Quantitative genetic analysis is often fundamental for understanding evolutionary processes in wild populations. Avian populations provide a model system due to the relative ease of inferring relatedness amongst individuals through observation. However, extra-pair paternity (EPP) creates erroneous links within the social pedigree. Previous work has suggested this causes minor underestimation of heritability if paternal misassignment is random and hence not influenced by the trait being studied. Nevertheless, much literature suggests numerous traits are associated with EPP and the accuracy of heritability estimates for such traits remains unexplored. We show analytically how non-random pedigree errors can influence heritability estimates. Then, combining empirical data from a large great tit (Parus major) pedigree with simulations, we assess how heritability estimates derived from social pedigrees change depending on the mode of the relationship between EPP and the focal trait. We show that the magnitude of the underestimation is typically small (<15%). Hence, our analyses suggest that quantitative genetic inference from pedigrees derived from observations of social relationships are relatively robust; our approach also provides a widely-applicable method for assessing the consequences of non-random EPP.

Pedigree DataThe .Rdata file containing two objects. 'ped' contains the full pedigree, with the columns of id (unique individual identity), dam (the mother), dad (the social father), sire (the genetic father), long (longitude position of brood), lat (latitude position of brood), brood (unique ID of the brood the individual was born in), year (the year the individual was born). 'males' contains all the males that could have potentially been the genetic sires of offspring for each year and includes columns of id (unique ID corresponding to the 'ped' dataframe), year (the year this ID could have sired genetic offspring), brood (the brood that this male was identified at this year - also corresponds to 'ped' dataframe), lat (latitude to brood position), long (longitude of brood position). The R script for simulating additional pedigrees using this data but with different parameters is included in the manuscript Supplementary Information.ped_and_males.RData