“In 2003, [Ricky-John Spencer from the University of Western Sydney] collected clutches of wild eggs, split them into two groups, and incubated them at either 25 or 30°C. He reunited the eggs, and found that they still hatched together. Despite the developmental boost that the hotter half received, the colder ones still emerged in time with them. They either accelerated their development, or they hatched prematurely.
“To work out which, Spencer’s student Jessica McGlashan captured pregnant Murray River turtles and allowed them to lay their eggs in a lab. Just as Spencer did previously, she split the clutches into two groups. In some cases, she incubated both groups at 26°C; in others, she incubated one group at 26°C and the other at 30°C. She reunited the eggs a week later and monitored the metabolism of each embryo by measuring how fast its heart was beating, and the amount of carbon dioxide it gave off.
“McGlashan found that the embryos sped up their development if they were incubated with advanced peers, who had enjoyed a week at 30°C. In the weeks before hatching, their heart rates went up and they exhaled 67 per cent more carbon dioxide than turtles whose siblings had all stayed at 26°C.”