Investigating the Heritability of Egg Traits in Blue Tits (Cyanistes caeruleus)

Abstract

Like most members of the family Paridae blue tits lay white eggs speckled with reddish brown spots. Patterns of these spots vary in every egg, over the period several hypotheses have been proposed to understand the reasoning behind these spots, however very little have been known about mode of heritability and genetic architecture of these maculation spots. In an order to understand genetics behind these spots we studied wild population of blue tits in southwestern Finland. Firstly, we did a scoring test for three traits (distribution, size and intensity) of maculation spots. Then we did variance partitioning of all three maculation traits along with the mass of eggs while examining the effect of age and tarsus size of each female and found individual heritability estimate of each trait. We found out that most of these traits were heritable and we also found out that younger females were laying bigger eggs. In the end by using multivariate model, we found out the genetic correlation between three maculation traits to see if they can evolve independently. We found out that size and intensity of spots have positive correlation, eggs with more intense spots also tend to have bigger sized spots on the other hand distribution of spots didn’t show any such relationship. Overall, our results contribute to understanding the evolution of avian eggshell, however further improvements are necessary in an order to understand the genetic architecture of eggshell spottiness better.