Suggested Citation:
Coen, Amanda, Fraser M. Shilling, Andrea Schreier (2016) Pilot Study: Do California Highways Act as Barriers to Gene Flow for Ground-Dwelling Mammals?. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-16-22

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, we studied coyote populations due to their important role as mesopredators and as a model to investigate how four Northern California highways affect gene flow of ground-dwelling mammals. We collected coyote scat samples from opposite sides of a stretch of I-580 and I-680 in the Bay Area and I-80 and SR 50 in the Sierra Nevada foothills. We extracted DNA and genotyped each coyote at 13 microsatellite loci. We estimated genetic diversity and determined how that diversity was partitioned across the landscape in each region.

Genetic diversity among coyotes was high and comparable to other studies. We found little evidence of contemporary genetic structure across highways in the Bay Area or Sierra Nevada foothills. In the Bay Area, two populations were identified but signals of population structure did not correspond to opposite sides of the highways. In the Sierra Nevada foothills, only a single population was identified. There are two alternative explanations for these findings. Our study highways may be permeable to coyote movement due to successful road crossings or use of crossing structures. Alternatively, our study highways may not have existed long enough to produce detectable signals of population structure. Because coyotes are a relatively large bodied, wide-ranging species with high genetic diversity, results from this study may not be generalizable to endangered or small-bodied wildlife.