Population genomic structure of endangered caribou in British Columbia

Wildlife populations in Canada and around the world are increasingly challenged by pressures resulting from human-induced environmental change. Human activity is also rapidly removing or fragmenting habitat, leading to population declines and restricting genetic exchange among populations. Caribou (Rangifer tarandus) are particularly vulnerable to these threats, with recent significant declines in multiple populations across western Canada having led to caribou groups—defined as “Designatable Units” (DUs), comparable to Evolutionarily Significant Units (ESUs)—being listed as endangered, threatened, or of special concern under the Canadian Species at Risk Act. Canadian caribou have been subject to genetic studies aimed at characterizing genetic variation and population structure to help inform species management and conservation decisions. With the rise of new technologies, it is now feasible to bolster previous genetic work with genomic data. Using 766 individuals from 43 currently recognized populations distributed across British Columbia (BC) and trans-provincially, we conducted a study of genetic diversity by examining approximately 75,000 single nucleotide polymorphisms (SNPs) found throughout the caribou genome. We combined individual-based genomic and spatial data to characterize caribou population structure across BC, delineate/clarify DUs, and identify populations/individuals contributing most to local and regional genetic diversity. n this study, we demonstrate that population genetic differentiation in BC caribou does not fully align with the currently recognized DUs (which have been defined in previous caribou assessments based on a combination of genetic, phylogeographic, ecological, and behavioral factors). Based on genomic data, caribou cluster into more genetic groups than the four DUs currently found in BC. This indicates that caribou DUs and management actions in BC could be revised in light of new genomic information to maximize species survival and evolutionary potential. The need to revisit caribou DU delineation also suggests a need to rethink the definition of a caribou DU in the context of populations, metapopulations, and ESUs.