Postglacial dispersal of freshwater fishes into Ontario

Abstract

The present-day distributions of 117 native freshwater fishes in Ontario have been shaped by processes active following the Wisconsinan glacial period, 80 000–10 000 years before present. During this glacial period, these species survived in unglaciated réfugia. To understand the processes that resulted in the recolonization of Ontario by fishes following the last glacial period, the refugial areas occupied by each species were determined using a refugial index, and glacial water bodies used as dispersal routes were identified. The refugial origins of the Ontario populations of 91 species were resolved. Seventy-two species resided in the Mississippian refugium, 13 species in the Atlantic Coastal refugium, 4 species in dual Atlantic Coastal – Mississippian refugia, 1 species in a Missourian refugium, and 1 species in Atlantic Coastal, Mississippian, and Missourian refugia. These conclusions differed significantly from those of other studies. Five general patterns were identified from the distributions of 104 species. In addition, there are 13 species that do not fit any of the general patterns. Most species with similar distributions in Ontario shared the same refugia and dispersal routes in eastern North America, therefore it is hypothesized that historical processes were important in shaping the present-day distributions of Ontario freshwater fishes.

The Maintenance of Genetic Variation Due to Asymmetric Gene Flow in Dendritic Metapopulations

“…Given the generation times of many organisms and the temporal scales during which drainage arrangements are constant, these equilibria are unlikely to be reached in many systems. For example, the current drainage arrangement within the Laurentian Great Lakes in eastern North America has only existed for about 6,000 years (Fulton 1989;Mandrak and Crossman 1992), and even in nonglaciated landscapes, drainages can change due to processes such as river capture or anthropogenic diversions (Bishop 1995). But, while genetic processes may reach equilibria in few watersheds on these timescales, asymmetric migration may nonetheless lead to elevated levels of diversity.…”

“…Even in the absence of mutation (see fig. A2 in the online edition of the American Naturalist), the erosion of this initial diversity has the potential to be effectively stalled in dendritic landscapes relative to the timescales at which drainage patterns are constant in temperate regions (Fulton 1989;Mandrak and Crossman 1992).…”

Ancient Lake Maxima and Substrate-dependent Riverine Migration Have Defined the Range of the Mudpuppy (<i>Necturus maculosus</i>) in Southern Ontario Following the Wisconsinan Glaciation

“…With the higher-level Nipissing maximum coming in the future, it would be impossible to say with certainty whether the Mudpuppy was in the lakes at this time, because this range-defining maximum would have been erased with the yet-to-come higher Nipissing maximum. However, the Great Lakes Basin had no connection to the Mississippi River system at this time (Mandrak and Crossman 1992a;Clark et al 2012), so feasible dispersal was not possible. Arguments made for the Mudpuppy's entrance into the Great Lakes from the west via ancient Lake Superior are unlikely because the latter was still bound by the Laurentide Ice Sheet at this time.…”

“…During the Wisconsinan glaciation, the Great Lakes region was completely inhospitable to ectotherms, which survived in refugia (Haffer 1969) to the south where more suitable climates prevailed (Mandrak and Crossman 1992a).As the Laurentide Ice Sheet retreated northward and warmer thermal regimes returned to the Great Lakes Basin, these species dispersed northward into suitable environments (Holman 1995). The Mudpuppy would have been one of these species, although unlike other terrestrial herpetofauna, its route of colonization was via waterways only (Hecht and Walters 1955;Mandrak and Crossman 1992a).…”

“…The Mudpuppy would have been one of these species, although unlike other terrestrial herpetofauna, its route of colonization was via waterways only (Hecht and Walters 1955;Mandrak and Crossman 1992a).…”