Heterozygosity is unrelated to adult fitness measures in a large, noninbred population of great tits (Parus major)

The extent to which heterozygosity-fitness correlations (HFCs) are expected in wild populations is an important and unresolved question in evolutionary biology, because it relates to our understanding of the genetic architecture of fitness. Here, we report a study of HFCs in a wild, noninbred population of great tits (Parus major), based on a sample comprising 281 individuals typed at 26 markers, resulting in a data set comprising over 5600 genotypes. We regressed pedigree-derived f-score and multilocus genetic diversity against eight life-history traits known to be associated with fitness in this population, including lifetime reproductive success (LRS), as well as several morphological traits under weak selection. We found no evidence for either multilocus or single-locus HFCs for any morphological or fitness trait, and further found no evidence that effect sizes were stronger for those life-history traits more closely associated with reproductive fitness. This result may, in part, be explained by the fact that we found no evidence that our set of 26 markers had any power to infer genome-wide heterozygosity in this population and that marker-derived heterozygosity was uncorrelated with pedigree-derived f-score. Overall, these results emphasize the fact that the often-reported strong HFCs detected in small, inbred populations do not reflect a general phenomenon of increasing individual reproductive fitness with increasing heterozygosity.