Origin of the Laurentian Great Lakes fish fauna through upward adaptive radiation cascade prior to the Last Glacial Maximum

Abstract

The evolutionary histories of adaptive radiations can be marked by dramatic demographic fluctuations. However, the demographic histories of ecologically-linked co-diversifying lineages remains understudied. The Laurentian Great Lakes provide a unique system of two lineages that are dispersed across depth gradients with a predator-prey relationship. We show that the North American Coregonus species complex radiated rapidly prior to the Last Glacial Maximum (80–90 ka), a globally warm period, followed by rapid expansion in population size. Similar patterns of demographic expansion were observed in the predator species, Salvelinus namaycush, following a brief time lag, which we hypothesize to be driven by predator prey dynamics. Diversification of prey into deepwater created ecological opportunities for the predators, facilitating their demographic expansion through an upward adaptive radiation cascade. This study provides a new timeline and environmental context for the origin of the Laurentian Great Lakes fish fauna, and firmly establishes this system as drivers of ecological diversification and rapid speciation through cyclical glaciation.

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

“…We note too that the total ice-free period encompasses the 10-kyr interglacial between the Illinoian and Wisconsinan, when GMSLs were higher yet, averaging approximately −10 m. Therefore, Dalton 2022) best (but still low-confidence) estimates of ice margins suggest a 65-kyr uninterrupted period for deepwater Cisco to evolve in the ancestral Great Lakes. The end of this uninterrupted period at 65 ka matches an estimate of when Lake Superior Cisco reached demographic independence (Backenstose et al 2023). At that time, divergence of deepwater Cisco from a common ancestor was associated with the start of the complete destruction of lacustrine habitats.…”

“…We indicated that our scenario of a massive introgression event approximately 65 ka may have followed an unglaciated period lasting about 65 kyr-an even longer time for divergence to develop among Cisco lineages. The existence of a long unglaciated period preceding demographic independence (Backenstose et al 2023) is not critical to our overall hypothesis. The question of how long Cisco lineages can be isolated and still introgress is important though, and the secondary contact data based on neutral markers indicate that it is at least 30 kyr.…”