Abstract
The age, sex, and sexual maturity of individual animals are key parameters in assessing wild populations and informing conservation management strategies. These parameters represent the reproductive potential of a population and can indicate recovery rates or vulnerabilities. Natural populations of wild animals are difficult to study; logistically, economically, and due to the impacts of invasive biomonitoring. Genetic and epigenetic analyses offer a low impact, low cost, and information-rich alternative. As epigenetic mechanisms are intrinsically linked with both biological aging and reproductive processes, DNA methylation can be used as a suitable biomarker for population biology study. This review assesses published research utilizing DNA methylation analysis in relation to three key population parameters: age, sex, and sexual maturity. We review studies on wild vertebrates that investigate epigenetic age relationships, with successful age estimation assays designed for mammals, birds, and fish. For both determination of sex and identification of sexual maturity, very little has been explored regarding DNA methylation-based assays. Related research, however, confirms the links between DNA methylation and these processes. Future development of age estimation assays for underrepresented and key conservation taxa is suggested, as is the experimental development and design of DNA methylation-based assays for both sex and sexual maturity identification, further expanding the genomics toolkit for population biology studies.
Highlights
We are currently experiencing a worldwide environmental crisis, with animal species increasingly threatened by habitat loss, pollution, climate change, and overexploitation (Thomas et al, 2004; Hooper et al, 2012; Darimont et al, 2015; Maxwell et al, 2016; Hammerschlag and Gallagher, 2017; Nabi et al, 2018; Zabel et al, 2019)
We identify recent advances within the discipline and important ecologically focused studies utilizing DNA methylation (DNAm) analysis across three key population biology parameters: age, sex, and attainment of sexual maturity
Contaminant exposure, and tissue type on global DNAm variation in wild reptiles Mercury and aging impacts on DNAm levels in wild reptiles Investigation of age related CpG sites in a marine mammal Development of an age estimation tool for a marine mammal DNAm relationships with age and sexual trait expression in wild birds Age estimation assay for wild apes Age estimation assay for a wild marine mammal
Summary
The age, sex, and sexual maturity of individual animals are key parameters in assessing wild populations and informing conservation management strategies. This review assesses published research utilizing DNA methylation analysis in relation to three key population parameters: age, sex, and sexual maturity. We review studies on wild vertebrates that investigate epigenetic age relationships, with successful age estimation assays designed for mammals, birds, and fish For both determination of sex and identification of sexual maturity, very little has been explored regarding DNA methylation-based assays. Future development of age estimation assays for underrepresented and key conservation taxa is suggested, as is the experimental development and design of DNA methylation-based assays for both sex and sexual maturity identification, further expanding the genomics toolkit for population biology studies
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