Reconciling Zoogeography and Genetics: Origins of Deepwater Cisco Coregonus artedi (sensu lato) in the Great Lakes

Abstract Objective We propose that deepwater Cisco Coregonus artedi (sensu lato ) survived Wisconsin ice advances through introgression with shallow‐water Cisco ~65 ka followed by expression of introgressed genomic fragments after the last retreat of ice from the Great Lakes ~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 ~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.