Postglacial fish dispersal from the Mississippi refuge to the Mackenzie River basin

Abstract

Wisconsinan glaciation had a profound impact on fish faunas in North America, and deglaciation led to the dispersal of approximately 28 species from the Mississippi glacial refuge into the Mackenzie River basin. A hypothesized dispersal 11 500 years ago via glacial lakes Agassiz and Peace is difficult to verify and hydrologic linkage between these lakes was sporadic and short lived. Geomorphic evidence indicates that glacial Lake Agassiz drained into the Mackenzie basin via the Clearwater River, Saskatchewan, 9900 years ago and created a second opportunity for fish dispersal northward. Fish distribution data indicate a 96% similarity between Mississippi species in the Mackenzie basin and species occupying the former Agassiz-Clearwater corridor. Fifteen species dispersed into the headwaters of the Clearwater River during hydrologic linkage to Lake Agassiz and are now isolated above an 18.5 m waterfall. Previous genetic data suggest lake trout (Salvelinus namaycush) used the Agassiz-Clearwater corridor for two-way dispersal between Beringia and the Great Lakes basin. Lake whitefish (Coregonus clupeaformis) populations of Mississippi origin are distinguished by a marker allele of glucose-3-phosphate dehydrogenase, G3PDH-1*b, that is absent from modern populations within the former Lake Peace region and the distribution of Mississippi whitefish across Canada is best resolved by our Agassiz-Clearwater dispersal hypothesis. Our research substantially alters the interpretation of fish biogeographic patterns in Canada and generates testable hypotheses for future studies.