Polymorphisms and divergence among North Pacific albatrosses at multiple loci and application to species conservation

To forestall local and/or global extinctions, documented population declines for North Pacific albatrosses must be met with efficient conservation strategies. Coincident with increasing incidental mortality in fishing operations throughout their vast ranges, black-footed albatross (Phoebastria nigripes) populations endemic to Northwestern Hawaiian and Japanese islands are expected to decline by up to 5% annually. Proactive protection and management of these populations requires knowledge of relevant population parameters such as effective population sizes, rates and directions of gene flow among breeding colonies, and observed levels of standing genetic diversity, as well as knowledge of the degree of isolation among individuals derived from separate breeding colonies. In the present work, DNA sequence data were collected for one mitochondrial and 25 nuclear genes to assess demographic parameters and degrees of genetic introgression within and between two albatross species endemic to the North Pacific: black-footed albatrosses, and their sister species, Laysan albatrosses, (Phoebastria immutabilis). Results indicated significant regional differentiation between Hawaiian and Japanese black-footed albatrosses, extremely low level gene flow between these regions, and that their divergence began ∼400,000 years ago. One hundred black-footed albatross bycatch specimens were assigned to region of origin based on mitochondrial DNA profiles, indicating that both Hawaiian and Japanese regions are affected equally, with bycatch being taken in proportion to census population sizes. Birds from both Hawaii and Japan overlapped in their at-sea distributions. The much smaller Japanese population appears to have retained a large fraction of nuclear genetic diversity, probably due to recency of the severe population decline caused by overharvesting of individuals for the millinery trade of the early twentieth century. Overall gene flow was too low to homogenize populations between geographic regions, but was four times higher from Japan into Hawaii than in the reverse direction. Mitochondrial gene flow was lower than that for nuclear loci, a possible symptom of male-biased dispersal. Unidirectional primary hybridization was documented between female Laysan and male black-footed albatrosses, and appears to have been a feature of their long term evolutionary dynamics, though contemporary backcrossing is constrained and introgression between genomes of these species ceased ∼280,000 years ago.