Ouachita Streambed Salamander

The Ouachita streambed salamander (Eurycea subfluvicola) is a species belonging to the Class Amphibia, Order Caudata, and Family Plethodontidae. It is a relatively newly described Arkansas endemic species, found at a single locality in the Ouachita Mountain physiographic province, and has one of the smallest, perhaps the smallest, known geographic distribution of any North American salamander.

The original specimen was collected in May 2011 by researchers from the Arkansas Game and Fish Commission and Tulsa University in Oklahoma. Because the specimen was similar in morphology to the larvae of many-ribbed salamanders (Eurycea multiplicata), which are common in the area and inhabit the same stream, collectors did not initially realize they might have a new species in hand. Once they returned to the laboratory and conducted DNA sequence studies, they determined that the salamander represented a new taxon. Soon thereafter, these researchers notified personnel at Lake Catherine State Park in Arkansas to obtain clearance for scientific collecting in the park and began searching for additional salamanders along park streams. Due to severe drought conditions in the area, however, the research team had to spend nearly two years searching for a second specimen to confirm their initial findings. Intensive search efforts were realized in 2013 when additional specimens were finally collected, and further DNA analyses revealed that these salamanders were most closely related to, but still highly divergent from, E. multiplicata and all other described salamanders.

These salamanders typically dwell below the streambed and retreat below when precipitation ceases and surface waters eventually dry up. Interestingly, despite similar microhabitat close by, and even with extensive searching effort, the Ouachita streambed salamander has been found only seasonally at two small stream sections within Lake Catherine State Park. These sites are located within a Hot Spring County section of the Trap Mountains and include a 15 m (49 ft.) section of Slunger Creek and a 50 m (164 ft.) section of an unnamed tributary within the Slunger Creek alluvial valley, about 135 m (443 ft.) apart from one another.

In coloration, the dorsum of E. subfluvicola is primarily uniform with an amber/yellow background, pigmented with numerous dark brown melanophores, which create irregularly shaped blotches throughout its dorsum and flanks. In many specimens, irregularly spaced spots are formed by the absence of melanophores along the dorsolateral region of the trunk, possibly indicative of a lateral line. On the other hand, the semi-transparent venter is unpigmented, except for a few widely dispersed melanophores under the tail. The dorsal and ventral coloration is separated along the trunk by a sharply defined ventral-lateral boundary.

In terms of reproduction, the species is paedomorphic, meaning they retain larval morphological characteristics (particularly external gills) into adulthood and, as such, are sexually mature adults. In males, testicular enlargement has been documented in February, reaching maximum size by summer months (late June and July) in the lab and corresponding to the mating season. In females, a maturing egg follicle has been observed in the field during late November, but in a more controlled laboratory setting, they matured through the summer. The species typically reaches full sexual maturity at lengths as short as 32 mm (1.3 in.). Mature male snout-vent length (SVL) ranges from 35 to 46 mm (1.4 to 1.8 in.), with female SVL not being noticeably different, ranging from 35 to 46 mm (1.4 to 1.8 in.).

The Arkansas Game and Fish Commission designated E. subfluvicola as a regulated species and a Species of Greatest Conservation Need. By 2021, it had still not been listed under NatureServe or the IUCN Red List of Threatened Species. In terms of conservation efforts, there is a vital need to establish the extent of the geographic distribution of E. subfluvicola to help develop appropriate conservation measures or actions. In addition, there is an urgent need to document and explore local stream ecological parameters to determine factors that dictate the distributional limits of the species. Indeed, after locations were mapped where researchers have found salamanders, they determined that one site was about to be damaged by sediments washed downstream, which threatened to fill in a pool in which the salamanders were most abundant. A mitigating project was undertaken by the Arkansas Game and Fish Commission’s Stream Team Program and Lake Catherine State Park staff to remove excess sediment from the streambed and construct a sediment trap to retard movement of additional sediments into the pool.

Although several parasites have been reported from the related many-ribbed salamander in Arkansas, no surveys, to date, have been conducted on E. subfluvicola because of its protective status. One would assume similar parasites would be harbored by this species.

For additional information:
Bonett, Ronald M., and Paul T. Chippindale. “Speciation, Phylogeography and Evolution of Life History and Morphology in the Salamanders of the Eurycea multiplicata Complex.” Molecular Ecology 13 (2004): 1189–1203.

———. “Streambed Microstructure Predicts Evolution of Development and Life History Mode in the Plethodontid Salamander Eurycea tynerensis.” BMC Biology 4 (2006): 6.

Bonett, Ronald M., Michael A. Steffen, S. M. Lambert, J. J. Wiens, and Paul T. Chippindale. “Evolution of Paedomorphosis in Plethodontid Salamander: Ecological Correlates and Re-Evolution of Metamorphosis.” Evolution 68 (2014): 466−482.

Chippindale, Paul T., Andrew H. Price, J. J. Wiens, and David W. Hillis. “Phylogenetic Relationships and Systematic Revision of Central Texas Hemidactyliine Plethodontid Salamanders.” Herpetological Monographs 14 (2000): 1−80.

Duellman, William E., and Linda Trueb. Biology of Amphibians. New York: McGraw-Hill, 1986.

McAllister, Chris T., and Charles R. Bursey. “Nematode Parasites of the Many-Ribbed Salamander, Eurycea multiplicata (Caudata: Plethodontidae), from Arkansas and Oklahoma.” Proceedings of the Oklahoma Academy of Science 90 (2010): 69‒73.

McAllister, Chris T., Matthew B. Connior, Charles R. Bursey, and Henry W. Robison. “A Comparative Study of Helminth Parasites of the Many-Ribbed Salamander, Eurycea multiplicata and Oklahoma Salamander, Eurycea tynerensis (Caudata: Plethodontidae), from Arkansas and Oklahoma.” Journal of the Arkansas Academy of Science 68 (2014): 87‒96. Online at https://scholarworks.uark.edu/jaas/vol68/iss1/15/ (accessed September 22, 2021).

Moore, George A., and R. C. Hughes. “A New Plethodontid from Eastern Oklahoma.” American Midland Naturalist 22 (1939): 696−699.

Petranka, James W. Salamanders of the United States and Canada. Washington DC: Smithsonian Books, 1998.

Steffen, Michael A., Kelly J. Irwin, Andrea L. Blair, and Ronald M. Bonett. “Larval Masquerade: A New Species of Paedomorphic Salamander (Caudata: Plethodontidae: Eurycea) from the Ouachita Mountains of North America.” Zootaxa 3786 (2014): 423–442.

Trauth, Stanley E., Henry W. Robison, and Michael V. Plummer. Amphibians and Reptiles of Arkansas. Fayetteville: University of Arkansas Press, 2004.

Chris T. McAllister
Eastern Oklahoma State College