Abstract
We evaluate the efficacy of environmental DNA (eDNA) techniques to locate wild populations and estimate the population size of the endangered big-headed turtle (Platysternon megacephalum) in Hong Kong. The results from this study are important for identifying priority sites for protection and further research. Additionally, we assess the impact of two environmental variables (temperature and pH) on eDNA quantity. We surveyed 34 streams for three years, sampling four times each year. Four new populations were first identified with eDNA analysis, and then verified by field surveys. Our multi-year survey highlights that eDNA detection can be inconsistent over time, even in streams with known populations. There was no significant relationship between eDNA quantity and the environmental variables tested. Lastly, our results suggest that eDNA methods remain promising to estimate population size, since number of positive detections were positively correlated with population size in streams with known populations. We conclude that eDNA methods are powerful, but care must be taken when interpreting field results as they are affected by species ecology and environmental conditions.
Highlights
The big-headed turtle (Platysternon megacephalum) is distributed across East and Southeast Asia (China, Thailand, Vietnam, Cambodia, Laos, and Myanmar) [1]
We evaluate the efficacy of environmental DNA techniques to locate wild populations and estimate the population size of the endangered big-headed turtle (Platysternon megacephalum) in Hong Kong
We field tested and validated a species-specific environmental DNA (eDNA) assay to detect and monitor the endangered P. megacephalum: sites with known turtle populations had positive eDNA detection, while new turtle populations were discovered in some streams
Summary
The big-headed turtle (Platysternon megacephalum) is distributed across East and Southeast Asia (China, Thailand, Vietnam, Cambodia, Laos, and Myanmar) [1]. Populations of P. megacephalum across its range have declined drastically due to severe hunting pressure [2,3,4,5]. This decline was highlighted in two studies conducted in South China, where they found only 16 individuals in over 4000 trapping days [6, 7]. This species is currently listed on CITES Appendix I [8] and classified as “Critically Endangered” on the IUCN Red List of Threatened Species [9] with recommendations [10]. Environmental DNA (eDNA) refers to DNA deposited in the environment (such as water, soil, and air) originating from the target species, and eDNA-based techniques provide a tool to assess the presence of a target species
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