Northern Dusky (Desmognathus fuscus)

7/17/2021

Recognized Subspecies in VA: None
Size: 2.25 - 4.5 inches
Status: Least Concern

Description & Behavior

Brown, nondescript, mottled salamander that is great at just being average. The Northern Dusky is bulkier than many salamanders, but also not as bulky as many others. Older adults are too large to be called small salamanders, and young adults are too small to be called medium-sized. This species is quite variable, but learning to ID this species makes IDing other Desmognathus species easier. The tail is strongly keeled, but not to the point it is paddled like that of the Blackbelly Salamanders. The pattern is generally a gray-brown base. Younger adults typically have a richer brown (often reddish or purplish) dorsal flanked by a rough, dark (often blackish) border; this fades with age. There is usually some darker mottling distributed around the back, and silvery-white salting on the flanks. The venter is typically pale (off-white to yellow) and has some specks of the dorsal color focused heavier on the edges. They have the eye-jaw stripe seen in most Desmognathus species, but it may vary. Usually it is white or cream in color, but some specimens may have yellow or orange, and many specimens in the central piedmont have broken, silvery eye-jaw stripes (note the wide variation on the individuals on this page). There is often a brighter red to yellow line down the keel of the tail.

Northern Duskies like to sit at the edge of streams. They are commonly flipped under rocks, logs, and leaf packs. It seems the best rocks are flat-bottomed, at the edge of the water where they look to be mostly on land, but when flipped one can see the bottom was in the water. They are nocturnal, so spotlighting streams at night gives one a good chance of spotting them hunting.

Habitat

Known & Predicted Range

This species is very abundant in the Blue Ridge region of Virginia and west, and gets scarcer as you get closer to the southern piedmont. Their range looks to overlap with the Flathead Salamander, Wolf Dusky, and Piedmont Dusky in areas, but they do not (ignoring the fringes where the two come together). The Northern Dusky (to our current understanding) is excluded from the Albemarle Sound Drainages of Virginia with exception to the Yadkin, most of the Staunton, and the headwaters of the Roanoke River. Knowing what watershed one is in may be the most important tool in identifying these four species.

We find this species most often in and around streams with lots of rocks, logs, and/or leaves for them to hide in. They are quite tolerant to muddy, silty streams, especially compared to most salamanders, but favor less polluted waters. Duskies often use crayfish burrows and gaps between rocks as their lairs, but can even use the gaps in log and leaf jams. They seem to like shelter that gives them the ability to move to the water and out of the water without being seen.

Similar Species

There are numerous Desmognathus species that are hard for people to discern from the Northern Dusky. They share much of their Virginia range with the Seal Salamander, which as adults have smudgy spots that favor that of a big cat. Seal Salamanders have slightly stronger keeled tails; plain, gray venters; and a longer snout as adults. Juvenile Seal Salamanders have distinct yellow to orange spots that zigzag down the tail base and often have two rows of faint spots down the back instead of a solid line. The Allegheny Mountain Dusky and Blue Ridge Dusky are slimmer, lankier and have cylindrical or weakly keeled tails. Both species of our Blackbelly Salamanders are bulkier with thick, paddle-tails, big heads with "bug-eyes", and very distinct patterns. The Flathead Salamander, Piedmont Dusky, and the Wolf Dusky are so complex and poorly understood that I feel it best to discuss the differences with the Northern Dusky in their own pages as to not draw this one out too much, especially since range is likely one's best friend in IDing these species. I will also do this with the other members of the genus Desmognathus as they are all "similar" but many are found in small ranges or are quite uncommon.

Taxonomy & Phylogeny

This is a very complicated and interesting topic for this species. I have a lot I want to say, but I cannot say but so much because we just do not know a lot of what is going on as of yet. Back around 2020, some of my colleagues and I started pointing out that many of the "Northern Duskies" in certain areas of the Virginia and North Carolina piedmont and coastal plain look more like what we were calling "Holbrook's Southern Dusky (D. auriculatus)" at the time than they did Northern Duskies. These were features such as portholes (a row of dots down the side of the tail), grainier patterns, strong eye-jaw stripes that were more often orange, darker venters and several other traits that were listed in papers that were supposed to be distinguishing features. We became reluctant over time to ID these as Northern Duskies and others pushed back. The issue was that many of these maps were drawn by researchers IDing a specimen here and there and many were preserved museum specimens. None of these maps matched and often times there was no photos or descriptions of the specimens, just a species name on a list. So, while we had nothing more than our interpretation of the animals' appearances (a rather weak argument) the academic consensus at the time had nothing more than this person (mostly people who have passed) called this specimen "this" and that one "that", lines grouping the dots together (which did not agree with other maps), and nothing to back up why they made those identifications in the first place. This is why photos are so important. Salamander wet specimens are almost non identifiable in museum collections as color and pattern fades very quickly. All of us could concede one thing: no one could conclude anything until there was genetic work on these animals.

In 2022, we got exactly that. Alexander Pyron and a team released a paper called Candidate-species delimitation in Desmognathus salamanders reveals gene flow across lineage boundaries, confounding phylogenetic estimation and clarifying hybrid zones. This paper answered our questions, and gave us several more questions. Yes, we were correct. Those salamanders across the piedmont were not Northern Duskies. That said, they were not Holbrook's Southern Duskies either. In fact, Holbrook's Southern Dusky was not actually a Virginia or North Carolina species as the genetics of the type specimen reflect it was only found in Georgia and Florida. Not only were we all wrong, but the shared foundation we based our arguments on was wrong. Now, genetically (nucellar DNA) these salamanders are closer to the Holbrook's Southern Dusky than the Northern Dusky, but the mitochondrial DNA was closer to the Northern Dusky. These salamanders were a few, undescribed species. Now, I am not going to get into a lot of detail on how these species could have arrose, as it is complicated, speculative, and we really do not have a lot of information; but essentially populations were divided, speciation occurred, those species came back together in some instances, hybridized, and speciation occurs again in those hybrid populations.

Where else do we see this? Well, mainly in ray-finned fishes tied to freshwater rivers and streams. Land and saltwater is a barrier, so how can a fish species get to other rivers? Massive floods can connect two watersheds and geographic events like stream piracy, topography change, and earthquakes can cause streams to connect and disconnect. These events often only happen every few hundred to several thousand years. This is why many drainages have unique species and there are very similar species in nearby drainages. Herpetologists are not used to this as most reptiles and frogs are not as strongly hindered by these boundaries. Sure, turtles and many frogs usually follow watersheds, but these animals can cross over to another watershed by crossing land. Many of these salamanders do not move far or fast enough to travel far from water before they desiccate, so they stay very close to the streams; moving much like we see in populations of small minnows. We even see many of these fish species that favor small streams find larger parts of rivers to be barriers, just like it appears these salamanders are.

Eventually Pyron and colleagues would describe many of the species. This included the Piedmont Dusky (D. bairdi). This was the identity of most of the salamanders which we had been arguing about in 2020. Our "Holbrook's Southern Dusky" was now the Wolf Dusky (D. lycos) as well as a population in the western piedmont that were also included in these discussions. This population is disjunct by the Piedmont Dusky, likely due to the geographic events I listed earlier and competition and hybridization. All is well that ends well... right?

Well, Pyron also found a few distinct populations of the Northern Dusky that he suggested were undescribed species. One would be (in Virginia) in the Powell and Clinch and maybe the Houlston and/or Big Sandy drainages. The other is just in the small expanse of the Yadkin in Carroll Co. No paper has came out to describe these at this time, so for now they will just reside under the label Northern Dusky; but perhaps one day Virginia will add two more species to its Desmognathus count.

Localized Variations

I wanted to discuss that this species is not just variable, but there are certain "norms" for populations that we do not usually see in other populations.

"Fuscus E" - Southern Carroll Co. (Yadkin Drainage)

Juvenile | © Ty Smith

Adult | © Ty Smith

Old Adult | © Ty Smith

This population is a candidate for its own species, and it is quite unique. Many of the juveniles are incredibly red. The young adults are also quite bright, but the old adults look like typical Northern Duskies.

Mount Rogers Area - Intersection of Grayson, Smyth, Washington Co.

Subadult | © Ty Smith

Older Adult | © Ty Smith

Young animals of this population are often very yellow in color, sometimes almost green or orange. They are much slimmer and seem to favor smaller streams. The adults often look more yellow as well and many have portholes. Pyron had reached out to me at one point to ask if I knew of any other populations that were unusual and this was the one I mentioned. Apparently despite them looking unique, they are genetically typical Northern Duskies.

Works Cited

Pyron, R. A., O’Connell, K. A., Lemmon, E. M., Lemmon, A. R., & Beamer, D. A. (2022). Candidate‐species delimitation in Desmognathus salamanders reveals gene flow across lineage boundaries, confounding phylogenetic estimation and clarifying hybrid zones. Ecology and Evolution, 12(2). Wiley Online Library. https://doi.org/10.1002/ece3.8574