Matriarchal population structure of introduced rainbow trout (Oncorhynchus mykiss) in the Lake Ontario watershed

A survey of 761 rainbow trout (Oncorhynchus mykiss) from eight naturalized populations in Lake Ontario revealed that significant differences in genetic architecture have developed among three groups at the lakewide geographic level. Based on maternal Lineage determined by restriction enzyme analysis of mitochondrial DNA, northern (Ontario) populations segregated from both migratory and isolated eastern (New York) populations, which also differed from each other regionally. New York populations were distinguished by lower diversity and by the predominance of one haplotype in fish from migration-accessible streams. Ontario populations had higher, more evenly distributed diversity for both migratory and isolated populations. Haplotype frequency distribution for one Ontario population was dissimilar from that in neighbouring streams colonized earlier. A potential for differentiation was found between local sites within two Ontario streams. Repeated, sporadic introductions from multiple sources and population expansion probably account for high haplotypic diversity in Ontario populations. The lower diversity and distinctive haplotype of New York migratory populations, however, may be a consequence of recent massive stocking, which likely altered the original trajectory of population structuring.