Gene flow increases temporal stability of Chinook salmon (Oncorhynchus tshawytscha) populations in the Upper Fraser River, British Columbia, Canada

Abstract

Temporal instability in population genetic structure has significant implications for management and conservation decisions. Here, we evaluate temporal stability in five populations of Chinook salmon ( Oncorhynchus tshawytscha ) from the Upper Fraser River, British Columbia, Canada, based on estimates of temporal allelic variance and effective population size (Ne) at 11 microsatellite loci. Significant temporal variation in allele frequencies was found within individual populations sampled at 5- to 12-year intervals. Removal of migrant fish or correcting for migrants resulted in higher allelic variance or reduced Ne. Populations with higher levels of temporally consistent gene flow show reduced temporal allelic variance (i.e., reduced genetic drift) and higher Ne. This study is an important empirical example of the effect of gene flow on genetic stability and Ne. In salmonids, low straying levels may have evolved to favor local adaptation; however, we show that even such low levels of gene flow can elevate effective population sizes and preserve genetic variability. This study highlights the importance of considering gene flow acting to temporally stabilize populations, particularly small ones, and should migration be interrupted, Nelevels may decline with no obvious change in census population sizes.