Turtles signal hatching from inside their eggs

By Emily Verdouw with AAP 12 December 2011
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Mary River turtles can coordinate hatching by communicating from within the eggs, new research shows.
AUSTRALIAN NATIVE TURTLES ARE communicating to each other while still in their eggs, for the sole purpose of hatching at the same time – a feat previously believed biologically impossible.  
The freshwater turtles from the Murray River were tested by a research team based at the University of Western Sydney (UWS), and it was found that turtles in more advanced stages of development can signal their progress to their less-advanced counterparts.
Previously, turtle development had been linked to changes in temperature. Because the more advanced are found at the top of the clutch, it was supposed that temperature was a signal for development because the further away the eggs are from the cool sand, the higher the surrounding temperature.
“It was so interesting to think that an animal that relies so heavily on its surrounding environment to grow and metabolise, can actually increase development independent of temperature,” she says. 
Dr Ricky Spencer, a zoologist at the University of Western Sydney and Jessica’s supervisor, believes the relative location of the eggs is an evolutionary instinct to give turtles have a better chance of survival post-hatching.
“Those on the bottom are choosing to do something about it… ‘Do I hatch early of do I just develop as normal?'” he says. “Their brothers and sisters are getting out of the nest and attracting predators back to the nest and they’re thinking – in an evolutionary context – ‘If I stay in the egg I’ve got no hope.'” 

Turtle hatchlings communicate to survive 

Honours student Jessica McGlashan monitored the heart rates of turtles in under-developed eggs, comparing them to rates of advanced eggs.
She found that although rates differed at the beginning of testing, by the end, the cooler turtles had increased their heart rates allowing, them to catch up and hatch with the warmer eggs. 
Essentially, what Ricky and Jessica found is that the under-developed eggs are trying to play catch-up in order to survive once they hatch – without the assistance of temperature, as previously thought, but by responding to their neighbours and accelerating their metabolic rates, and therefore their development.
But how remains a mystery.

How turtles communicated in their eggs

Ricky says there are many possible answers, but says because the embryos are breathing, (taking in oxygen and expelling carbon dioxide), it’s possible that if there are more developed eggs in the nest, then “there might be higher carbon dioxide levels… which can increase metabolic rates.”
Jessica is now using her PhD to solve the mystery behind how the eggs are communicating, “whether it’s through heart rates or respiration, carbon dioxide levels in a nest, thyroid levels in yolk during development or from hatching cues,” she says.
The cues could be anything from stronger heart rates of well-developed eggs creating vibrations and signalling to the slower ones to hurry-up, or water levels increasing in the nest and vibration occurring that way.


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