An epigenetic aging clock in butterflies

In studies of aging in mammals it has become evident that epigenetic markers can accurately predict age. Using machine learning methods, molecular clocks can be constructed based on DNA methylation patterns. Much less is known about epigenetic aging in other animals, such as insects, but it is possible that most animals show signals of epigenetic aging. The prospect of measuring age using epigenetic markers is exciting not only for understanding the molecular processes of aging but also because it allows for previously infeasible ecological inferences, such as movement across time and space. Here, we present the first epigenetic clock in Lepidoptera, estimated for the painted lady butterfly (Vanessa cardui). We show that DNA methylation levels can be used to predict chronological age with adult lifespans measured in days rather than years. We show that the clock is accurate for laboratory-raised butterflies and can be used for reasonable age predictions of wild butterflies. This, in turn, allows for ecological inferences, such as daily flight distances during the trans-Saharan migrations undertaken by this migratory species, which we estimate to range from 187 to 796 km per day. Our findings provide a first blueprint for how molecular aging tools can advance the study of insect behavioral ecology.