Julia Owen-Ramos

UC Davis

“Use of whole genome sequencing to investigate the evolutionary history of island spotted skunks”

Island species have long been considered an important tool for understanding speciation and to investigate forces driving evolution. The Island spotted skunk (Spilogale gracilis amphiala) is an endemic insular carnivore found on two of the California Channel Islands: Santa Rosa Island and Santa Cruz Island. Their morphological similarity to the western spotted skunk (S. gracilis spp.) fueled speculation that they were brought to the Channel Islands since European colonization. However, genetic studies suggest a longer evolutionary history of spotted skunks on the islands. To further investigate the evolutionary history of island spotted skunks, we sequenced whole genomes from Santa Cruz Island, Santa Rosa Island, and the California mainland. Our results support the antiquity of island spotted skunks. We found increased inbreeding in island populations and a distribution of runs of homozygosity (ROH) lengths consistent with a past bottle neck and continuous small population size. We also found that island and mainland populations stopped sharing a demographic trajectory around 20,000 years ago, and the two island populations also show a divergence of roughly 20,000 years ago.

ABSTRACT

The Island spotted skunk (Spilogale gracilis amphiala) is an endemic insular carnivore found on two of the Channel Islands off the coast of southern California. To investigate their evolutionary history on the islands, we sequenced two whole genomes from each island and two from the California mainland. Ultimately, our results show that island populations have likely been separated from one another and from their mainland counterpart for roughly 20,000 years.
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