Data and code from: A review of cisco form diversity and lake depth

Cisco form diversity overlaps with glacial lake coverage in North America.
A recent hypothesis proposes that secondary contact among refugial cisco
lineages during retreat of the Laurentide Ice Sheet was the basis for the
geography of cisco diversity in North American lakes. Glacial lake
coverage in North America is also a map of Mysis diluviana distribution, a
glacial relic species found in lakes including the Laurentian Great Lakes.
The presence of Mysis increases isotopic niche size of cisco, a necessary
condition for Mysis to be a key element of cisco clade diversification. We
reviewed literature on cisco forms in North American lakes to determine if
cisco diversity is related to an ecological opportunity gradient, maximum
lake depth with the presence of Mysis. Cisco form diversity increases with
lake maximum depth in North America in the presence of Mysis with deeper
lakes increasingly likely to hold multiple forms. Lakes without Mysis had
only one cisco form and were shallower in general. We hypothesize that
Mysis is the basis for the relationship between lake depth and cisco form
diversity because of the complex behavior and distribution of Mysis that
stems from increasing lake depth. We propose the geography of cisco
diversity in North America results from within lake predator–prey
processes as a function of lake depth under the Mysis hypothesis vs.
secondary contact priming genetic diversity. The two hypotheses are not
mutually exclusive. Analysis of a lake set covering both cisco and Mysis
ranges points to more lakes having multiple cisco forms.