Population level mitogenomics of long-lived bats reveals dynamic heteroplasmy and challenges the Free Radical Theory of Ageing.

Bats are the only mammals capable of true, powered flight, which drives an extremely high metabolic rate. The "Free Radical Theory of Ageing" (FTRA) posits that a high metabolic rate causes mitochondrial heteroplasmy and the progressive ageing phenotype. Contrary to this, bats are the longest-lived order of mammals given their small size and high metabolic rate. To investigate if bats exhibit increased mitochondrial heteroplasmy with age, we performed targeted, deep sequencing of mitogenomes and measured point heteroplasmy in wild, long lived Myotis myotis. Blood was sampled from 195 individuals, aged between <1 and at 6+ years old, and whole mitochondria deep-sequenced, with a subset sampled over multiple years. The majority of heteroplasmies were at a low frequency and were transitions. Oxidative mutations were present in only a small number of individuals, suggesting local oxidative stress events. Cohort data showed no significant increase in heteroplasmy with age, while longitudinal data from recaptured individuals showed heteroplasmy is dynamic, and does not increase uniformly over time. We show that bats do not suffer from the predicted, inevitable increase in heteroplasmy as posited by the FRTA, instead heteroplasmy was found to be dynamic, questioning its presumed role as a primary driver of ageing.