Colonization and local adaptation of sockeye salmon (oncorhynchus nerka) of Lake Clark, Alaska
Dates
Year
2006
Citation
Ramstad, Kristina Marie, 2006, Colonization and local adaptation of sockeye salmon (oncorhynchus nerka) of Lake Clark, Alaska: University of Montana.
Summary
Adaptive divergence is expected among sockeye salmon (Oncorhychus nerka) populations because they spawn in diverse habitats and experience spatially and temporally restricted gene flow. Genetic bottleneck effects are also expected among sockeye salmon populations because they are a highly structured species with excellent colonizing abilities. To test if phenotypic divergence among sockeye salmon populations is due to local adaptation or genetic drift, I compared neutral genetic and heritable phenotypic variation in spawning populations of sockeye salmon throughout the Lake Clark area of Alaska. I assessed nuclear (microsatellites and allozymes) and mitochondrial DNA variation of 15 sockeye salmon populations. Reduced allelic and haplotypic [...]
Summary
Adaptive divergence is expected among sockeye salmon (Oncorhychus nerka) populations because they spawn in diverse habitats and experience spatially and temporally restricted gene flow. Genetic bottleneck effects are also expected among sockeye salmon populations because they are a highly structured species with excellent colonizing abilities. To test if phenotypic divergence among sockeye salmon populations is due to local adaptation or genetic drift, I compared neutral genetic and heritable phenotypic variation in spawning populations of sockeye salmon throughout the Lake Clark area of Alaska. I assessed nuclear (microsatellites and allozymes) and mitochondrial DNA variation of 15 sockeye salmon populations. Reduced allelic and haplotypic diversity and strong divergence of Lake Clark populations relative to Six-mile and Iliamna Lake populations suggest a bottleneck associated with the colonization of Lake Clark by sockeye salmon between 100 and 400 generations ago. The Sucker Bay Lake population had an exceptionally severe reduction in allelic diversity at microsatellite loci but not mtDNA, suggesting this population has experienced consistently smaller effective population size than other Lake Clark populations. Geographic distance and spawning habitat apparently do not contribute to neutral genetic divergence among populations. However, temporal isolation based on spawning time and founder effects associated with ongoing glacial retreat contribute to the genetic population structure of Lake Clark sockeye salmon. Significant phenotypic divergence among spawning populations was associated with spawning habitat differences, but not neutral genetic divergence among populations. For example, female body color was lighter and egg color darker in glacial than non-glacial habitats due possibly to reduced selection for red spawning color in glacial habitats and an apparent trade-off between body and egg color in females. Mean PST (phenotypic divergence among populations) exceeded neutral FST for most phenotypic traits indicating that phenotypic differences among populations could not be explained by genetic drift alone. Plasticity is an unlikely source of phenotypic differences because Lake Clark sockeye salmon spend nearly all their lives in a common environment. These data suggest that Lake Clark sockeye salmon populations are adapted to spawning in beach, tributary, and glacial habitats and provide the first evidence of a glacial spawning phenotype among sockeye salmon.
