Molas have mighty mitochondria: intensified purifying selection on mtDNA despite presumed “low-energy” lifestyles in ocean sunfishes (family Molidae)

Because locomotory capacity has been identified as a driver of evolution in animal mitochondrial genomes (mtDNA), ocean sunfish are expected to show signatures of relaxed selection on mtDNA compared to closely related, more energetic species.

Contrary to expectations, ocean sunfish showed lower <i>d</i>_N/<i>d</i>_S ratios (the ratio of non-synonymous to synonymous substitution rates) in all mitochondrial-encoded genes and further analyses strongly suggest this is due to increased purifying selection on mtDNA within Molidae. Population genetic data also support more intense selection on ocean sunfish mtDNA. These results agree with recent studies recharacterizing ocean sunfish as active swimmers with a complex lifestyle including extreme vertical migrations, behavioral thermoregulation, and extreme fecundity.