Allometry of mass and composition in bird eggs: effects of phylogeny and hatchling maturity

This review examines the allometric relationships between initial egg mass and components, i.e. shell, yolk and albumen. The intention was to better understand how egg mass is divided between the different components in a wide variety of bird species. Two hundred and seventy-nine species from 21 Orders are represented in the data set, which details initial egg mass as well as the masses of the shell, yolk and albumen for each species. Linear regression analysis techniques were used to determine allometric relationships between Log transformed values for egg components and initial egg mass. The influence of phylogenetic relatedness and effect of developmental maturity of the hatchlings were investigated using analysis of covariance and comparative analysis by independent contrasts. Both phylogeny and developmental mode have significant effects on egg composition. This analysis shows that with regard to initial mass, egg composition is influenced by both phylogeny and developmental maturity and that single allometric relationships cannot be reliably applied to all bird species. A hypothesis is proposed that states that intra-specific variation in egg composition was important in the evolution of different hatchling maturities.