Phylogeographic Relationships among Bombyx mandarina (Lepidoptera: Bombycidae) Populations and Their Relationships to B. mori Inferred from Mitochondrial Genomes

SIMPLE SUMMARY: Bombyx mandarina (Lepidoptera: Bombycidae), the presumed ancestor of B. mori, has long been a subject of study to illustrate the geographic variation in relationship to origin of B. mori. We report 37 mitochondrial genome (mitogenome) sequences of B. mori strains obtained by whole-genome sequencing and four of B. mandarina individuals obtained by Sanger sequencing from South Korea. These mitogenome sequences were combined with 45 public data to uncover the population genetic and phylogenetic relationships among regional populations of B. mandarina and their relationships to B. mori. A substantial genetic reduction in B. mori strains compared to the B. mandarina was detected, with the highest diversity detected in the Chinese origin B. mori. Chinese B. mandarina were divided into northern and southern groups, largely concordant to the Qinling–Huaihe line, and the northern group was placed as an immediate progenitor of monophyletic B. mori strains in phylogenetic analyses. The enigmatic South Korean population of B. mandarina, which has often been regarded as a closer genetic group to Japan, was most similar to the northern Chinese group, evidencing substantial gene flow between the two regions. This is the first report that the South Korean B. mandarina are closer genetically to the northern Chinese group. ABSTRACT: We report 37 mitochondrial genome (mitogenome) sequences of Bombyx mori strains (Lepidoptera: Bombycidae) and four of B. mandarina individuals, each preserved and collected, respectively, in South Korea. These mitogenome sequences combined with 45 public data showed a substantial genetic reduction in B. mori strains compared to the presumed ancestor B. mandarina, with the highest diversity detected in the Chinese origin B. mori. Chinese B. mandarina were divided into northern and southern groups, concordant to the Qinling–Huaihe line, and the northern group was placed as an immediate progenitor of monophyletic B. mori strains in phylogenetic analyses, as has previously been detected. However, one individual that was in close proximity to the south Qinling–Huaihe line was exceptional, belonging to the northern group. The enigmatic South Korean population of B. mandarina, which has often been regarded as a closer genetic group to Japan, was most similar to the northern Chinese group, evidencing substantial gene flow between the two regions. Although a substantial genetic divergence is present between B. mandarina in southern China and Japan, a highly supported sister relationship between the two regional populations may suggest the potential origin of Japanese B. mandarina from southern China instead of the Korean peninsula.