Designing epigenetic clocks for wildlife research

The potential applications of epigenetic clocks are expanding in wildlife
conservation and management. The pace at which they are being adopted
highlights the need for field-specific design best practices. Epigenetic
clocks were originally developed for human studies, presenting challenges
for their adoption in wildlife research. Most notably, the estimated ages
of sampled wildlife can be unreliable, and sampling restrictions limit the
number and variety of available samples, which can reduce the accuracy of
epigenetic clocks for wildlife. In this article, we present a detailed
workflow for designing, validating, and applying wildlife epigenetic
clocks in a way that accounts for sampling constraints. We provide
recommendations for two main applications of wildlife epigenetic clocks:
estimating unknown ages and assessing cumulative biological aging. Our
simulations and analyses, applied to an extensive polar bear dataset from
across the Canadian Arctic, demonstrate that accurate epigenetic clocks
for wildlife can be constructed and validated with limited samples,
accommodating projects with small budgets and sampling constraints. With
our workflow and examples, we hope to make epigenetic clocks more
accessible and widespread in wildlife conservation and management.