Abstract
Suruga fundicola, one of the few known deep-dwelling gobies, is found in Japan, South Korea, and China. Owing to the limited availability of specimens, little is known about its mitogenome characterization, phylogenetic relationship, and adaptive evolution. In this study, we sequenced four complete mitogenomes using the DNBSEQ platform and Sanger sequencing. The mitogenomes in length ranged from 17,138 to 17,352 bp, primarily due to the variation in the number of long tandem repeat (LTR) sequences within variable region 3 (VR3). Although the gene composition and arrangement of the S. fundicola mitogenome are largely consistent with those of other gobies, we identified an expansion of the ND2 gene (78 bp), and an unexpected noncoding region (NC, 35 bp) located between the ND2 and tRNA(trp) genes. To further investigate the variation in VR3, we sequenced this region in all nineteen individuals with the Sanger sequencing method. We detected eight distinct LTR types, containing one-three mutation sites, which formed ten different VR3 patterns. Most VR3 patterns (14/19) consisted of a single type of pure LTR, while the remaining five exhibited heterogeneous patterns composed of two different LTRs. Notably, in LTR types T1 and T3, which co-occur in heterogeneous patterns P1 and P9, we found their respective pure patterns (P2-3 and P7). Recombination provides a better, more plausible mechanism for generating the heterogeneity patterns than slipped-strand mispairing, which better explains the homogeneous LTR expansions. These findings provide evidence of recombination in the control region of a vertebrate mitogenome. A phylogenetic analysis confirmed that S. fundicola has a close relationship with Am. hexanema and C. stigmatias. Compared to five shallow-water species of the AcanthogobiusGroup, the deep-dwelling goby S. fundicola was found to be under stronger purifying selection. Within its mitochondrial protein-coding genes (PCGs), ND2 and ND6 genes were subject to stronger purifying selection than the others. Additionally, four genes showed signs of selection sites with high credibility (one in ATP6, ND3, and ND4; eight in ND2). This study provides valuable genomic resources for S. fundicola and enhances our understanding of the phylogenetic relationship, mitogenome recombination, and adaptive evolution of the goby.