Tale of Two Salamanders

I held tight to my camera as the truck lurched forward, front tires plunging into several inches of mucky water.  Carl and I had chuckled at the prominent yellow signs, declaring “road may flood,” on the way in.  With each pass around the forested wetland, the water had risen by several inches, sinking our tires further and further into the oily blackness.  With the road now well under a foot of water, I was beginning to question our bravado.  “What is that!?” Carl exclaimed as something furry and brown half scurried, half swam out from under our advancing vehicle.  It was a muskrat, swimming over the two lanes like this was just another stream.  As the aquatic rodent dove under the surface, its body undulated, revealing a long, flattened rat-like tail.  

Getting stuck on some back country road an hour south of Athens wasn't on my to-do list for the night. Thankfully, Carl's trusty four-wheel drive pickup rumbled heartily through the deepest stretches of water. I hadn't anticipated how quickly the surrounding wetlands would overflow, turning the entire landscape into one big vernal pool.  As the rains picked up, the light traffic dropped to about zero.  This was good for migrating amphibians and other water-logged wildlife, but I wondered how long it would be before anyone noticed us if we did get stranded out here.

Cambarus bartonii cavatus an undescribed species.  Note the dozens of babies under its tail.

Reaching higher ground, we spotted something small and shiny crawling lamely over the asphalt.  Expecting an injured amphibian, I was instead met with the largest crayfish I had ever seen.  This land-dwelling crustacean (Cambarus bartonii cavatus, evidently an undescribed species) was a good sign for the mole salamanders we were looking for.  Crayfish dig extensive burrows in the surrounding woodlands, lawns, and agricultural fields, providing fossorial amphibians with a refuge during the summer and winter months.  Rain floods these burrows and forces their occupants to find new hiding places.  Whether it be invertebrates, amphibians, reptiles, or even mammals, rain makes wildlife move.  As we drove along, the eyeshine of an opossum was illuminated by our headlights; the two eery points of green light faded back into the darkness as the gray, shaggy marsupial moved away.

Spring peepers and wood frogs hopped across the road every few feet.  Their high pitched whistles and guttural whines resonated from the nearby pools and streams.  Carl hadn't visited these routes for a few years (save for a brief trip we made in late autumn).  I was impressed that he retained a mental map of the area.  When I road cruise (the term herpers use for driving around and looking for amphibians and reptiles), I usually creep along at 15-20 miles per hour.  Any faster and I worry I’ll miss or hit something.  Carl, on the other hand, does something more like speed cruising.  Rocketing down the backroads, he straddles anything that could be alive, then rapidly backs up for a better look.  It’s efficient and effective, but for someone like myself who can get motion-sickness sitting in a parked car, it’s a bit of a challenge.  I tried to focus on scanning the pavement for movement as we zipped along.  It was a good distraction, but no replacement for getting out into the fresh air.  

The streamside salamander (Ambystoma barbouri)

After a few stops to inspect peepers, wood frogs, and spotted salamanders, there, stretched across the pavement—a salamander I had never seen before.  Upon closer inspection, nothing was particularly striking about this unassuming salamander.  Its body was chunky, though smaller proportioned than a spotted or a jefferson.  It displayed no bright colors or distinct markings; two shades of light gray frosted its back and sides.  The head was held high, peering up at us—an unusual behavior for this stubborn species.  Its head was also disproportionately small and snub-nosed, at least for a member of the “logger-headed” mole salamanders.  A thin, yellow line stretched across its rounded face—giving the salamander a content smile.  

“That’s our barbouri,” Carl commented as he looked down at our find.  Ambystoma barbouri, the streamside salamander.  Streamsides are unique among mole salamanders—not for their appearance, but for their behavior.  They don't breed in the temporary vernal pools that other members of this group migrate to every spring or fall.  Instead, their courtship and egg laying takes place in shallow headwater streams.  They attach their eggs to the underside of flat stones, and after hatching, the larvae grow and develop in these streams.  A. Bourbori occupy a limited range in southwestern Ohio and other nearby states where they inhabit upland forested hillsides during the summer.  

Travel just a few counties north of the streamside’s range, and you might encounter a salamander that looks nearly identical.  Until as recently as 1989, the streamside salamander was thought to be a stream-dwelling form of Ambystoma texanum, or the small-mouthed salamander.  Small-mouthed salamanders differ in appearance from the streamside in a few unremarkable ways.  They have a slightly longer snout, unique dentition with two rows of teeth, and a more wedge-shaped tail.  The most important behavioral difference is that small-moutheds breed in vernal pool habitat like the rest of the mole salamanders.  It is thought that about 4 million years ago, these two species split when A. barbouri began utilizing stream habitats.  However, breeding behavior is not a sure-fire way to tell these species apart, as both texanum and barbouri have been reported utilizing both streams and pools.

The following night, Carl and I traveled an hour north of Athens.  On a short stretch of road that cut through a patch of forest between a cornfield and tiny town, Carl spotted a single small-mouthed salamander.  Another lifer for me.  Small-moutheds inhabit lowland forests, floodplains, and fields.  If I hadn't known differently, I never would have made the distinction between this individual and the salamander from the night before. 

The small-mouthed salamander (Ambystoma Texanum)

This classic case of a cryptic species is made even more confusing by the genetic netherworld that these salamanders emerge from.  The more widespread and abundant Small-mouthed salamander (found from Ohio to Texas) is commonly parasitized by the ambystoma unisexual complex.  This group of all-female salamanders actually steals genetic information from other salamander species and incorporates it into their polyploid (more than two sets of chromosomes) genome.  This can result in animals that look quite like small-mouthed salamanders but who don't belong to the species and who might also contain the genetic information of blue-spotted salamanders and even tiger salamanders.  

In areas where A. texanum and A. barbouri overlap, some interbreeding, either historically or on going, is thought to occur.  This can blur the line between these two species and endanger the unique genetic identities of each (particularly A. barbouri due to its much smaller population).  To determine range maps where different species live, genetic testing is often helpful when dealing with cryptic species.  

When it comes to barbouri and texanum, however, genetics is another hurdle herpetologists must overcome.  The interbreeding that has taken place between these two species has left its signature in the genes of some A. texanum.  This phenomenon is called mtDNA introgression.  Mitochondrial (mt) DNA is inherited from the mother, and doesn't change much from generation to generation.  This makes it important for determining unique species lineages.  What's so difficult for this species in particular, is that entire populations of small-mouthed salamanders possess the mtDNA of streamside salamanders left over from interbreeding events.  Individuals with this condition can still be told apart by their anatomy, but this often requires collection or dissection, something most herpers aren't prepared or willing to do.  

The small-mouthed salamander we found on the second night was from a population that possess the mtDNA of the streamside salamander.  While this lends some question as to the true identity of these salamanders, the population is continuous with the known small-mouthed range.  For this reason, as well as anatomical features, we are comfortable calling them true small-moutheds.  This really shouldn't be the stopping point, however. Countless more questions need to be asked in order to expand our knowledge and better our understanding of these unique and unusual creatures. 

Even when they seem dull or indistinguishable, herps often hide some baffling secrets.  Salamanders are funny that way.  These slimy puzzles force us to think outside of what's familiar and comfortable.  I think that's why they fascinate me so much.