Embryos in eggs move to get comfy

Even before hatching, some reptiles and birds can shift toward favorable

SMART BLOB  Embryos may not look as if they can do much, but new tests suggest that a lot of unfinished creatures, such as this unhatched chicken, can regulate their temperatures by moving to warmer or cooler zones of eggs.

Teng Li

The power to cuddle up to warmth or cringe away from overheating may be widespread among reptile and bird embryos still in the egg, researchers say.

Earlier studies found two species of turtle embryos moving toward warmth or away from dangerously high heat (SN: 6/18/11, p. 9). Now tests of 12 diverse species find active repositioning, says ecologist Wei-Guo Du of the Chinese Academy of Sciences in Beijing.

Embryonic Chinese alligators (Alligator sinensis) shifted more than a centimeter toward heating pads, Du and his colleagues report in the March American Naturalist. Embryos of Pekin ducks (Anas platyrhynchosdomestica) repositioned almost a centimeter, and those of three other birds on average shifted a few millimeters. Embryos of three kinds of snakes edged several millimeters toward warmth or several millimeters away from excessive heat. Only the two lizard species the researchers tested failed to budge, as the scientists had predicted for species with small eggs.

The research fuels emerging appreciation of the unhatched. Other studies found that predator vibrations trigger quick-escape hatching in frog embryos (SN: 8/15/09, p. 27). And cuttlefish learn preferences from seeing food from their clear eggs (SN: 8/2/08, p 10). 

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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