Quantitative genetics of eggshell colouration

Exploring the evolutionary architecture of female sexual traits and their
potential evolvability is important to understand their possible role as
post-mating sexual signals. Egg colouration has been proposed to be one of
these post-mating sexual signals, honestly advertising female quality in
birds, especially in blue-green laying species. In this study, we used an
animal model in a Bayesian framework to estimate the evolvability of
multiple descriptors of blue-green egg colouration and egg size in a wild
long-term monitored population of spotless starlings (Sturnus unicolor).
Our results show low to moderate heritability (h2 = 0.31 – 0.44) for three
egg colour descriptors (blue-green chroma, chroma and lightness) and egg
size. Using the coefficient of additive genetic variance (CVA) and the
evolvability (IA) as proxies of evolutionary potential of all components
of this trait, we found low values of CVA for all these variables,
suggesting a small evolutionary potential of these phenotypic traits,
contrasting to previous results reported in another blue-green egg laying
species. Our results indicate a modest raw genetic material of this trait
on which sexual selection can act upon and, therefore, a small probability
for these traits to respond easily to selection.