No evidence for assortative mating in the Atlantic puffin

Assortative mating occurs when individuals with similar phenotypes mate together more often than by chance and can contribute to increases in homozygosity, linkage disequilibrium between loci, and premating isolation in a phenotypically divergent population. While this phenomenon has been well documented in many avian species, evidence is relatively scarce in seabirds. Most seabirds are long-lived, monogamous, and form multi-year pair bonds, so assortative mating is hypothesized to occur if individuals pair early in life and change predictably over time. Furthermore, most seabirds are sexually monomorphic, which may in part result from mutual mate choice on the same traits. In this study, we looked for evidence of assortative mating in Atlantic Puffins across 11 traits: current body condition, structural size (wing length), bill size (depth and culmen length), bill shape (three measures from geometric morphometric analyses), and bill colouration (four regions). Despite a large sample size, we detected only weak support for non-random pairing. Specifically, we found evidence for positive assortative mating on cere colour, but no other trait under investigation. We discuss these results in the context of poorly understood mate choice behaviours in Atlantic Puffins and argue that determining the individual age of these long-lived animals would help resolve many unanswered questions.