Analysis of the Complete Mitochondrial Genome of Pteronura brasiliensis and Lontra canadensis

SIMPLE SUMMARY: Mitochondria, the energy metabolism center, provide most of the energy required for life processes through oxidative phosphorylation (OXPHOS). Mitochondrial genomes, a useful type of genetic marker, are widely used in phylogenetics and evolutionary and ecological research. Herein, the full-length mitochondrial genome sequences of two otter species, Pteronura brasiliensis (P. brasiliensis) and Lontra canadensis (L. canadensis), were constructed for the first time. Comparative mitochondrial genome, selection pressure, and phylogenetic independent contrasts (PICs) analyses were employed to unveil the structure and evolutionary characteristics of their mitochondrial genomes. Additionally, phylogenetic analysis confirmed the phylogenetic positions of these otter species. ABSTRACT: P. brasiliensis and L. canadensis are two otter species, which successfully occupied semi-aquatic habitats and diverged from other Mustelidae. Herein, the full-length mitochondrial genome sequences were constructed for these two otter species for the first time. Comparative mitochondrial genome, selection pressure, and phylogenetic independent contrasts (PICs) analyses were conducted to determine the structure and evolutionary characteristics of their mitochondrial genomes. Phylogenetic analyses were also conducted to confirm these two otter species’ phylogenetic position. The results demonstrated that the mitochondrial genome structure of P. brasiliensis and L. canadensis were consistent across Mustelidae. However, selection pressure analyses demonstrated that the evolutionary rates of mitochondrial genome protein-coding genes (PCGs) ND1, ND4, and ND4L were higher in otters than in terrestrial Mustelidae, whereas the evolutionary rates of ND2, ND6, and COX1 were lower in otters. Additionally, PIC analysis demonstrated that the evolutionary rates of ND2, ND4, and ND4L markedly correlated with a niche type. Phylogenetic analysis showed that P. brasiliensis is situated at the base of the evolutionary tree of otters, and then L. canadensis diverged from it. This study suggests a divergent evolutionary pattern of Mustelidae mitochondrial genome PCGs, prompting the otters’ adaptation to semi-aquatic habitats.