Detecting Hellbenders Using eDNA in Samples of Stream Water
By Zachary H. Olson and Rod N. Williams
The eastern hellbender is a large, aquatic salamander that historically occurred throughout much of the eastern United States. Research has suggested that once abundant hellbenders, which eat crayfish and live under rocks in cool, clear streams and rivers, have experienced sharp declines across their range. We suspect that habitat degradation, illegal collection, disease, and probably angling mortality factor into the declines. But, hellbenders are difficult to monitor, making it challenging to link declines to specific causes. This uncertainty in turn makes it difficult to know how to address the declines with appropriate conservation actions.
The most effective method to collect information about hellbenders involves teams of biologists flipping large rocks in the water to find them. Not only is this work labor intensive, time consuming, and logistically challenging, it is potentially dangerous for researchers and hellbenders. We needed another option to help us monitor hellbenders in the wild, and a Christine Stevens Wildlife Award allowed us to adapt an exciting new method from the field of non-invasive genetics to determine where hellbenders occur simply by collecting stream water.
This new method is made possible by detecting hellbender DNA directly from the environment. We know that DNA works like a chemical alphabet that spells out a huge book describing how cells should behave. We also know that if we sift carefully through that book we can find sections that make species unique, and even other sections that make individuals different.
To cheaply view those small differences of interest instead of reading through the whole DNA book, scientists developed tiny bookmarks called “molecular markers”— those discreet locations on the DNA sequence that can identify a particular species or individual. The field of non-invasive genetics traditionally has combined the use of these molecular markers with DNA collected from items such as shed feathers, hair, or feces. A few years ago, scientists in France coined the term ‘environmental DNA’ (or eDNA) to describe a new method in non-invasive genetics that allowed them to detect bullfrogs from wetlands simply by collecting water samples.
eDNA studies involve 3 main steps: (1) water is collected from a body of water (a cup to more than a gallon of water have been used), (2) any DNA or cells are separated out of the water using a sterile filter or gravity, and (3) researchers use specially designed molecular markers to probe all of the DNA and cell contents collected from the water to find those small differences that are the hallmark of their study species. If the molecular markers can find those small differences, the scientists know that DNA from their study species was present.
We developed a molecular marker that is specific to hellbender DNA, and sensitive enough to allow us to detect hellbenders even where they occur at very low abundances —and with much less effort than traditional sampling. We also found that we might be able to broadly predict how many hellbenders occur in a section of stream using eDNA. It is our hope that this new method will allow scientists to identify where hellbenders still occur, piece together the causes of their decline, and target those causes with much needed conservation action.