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

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.

The Complete Mitochondrial Genome of Chilo infuscatellus (Lepidoptera: Pyralidae), and Related Phylogenetic Analysis

“…PCGsThe A + T content in the PCGs of the C. infuscatellus mitogenome was measured to be 78.38%, which was signi cantly higher than the G + C content (21.62%). Notably, the A + T content at the third codon position was the highest (91.16%) (Table2), which is consistent with other insect mitogenomes(Boore, 1999;Tang et al, 2014;Yang et al, 2021;Kim et al, 2022). GC skewness was lower than AT skewness in 13 PCGs, which was in contrast to the skewness observed in the entire mitogenome.…”

Molecular diagnosis of 5 silkworm strains endemic to South Korea using single-nucleotide polymorphisms selected from whole-genome sequences

“…However, these SNPs were limited to only the 3 endemic strains, namely, SMH, SN7, and SDS. Despite the mitogenome being relatively small (~16.5 kb in insects, including B. mori ) ( Kim et al 2021 , 2022b ), it holds an advantage due to its matrilineal inheritance, necessitating only a quarter of the effective population size compared to nuclear DNA ( Birky et al 1983 , Lukoschek et al 2008 ). As a result, the molecular variation becomes more rapidly fixed within a strain, thus amplifying the possibility of detecting strain-specific SNPs, even given the genome’s smaller size compared to the nuclear genome.…”

“…However, there has been a notable lack of efforts directed toward diagnosing endemic silkworm strains, with the exception of recent study that employed a mitochondrial genome (mitogenome)-based approach ( Park et al 2022a ). In that study, we endeavored to diagnose 5 endemic strains using mitogenome sequences ( Park et al 2022a ), which we derived from prior whole-genome sequences ( Kim et al 2022a , 2022b ). Through this process, we identified a total of 15 single-nucleotide polymorphism (SNP) markers capable of differentiating 3 target strains (SN7, SDS, and SMH) from the rest.…”

“…In this study, we employed SNPs to construct a decision tree for each 5 endemic strains including the 2 strains which did not reveal any SNP in the mitogenome-based study, by drawing the SNPs from a pool of 39 silkworm premium strains which included the 5 endemic strains ( Kim et al 2022b ). The 5 endemic strains were individually distinguished from the 38 nontarget strains by 2 established methods, the tetra-primer amplification refractory mutation system-polymerase chain reaction (tetra-primer ARMS-PCR) and PCR-restriction fragment length polymorphism (PCR-RFLP) methods.…”