Temporal variation in phenotypic and genotypic traits in two sockeye salmon populations, Tustumena Lake, Alaska

Sockeye salmon Oncorhynchus nerka in two tributary streams (about 20 km apa rt) of the same lake were compared for temporal variation in phenotypic (le ngth, depth adjusted for length) and genotypic (six microsatellite loci) tr aits. Peak run time (July 16 versus 11 August) and run duration (43 versus 26 d) differed between streams. Populations were sampled twice, including a n overlapping point in time. Divergence at microsatellite loci followed a t emporal dine: population sample groups collected at the same time were not different (F-ST = 0), whereas those most separated in time were different ( F-ST = 0.011, P = 0.001). Although contemporaneous sample groups did not di ffer significantly in microsatellite genotypes (F-ST = 0), phenotypic trait s did differ significantly (MANOVA, P < 0.001). Fish from the larger stream were larger; fish from the smaller stream were smaller, suggesting differe ntial fitness related to size. Results indicate run time differences among and within sockeye salmon populations may strongly influence levels of gene flow.