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 clock use more accessible and widespread in wildlife conservation and management.