Influence of life-history traits on mitochondrial DNA substitution rates exceeds that of metabolic rates in teleost fishes

Understanding the molecular relevance of metabolic rate is crucial for unveiling the mechanisms driving the evolution of animals. In this study, we investigated the association between mitochondrial DNA characteristics and both resting and maximal metabolic rates in conjunction with life-history traits among 139 species of teleost fish. We gathered fish MR data from various sources and procured sequences of 13 mitochondrial protein-encoding genes. We calculated the absolute substitution rate for entire nucleotide sequences and four-fold degenerate sites of each gene, along with encoding amino acid sequences. Using the phylogenetic comparative method, we then explored the associations between metabolic rate and mitochondrial DNA absolute substitution rate. Additionally, we screened metabolic rate-associated single nucleotide variants in mitochondrial DNA. The findings indicate no positive correlation between metabolic rates and any substitution rate values of both combined sequences and individual mitochondrial protein-coding genes, refuting the metabolic rate hypothesis. Instead, both maximum body size and longevity correlated negatively with molecular substitution rates, suggesting their influences on both mutation and fixation within mitochondrial genes in fish. Results also revealed significant correlations between base variation at ATP6_169 and both resting metabolic rate and maximum metabolic rate, identifying the unique ATP6_169G in Scombridae fish, which results in an extremely low pI value of the ATP6 protein. Considering its functional significance, the ATP6_169G in Scombridae fish might link to their lifestyle characterized by fast locomotion and high metabolic demands alongside a slower molecular evolutionary rate.