Genetic founder effects and admixture in California's non-native red foxes

Variation at mitochondrial D-loop sequences and microsatellite loci were studied in three sub-populations of recently introduced red foxes (Vulpes vulpes) in California. Red foxes were introduced separately in northern and southern California near the beginning of the 20th century, and have become abundant and widely distributed in recent decades. Strong evidence of population subdivision was found, but this may reflect idiosyncracies of the invasion process rather than a natural biogeographic pattern. All sub-populations showed evidence of deviation from mutation-drift equilibrium. The northernmost and southernmost samples showed genetic signatures of founder effects, while the intermediate location appeared to be an admixture between northern and southern invaders. These results are consistent with the known history of non-native red foxes in California. This study is among the first to explicitly describe the effects of population admixture on heterozygosity and variance of microsatellite repeat number. The results are not unexpected, but highlight the difficulty of interpreting observed deviations from mutation-drift equilibrium in the absence of independent information about population history.