Abstract
Defining units of conservation below the species level is a widely accepted conservation priority, but is especially challenging for widespread taxa that have experienced diverse geographic histories and exist across heterogenous environments. The lake chub (Pisces: Couesius plumbeus) is a widespread freshwater fish in North America and occurs from the southcentral USA to northwestern Alaska and Canada. We used mtDNA sequence analysis to test for divergent lineages predicted to occur as a result of survival of lake chub in distinct glacial refugia. Lake chub consisted of two major mtDNA lineages separated by 3.8% sequence divergence which are probably late to pre-Pleistocene in origin. We combined these data with those consistent with thermal adaptation in fish living in thermal springs versus those living in a lake with wide seasonal temperature variation, and with data on distribution of lake chub in major watershed units. We assessed these data against objective criteria developed to identify conservation units under Canadian endangered species legislation. Our analysis identified twelve major units of conservation within C. plumbeus that could be assessed under Canada’s Species-at-Risk Act. Our study illustrates how different character traits manifested at very different spatial scales can be used to define conservation units within widely-distributed taxa.
Highlights
A basic tenet of conservation biology is the desire to conserve phenotypic and genetic variability within species, and the evolutionary processes that generate such variability, to promote the long-term persistence of species across a geographic mosaic of habitats under environmental change (e.g., [1,2])
We describe the application of the DU concept to lake chub across their distribution in Canada, by (i) applying molecular assays to assess the validity of proposed morphologically-defined subspecies and to test hypotheses about the existence of distinct phylogeographic lineages within the species, their date of evolutionary origins and association with suspected vicariant events, and (ii) applying the COSEWIC criteria for DU recognition by combining the phylogeographic data with the physiological data on temperature tolerance to test for evolutionarily significant subdivisions within the species
Assigning conservation priority to species with broad geographic distributions is challenging because such taxa often comprise multiple, potentially cryptic, evolutionary lineages and divergent selection across variable environments may generate adaptive variation that is important to long-term persistence across a landscape
Summary
A basic tenet of conservation biology is the desire to conserve phenotypic and genetic variability within species, and the evolutionary processes that generate such variability, to promote the long-term persistence of species across a geographic mosaic of habitats under environmental change (e.g., [1,2]). It is possible, that the lake chub consists of three DUs in Canada based on putative subspecies alone. The extensive geographic range of the lake chub in North America suggests that it may consist of several distinct phylogeographic lineages because its range overlaps several known. We describe the application of the DU concept to lake chub across their distribution in Canada, by (i) applying molecular assays to assess the validity of proposed morphologically-defined subspecies and to test hypotheses about the existence of distinct phylogeographic lineages within the species, their date of evolutionary origins and association with suspected vicariant events, and (ii) applying the COSEWIC criteria for DU recognition by combining the phylogeographic data with the physiological data on temperature tolerance to test for evolutionarily significant subdivisions within the species
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