Molecular evolution of mitochondrial coding genes in the oxidative phosphorylation pathway in malacostraca: purifying selection or accelerated evolution?

The mitochondrion is the energy-producing factory of eukaryotic cells, in which oxidative phosphorylation (OXPHOS) is the main pathway for the production of adenosine triphosphate (ATP) by cellular respiration. Because of their vital role in metabolism, mitochondrial proteins are predicted to evolve primarily under constant purifying selection. However, all mitochondrial coding genes of malacostraca had a significantly higher synonymous nt divergence (Ks) in this study. Complex I (NADH dehydrogenase) and complex V (ATP synthase) had a much higher ratio of non-synonymous to synonymous nt divergence (Ka/Ks) and non-synonymous diversity (πNS), whereas complex III (cytochrome bc complex) and complex IV (cytochrome c oxidase) had a significantly lower Ka/Ks and non-synonymous diversity (πNS). The Ka/Ks, πNS, πS, and Ka results revealed that two types of mitochondrial genes, NADH dehydrogenase and ATP synthase, in malacostraca were consistent with accelerated evolution. Furthermore, two other types of mitochondrial genes, cytochrome bc complex and cytochrome c oxidase, were consistent with purifying selection. Generally, the evolutionary pattern of all mitochondrial proteins of the OXPHOS pathway in malacostraca was not entirely consistent with purifying selection.