Effect of shell type on the composition of chelonian eggs

Abstract

This study examined the hypothesis that composition of chelonian eggs, i.e. masses of shell, yolk and albumen, would be influenced by the structure of the eggshell. In particular, because albumen is a store of water in an egg, it was predicted that rigid-shelled eggs would have more albumen than pliable-shelled eggs because they have less scope for absorbing water from the incubation environment. Data were collected from the published literature for 23 chelonian species that exhibited either pliable or rigid-shelled eggs (11 and 12 species in each category, respectively). Linear regression analysis was used to describe relationships between mass of the egg and the three different components. For any given egg mass a rigid shell was heavier than a pliable shell and the exponent for rigid-shelled eggs was significantly higher than that for pliable-shelled eggs. By contrast, there were no significant effects of shell type on the masses of yolk or albumen. The ability of turtle eggs to absorb water during incubation was not, therefore, reflected in the mass of the albumen. Differences in shell structure in chelonians must have evolved for another reason that has yet to be investigated