Evidence of partial anadromy and resident-form dispersal bias on a fine scale in populations of Oncorhynchus mykiss

We examine sympatric anadromous (steelhead) and nonanadromous (resident) rainbow trout (Oncorhynchus mykiss) from neighboring locations to test three hypotheses: (1) the sympatric life history types are not genetically different; (2) fine-scale dispersal is the same for both sexes, and (3) fine-scale dispersal is the same for steelhead and resident individuals. Data from 13 microsatellite loci reveal no genetic difference between sympatric steelhead and resident O. mykiss but moderate population structure (F-ST=0.019-0.028) between adjacent samples, regardless of life history type. Our results provide further evidence of partial anadromy and suggest that geographic proximity and genetic history, more than migratory type, should be considered when identifying populations for use in restoration of local genetic diversity. We find evidence of resident-form dispersal bias on a fine spatial scale, however, we find no evidence that fine-scale dispersal varies by gender. Conservation strategies should aim to maintain resident and anadromous forms when they occur in sympatry, as they may be important in facilitating gene flow on small and large spatial scales, respectively.