When Chum Salmon Meet: Examining a Zone of Secondary Contact in Alaska Using Single Nucleotide Polymorphisms

Changing climatic conditions that fragment habitats can facilitate demographic changes and provide opportunities for adaptation to occur. The climatic changes of the Last Glacial Maximum (LGM) ca 21kyr ago had a large impact on the distribution and evolution of species in North America. The genetic composition of various aquatic vertebrates is thought to retain the signature of the LGM upheavals, as alleles were lost in bottlenecks and founder events, and mutations which conferred selective advantages became prevalent in different populations.

Previous research suggests that the Alaska Peninsula is a zone of secondary contact between two genetically distinct lineages of chum salmon (Oncorhynchus keta) that survived the LGM in separate glacial refugia.   Preliminary evidence suggests that this area is also a hybrid zone: a region in which genetically distinct groups of individuals reproduce, resulting in some offspring of mixed ancestry. Hybrid zones offer a unique opportunity to study selection and differential gene flow in wild populations, enabling us to understand how adaptive genes move across a landscape. We use 171 single nucleotide polymorphisms (SNPs) to address the following questions: (1) Are observed genetic patterns in the contact zone due to hybridization between the two lineages? (2) Do any SNP loci show evidence of selection in either lineage? (3) How does gene flow in loci under selection compare to that of neutral loci in the contact zone?