Of Ecosystem Engineers and eDNA: An Update on TWI Grant 006

By Victoria Zero

Why Wyoming?
You would not be amiss to ask, “Are there really amphibians in Wyoming?” In point of fact, it’s a funny place to study amphibians: Wyoming has some of the lowest amphibian species diversity in North America.  It’s also subject to extreme cold and limited rainfall.  The state is also generally behind the times with our knowledge of amphibian distributions.  To my mind, these facts make this a fascinating place to work with native amphibians.  Those that occur here tend to be common, widespread species that are likely on the edge of their ecological tolerances.  This makes them good ecosystem indicators.

You might also ask, “Why focus on species that are considered common and widespread?”  Unfortunately, it is not just protected amphibians that need our attention. A recent study by Michael Adams and colleagues revealed that use of long-term wetland monitoring sites by amphibian species categorized as Least Concern by the IUCN declined 2.7% annually from 2002 to 2011.  These data really drive home the importance of monitoring, even when species are perceived to be “everywhere.”

I conducted my Master’s research from 2012-2013 under the guidance of Dr. Melanie Murphy at the University of Wyoming.  Our sites were near Laramie, Wyoming in the Medicine Bow National Forest.  This region is home to three species of native amphibian: Northern leopard frog (Lithobates pipiens), Boreal chorus frog (Pseudacris maculata), and Barred tiger salamander (Ambystoma mavortium).  The Northern leopard frog is declining throughout most of its western range, while little is known about the population trends of the other two species in most areas, particularly within Wyoming.  My study was an attempt to 1) determine habitat preferences and 2) develop molecular tests for each of the three species.

Leave it to Beaver
The most interesting story to emerge out of our investigations into habitat preferences involves beavers.  All three amphibians may use a range of wetland habitat types.  Chorus frogs generally rely on highly ephemeral pools of water, while leopard frogs typically depend on more semi-permanent water sources, and tiger salamanders probably fall somewhere in the middle of this water availability continuum.  Beavers are often referred to as “ecosystem engineers” owing to their profound impacts on hydrology and habitat.  Beaver ponds may improve water availability and quality, as well as provide high quality habitat for pond-breeding amphibians.  Leopard frogs were anecdotally noted to breed in non-beaver wetlands in high water years, but relied entirely on beaver ponds for breeding during the course of this study.  What about the other species? Our findings further suggest that tiger salamanders and chorus frogs may prefer to breed in non-beaver wetlands when water in plentiful, but may switch to laying their eggs in beaver ponds in dry years.  This suggests that the presence of beaver ponds is likely critical for the long-term population viability of these three species in semi-arid, mountainous systems like those examined in this study.  Beavers are contentious critters and considered pests by many, but we hope that landowners and managers will consider using them as tools for native amphibian conservation.

DNA in a Haystack
The second part of my thesis involved developing tests for environmental DNA (eDNA) of all three species from water samples.  We can detect even tiny quantities of species-specific DNA fragments that are shed into the water through the use of standardized laboratory techniques.  This technique has become especially popular in programs that monitor invasive or endangered species.  We were surprised that the use of eDNA increased the number of detections by as much as 1.5 times for what we consider to be an easily detectable species (e.g. Northern leopard frogs). We only saw tiger salamanders at 5 sites in 2013, but eDNA detected them at 16 wetlands.  We saw similar improvements for chorus frogs, with as much as a fourfold increase in the number of sites where they were detected.  This suggests that eDNA can be useful not just for monitoring hard-to-detect species, but more common and conspicuous species as well.  There is increasing interest in employing eDNA techniques to amphibian studies in Wyoming, and we hope that other researchers will use the molecular tests we developed in their own research.  These data also provide important baseline records for amphibians in the region.

Victoria Zero recently graduated with a Master’s degree in Rangeland Ecology and Watershed Management from the University of Wyoming.  The eDNA portion of her thesis research was supported in part by funds generously provided by Tree Walkers International.  She is now continuing her focus on amphibians and reptiles as a herpetologist for the Wyoming Game and Fish Department.

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