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Eurycea aquatica Rose and Bush, 1963
Brown-backed Salamander
Federal Protection: No US federal protection
State Protection: No Georgia state protection
Global Rank: G3
State Rank: S1
Element Locations Tracked in Biotics: Yes
SWAP 2015 Species of Greatest Conservation Need (SGCN): Yes
SWAP 2025 Species of Greatest Conservation Need (SGCN): Yes
2025 SGCN Priority Tier: Moderate Conservation Concern
Element Occurrences (EOs) in Georgia: 15
Habitat Summary for element in Georgia: Springs in RV and Cumberland Plateau
The brownback salamander is a moderately sized (6.2-9.5 cm or 2.4-3.5 inches total length) member of the lungless salamander family. As its common name implies, the brownback salamander (Eurycea aquatica) is characterized by a brownish light band that extends down the back and the length of the tail which is flanked by dusky black lateral stripes on either side which also extend to the tip of the tail. The body and legs are short and stout. Unlike other members of the E. bislineata (two-lined salamander) species complex characterized by relatively long tails (making up more than half of their body length), the tail of E. aquatica makes up less than 50% of its body. The belly is yellow and nearly unmarked with dark pigmentation. While in breeding condition, males can easily be distinguished from females from their enlarged head and their small, but distinct cirrus (slender flexible, downward extension of the upper lip below each nostril). While both the brownback and the southern two-lined salamander (E. cirrigera) exhibit sexual dimorphism (marked physical differences between the sexes – for the brownback salamander, males exhibit an expanded region of the head behind the eyes, but do not differ in body length with that of females), male E. aquatica typically have even wider heads than male E. cirrigera. Like most plethodontid salamanders, larvae are aquatic and retain external gills until metamorphic transformation is complete. Though the patterning of brownback larvae varies, they are generally black in coloration with a belly free of pigmentation. As development progresses the coloration of the back lightens to a brown band as seen in adults, but the sides remain darkly pigmented.
The brownback salamander is most similar in appearance, and arguably the most genetically related to E. cirrigera with which it is broadly sympatric (overlapping geographic distribution). The extreme eastern portion of the brownback’s range in Georgia may also overlap with that of the Blue Ridge two-lined salamander (E. wilderae). However, E. aquatica is not known to be syntopic (occupying the same microhabitats) with either species in Georgia. Both E. cirrigera and E. wilderae are less robust than E. aquatica in general body form. Further, adults of these three salamander species of the E. bislineata species complex can be distinguished from one another based on the relative appearance of their lateral stripes. On the southern two-lined salamander, a lightly colored mid-dorsal stripe is flanked by dark, thin lateral stripes, starting at the head, and continuing down the length of the tail. The Blue Ridge two-lined salamander is similar in appearance, but its lateral stripes characteristically break up on the distal half of the tail. Wide dusky black lateral stipes extend down the body and the length of the tail of brownback salamanders. Compared to other members of the E. bislineata species complex, brownback larvae are darker, have less reticulation laterally, and usually lack the two rows of dorsal spots characteristically found on the backs of southern two-lined salamander larvae. They have well developed tail fins, but not as high as two-lined salamander larvae. Blue Ridge two-line salamander larvae are differentiated by the presence of three rows of unpigmented lateral line spots, a mottled belly, and as in adults, broken dorsolateral stripes.
Brownback salamanders are largely restricted to headwater springs and spring runs that flow from groundwater at faults or contacts between geologic formations and are associated with small streams (1st and 2nd order) that are typically within a forested landscape; these habitats often support a lush growth of watercress (Nastrurium officinale) (an introduced exotic plant) within the water column. Flow of these springs is generally shallow and relatively constant with small fluctuations primarily related to varying levels of precipitation. Average water temperature is 16˚C (61˚F). Spring substrate consists of gravel or sand, or fine silt where water is slow moving.
No studies of diet have been performed for any life stage of this species. Feeding by adults is probably limited during the winter months, which is also when adults are found in aquatic habitats. Adults likely forage within the leaf litter of the forest floor within upland habitats (in spring, summer, and fall) on a variety of invertebrate prey. Larvae are carnivorous and likely eat a variety of insect and other invertebrate prey as they forage nocturnally among the stems of aquatic plants.
As brownback salamanders are difficult to locate within upland habitats surrounding isolated spring wetlands, they were initially only known to inhabit aquatic environments. Consequently, when the species was first described they were thought to be completely aquatic. The specific epithet “aqautica” means, “belonging to water.” Today it is known that these salamanders participate in annual migrations to isolated springs and stream habitats that they use for courtship and breeding. Adults are typically found within these aquatic habitats from January-March attending nests of eggs. The average clutch of Coosa Valley clade (i.e., genetically related group) females contains 73 eggs, which is the largest clutch size of any other clade of E. aquatica or species of the E. bislineata species complex. Attendance of the nest by both males and females is not uncommon. Brownback salamanders are not known to be territorial, but males will ward off other males while attending a nest. In April and subsequent months individuals disperse to upland habitats and elusively forage there until the next breeding migration the following winter. Based on observations demonstrating the typical presence of two distinct age/size classes of E. aquatica larvae in a given occupied aquatic habitat, it is thought that this species has a two-year larval period.
Because the brownback salamander can be difficult to find outside of its breeding season (January – March), surveys for this salamander focused on 1st and 2nd order streams and springs exhibiting habitat suitability should be conducted in the early months of the year by turning cover objects in and around identified spring and stream habitats. Surveyors should be cognizant of the brownback’s ability to temporarily alter its coloration and appearance. Brownback salamanders collected in the field have frequently become considerably lighter in coloration (more closely resembling southern two-lined salamanders) after a short period in captivity, exhibiting a more yellow color with less distinctive brown dorsolateral stripes. Since the distributional pattern of the Coosa Valley clade of the brownback salamander is thought to correspond to the geographical distribution of the coldwater darter (Etheostoma ditrema), locations of documented occurrences for this spring-endemic fish species should be evaluated for habitat suitability for E. aquatica and subsequent surveys conducted where appropriate. Suitable habitat for the species undoubtedly occurs within government landholdings including U.S. Forest Service ownership. Previously published surveys of groundwater resources (Georgia Geological Survey), which identity locations of major groundwater springs, many likely consistent with the habitat preference of this species, exist for every county within the brownback’s likely distributional extent in Georgia; these resources should be utilized in an effort to identify suitable wetland habitat. As E. aquatica also occurs on the Cumberland Plateau in Alabama (albeit much less commonly), this same region in Georgia should not be excluded from future survey efforts (i.e., Dade County).
While the full extent of the range of this species is imprecisely known (particularly in Georgia), brownback salamanders inhabit springs in areas of limestone geology of northern Alabama, northwestern Georgia, and portions of Tennessee. The current range of E. aquatica is not only influenced by the distribution of isolated surface springs and associated geologic faults, but also by the paleo-drainage patterns of rivers from the geologic past. Though likely confined to the Ridge and Valley Physiographic Province within Georgia, past survey efforts have demonstrated that the species is apparently absent from areas south of the Coosa River despite the presence of seemingly suitable spring and stream habitats there. Salamanders from the Coosa Valley (Georgia) are a separate clade from those found in the Birmingham Valley or the Cumberland Plateau/High Rim of Alabama – clades that are thought to have diverged and been isolated from one another since the early Pliocene to late Miocene (2.5-6.1 million years ago). These three clades may very well be determined in the future to represent separate undescribed species; the extent to which salamanders differ in physical traits among these clades has not been thoroughly investigated.
Direct hydrologic alteration of isolated spring habitats poses a threat to both the wetland habitats inhabited by the brownback salamander and the salamander species itself. Associated spring habitats are typically small and potentially susceptible to detrimental impacts from agricultural runoff. Potential contamination and dewatering of local aquifers present an additional host of indirect threats to isolated spring habitats. Similarly, immense interest in spring-endemic fishes and associated impacts to habitats from intensive fish surveys, as well as undisciplined collection of this salamander species are sources of direct impact to both brownback salamander populations and the aquatic habitats upon which they depend.
Though not yet reported from the wilds of North America, salamander chytrid fungus (Batrachochytrium salamandrivorans) [or Bsal] has caused a 90% reduction in some salamander populations in Europe. While different species and groups of salamanders show differences in susceptibility to the disease and in the severity of resulting chytridiomycosis, this emergent disease for some plethodontid salamanders has been shown to be lethal in laboratory experiments. Although E. aquatica has not undergone such testing, it is likely vulnerable to Bsal. The closely related E. wilderae demonstrated differing mortality rates for different portions of its range – from 80% survival (Virginia E. wilderae) to 100% mortality 25 days following exposure (GA E. wilderae).
| Threat 1 | Threat 2 | Threat 3 | |
|---|---|---|---|
| General Threat | Natural system modifications | Residential & commercial development | Invasive & other problematic species, genes & diseases |
| Specific Threat | None | None | None |
While the brownback salamander is not currently known from any protected areas in Georgia (likely due to limited species survey effort to date), the species does occur within a relatively unaltered spring habitat owned by a municipality – conveying some level of protection. This species was designated as a Category 2 Candidate Species from 1985 until the discontinuation of this list by the US Fish & Wildlife Service in 1996 (i.e., species for which information indicating that protection under the US Endangered Species Act may be warranted, but for which sufficient information on status and threats was lacking). Originally described in 1963, recognition as a distinct species was disputed and debated by the scientific community until the publication of genetic research in 2006 and 2009 that conformed genetic differentiation from the two-lined salamanders rather than merely representing robust spring-adapted morphs of the southern two-lined salamander. With the renewed recognition of this species and a realization of limited available information as to the species’ distribution in Georgia or its current conservation status, it was added to the list of High Priority Species within the 2015 revision of Georgia’s Wildlife Action Plan.
Specific body to tail ratios for members of the two-lined salamander species complex were established from observations outside to the Coosa Valley in Georgia. Survey efforts for the brownback salamander in Georgia should assess whether these body proportions apply equally to salamanders found in Georgia. Known populations of the brownback salamander in Georgia should be monitored periodically to confirm the species’ continued presence and to determine possible changes in abundance over time at each site. Further concerted survey effort within the predicted range in Georgia, targeting publicly owned lands within the Coosa Valley, is suggested to determine the full extent of the species distribution, abundance, conservation status, and needed management actions for specific populations.
Alcorn, M. A., J. Deitloff, S. P. Graham, E. K. Timpe. 2013. Sexual dimorphism in head shape, relative head width, and body size of Eurycea aquatica and Eurycea cirrigera. Journal of Herpetology 47(2): 321–327.
Carter, E. D., D. L. Miller, A. C. Peterson, W. B. Sutton, J. P. W. Cusaac, J. A. Spatz, L. Rollins-Smith, L. Reinert, M. Bohanon, L. A. Williams, A. Upchurch, and M. J. Gray. 2019. Conservation risk of Batrachochytrium salamandrivorans to endemic lungless salamanders. Conservation Letters 13:e12675. https://doi.org/10.1111/conl.12675
Graham, S. P., E. K. Timpe, S. K. Hoss, M. Alcorn, and J. Deitloff. 2010. Notes of reproduction in the brownback salamander (Eurycea aquatica). IRCF Reptiles & Amphibians 17(3): 168-172.
Jones, T. R. 1980. A reevaluation of the salamander, Eurycea aquatica Rose and Bush (Amphibia: Plethodontidae). M.S. Thesis, Auburn University. 77pp.
Kozak, K. H., R. A. Blaine, and A. Larson. 2006. Gene lineages and eastern North American palaeodrainage basins: phylogeography and speciation in salamanders of the Eurycea bislineata species complex. Molecular Ecology 15: 191–207.
Rose, F. L. and F. M. Bush. 1963. A new species of Eurycea (Amphibia: Caudata) from the southeastern United States. Tulane Studies in Zoology 10: 121-128.
Timpe, E. K., S. P. Graham, and R. M. Bonett. 2009. Phylogeography of the brownback salamander reveals patterns of local endemism in Southern Appalachian springs. Molecular Phylogenetics and Evolution 52: 368–376.
US Fish and Wildlife Service. 1996. Endangered and Threatened Wildlife and Plants; Notice of Final Decision on Identification of Candidates for Listing as Endangered or Threatened. Federal Register (235): 64481-64485.
Thomas Floyd
T. Floyd, February 2023: original account
