Abstract
An accurate inference of the chronological and biological age of
individuals is fundamental to population ecology and our understanding
of ageing itself, its evolution and the biological processes that affect
or even cause ageing. In humans, epigenetic clocks based on the DNA
methylation (DNAm) at selected CpG sites correlate highly with
chronological age. Discrepancies between the inferred epigenetic and
known chronological age predict morbidity and mortality, and therefore
epigenetic clocks are thought to reflect biological age. Recently, a
growing number epigenetic clocks in non-model organisms have been
developed towards a diverse array of purposes in commercial,
conservation and ageing research. Here we review those studies and
conduct the first meta-analysis to assess the effects of different
aspects of experimental protocol on the accuracy of epigenetic clocks
for non-model species. Our analysis reveals higher coefficients of
determination (R2) of chronological age for
epigenetic clocks based on the HorvathMammalMethylChip4, compared to
other DNAm quantification approaches. No dependence of
(R2) was detected for the number of CpG sites
in a clock; the sample size; the number or kind of tissue(s) used; the
class of animals; or whether captive or wild animals were sampled to
infer the epigenetic clocks. We further conclude that epigenetic clocks
can predict chronological age with relatively high accuracy, suggesting
great potential for the field of ecological epigenetics. We therefore
encourage further research on the topic of ecological epigenetics in
relation to ageing and, perhaps more importantly, discuss the potential
of employing DNAm to assess key traits other than age.