The effect of age and sex on the rate of germline mutations in barn owls

The rate of new mutations is the ultimate source of genetic variation, and thus, a fundamental quantity in evolution. Mutation rates vary across the tree of life, influenced by selection pressures and life-history traits. Within species, mutation rates and types show differences between sexes as well as a positive association with parental age. Most of the direct estimates come from a few mammal species, often primates, and their generality has not been fully realised. Using 33 parent-offspring trios, we investigate the mutation rate in the barn owl (Tyto alba) and show that the species has a mutation rate of 4.96 × 10−9 per site per generation, matching rates of passerine species with a similar generation time of 2-3 years. Using read- and trio-based phasing methods we find that fathers pass on twice as many mutations as mothers and identify subtle differences in the sex-specific spectra of mutations. We also show that the number of mutations increases with paternal age, bringing direct evidence for germline senescence in birds. While across-species mutation rates and types appear conserved, the potential for within species variation due to age is substantial.