Reconciling zoogeography and genetics: Origins of deepwater Cisco Coregonus artedi (sensu lato) in the Great Lakes

Objective: We propose that deepwater Cisco Coregonus artedi (sensu lato) survived Wisconsin ice advances through introgression with shallow-water Cisco similar to 65 ka followed by expression of introgressed genomic fragments after the last retreat of ice from the Great Lakes similar to 15 ka. Methods: We reviewed Wisconsin Glaciation in relation to putative introgression within Cisco and employed a phylogeographic approach to substantiate locations of Cisco refugia and the implications for dispersal of Cisco ahead of the last advance of Wisconsin ice. Result: We showed that deepwater Cisco, in contrast to shallow-water Cisco, were very unlikely to have survived glacial advances and that a massive introgression event between both types likely occurred as the first of two Wisconsin ice advances reached the Great Lakes similar to 65 ka. Conclusion: The most-parsimonious explanation for the distribution of deepwater Cisco involves long-ago introgression as a precursor to its divergence from shallow-water Cisco following the final retreat of Wisconsin ice.