Contemporary genetic structure of walleye (Sander vitreus) reflects a historical inter-basin river diversion

Abstract

River diversions can have unexpected biological consequences. In the mid-20th century, the upper Ogoki River in northern Ontario was diverted from its original Hudson Bay drainage to flow into the Great Lakes. Although walleye were present in both systems prior to the diversion, the Hudson Bay and Great Lakes watersheds had previously been separated since the early Holocene (7500–8500 years ago). We assessed the effects that this inter-basin diversion has had on the genetic structure of two formerly allopatric populations. We assessed the genetic structure and diversity of walleye in the Ogoki and Little Jackfish river systems and Lake Nipigon (number, distribution, and divergence of identified genetic groups) and quantified the contribution of fish from the historical population (Hudson Bay drainage Ogoki River) and Lake Nipigon to walleye in the Ogoki and Little Jackfish Rivers. Walleye from Ogoki Lake, the Ogoki River diversion through the Little Jackfish River, Lake Nipigon and Nipigon Bay were genotyped at 10 microsatellite loci. Significant genetic differences were detected among sampling locations: walleye from Ogoki Lake, presumably representing fish originally from the historical Ogoki River gene pool, were genetically similar to but statistically distinct from walleye within the diversion. Walleye from sample sites within the diversion and Ombabika Bay appear to form a single genetic group that is largely derived from the Ogoki watershed and differs significantly from walleye in Lake Nipigon and Nipigon Bay. Our findings confirm that the historical river diversion has had long-term effects on the genetic composition of contemporary walleye populations.