Molecular identification of a backcross between a female common murre × thick-billed murre hybrid and a male common murre

Reports of interspecific hybrids that are based on morphological characters are often questioned, but new techniques in molecular genetics permit reliable identification of hybrids as well as sensitive detection of introgression. As part of a larger population survey, morphology, allozymes, and mitochondrial DNA were compared among 239 thick-billed murres (Uria lomvia) from five Atlantic colonies and 143 common murres (Uria aalge) from four Atlantic colonies. One murre possessed the morphology and electrophoretic profile of a common murre, and the mitochondrial cytochrome b genotype of a thick-billed murre. Its genetic constitution suggests that a female thick-billed murre bred with a male common murre, producing a daughter that subsequently bred with a male common murre.