Australasian Science: Australia's authority on science since 1938

Mother Knows Best

An adult female green turtle returning to the sea after nesting.

An adult female green turtle returning to the sea after nesting. Photo: T. Franciscus Scheelings

By Anthony Rafferty

Why do turtles lay eggs when their close relatives evolved live birth? A study of their reproductive physiology reveals how egg-laying improves the survival prospects of hatchlings.

The full text of this article can be purchased from Informit.

Turtle embryos stop developing inside their eggs at just a few days old – when they are still inside the mother’s reproductive tract. They only start growing again after the eggs are laid.

By careful studies in both freshwater and marine turtles, we have found that this strategy gives turtle mothers the flexibility to choose when and where to lay their eggs for the best chances of survival of their young. What’s more, we have been able to work out how they do it.

The Evolution of Live Birth

There are two main ways to reproduce: by laying eggs or giving birth to live young. Egg-laying is considered an ancestral reproductive mode from which live birth evolved. The transition from egg-laying to live birth requires periods of extended egg retention during which embryos develop to increasingly advanced stages inside the mother.

Live birth is generally associated with mammals, but has evolved in nearly 140 reptile lineages and been documented in various prehistoric aquatic reptiles. In these latter instances, live birth presumably allowed an exclusively aquatic existence, free from the need to lay eggs on land.

Surprisingly, live birth of reptiles has only evolved in lizards and snakes but never in turtles or crocodiles, which is fascinating considering these latter groups live a primarily aquatic lifestyle. So why have these reptiles...

The full text of this article can be purchased from Informit.