Turtle embryos can speed up their development to hatch together with their siblings

A clutch of a dozen turtle eggs lies buried in the bank of Australia’s Murray River. For the embryos inside, timing is everything. In a few days, they will all hatch together, finding safety in numbers in their vulnerable first moments. But such synchrony isn’t easy. To achieve it, the embryonic turtles need to coordinate the pace of their development, keeping in time with one another even before they experience the outside world. Although all the eggs were laid at the same time, in the same nest, they experience radically different environments. Those at the top of the nest, buried in warmer sun-soaked soil, can be up to six degrees Celsius warmer than those at the bottom. That’s a problem because the embryos develop at different rates depending on how hot they are. Given the gradient of warmth in the nest, the topmost turtles should hatch well before their siblings ...