Saturday, April 25, 2015

The Red-Backed Salamander, Plethodon cinereus

I've been wanting to do a big post on a species of amphibian that is near and dear to my heart for awhile now. With the semester coming to an end, I've finally gotten the chance to write it. This post is all about the Red-Backed Salamander, Plethodon cinereus. My aim is to give a general overview, with some interesting detailed bits, of this incredibly common species. Why is it so special to me? P. cinereus is the first species I've ever had the chance to do real research on. Starting back in the fall of 2014, I began a job as an undergrad research assistant at Ohio University. I work in Dr. Shawn Kuchta's lab under Maggie Hantak, one of Dr. Kuchta's Ph.D students. It's been an incredibly fun, and incredibly educational, experience so far. I'll talk more about her research and what I do at the end of this post.

That aside, let's move on to some basics! Be warned, this is going to be a really long post.

Red-Backed Salamander, Plethodon cinereus
The Red-Backed Salamander, Plethodon cinereus, is a terrestrial species of Plethodontid salamander. As with all other salamanders in the family Plethodontidae, the Red-Backed is lungless. Since they lack lungs, respiration instead occurs across the skin and the lining of the mouth. For these salamanders to breathe correctly, they must remain moist so gas can be exchanged freely across the cells in the skin. As a result, desiccation (drying out) is a constant threat to this salamander. In order to remain moist, they must inhabit areas that meet a certain threshold for moisture. These salamanders can be found in deciduous forests, mainly under rocks and logs where moisture is retained. When it is wet enough, they will travel throughout the leaf litter on the forest floor in search of food. During the summer months, when the heat dries out the top layers of the forest floor, P. cinereus will move into the ground, using old worm burrows or possibly making burrows itself.

P. cinereus
is an incredibly abundant species in the forests of the Northeast part of the US, and it can be found in nearly every county here in Ohio. In fact, P. cinereus is thought to be the most abundant vertebrate species in the Northeast quarter of the US. They can reach densities of 2.8 individuals per square meter in good habitats, making this species more abundant than birds and mammals combined. In addition, there is some compelling evidence that the 2.8 individuals per square meter number is actually an underestimate; it might be double that number (See Semlitsch et al., 2014)! It is important to note that the bulk of a given population of Red-Backed Salamanders lives below the surface, so trying to accurately estimate a population is difficult when you can only find those individuals who are on the surface (See Taub 1961). When Maggie and I travel to a good location in Northern Ohio, we can normally find at least one individual under every rock or log you flip. It's amazing to think that all those individuals we readily find under cover objects represent only a fraction of the individuals actually living in that location.

Red-Backed Salamander morphs
The two common morphs of the Red-Backed Salamander, with the red-stripe morph on the right, and the lead morph on the left.
One of the really interesting characteristics about this salamander is its color polymorphism. Polymorphism is where there are two or more clearly different phenotypes (an individual's set of physical traits) in a species. Generally speaking, P. cinereus exhibits three color morphs. First is the red-stripe morph (pictured above on the right). This is by far the most common morph. The second most common morph is the lead (or lead-backed) morph (pictured above on the left). The third morph is the erythristic morph, which is very rare. The erythristic morph is essentially all red with a creamy white stomach. In addition to these three morphs, there are several other rare color anomalies: iridistic, albino, leucistic, amelanistic, and melanistic. You can read more about the different color phenotypes in J.D. Moore's paper here.

As stated previously, the red-stripe morph is by far the most common, especially in Ohio. There are, however, many polymorphic populations. Northern Ohio has a relatively high density of polymorphic populations, where one can find both the lead and red-stripe morph (and occasionally the erythristic morph) all living together in the same location. The ratios between the morphs vary according to each site. Interestingly, there are a few all-lead populations in Ohio, such as the population on South Bass Island. This is not a common occurrence by any means.

Iridistic Red-Backed Salamander
There is an extreme amount of color variation not only between color morphs, but also within the morphs and anomalies. At some locations we visit, the red-stripe morphs have a very bright and well defined red stripe. At other locations, the red stripe is very mottled and dull with high amounts of black across the body. On the other side of the coin, the leads at some locations are a very dull and subdued black, while other locations have very iridescent and beautiful leads, like the one pictured above.

Red-Backed Salamander juvenile
Unlike many salamander species, P. cinereus does not have an aquatic larval stage. The entire life cycle is terrestrial, and that means we run into many juvenile individuals when in the field. And the juveniles are cute. Extremely cute. Pictured above is a small (yes, small) adult red-stripe individual next to a juvenile lead individual. Many of the juveniles we find could easily fit on a penny.

Red-Backed Salamander eggs
Most, but not all, salamanders lay eggs, and this includes the Red-Backed Salamander. When we measure the salamanders, we are able to see the eggs of any pregnant females. These eggs can be very pronounced, as the photo above shows. If you count carefully, you can see a total of 8 eggs (the white blobby things in the abdomen) in the individual above. As mentioned earlier, while many salamanders have an aquatic larval stage, the Red-Backed is completely terrestrial. The eggs are laid in a protected area, mainly in rotten logs. There is a larval stage, but this stage happens completely in the egg. Upon hatching, the juveniles are fully developed and essentially a smaller version of the adult.

Red-Backed Salamander male and female
How do you tell the sex of a Red-Backed Salamander? There are a few differences between the two sexes, but the easiest way is to look at their heads. Females have a very round snout. Males, on the other hand, have a very broad, square-like snout, which you can see above. Another feature to look for is the presence of cirri. Cirri (singular cirrus) are a fleshy downward extension of the upper lip. Cirri function as chemoreceptors, and the males use these for a multitude of reasons, most commonly to sense out a potential mate's pheromones. You can see the cirri on the male above; they are the two tiny, mustache-like extensions hanging down on either side of the snout. As always, you can click on a photo to view a larger version of it.

Red-Backed Salamander missing tail
One of the incredibly interesting characteristics of salamanders is their ability to regenerate whole limbs and parts of major organs. It's a tough world out there, and salamanders can lose parts of their body due to predators, but also due to fights with larger salamanders. Red-Backed Salamanders are known for being fiercely territorial, and they will defend their territories against many different intruders like the Northern Ravine Salamander, Spotted Salamanders, or centipedes, occasionally resulting in the loss of limbs. The tail is the part that is most often lost, like in the individual above. When it comes to tails, salamanders are like lizards. When in a situation with a predator, the Red-Backed Salamander will wave its tail in an attempt to get the predator to go after that part instead of elsewhere. As soon as the predator latches onto the tail, the tail pops off giving the salamander time to escape. The tail wiggles violently for a short bit to confuse the predator even further in order to hopefully allow a safe escape for the salamander. Salamanders can regrow legs in only 7-10 weeks, but tails take a little long due to their size and how much actually comes off. The individual above (who was found in the Fall) probably has a fully regrown tail by now.

Red-Backed Salamander diet
While the Red-Backed Salamander is a prey item for many other animals, it is still a ferocious predator itself. I'm currently in the middle of a dietary study that aims to find out if there is a difference in the type of food the red-stripe and lead morphs eat. The Red-Backed Salamander eats a large variety of arthropods, although I did find a weird one who ate a mushroom. The photos above give you an idea of some of their usual prey items. On the far right is their favorite type of food, mites. There's an incredible diversity of mite species on the forest flood, and the salamanders will eat many of them. In the center are Springtails, another favorite. On the far left is a pseudoscorpion, one of the more awesome-looking arthropods they eat. In addition, they also consume ants, beetles, assorted tiny wasps, spiders, and more.

Partially erythristic Red-Backed Salamander
One of more interesting individuals we've come across so far this Spring is the one pictured above. We had traveled to a location where around 15% of the population was erythristic (an unusual reddish or orange coloration). While we didn't find any completely erythristic individuals, Maggie did find the one above which exhibits partial erythrism. Note how most of the body is a red-orange, while the stomach is a creamy white. There's too much black on the individual for it to be considered completely erythristic, but you can tell it is definitely not a normal red-stripe individual. If you're interested in learning more, partial erythrism and erythrism in general is covered in the J.D. Moore paper that I linked to earlier in the post.

Silver-Striped Red-Backed Salamander
Several weeks after I wrote this initial post, we came across another interesting individual, pictured above. This is what has been called the "Silver-Striped" or "Silver-Backed" variant of the Red-Backed Salamander. As you can see, the stripe running down the back in this individual is a silvery-grey color instead of the normal red color. Sadly there's not much information I can find on this color abnormality other than assorted photos of similar individuals. Vincent Farallo, an Ohio University graduate student, did tell me that he has seen a lot of individuals like this at Strouds Run State Park in Athens County.

Maggie Hantak
Maggie Hantak measuring a Red-Backed Salamander using a method termed "Mander-Mashing." Seriously. (No salamanders are harmed in this process.)
As I mentioned earlier, I currently have a job as an undergrad research assistant. My job is essentially to help Maggie Hantak, a Ph.D student at Ohio University, collect data at her field sites in Northern Ohio, as well as working independently on a dietary study for her. In a nutshell, Maggie is exploring multiple facets of the evolutionary ecology of the Red-Backed Salamander with regard to the differences between the red-stripe and lead morphs. She's been a wonderful mentor to me and has helped me get involved in real research. I'll be spending the first half of this summer in Northern Ohio as her field assistant, with the last half spent down in Athens to try and finish the dietary study. I'll also hopefully have the opportunity to begin my own research on Plethodon electromorphus, the Northern Ravine Salamander, this summer.  As of October, 2016, I am beginning my own independent project on the Northern Ravine Salamander. Stay tuned for more information in the upcoming months!

I've got several more salamander posts in the works that I'll hopefully be finishing up sometime during Summer, so if you're a herpetology person, stay tuned! Otherwise, I'll be covering the usual interesting things I come across this summer, including flowers, birds, insects, parks and more. Thanks for reading!

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