They First Ate the Chicken and then the Egg

How did such an amazing animal end up feeding solely on eggs? Alan de Queiroz and Javier Rodriguez-Robles, from University of Nevada, Las Vegas, have analyzed the family tree of four snake species that specialize in eating eggs and found that their ancestors originally ate the lizards that lay the eggs. Only later, did the snakes develop a taste for eggs and eventually lost the ability to catch the lizards.

"Feeding on the eggs of birds or of squamate reptiles (scaled reptiles: lizards and snakes) tends to occur in lineages that already feed on birds or squamates," explain the authors.

The eggs might sometimes have been in the same place as the hunted bird or lizard, but how did the snake figure out that that oval shape nearby was comestible? The authors suggest that it's all down to the fact that these snakes use smell to recognize their prey. They saw the eggs as potential food because the eggs have a similar chemical composition as the animals that lay them.

In other words, the snakes might have not realized at all that they were changing diet. To them the eggs were simply some lizards standing still and easier to catch. Eventually, as they relied more and more on "catching" these easy preys, they lost their original ability to catch the actual lizards (or birds). It's as if their previous diet and their chemical prey identification system predisposed them on becoming egg-eaters.

"The effects of predispositions on the origins of egg-eating and, ultimately, the evolution of highly specialized egg-eating taxa, represent subtle but important historical influences on the present-day attributes of species," conclude the authors.