Genetic integrity, diversity, and population structure of the Cascade red fox

The Cascade red fox (CRF) occurred historically throughout subalpine and alpine habitats in the Cascade Range of Washington and southernmost British Columbia, but now appears to be extremely rare. Causes for its apparent decline are unknown, as is the current distribution and connectivity of its populations. Additionally, the introduction of nonnative (fur-farm) red foxes to surrounding lowland areas during the past century raises concerns about their expansion to higher elevations and potential hybridization with the CRF. We conducted noninvasive genetic sampling and analyses of CRFs in a 5575 km2 region in the southern portion of its range, which is thought to contain a significant proportion of the current population. We obtained 154 mitochondrial DNA sequences and microsatellite genotypes for 51 individuals to determine trends in genetic diversity, assess evidence for nonnative introgression, and describe population structure. Although heterozygosity (He = 0.60, SE = 0.03) was only slightly lower than an estimate obtained from samples collected during the 1980s (He = 0.64, SE = 0.05), genetic effective size of the current population based on a one-sample estimate was very small (Ne = 16.0, 95% CI 13.3–19.4), suggesting a loss of genetic diversity and the potential for inbreeding depression in future decades. Genetic connectivity was high and we found no evidence for hybridization with nonnative lowland red foxes. Thus, although a small effective population size indicates the possibility of inbreeding depression and loss of evolutionary potential, high connectivity and genetic integrity could mitigate this to some extent, indicating that the population could respond to conservation efforts. Ultimately, successful conservation of this species depends on a better understanding of the factors that originally contributed to its decline and that currently limit its growth.