Sibling competition is stronger in blue tit homozygous broods

It is known that heterozygosity affects mate selection in various taxa. But also beyond mating, in species with parental care, heterozygosity can modulate interactions among family members and their fitness-related decisions. However, to date, this question remains little explored. Here, we studied whether nestling heterozygosity was related to parent-offspring interactions and sib-sib competition in the blue tit, Cyanistes caeruleus, while controlling for the degree of relatedness among nestlings. It has been argued that heterozygosity-fitness correlations are more easily detected under demanding environmental conditions. Thus, we also investigated whether the decision rules of family members according to offspring heterozygosity were affected by brood size, as a proxy of the strength of sibling conflict. First, we found that chick individual heterozygosity was positively although weakly associated with individual body mass. Mean brood heterozygosity did not predict fledging success, b...