The eastern tiger salamander is a large, charismatic salamander found along the Atlantic coast that is threatened or endangered in much of its range. Habitat degradation and destruction are key threats to this species; identifying and protecting habitats where the species is still found is a key conservation measure to prevent further losses to the species.
The Cornell Wildlife Health Lab is collaborating with the New York State Department of Environmental Conservation to develop and refine methods to detect eastern tiger salamander environmental DNA (eDNA) in wetlands that the species may use for breeding. First, we developed a custom species-specific molecular tool called quantitative PCR (qPCR) that can be used to exclusively identify eastern tiger salamander DNA. Next, we performed a proof-of-concept field trial to determine the most effective method of collecting eastern tiger salamander eDNA samples in pools with known high-density salamander populations. Now, we are applying these methods to better understand how to achieve the greatest sensitivity in detecting eastern tiger salamander eDNA in pools across a spectrum of population densities.
During our first field season, we tested three different filter sizes every week for eight consecutive weeks, coinciding with the peak eastern tiger salamander breeding and egg-laying season. Our goal was to find a filter that could strike the right balance between capturing a lot of eastern tiger salamander eDNA and not many qPCR inhibitors, since both compounds are likely to be present in breeding pool water. We found that eastern tiger salamander eDNA detection was most sensitive when using either the smallest or the largest filter pore size. Smaller filters clogged more quickly and could filter a smaller volume of water, but also captured fewer qPCR inhibitors from the environment. Larger filters clogged slowly, allowing a larger volume of water to be filtered, and we captured enough tiger salamander eDNA for our molecular tools to work, even with qPCR inhibition. Moderately sized filters performed poorly, as they failed to capture sufficient eastern tiger salamander eDNA to overcome qPCR inhibition.
This year, we are using the lessons learned from our first field season to test the limits of our test sensitivity at sites with variable eastern tiger salamander population density. We know our tools work well when there are a lot of salamanders breeding at a sampled wetland; how well do they work with a moderate or low population density? We know that tiger salamanders are present at a site if we find eDNA in a pool’s water, but what if we don’t find any eDNA? What is the minimum number of samples we need to take from a wetland to be confident that tiger salamanders are absent at that site? By answering these questions, we can determine the most effective use of eastern tiger salamander eDNA as a surveillance tool to identify and monitor wetlands that may be crucial for the species' survival.
