Morphological and genetic divergence among Alaskan populations of Brachyramphus murrelets

We studied morphological and mitochondrial DNA (mtDNA) divergence among three populations of Brachyramphus Murrelets: Kittlitz's Murrelets (B. brevirostris), and tree-nesting and ground-nesting Marbled Murrelets (B. marmoratus). We found little morphological divergence in external and skeletal measurements among Marbled Murrelets, but both populations were easily distinguished from Kittlitz's Murrelets. Principal components analysis (PCA) of external measurements showed that Kittlitz's Murrelets occupied a distinct cloud in multivariate space separate from Marbled Murrelets. However, tree-nesting and ground-nesting Marbled Murrelets were indistinguishable. We obtained the same pattern from PCA of skeletal dimensions. Analysis of mtDNA revealed an estimate of sequence divergence of 4.4%-5.0% between Marbled Murrelets and Kittlitz's Murrelets, suggesting a divergence of about 2.2 MYBP. The difference between ground- and tree-nesting murrelets was 0.03%. This analysis suggests little divergence has occurred between tree- and ground-nesting populations of Marbled Murrelets.