.

The authors of this paper tested the hypothesis that some form of communication between eggs is involved. They exposed eggs to different temperatures, to get different stages of development, then mixed them to see whether the less-advanced eggs accelerated their development when mixed with more-developed eggs.

Mixing with more-developed eggs led to higher respiration rates and heart rates, both of which were measured noninvasively. You might expect that accelerating hatching would lead to problems, but apparently not: the baby turtles were just as good at righting themselves after being turned over.

It would be interesting to compare the question of synchronous emergence in turtles versus germinating seeds. A group of seeds might mostly come from the same mother plant. So, like turtles, they would have fairly high genetic relatedness, which would tend to promote cooperation. But a seed that germinates a little sooner than its neighbors may end up shading them all season. What about turtles? The last turtle to reach the water may have the highest risk of predation, but the first one isn't necessarily safer than those in the middle. Adult trees may benefit from synchronizing their seed production, for predator-saturation reasons similar to those that apply to turtles. But for seed germination, the benefits of being first may outweigh any benefits of synchrony.

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