Mitochondrial genome-based synthesis and timeline of Eurasian otter (Lutra lutra) phylogeography

Eurasian otters (Lutra lutra) have a broad distribution across Eurasia, but biogeographic data outside of western Europe is limited to disconnected pockets. Based on current subspecies designations, Asia appears to harbour a large proportion of the species' diversity, with 10 of 12 Eurasian otter subspecies found in Asia. Here we provide a range-wide synthesis of mitochondrial data, inferring a timeline and pattern of phylogeographic signals. Whole mitochondrial genomes of 27 Eurasian otters across 4 subspecies are presented from newly generated data (n = 6; 4 from Korea, 1 from Hong Kong and 2 from UK), assembled from the Sequence Read Archive (n = 4), and sourced from GenBank (n = 17). We then combined whole mitochondrial genome results with cytochrome b data to increase the sample size and contextualise our results with prior studies. We identified five distinct lineages that were discordant with current subspecies classification. Phylogenetic dating revealed that the earliest diverging lineage was the Japanese lineage, with remaining lineages diverging >= 0.08 million years ago. Mitochondrial diversity calculated by sample locations seemed mainly driven by the presence of multiple lineages. When grouping samples by lineage, genetic diversity was highest in Lineage 1 (primarily found in China and Laos), followed by Lineage 2 (primarily found in Korea), and lowest diversity identified in Lineage 3 (primarily found in Europe). Our findings highlight previously undetected lineage diversity within Eurasian otters, but also the need for further taxonomic and genomic evaluation of the species in Asia. The identified unique, distinct lineages of Eurasian otters also warrant urgent conservation attention.