Baby talk: Turtle eggs communicate in the nest

Turtle hatching

Researchers at the University of Western Sydney have eavesdropped on clutches of Australian freshwater turtle eggs to find they 'communicate' with each other to synchronise their development. 

The results of this unique study are reported this week in the prestigious international journal, Proceedings of the Royal Society B, by Dr Ricky Spencer and colleagues in the UWS School of Natural Sciences.

Under carefully controlled conditions in the lab, the UWS team examined the development of clutches of Emydura macquarii (E. macquarii) - a native freshwater turtle found in the Murray River in South East Australia.

Like other reptiles, turtle development within the egg is influenced by external conditions such as temperature. The different temperature zones within the turtle nest should result in different rates of development. Those in warmer sections should develop faster and hatch sooner than those in cooler areas.

Yet, somehow E macquarii pick up on cues from their siblings to synchronise their maturation and emerge from their shells equally developed and at exactly the same time - a feat that appears to be biologically impossible.

The power of synchronicity or coordinated activity in nature is not uncommon. Fish swim in schools as if they are of one mind. Coral spawn en-mass. Birds fly in perfect formation. Often it's for protection and for the E. macquarii hatchlings this is probably true as well.

"Female turtles lay their eggs and then abandon the nest. Without the protection of adult turtles there is a distinct advantage for a coordinated departure from the nest for the young turtles," says Dr Spencer.

"The mass escape from the nest may confuse predators, decrease the chances of individuals being eaten and the combined effort of digging out of the nest is undoubtedly easier than going it alone."

While the benefits of synchronous hatching in the wild are clear it would take clever science in the lab to uncover the mystery buried in the nest. Just how does this little turtle from the Murray beat the laws of biology?

Dr Spencer, fellow UWS researcher Dr Julie Old and UWS PhD candidate Jessica McGlashan divided clutches of E. macquarii eggs and incubated some at 30 degrees Celsius and some at 26 degrees for seven days before reuniting them to complete their development at the same temperature in close proximity in the same 'nest'.

The embryos in the eggs which experienced a period of warmer temperature were - as expected - more developed compared to their 'cooler' siblings at the time they were reunited.

The team then used sophisticated instruments to measure the metabolic rates of the reunited eggs right through to hatching.

A non-intrusive method using infrared transmitters and sensors amplified the cardiovascular signal of an embryo within the egg by 20,000 times. The respiration of the egg was measured by plotting the production of carbon dioxide in a special enclosed monitoring system.

"It was assumed turtles had a very limited capacity to regulate metabolic processes independent of temperature. Increasing metabolic rates and boosting development rates without raising temperatures in the nest was really considered impossible," says Dr Spencer.

"However, our study revealed in the presence of more developed E. macquarii embryos, under-developed embryos do accelerate their heart rates, their metabolic rates and as result their development accelerates to catch up to their siblings in the nest. Just as in the wild, the lab turtles hatched equally developed and at the same time despite only experiencing similar nest conditions for part of the time."

Dr Spencer and his colleagues also monitored the health and behaviour of the newly hatched turtles to detect any penalties for those accelerating their development. There were none. All the hatchlings, regardless of their rate of development, emerged with similar neuromuscular abilities. However, the accelerated turtles did have smaller egg yolks which are thought to be used as an extra source of energy in the first weeks outside the egg.

"Other synchronously hatched animals, including other turtle species, pay a penalty for hatching early. Those animals don't accelerate their development they just hatch early and emerge less developed and presumably more vulnerable," he says.

Now that Dr Spencer and his colleagues have shown the little turtle from the Murray has pushed the limits of biology, the focus turns to understanding just how they do it.

"Turtle nests have ideal conditions for sharing 'information'. The nest is fully enclosed and the eggs are tightly packed. The cues being picked up by the young turtles could hormonal or it could be the higher concentrations of carbon dioxide from more developed embryos triggering a metabolic response in their siblings," says Dr Spencer.

"We don't yet know exactly how they do it, but somehow E. macquarii can control their rate of development - quite independent of external environmental conditions - and this challenges our understanding of reptile biology."



1 December 2011