Abstract

Estimation of age in wild cetaceans is pivotal for conservation, enabling understanding of population demographics and survival probability. Handling of at-risk cetaceans can be challenging therefore developing remote sampling tools to assess health status is critical. Epigenetics, specifically DNA methylation, provides this opportunity to develop a remote sampling diagnostic aging tool, utilizing DNA extracted from skin biopsy samples. DNA methylation is the addition of methyl groups to cytosine-phosphate-guanine (CpG) sites and occurs systematically with age; therefore, methylation assessment can provide a chronological age estimate. Additional CpG sites can become methylated due to biological changes and can indicate health status or biological age. We previously established a multi-tissue epigenetic aging clock in 34 U.S. Navy bottlenose dolphins (Tursiops truncatus) identifying 195 CpG sites from 37,491 assessed, associated with chronological aging (R²=0.95).¹

In collaboration with local scientists in Brazil, we are applying this epigenetic clock to the Lahille’s bottlenose dolphin (Tursiops truncatus gephyreus) (Tg) a vulnerable cetacean, found in two geographically isolated subpopulations from Southern Brazil to Argentina.² With only 600 individuals remaining and an estimated 360 capable of reproducing, the population is at high risk of extinction. Remote biopsy skin samples have been collected from 52 Tg dolphins, to enable DNA extraction and application of this newly established bottlenose dolphin aging clock to estimate the individual’s age. Future application to less tractable large cetaceans could expand conservation opportunities. In endangered species, knowledge of population demographics can aid interpretation of biological health data influencing conservation medicine approaches and management decisions.

Acknowledgements

This research was funded by a generous grant from the National Marine Mammal Foundation Board of Directors. The authors thank Len Thomas, Theoni Photopoulou, Enrico Pirotta, Ryan Takeshita and Peter Tyack for their epigenetic clock statistical analysis and support.

The authors also thank Eric Jensen, Mark Xitco, and the U.S. Navy Marine Mammal Program staff for their support; Sam Ridgway and the National Marine Mammal Foundation animal care, medical records experts and veterinary staff who facilitated this study.

Literature Cited

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2.  Genoves RC, Fruet PF, Botta S, Beheregaray LB, Möller LM, Secchi ER. 2020. Fine-scale genetic structure in Lahille’s bottlenose dolphins (Tursiops truncatus gephyreus) is associated with social structure and feeding ecology. Mar Biol 167(3):1–16.