Ouachita Streambed Salamander

This species is defined primarily in comparison to juvenile-stage Eurycea multiplicata, with which its physical characteristics are remarkably similar, and thus does not have a detailed individual description. The species typically reaches full sexual maturity at lengths as short as 32 mm. Mature male snout-vent length ranged from 34.9 to 45.7 mm with a mean of 40.8 mm and female snout-vent length ranging from 34.9 to 45.7 mm with a mean of 41.1 mm (Steffen et al. 2014).Eurycea subfluvicola is distinguished from syntopic, larval E. multiplicata through a number of defining characteristics: firstly, Eurycea subfluvicola is paedomorphic, containing functioning reproductive organs despite appearing outwardly to be in larval stage. Additionally, the morphology of the head and the body varies significantly between E. subfluvicola and larval E. multiplicata. Similar results were observed when focusing solely on the comparison of E. subfluvicola of smaller stature with larval E. multiplicata, showing that E. subfluvicola has a longer trunk with a shorter and narrower head relative to E. multiplicata. Furthermore, E. subfluvicola, relative to E. multiplicata larvae, has a flatter head and more prolonged snout, with eyes that are smaller in diameter and more sunken into the face. Eurycea subfluvicola is more attenuate in body form than E. multiplicata larvae through the relatively reduced diameter of its trunk and tail, the latter of which deviates very significantly. Finally, a black-pigmented stripe found along the lateral side of the snout and head in E. multiplicata is absent in E. subfluvicola. Trunk vertebral counts range from 21 - 22, while in nearby E. multiplicata populations they are 21. Eurycea subfluvicola trunk vertebrae also appear longer and narrower than E. multiplicata. The quadrate and squamosal in the mandibular suspensorium are more robust in E. subfluvicola than in E. multiplicata. Eurycea subfluvicola contains 3 cartilagenous epibranchials, and in some individuals these structures are partially ossified, while no ossification is apparent in E. multiplicata. Eurycea subfluvicola has much fewer iridophores in its irises, as well as a reduction in their coloration that makes the eyes principally black in color (Steffen et al. 2014).The dorsum is of a consistent yellow-amber color. It is pigmented with a number of dark brown melanophores, which create irregular patches of coloration on the dorsal and lateral surfaces of the organism. In many of the collected specimens, irregular splotches form in the absence of melanophores on the length of these surfaces. The abdomen is translucent and unpigmented save for a few melanophores spread out on the underside of the tail. The coloration difference between the dorsum and the venter is starkly defined by a lateral boundary that travels along the trunk (Steffen et al. 2014).Observed variation within the species is based on 24 adult specimens of E. subfluvicola, of which 8 are male and 16 female. There are no somatic differences between the sexes, and individual differences are restricted to minor variations in coloration (Steffen et al. 2014).The species authority is: Steffen, M. A., Irwin, K. J., Blair, A. L., and Bonett, R.M. 2014. "Larval masquerade: a new species of paedomorphic salamander (Caudata: Plethodontidae: Eurycea) from the Ouachita Mountains of North America". Zootaxa 3786 (4): 423–442.Based on the Bayesian analysis of E. subfluvicola and its relatives built on mitochondrial (Cytb and Nd4) and nuclear (Rag1) genes, E. subfluvicola is most closely related to E. multiplicata, followed by E. tynerensis and E. spelaea, and then the remaining members of the Eurycea genus. Analysis of Cytb and 18 sites with heterozygous positions across all individuals of E. subfluvicola for Rag1 revealed 0.1 - 0.3% nucleotide divergence with uncorrected p (Steffen et al. 2014).The species epithet, ‘subfluvicola’ is an adjective derived from the Latin prefix, sub- meaning “below”, fluvius which is “a stream”, and colo meaning “to dwell.” The translation then is “dwells below the stream”, in reference to its existence below the streambed during xeric conditions (Steffen et al. 2014).

The known distribution of Eurycea subfluvicola is currently limited to the Trap Mountains, in the southeastern portion of the Ouachita Mountais. Eurycea subfluvicola is only known from two sites: a 15 m section of Slunger Creek and a 50 m section of an unnamed tributary within the Slunger Creek alluvial valley which are about 135 m from each other. The entirety of the Lake Catherine State Park, which houses all the known E. subfluvicola specimens, rests at an elevation of 169 meters above sea level. Most vegetation at the type locality is second growth mixed pine-hardwood forest composed of Pinus echinata as well as Acer, Celtis, Cornus, Liquidambar, Ulmus, and Quercus (Steffen et al. 2014).

In males, enlargement of the testes can be observed in February, reaching maximum size by late June and July in a laboratory setting and corresponding to the mating season. In females, a maturing egg follicle was observed once in the field during late November, but in a laboratory setting they matured through the summer (Steffen et al. 2014).There is evidence suggesting facultative metamorphosis may be possible within the species. Large captive males were observed to begin metamorphosis in captivity in a process that took over 2.5 months, but died before it could be completed due to unspecified causes. In comparison, E. multiplicata completes its metamorphosis in one month in similar conditions. Some of the partially metamorphosed E. subfluvicola showed remodeling of the hyobranchial apparatus, including the loss of larval epibranchials, the formation of adult epibranchials, the reshaping of the ceratohyal, basibranchials, and ceratobranchials. Adult maxillary morphology began to take form in some specimens, and the small external gills were never completely absorbed. However, it is important to note that only the largest, most reproductive males underwent metamorphosis, and that none of the females did (Steffen et al. 2014).Surface activity of E. subfluvicola is primarily nocturnal, with individuals occasionally leaving the cover of rocks or leaf litter during the day. Subterranean ecology of E. subfluvicola is completely unknown (Steffen et al. 2014).