Do California Highways Act as Barriers to Gene Flow for Ground-Dwelling Mammals?

Roads have the potential to fragment wildlife populations, leading to genetic diversity loss, inbreeding, and increased extinction risk for small, isolated populations. In this study, the authors used coyote as a model to investigate how four Northern California highways affect gene flow of ground-dwelling mammals. The authors collected coyote scat samples from opposite sides of a stretch of I-580 and I-680 in the Bay Area and I-80 and US 50 in the Sierra Nevada foothills. The authors extracted DNA and genotyped each coyote at 13 microsatellite loci. The authors estimated genetic diversity and determined how that diversity was partitioned across the landscape in each region. Genetic diversity levels in coyotes were high and comparable to other studies. The authors found significant genetic structure in both the Bay Area and Sierra Nevada foothills, although it didn’t always correspond to highway presence. In the Bay Area, two populations were identified and although some evidence suggested I-580 was a significant barrier to gene flow, the authors identified migrants across the highway. One of the two populations in the Bay Area contained many second order relatives, suggesting limited gene flow into that population. There was evidence of dispersal out of that population, however. In the Sierra Nevada foothills, the authors identified three populations. Individuals from one population were sampled across highway I-80 suggesting it was not a significant barrier to movement. The most genetically divergent population in the Sierra Nevada foothills was also the most geographically distant and therefore it was difficult to determine whether gene flow into that population was limited by highway presence or simply geographic distance from other populations. The conclusions drawn in their pilot study are limited by the small number of samples they were able to genotype completely in the timeframe of this project. The authors are going to continue analyzing samples that currently have only partial genotypes and add those to their regional datasets. Genetic analysis with these larger samples will allow them to better understand the role of highways in structuring coyote populations in the Bay Area and Sierra Nevada foothills. View the NCST Project Webpage