Nile crocodile (Crocodylus niloticus) : egg mass relative to egg component mass in unbanded and fertile eggs

Abstract

Crocodylus niloticus eggs are a useful starting point to study reproduction in this species. Using samples collected from a single farm during a single breeding season, the present research aimed to describe and compare the masses of unbanded and fertile eggs and their components. The clustering effect of clutch on egg and egg component mass was investigated, and the relationship between the mass of unbanded eggs and their components, together with the effect of possible confounding variables was explored.

Estimated egg volume (ellipsoid volume) was strongly positively correlated with egg mass. A strong positive linear relationship existed between egg mass and the combined mass of the foetus and intra-abdominal yolk, as well as between egg mass and the isolated yolk-free foetal mass. If egg mass and incubation period were kept constant, foetal mass increased by 1.1 g for each gram that yolk decreased. The wet yolk and dried shell masses of fertile eggs were significantly lower than those of size-matched unbanded eggs. Clutch had a strong clustering effect on all component masses, particularly total egg mass and hatchling mass. Unbanded egg mass and its individual component masses tended to be similar within a clutch, however some variability existed which should not be discounted.

The mass of an egg was strongly positively linearly correlated with the mass of each of its components.

The period within the laying season an egg was laid had no effect on its mass nor the mass of any of its components, whereas the breeding pond in which the female resided did affect these measurements.

The strong clustering effect of clutch on total egg mass and the masses of all egg components must be accounted for when selecting samples for future studies. The potential confounding effect of breeding pond of origin (which related to female size in the current study) should be considered, particularly where the age or size of females differ among ponds.