Population differentiation of inconnu, Stenodus leucichthys, in the Mackenzie River system

In northwestern Canada, populations of inconnu (Stenodus leucichthys ) are anadromous in the lower Mackenzie River region, migrating extensively between coastal feeding areas and upstream spawning sites, whereas populations in the Great Slave Lake area are year-round residents of freshwater.; To test predictions that relate life history characteristics of fish populations to habitat use and migratory behavior, I compared representative populations of freshwater and anadromous inconnu. Life history patterns did not fully conform to model predictions; in particular, growth and fecundity were higher in the freshwater vs. anadromous inconnu. Although some of the differences between populations can be related to differences in migratory distance, departures from expected patterns also appear to be associated with "atypical" characteristics of the freshwater feeding habitats, e.g., relatively high productivity and a longer growing season.; Phenotypic differences I observed between populations can result from differences in genotype, differences in the environment, or some combination of the two. I incubated eggs of freshwater and anadromous inconnu and reared the offspring in a common environment to determine the importance of these two influences on several biologically relevant traits. Rates of egg development and salinity tolerance differed among life history types, whereas juvenile growth rates did not, suggesting that the former two are under a significant degree of genetic control but the latter may be more strongly influenced in the wild by environmental differences.; Molecular genetic relationships (mitochondrial DNA) indicate that inconnu in the Mackenzie River basin originated from the Yukon River system. Geographic isolation and past glacial history appear to have been dominant forces shaping the current patterns of genetic variation of inconnu, with life history pattern having had little influence. Freshwater populations likely arose through multiple, independent divergences from anadromous populations following post-glacial dispersal and establishment in different areas.