Talk about egging your siblings on. Baby turtles communicate before hatching to coordinate their arrival into the world.
Australian river turtles (Emydura macquarii) lay eggs in a hole in a sandy riverbank. Eggs at the cooler base of the nest develop more slowly and should hatch later than their warmer brethren at the top, says Ricky-John Spencer at the University of Western Sydney, Australia – but all eggs apparently hatch together.
To confirm this, Spencer took eggs from the same clutch and held half at a low and half at a high temperature for two-thirds of the incubation period. When he reunited the eggs for the final third, the formerly cooler eggs used the time to play catch-up so that all eggs hatched together.
The eggs might communicate using chemical cues, says Spencer. "An egg is actually breathing. It's sucking in oxygen and expiring carbon dioxide," he says. "If you've got a lot of well developed eggs in the nest, there would be more CO2." This build up of CO2 in the nest could trigger under-developed embryonic turtles to increase their metabolic rate.
Doing so makes sense from an evolutionary perspective, adds Spencer. Coordinating hatching times lets the vulnerable young turtles leave the nest in a group, making them less of a target for predators. "If they don't hatch out with their siblings, they'll be sitting ducks," he says.
Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2011.2074
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