Spatial genetic structure and asymmetrical gene flow within the Pacific walrus
Return to Arctic Science for Decisions Home
Full Publication: http://www.asmjournals.org/doi/abs/10.1644/11-MAMM-A-344.1Product Type: Journal Article
Year: 2012
Authors: Sonsthagen, S. A., C. V. Jay, A. S. Fischbach, G. K. Sage, and S. L. Talbot
Suggested Citation:
Sonsthagen, S. A., C. V. Jay, A. S. Fischbach, G. K. Sage, and S. L. Talbot. 2012. Spatial genetic structure and asymmetrical gene flow within the Pacific walrus. Journal of Mammalogy 93(6):1512-1524. doi:10.1644/11-MAMM-A-344.1
Abstract
Pacific walruses (Odobenus rosmarus divergens) occupying shelf waters of Pacific Arctic seas migrate during spring and summer from 3 breeding areas in the Bering Sea to form sexually segregated nonbreeding aggregations. We assessed genetic relationships among 2 putative breeding populations and 6 nonbreeding aggregations. Analyses of mitochondrial DNA (mtDNA) control region sequence data suggest that males are distinct among breeding populations (φ ST = 0.051), and between the eastern Chukchi and other nonbreeding aggregations (φ ST = 0.336–0.449). Nonbreeding female aggregations were genetically distinct across marker types (microsatellite FST = 0.019; mtDNA φ ST = 0.313), as was eastern Chukchi and all other nonbreeding aggregations (microsatellite FST = 0.019–0.035; mtDNA φ ST = 0.386–0.389). Gene flow estimates are asymmetrical from St. Lawrence Island into the southeastern Bering breeding population for both sexes. Partitioning of haplotype frequencies among breeding populations suggests that individuals exhibit some degree of philopatry, although weak. High levels of genetic differentiation among eastern Chukchi and all other nonbreeding aggregations, but considerably lower genetic differentiation between breeding populations, suggest that at least 1 genetically distinct breeding population remained unsampled. Limited genetic structure at microsatellite loci between assayed breeding areas can emerge from several processes, including male-mediated gene flow, or population admixture following a decrease in census size (i.e., due to commercial harvest during 1880–1950s) and subsequent recovery. Nevertheless, high levels of genetic diversity in the Pacific walrus, which withstood prolonged decreases in census numbers with little impact on neutral genetic diversity, may reflect resiliency in the face of past environmental challenges.
Keywords: Pacific walrus, gene flow, genetic structure, climate change, environmental stressors
Annotation
Current climate change predictions suggest that walruses will likely encounter increased levels of anthropogenic and environmental stressors associated with the loss of Arctic sea ice. Connectivity among populations is likely an important component for the maintenance of genetic diversity and the ability of marine mammals to withstand periods of reduced census population size. A greater understanding of historical structuring of diversity in ice-associated marine species is essential for predicting the future response and persistence of species to changing Arctic ecosystems. High levels of genetic diversity in the Pacific walrus, which withstood prolonged decreases in census numbers with little impact on neutral genetic diversity, may reflect resiliency in the face of past environmental challenges.