The Origin and Invasion Pathway of Brown Rats Rattus norvegicus on Dok-Do Island Revealed by Genome-Wide Markers from 3-RADseq Approach

SIMPLE SUMMARY: Biological invasion on islands poses ecological threats, and understanding invasion pathways can aid in preventing invasive species. Recently, brown rats (Rattus norvegicus) arrived on Dok-do, a remote, small island in the East Sea of Korea. Due to strict regulation on human disturbances, including trapping, we adopted 3-RADseq to compensate for our small sample size and determine the origin of the invading rats. Our genomic analysis will aid in controlling and managing invasive species on this protected island. ABSTRACT: Biological invasions are known to cause local extinctions on islands. Dok-do, a small, remote volcanic island in the East Sea of Korea in the western Pacific, has recently been invaded by rats, posing ecological problems. To infer their origin and invasion pathway, we collected rats from Dok-do and from the potential introduction source locations, Ulleung-do in the Pacific Ocean, and four east coastal ports. First, we identified that the brown rat (Rattus norvegicus) was the only rat species occurring at collecting sites based on the key morphological characteristics. To determine the population-level genetic diversity pattern, we applied the 3-RADseq approach. After a series of filtrations (minor allele frequency < 0.05, Hardy–Weinberg equilibrium p < 1 × 10(−7)), 4042 SNPs were retained for the final dataset from the 25,439 SNPs initially isolated. The spatial structure and genetic diversity pattern of brown rats suggested that the rat population on Dok-do was likely introduced from Ulleung-do. Our work provides practical information that will assist in the management of invasive brown rats in vulnerable island ecosystems.