eDNA for turtle conservation

Environmental DNA (eDNA) allows us to detect the presence of organisms without direct observation. Plants and animals shed cellular material in their surrounding environment, and this material can be collected and analyzed. Traces of DNA extracted from environmental samples can be used to determine if a target species has been in the vicinity of a sampling site. 

Surveys based on eDNA sampling have potential for applied conservation through detection of rare or cryptic species that may be overlooked with traditional survey methods. Species of conservation concern often fall into this category due to low population numbers, and eDNA surveys have facilitated detection of a range of threatened taxa.

According to the IUCN turtles are in serious trouble. They are among the world’s most endangered vertebrates, with about half of their more than 300 species threatened with extinction. They are being collected, traded, and eaten or used for food, as pets,in  traditional medicine. Eggs, juveniles, adults,

body parts, everything exploited indiscriminately, with little regard for sustainability. On top of this, their habitats are being increasingly fragmented, destroyed, and polluted. Here in Canada seven of our eight native freshwater turtle species are at risk. 

Surprisingly, the eDNA approach had not been applied to turtles in aquatic environments. Visual and/or physical detection rates for turtle species vary substantially among sites and species, as well as among survey methods. Rare species can be particularly difficult to detect with traditional methods, especially in turbid waterways. Detection of eDNA could provide a more rapid, cost-effective, and potentially more sensitive survey tool to identify areas where turtle species are present, which can then be prioritized for intensive trapping surveys. 

Colleagues here in Ontario wanted to test whether turtle eDNA can be successfully detected in samples from aquaria and in the wild. They developed DNA primers (using DNA Barcodes) for a suite of nine sympatric freshwater turtles, and used it to compare their results to traditional field survey data from two sites in their target area.

Not only were they able to show that eDNA from turtles can be detected using both conventional PCR and quantitative PCR but also that the cost of detection through traditional survey methods is considerable higher than eDNA methods.

Compared to our simplified cost estimate of $500.00 to detect eDNA from a single turtle species at a site (assuming that detection would be successful), the cost to detect species through traditional field surveys ranged from $100 to $4,100 per detected species, and some species were not detected using either trapping or visual surveys.

This might represent a big step forward for the conservation of many endangered turtle species. Here in Canada it certainly would:

In Canada, federal and provincial conservation legislation provides protection to the habitat of at-risk species in many areas. However, this legislation does not apply until the species’ presence at a site (habitat) is confirmed. Our field data demonstrate that the amount of survey effort required to detect some species may be prohibitive, and that even with hours of intensive visual and trapping surveys, some species may go undetected.

Time to get to the task. Turtles worldwide don't have much time left.