A Field Herp Student’s Intro to Dusky Salamander Diversity

It was a dark and stormy night at Mountain Lake Biological Station in southwest Virginia, and my classmates and I were crouched over a patch of moss looking desperately at a small salamander. Out for a nighttime stroll in the rain, he had no idea his appearance was giving a group of amateur herpetologists anxiety. “Yeah, that head looks froggy to me.”

“Definitely a Desmognathus. Or wait…”

“Is the tail laterally compressed?”

“I think it’s P. cinereus.”

“Did anyone flip it over to look at the underside?”

I knew it was in the Desmognathus genus by its head, and the tail looked flattened to me. I turned to our TA, who was waiting on our ID. “Is it D. fuscus?” He smiled.

“Nope! D. ochrophaeus. That tail is rounded.” We all groan. This is probably the twentieth Desmognathus ochrophaeus we’ve seen in the past half hour, and we still can’t recognize them reliably. We stand up, scribble in our field notebooks, and start creeping our way to the next sighting. Among the local salamanders we learned to identify in our field herpetology class at MLBS, those in the genus Desmognathus were the most difficult by far. Also known as the dusky salamanders, they’re found in and around rocky streams from east Texas all the way up to Canada, where they’ve split into many species. Exactly how many? That’s a question still being answered. The more I learn about them and the taxonomic shuffle they’re undergoing, the more interested in them I become.

Two different-looking D. ochrophaeus trying their best to confuse us. Photo: Becky Williams

While we puzzled over D. fuscus and D. ochrophaeus – two species that are most definitely distinct, no matter what my field notes say – there were others at the field station tackling much harder distinctions. As it turns out, the Desmognathus genus is full of ecomorphs, or populations that have evolved slight differences that help them in the specific habitat they specialize in. In a group of salamanders within a certain ecosystem, some might become more aquatic with a compressed tail that helps them swim, some might spend their time among leaf litter and develop a pattern that helps them blend in, and all of them might change sizes to take advantage of the food they eat; eventually, these different groups can isolate from each other and become distinct species. This spells trouble for biologists trying to figure out who’s who: depending on where you are, the “mountain dusky salamander” ecomorph that has developed a black belly, relatively large size, and tendency towards stream bottoms could be several different species that aren’t each other’s closest relatives.

Thankfully, our field herpetology professor never expected us to tell the difference between these different Desmognathus ecomorphs. But whenever we did have questions we knew exactly who to ask, since we were sharing the field station with Dr. David Beamer, one of the researchers puzzling out the evolution of all these tricky look-alikes. I got to attend a talk of his about how he and his colleagues went about identifying the different Desmognathus species. Their most helpful tool is DNA sequencing, which is cheaper and more accurate than ever before and can tell researchers which populations of salamanders are more closely related based on how similar their DNA is. But with so many salamanders from so many different places across the region, how did they know where to center their analyses? The answer required them to imagine how the Desmognathus salamanders split from one another in the first place.

Desmognathus orestes, an ecomorph of D. ochrophaeus. If we weren’t in a different part of the state when we found this guy, we wouldn’t be able to tell the difference. Photo: Kyle Moxley

One of the reasons there’s so many ecomorphs of Desmognathus is likely because of how little these salamanders move around. They’re small, they’re slow, they need moisture, and they make tasty food for a number of animals, meaning one big hill or rocky outcrop can easily form a huge and unnecessary barrier to their activity. This makes them susceptible to getting separated from each other pretty quickly, which leads to genetic isolation and eventually different species. Once you understand what features of the environment might make salamander movement easier or harder, it’s a lot easier to imagine where the closely related groups might end up. That’s why Dr. Beamer and his colleagues focused their analyses of Desmognathus salamanders around separate river drainages and areas of uninterrupted habitat that might be isolating groups of salamanders from each other. Instead of thinking about the features of the salamander that seemed similar, they thought about the features of the environment that might cause a group to get cut off from others and form its own ecomorphs. The result was an increased understanding of which related groups of salamanders exist where, an enormous aid in identifying which species are distinct. New species descriptions are following rapidly.

Why do I care so much about the taxonomy of these little salamanders? As someone who struggled to tell the difference between some of the most different Desmognathus species, I have a great appreciation for the research going into much more subtle variations within the genus. There are many practical advantages to understanding an organism’s taxonomy — to protect salamanders in an increasingly polluted and habitat-sparse world, it’s important to know which groups within Desmognathus are the same and which groups hold hidden diversity in danger of disappearing. For me, these taxonomic complications are a reminder of the incalculable diversity nature holds and its infinite potential for discovery. As long as we are looking, there will be more to see. Especially among dusky salamanders.

Thanks to David Beamer, my professor Christian Cox, my TA Albert Chung, and all my classmates for helping me through my first experience in field herpetology this past summer. 30 herp points to all of you!