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

This article focuses on the evolutionary history and survival of deepwater Cisco (Coregonus artedi sensu lato) during the Wisconsin Glaciation, proposing that deepwater Cisco genomes persisted through introgression with shallow-water Cisco around 65,000 years ago (65 ka), with expression of these introgressed genomic fragments occurring after the last ice retreat approximately 15 ka. The authors argue that deepwater Cisco were unlikely to survive glacial advances in their specialized habitats and instead survived via hybridization with shallow-water forms, which were better suited to refugial environments. Phylogeographic and genomic evidence supports multiple refugia in Mississippi River tributaries and secondary contacts facilitating introgression, shaping the current distribution and diversity of Cisco. This hypothesis contrasts with alternatives suggesting either preglacial survival of deepwater Cisco or purely postglacial divergence without introgression, and it has implications for conservation and restoration efforts by highlighting hybridized populations as a natural component of Cisco biology.