MONASH (AUS) — To give their young the best chance of survival, female turtles have the unique ability to wait to lay their eggs on land when conditions are right.
A new study published in the American Society of Naturalists shows that egg-carrying females have low oxygen levels in their reproductive tracts, or oviducts—conditions that halt embryonic growth at a certain stage. Ova kept at optimal conditions continue to develop normally.
It’s likely the low oxygen environment is actively created by the female and explains how turtles are able to store eggs by halting development until they can lay them safely on land, says Anthony Rafferty, a PhD student at Monash University.
“Surprisingly, live-birth has evolved in over 120 lizard and snake species, but never in closely related crocodile or turtle groups,” Rafferty says. “Until now, the reasons why live-birth has not evolved in these reptile groups were unknown.
“It appears the female actively produces a mucus-like substance inside the reproductive tracts where the eggs are stored, to lower oxygen levels and cause the eggs to stop developing.”
This allows the turtle to select when and where to lay the eggs on land, taking into account access to adequate food sources and a secure environment.
“After an egg is laid the membrane inside the egg connects and so the egg can’t be turned at all or the young will die.
“We think she wants to stop the development of the egg before it reaches that stage because if she was laying the egg, and it turned at all during the laying, it would die if it were at any further stage of development.”
This insight into evolutionary biology has implications for conservation, particularly the preservation of the endangered leatherback turtle because more than half of the eggs laid in each nest never hatch.
“It seems that a lot of the embryos in those nests are failing to restart developing after they are laid, dying at the stage of development that we’re studying,” Rafferty says.
“We think that the trigger to restart development is not occurring in these eggs after they are laid and the embryos subsequently die. Further research will give us a better picture of this.”
Source: Monash University