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DNA methylation data facilitate the development of accurate molecular estimators of chronological age or epigenetic clocks. We present a robust epigenetic clock for the beluga whale, Delphinapterus leucas, developed for an endangered population in Cook Inlet, Alaska, USA. We used a custom methylation array to measure methylation levels at 37,491 cytosine-guanine sites (CpGs) from skin samples of dead whales (n = 67) whose chronological ages were estimated based on tooth growth layer groups. Using these calibration data, a penalized regression model selected 23 CpGs, providing an R 2 = 0.92 for the training data; and an R 2 = 0.74 and median absolute age error = 2.9 years for the leave one out cross-validation. We applied the epigenetic clock to an independent dataset of 38 skin samples collected with a biopsy dart from living whales between 2016 and 2018. Age estimates ranged from 11 to 27 years. We also report sex correlations in CpG data and describe an approach of identifying the sex of an animal using DNA methylation. The epigenetic estimators of age and sex presented here have broad applications for conservation and management of Cook Inlet beluga whales and potentially other cetaceans.

Bessey et al. present a method of passive eDNA collection from marine aquatic systems. This approach enables lower cost, high throughput sampling of aquatic environments and demonstrably collects high levels of eDNA for biodiversity studies.

Global biodiversity is declining at an ever-increasing rate. Yet effective policies to mitigate or reverse these declines require ecosystem condition data that are rarely available. Morphology-based bioassessment methods are difficult to scale, limited in scope, suffer prohibitive costs, require skilled taxonomists, and can be applied inconsistently between practitioners. Environmental DNA (eDNA) metabarcoding offers a powerful, reproducible and scalable solution that can survey across the tree-oflife with relatively low cost and minimal expertise for sample collection. However, there remains a need to condense the complex, multidimensional community information into simple, interpretable metrics of ecological health for environmental management purposes. We developed a riverine taxon-independent community index (TICI) that objectively assigns indicator values to amplicon sequence variants (ASVs), and significantly improves the statistical power and utility of eDNA-based bioassessments. The TICI model training step uses the Chessman iterative learning algorithm to assign health indicator scores to a large number of ASVs that are commonly encountered across a wide geographic range. New sites can then be evaluated for ecological health by averaging the indicator value of the ASVs present at the site. We trained a TICI model on an eDNA dataset from 53 well-studied riverine monitoring sites across New Zealand, each sampled with a high level of biological replication (nD16). Eight shortamplicon metabarcoding assays were used to generate data from a broad taxonomic range, including bacteria, microeukaryotes, fungi, plants, and animals. Site-specific TICI scores were strongly correlated with historical stream condition scores from macroinvertebrate assessments (macroinvertebrate community index or MCI; R² = 0:82), and TICI variation between sample replicates was minimal (CV = 0.013). Taken together, this demonstrates the potential for taxon-independent eDNA analysis to provide a reliable, robust and low-cost assessment of ecological health that is accessible to environmental managers, decision makers, and the wider community. [ABSTRACT FROM AUTHOR]

The Sahara desert is the largest warm desert in the world and a poorly explored area. Small water-bodies occur across the desert and are crucial habitats for vertebrate biodiversity. Environmental DNA (eDNA) is a powerful tool for species detection and is being increasingly used to conduct biodiversity assessments. However, there are a number of difficulties with sampling eDNA from such turbid water-bodies and it is often not feasible to rely on electrical tools in remote desert environments. We trialled a manually powered filtering method in Mauritania, using pre-filtration to circumvent problems posed by turbid water in remote arid areas. From nine vertebrate species expected in the water-bodies, four were detected visually, two via metabarcoding, and one via both methods. Difficulties filtering turbid water led to severe constraints, limiting the sampling protocol to only one sampling point per study site, which alone may largely explain why many of the expected vertebrate species were not detected. The amplification of human DNA using general vertebrate primers is also likely to have contributed to the low number of taxa identified. Here we highlight a number of challenges that need to be overcome to successfully conduct metabarcoding eDNA studies for vertebrates in desert environments in Africa.Key words: eDNA, spike, Mauritania, vertebrate, turbid, desert, biodiversity.Le desert du Sahara est le plus chaud au monde et constitue une region peu exploree. De petits plans d'eau sont presents dans le desert et sont des habitats cruciaux pour la biodiversite des vertebres. L'ADN environnemental (ADNe) est un outil puissant pour la detection des especes et il est de plus en plus employe pour realiser des mesures de la biodiversite. Cependant, il existe plusieurs difficultes liees a l'echantillonnage de l' ADNe au sein de tels plans d'eau troubles et il est souvent impossible d'avoir recours a des outils electriques dans des environnements desertiques isoles. Les auteurs ont mis a l'essai une methode de filtration manuelle en Mauritanie et ont fait appel a une pre-filtration pour contourner les problemes lies a l'eau trouble dans les regions arides eloignees. Des neuf especes de vertebres attendues au sein des plans d'eau, quatre ont ete detectees visuellement, deux via meta-codage a barres et une via les deux approches. Des difficultes liees a la filtration de l'eau trouble ont entraine de nombreuses contraintes, limitant le protocole d'echantillonnage a un seul par site ce qui peut expliquer que plusieurs des especes attendues n'aient pas ete detectees. L'amplification d'ADN humain a l'aide d'amorces generiques pour vertebres pourrait aussi avoir contribue au faible nombre de taxons identifies. Dans ce travail, les auteurs soulignent plusieurs defis qu'il faudra surmonter pour realiser avec succes des etudes de meta-codage a barres de l' ADNe chez les vertebres dans les environnements desertiques de l'Afrique. [Traduit par la Redaction]Mots-cles: ADNe, doper, Mauritanie, vertebre, trouble, desert, biodiversite., IntroductionKnowledge on species distribution is essential in many fields of biology, and the identification of areas with high species richness is crucial to protect global and regional hotspots of biodiversity [...]

Animal age data are valuable for management of wildlife populations. Yet, for most species, there is no practical method for determining the age of unknown individuals. However, epigenetic clocks, a molecular‐based method, are capable of age prediction by sampling specific tissue types and measuring DNA methylation levels at specific loci. Developing an epigenetic clock requires a large number of samples from animals of known ages. For most species, there are no individuals whose exact ages are known, making epigenetic clock calibration inaccurate or impossible. For many epigenetic clocks, calibration samples with inaccurate age estimates introduce a degree of error to epigenetic clock calibration. In this study, we investigated how much error in the training data set of an epigenetic clock can be tolerated before it resulted in an unacceptable increase in error for age prediction. Using four publicly available data sets, we artificially increased the training data age error by iterations of 1% and then tested the model against an independent set of known ages. A small effect size increase (Cohen's d >0.2) was detected when the error in age was higher than 22%. The effect size increased linearly with age error. This threshold was independent of sample size. Downstream applications for age data may have a more important role in deciding how much error can be tolerated for age prediction. If highly precise age estimates are required, then it may be futile to embark on the development of an epigenetic clock when there is no accurately aged calibration population to work with. However, for other problems, such as determining the relative age order of pairs of individuals, a lower‐quality calibration data set may be adequate. [ABSTRACT FROM AUTHOR]