An Investigation of the Variations in Complete Mitochondrial Genomes of Lingula anatina in the Western Pacific Region.

Lingula anatina is a brachiopod widely distributed in the western Pacific region. Even though L. anatina has been targeted for a number of biological studies, there is still limited information on intraspecific genetic variations of L. anatina. In this study, L. anatina specimens were collected from Korea and Vietnam, and complete mitochondrial genome (mitogenome) sequences were analyzed and compared with previous records. The total mitogenomes of L. anatina were 24,875 bp and 25,305 bp in size for Korean and Vietnamese specimens, respectively. Those mitogenomes are extraordinarily longer than the typical mitogenome size for an animal but shorter than the previous record from Yanagawa (Japan) for this species. The gene orders and the sizes of the protein-coding genes are also different from those for the Japanese specimen. Furthermore, the nonsynonymous (Ka) and synonymous (Ks) substitution rates in protein-coding genes (PCGs) were calculated to test the idea of evolutionary rate differences in mitochondrial genomes. The analyses showed relatively low Ka and Ks for the complete mitogenomes from Buan (Korea), Doson (Vietnam) and Yanagawa (Japan). The Ka/Ks ratio was less than 1 in comparisons of three localities, indicating the existence of purifying selection in this species. The phylogenetic analyses showed that L. anatina diverged among localities in the western Pacific region.