Pilot Study: Do California Highways Act as Barriers to Gene Flow for Ground-Dwelling Mammals?
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2015-12-01
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Abstract: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 used
coyote 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 US 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 levels in coyotes were high and comparable to other studies. We 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, we 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, we 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 our pilot study are limited by the small number of samples we were
able to genotype completely in the timeframe of this project. We are going to continue
analyzing samples that currently have only partial genotypes and add those to our regional
datasets. Genetic analysis with these larger samples will allow us to better understand the role
of highways in structuring coyote populations in the Bay Area and Sierra Nevada foothills.
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