Barton Springs Salamander Research Articles

Expression of rhodopsin and opsin in late‐stage epigean and hypogean salamander embryos

Evolutionarily, sensory systems have undergone extreme diversifications that have allowed vertebrates to survive diverse environments. The salamander clade Eurycea of Central Texas has branched out of its epigean ancestral roots and has successfully invaded subterranean environments. The San Marcos salamander (E. nana) and the Barton Springs salamander (E. sosorum) live above ground in springs and streams whereas the Texas blind salamander (E. rathbuni) occupies caves and recesses in the Edwards Aquifer. From an evolutionary perspective, it is thought that the hypogeal state is derived, but what remains a mystery is the developmental adaption of its sensory system to life under ground. The habitational broadening of the Eurycea salamander has been associated with the phenotype of reduced eyes exhibited in the Texas blind salamander. It is not clear whether this phenotype represents incomplete development, regression, or a combination of both. The clade of Eurycea is a prime model for comparing the molecular mechanisms that are involved in diverging neural systems, since species within the same clade present two extremes of phenotypes that are associated with their environment. Retinal development in embryonic E. rathbuni has been observed; however, the extent to which the retina develops is unknown. We identify retinal rod and cone photoreceptor cells along with their associated visual proteins (rhodopsin and opsin, respectively) in blind species and in epigean salamanders with fully developed eyes. Immunohistochemistry followed by confocal microscopy was applied for the investigation of sections of late embryonic stages of these salamander species. The results suggest opsin is expressed in the retina of E. nana and E. sosorum, and rhodopsin is expressed in all three species. Based on previous work indicating absence of visual pigments in adult Texas blind salamanders, we conclude expression of rhodopsin is transient or variable in this species. In future studies we will examine the expression of visual pigments at other stages to get a clearer picture of the time course and species‐level variability in expression.

Comparative development and ocular histology between epigean and subterranean salamanders (Eurycea) from central Texas.

The salamander clade Eurycea from the karst regions of central Texas provides an ideal platform for comparing divergent nervous and sensory systems since some species exhibit extreme phenotypes thought to be associated with inhabiting a subterranean environment, including highly reduced eyes, while others retain an ancestral ocular phenotype appropriate for life above ground. We describe ocular morphology, comparing three salamander species representing two phenotypes—the surface-dwelling Barton Springs salamander (E. sosorum) and San Marcos salamander (E. nana) and the obligate subterranean Texas blind salamander (E. rathbuni) - in terms of structure and size of their eyes. Eyes were examined using confocal microscopy and measurements were made using ImageJ. Statistical analysis of data was carried out using R. We also provide a developmental series and track eye development and immunolocalization of Pax6 in E. sosorum and E. rathbuni. Adult histology of the surface-dwelling San Marcos salamander (E. nana) shows similarities to E. sosorum. The eyes of adults of the epigean species E. nana and E. sosorum appear fully developed with all the histological features of a fully functional eye. In contrast, the eyes of E. rathbuni adults have fewer layers, lack lenses and other features associated with vision as has been reported previously. However, in early developmental stages eye morphology did not differ significantly between E. rathbuni and E. sosorum. Parallel development is observed between the two phenotypes in terms of morphology; however, Pax6 labeling seems to decrease in the latter stages of development in E.rathbuni. We test for immunolabeling of the visual pigment proteins opsin and rhodopsin and observe immunolocalization around photoreceptor disks in E. nana and E. sosorum, but not in the subterranean E. rathbuni. Our results from examining developing salamanders suggest a combination of underdevelopment and degeneration contribute to the reduced eyes of adult E. rathbuni.

Subterranean movement inferred by temporary emigration in Barton Springs salamanders (Eurycea sosorum).

Movement behavior is an important aspect of animal ecology but is challenging to study in species that are unobservable for some portion of their lives, such as those inhabiting subterranean environments. Using four years of robust-design capture-recapture data, we examined the probability of movement into subterranean habitat by a population of endangered Barton Springs salamanders (Eurycea sosorum), a species that inhabits both surface and subterranean groundwater habitats. We tested the effects of environmental variables and body size on survival and temporary emigration, using the latter as a measure of subterranean habitat use. Based on 2,046 observations of 1,578 individuals, we found that temporary emigration was higher for larger salamanders, 79% of which temporarily emigrated into subterranean habitat between primary sampling intervals, on average. Body size was a better predictor of temporary emigration and survival compared to environmental covariates, although coefficients from lower ranked models suggested turbidity and dissolved oxygen may influence salamander movement between the surface and subsurface. Surface population dynamics are partly driven by movement below ground and therefore surface abundance estimates represent a fraction of the superpopulation. As such, while surface habitat management remains an important conservation strategy for this species, periodic declines in apparent surface abundance do not necessarily indicate declines of the superpopulation associated with the spring habitat.

Discovery of central Texas Eurycea eggs in the wild

AbstractEurycea pterophila is a fully aquatic paedomorphic salamander species classified as under review for federal listing and distributed in restricted sections of the Comal River (Comal CO., TX). Unlike Eurycea sosorum, which constitutes the only documented wild sightings of Eurycea eggs in the region, no eggs of Eurycea pterophila have been documented in the wild. During a routine collection of Eurycea pterophila for a captive assurance population, two eggs were found in the Comal River, TX near Spring Island, and successfully raised in captivity. Captive Eurycea pterophila eggs were laid at the same time the wild eggs were found; thus, data are presented here for a comparison.

Effects of Season, Gravidity, and Streamflow on Body Condition from Tail Width in Two Federally Listed Salamanders, Eurycea sosorum and E. tonkawae

In population studies, individual physiological metrics can reveal important aspects of ecology and act as indicators of overall population health. Body condition is frequently used as a metric of physiological status and commonly quantified as some function of mass relative to structural size. In this study, we examined the natural variation in body condition of two central Texas spelerpines (Eurycea sosorum and E. tonkawae: Plethodontidae) to understand their nutritional status as a function of environmental variability and reproductive condition. Rather than using a mass-based metric to generate a body condition index (BCI), we used residuals from a linear regression of tail width vs. body length measured from subject photographs taken from the dorsal perspective. Overall, mean BCI for both species was lowest in the winter and generally higher in spring and summer. Streamflow had a small positive effect on E. tonkawae BCI and a negative effect on E. sosorum BCI. Gravid individuals for both species had lower BCI during autumn and winter (when the proportion of gravid individuals was the greatest) than nongravid individuals. By contrast, the few gravid E. sosorum we observed in summer had higher BCI than nongravid individuals. Our results provide important baseline information on the ecology of these federally protected salamanders and demonstrate the utility of a BCI based on width instead of mass.

Phenotypic Variation in Endangered Texas Salamanders: Application of Model-Based Clustering for Identifying Species and Hybrids

The endangered Barton Springs and Austin blind salamanders (Eurycea sosorum and E. waterlooensis, respectively) are micro-endemics to the Barton Springs segment of the Edwards Aquifer and its contributing zone in Central Texas. Although vertically segregated within the aquifer system, both species are known from the same spring outflows and occasionally hybridize. We used geometric morphometrics and model-based clustering applied to a large sample of standardized salamander photographs to evaluate the potential for objective phenotypic assignment to either species, as well as putative hybrids. In addition to characterizing variation in head shape, our analyses inferred sets of clusters corresponding to ontogenetic series in both species but did not infer any distinct hybrid clusters. Eurycea sosorum and E. waterlooensis have distinctive head size to trunk length allometries, which contributed to the effective clustering of species, even at small body sizes. We also observed subtle, but significant, microgeographic variation in E. sosorum, suggesting the possibility of population substructuring, phenotypic plasticity, or undetected hybridization.

A Vavraia-like microsporidium as the cause of deadly infection in threatened and endangered Eurycea salamanders in the United States

BackgroundEurycea sosorum (Barton Springs salamander) and Eurycea nana (San Macros salamander) are listed as endangered and threatened species, respectively, by the U.S. Fish and Wildlife Service (USFWS) with habitats restricted to small regions near Austin, Texas, USA. The conservation efforts with the Eurycea salamanders at the captive breeding program in San Marcos Aquatic Resources Center (SMARC), a USFWS facility, have seen an unexpected and increased mortality rate over the past few years. The clinical signs of sick or dead salamanders included erythema, tail loss, asymmetric gills or brachial loss, rhabdomyolysis, kyphosis, and behavior changes, suggesting that an infectious disease might be the culprit. This study aimed to identify the cause of the infection, determine the taxonomic position of the pathogen, and investigate the potential reservoirs of the pathogen in the environment.ResultsHistopathological examination indicated microsporidian infection (microsporidiosis) in the sick and dead Eurycea salamanders that was later confirmed by PCR detection. We also determined the near full-length small subunit ribosomal RNA (SSU rRNA) gene from the microsporidian pathogen, which allowed us to determine its phylogenetic position, and to design primers for specific and sensitive detection of the pathogen. Phylogenetic analysis indicated that this pathogen was closely related to the insect parasites Vavraia spp. and the human opportunistic pathogen, Trachipleistophora hominis. This Vavraia-like microsporidium was present in dead salamanders at SMARC archived between 2011 and 2015 (positive rates ranging between 52.0–88.9% by PCR detection), as well as in some aquatic invertebrates at the facility (e.g. snails and small crustaceans).ConclusionsA Vavraia-like microsporidian was at least one of the major pathogens, if not solely, responsible for the sickness and mortality in the SMARC salamanders, and the pathogen had been present in the center for years. Environmental invertebrates likely served as a source and reservoir of the microsporidian pathogen. These observations provide new knowledge and a foundation for future conservation efforts for Eurycea salamanders including molecular surveys, monitoring of the pathogen, and discovery of effective treatments.

Density-dependent and density-independent drivers of population change in Barton Springs salamanders.

Understanding population change is essential for conservation of imperiled species, such as amphibians. Worldwide amphibian declines have provided an impetus for investigating their population dynamics, which can involve both extrinsic (density‐independent) and intrinsic (density‐dependent) drivers acting differentially across multiple life stages or age classes. In this study, we examined the population dynamics of the endangered Barton Springs Salamander (Eurycea sosorum) using data from a long‐term monitoring program. We were interested in understanding both the potential environmental drivers (density‐independent factors) and demographic factors (interactions among size classes, negative density dependence) to better inform conservation and management activities. We used data from three different monitoring regimes and multivariate autoregressive state‐space models to quantify environmental effects (seasonality, discharge, algae, and sediment cover), intraspecific interactions among three size classes, and intra‐class density dependence. Results from our primary data set revealed similar patterns among sites and size classes and were corroborated by our out‐of‐sample data. Cross‐correlation analysis showed juvenile abundance was most strongly correlated with a 9‐month lag in aquifer discharge, which we suspect is related to inputs of organic carbon into the aquifer. However, sedimentation limited juvenile abundance at the surface, emphasizing the importance of continued sediment management. Recruitment from juveniles to the sub‐adult size class was evident, but negative density‐dependent feedback ultimately regulated each size class. Negative density dependence may be an encouraging sign for the conservation of E. sosorum because populations that can reach carrying capacity are less likely to go extinct compared to unregulated populations far below their carrying capacity. However, periodic population declines coupled with apparent migration into the aquifer complicate assessments of species status. Although both density‐dependent and density‐independent drivers of population change are not always apparent in time series of animal populations, both have important implications for conservation and management of E. sosorum.

New occurrence records for Eurycea sosorum Chippindale, Price & Hillis, 1993 (Caudata, Plethodontidae) in Travis and Hays counties, Texas, USA

We present 7 new occurrence records for the Barton Springs Salamander (Eurycea sosorum Chippindale, Price & Hillis, 1993) from Hays and Travis counties, Texas, USA, including the first for this species from the Trinity Aquifer. Eurycea sosorum is listed as endangered under the Endangered Species Act of 1973 due to ongoing threats from urbanization and aquifer overdraft throughout its narrow range. Although this species is more widely distributed than when it was first described in 1993, its range is still exceptionally small, restricted to portions of only two watersheds (Onion and Barton creeks) in one of the fastest-growing metropolitan areas in the United States (Austin, Texas). Under any ecologically-relevant criterion that is based on the best available scientific evidence, this species remains in danger of extinction throughout its range.

Effects of nitrogenous wastes on survival of the Barton Springs salamander (Eurycea sosorum).

The objective of our study was to determine the acute toxicity of 3 common aquatic nitrogenous toxicants to the federally endangered Barton Springs salamander (Eurycea sosorum). Based on our findings, the 96-h median lethal concentrations (96-h LC50) for un-ionized ammonia-N, nitrite-N, and nitrate-N to E. sosorum are 2.0 ± 0.32, 31.7 ± 4.02, and 968.5 ± 150.6 mg/L, respectively. These results establish a benchmark for the tolerance of plethodontid salamanders to these toxicants and indicate that current water quality criteria are adequate for their protection. Environ Toxicol Chem 2017;36:3003-3007. © 2017 SETAC.

Antipredator behavior of the Barton Springs salamander (Eurycea sosorum) in response to aquatic invertebrates: potential consequences of habitat restoration

The Barton Springs Salamander, Eurycea sosorum, is a fully aquatic salamander found in Barton Springs in Texas, USA, and has benefited from habitat restoration efforts. While important to improve overall habitat quality for this imperiled species, current management and restoration practices may also inadvertently increase the abundance of non-target organisms such as predatory invertebrates. Fish represent major predators of this species, but little is known about the role of invertebrates as potential predators. It is important to understand the role of these aquatic invertebrates as predators of E. sosorum, especially if habitat restoration also increases predator abundance. Using adult, predator-naive salamanders, we examined the antipredator response of E. sosorum to chemical cues from the following treatments: crayfish, dragonfly larvae, snails, and water. Salamanders decreased activity (antipredator behavior) only in response to the crayfish treatment. The responses to dragonfly larvae, snails, and water did not differ, suggesting that dragonfly larvae are not perceived as predators by these salamanders. Our study provides preliminary evidence suggesting that habitat restoration has unexpectedly increased crayfish abundance, which in turn may negatively affect E. sosorum, and that future management strategies should consider crayfish removal if salamander abundances decline with increasing crayfish abundance.

Multimodal communication, mismatched messages and the effects of turbidity on the antipredator behavior of the Barton Springs salamander, Eurycea sosorum

Prey may use multiple sensory channels to detect predators, whose cues may differ in altered sensory environments, such as turbid conditions. Depending on the environment, prey may use cues in an additive/complementary manner or in a compensatory manner. First, to determine whether the purely aquatic Barton Springs salamander, Eurycea sosorum, show an antipredator response to visual cues, we examined their activity when exposed to either visual cues of a predatory fish (Lepomis cyanellus) or a non-predatory fish (Etheostoma lepidum). Salamanders decreased activity in response to predator visual cues only. Then, we examined the antipredator response of these salamanders to all matched and mismatched combinations of chemical and visual cues of the same predatory and non-predatory fish in clear and low turbidity conditions. Salamanders decreased activity in response to predator chemical cues matched with predator visual cues or mismatched with non-predator visual cues. Salamanders also increased latency to first move to predator chemical cues mismatched with non-predator visual cues. Salamanders decreased activity and increased latency to first move more in clear as opposed to turbid conditions in all treatment combinations. Our results indicate that salamanders under all conditions and treatments preferentially rely on chemical cues to determine antipredator behavior, although visual cues are potentially utilized in conjunction for latency to first move. Our results also have potential conservation implications, as decreased antipredator behavior was seen in turbid conditions. These results reveal complexity of antipredator behavior in response to multiple cues under different environmental conditions, which is especially important when considering endangered species.

A Non-Invasive Water-Borne Assay of Stress Hormones in Aquatic Salamanders

Declines in amphibian populations are due to an array of anthropogenic and natural factors requiring a need to detect and monitor populations that are either in decline or at risk of decline. Physiological biomarkers, such as glucocorticoid stress hormones, present a viable option to monitor stress levels and, thus, the physiological health of vertebrate populations. We performed preliminary experiments necessary for the use of water-borne hormone assays to measure corticosterone (CORT) as an assessment of aspects of chronic stress for the management and conservation of three species of aquatic salamanders in central Texas (Eurycea, Plethodontidae). We examined the time for CORT levels to peak in response to capture and handling in populations of E. nana, E. sosorum, and E. tonkawae. Peak CORT release rates differed among species, with peak releases generally occurring in under 3 h. This highlights the need to obtain a timeline for CORT to mount so that peak rates are captured during the leaching phase. We also examined the responsiveness of the hypothalamic-pituitary-interrenal (HPI) axis using an adrenocorticotropic hormone (ACTH) challenge or exposure to an external stressor (agitation). Eurycea sosorum (one population) and E. tonkawae showed HPI responsiveness. To examine the relationship between field and laboratory CORT release rates, we compared baseline CORT release rates between captive and wild-caught populations of all three species. Once the preliminary studies have been performed, water-borne CORT release rates can be an effective biomarker to monitor whether a population is experiencing chronic stress. Water-borne hormone collection also allows for repeated sampling of individuals over time. Our experiments provide a foundation for future studies relating stress to HPI responsiveness in aquatic Eurycea, which, in turn, will help inform management of both wild and captive populations.

Dissolved oxygen fluctuations in karst spring flow and implications for endemic species: Barton Springs, Edwards aquifer, Texas, USA

• Concentrations of dissolved oxygen ( DO ) in a karst spring fluctuated by a factor of 2. • DO was modeled as a function of spring discharge and spring-water temperature ( T ). • An increase in T could lower DO to levels toxic to an endemic salamander. Karst aquifers and springs provide the dissolved oxygen critical for survival of endemic stygophiles worldwide, but little is known about fluctuations of dissolved oxygen concentrations ( DO ) and factors that control those concentrations. We investigated temporal variation in DO at Barton Springs, Austin, Texas, USA. During 2006–2012, DO fluctuated by as much as a factor of 2, and at some periods decreased to concentrations that adversely affect the Barton Springs salamander ( Eurycea sorosum ) (⩽4.4 mg/L), a federally listed endangered species endemic to Barton Springs. DO was lowest (⩽4.4 mg/L) when discharge was low (⩽1 m 3 /s) and spring water temperature was >21 °C, although not at a maximum; the minimum DO recorded was 4.0 mg/L. Relatively low DO (<6 mg/L) also was measured at relatively high discharge (3.2 m 3 /s) and maximum T (22.2 °C). A four-segment linear regression model with daily data for discharge and spring water temperature as explanatory variables provided an excellent fit for mean daily DO (Nash–Sutcliffe coefficient for the validation period of 0.90). DO also fluctuated at short-term timescales in response to storms, and DO measured at 15-min intervals could be simulated with a combination of discharge, spring temperature, and specific conductance as explanatory variables. On the basis of the daily-data regression model, we hypothesize that more frequent low DO corresponding to salamander mortality could result from (i) lower discharge from Barton Springs resulting from increased groundwater withdrawals or decreased recharge as a result of climate change, and (or) (ii) higher groundwater temperature as a result of climate change

Chemically Mediated Predator Avoidance in the Barton Springs Salamander (Eurycea sosorum)

Predation is a dominant and influential factor in most ecological communities. However, little is known about how the federally endangered Barton Springs Salamander, Eurycea sosorum, responds to predators. Using captive-hatched (predator-nasalamanders, we examined the antipredator response of E. sosorum to chemical cues from (1) native Western Mosquitofish (Gambusia affinis), (2) introduced Redbreast Sunfish (Lepomis auritus), (3) native Largemouth Bass (Micropterus salmoides), and (4) a blank water control. Salamanders decreased activity (antipredator behavior) in response to all fish treatments but not to the blank water control. There was no difference between the response to the G. affinis and L. auritus, but salamanders responded less to these treatments than to M. salmoides. The antipredator response to G. affinis may be an ontogenetic hold over as G. affinis has been found to consume amphibian larvae and eggs. In an additional study to test whether antipredator behavior was a generalized response to all fish species, we found that E. sosorum did not respond to small, nonnative, nonpredatory Guppies (Poecilia reticulata). This suggests that the observed behavior in our first experiment represents antipredator behavior specific to the species tested. Overall, these results indicate that E. sosorum has innate recognition of predatory fish, and that the stronger antipredator response to M. salmoides over the other fish species may be an outcome of risk assessment. The antipredator response to G. affinis has management implications as G. affinis is sympatric with the largest population of E. sosorum, and may be consuming both eggs and larvae of these salamanders.

Application Of Stable Isotope Analysis To Study Temporal Changes In Foraging Ecology In A Highly Endangered Amphibian

BackgroundUnderstanding dietary trends for endangered species may be essential to assessing the effects of ecological disturbances such as habitat modification, species introductions or global climate change. Documenting temporal variation in prey selection may also be crucial for understanding population dynamics. However, the rarity, secretive behaviours and obscure microhabitats of some endangered species can make direct foraging observations difficult or impossible. Furthermore, the lethality or invasiveness of some traditional methods of dietary analysis (e.g. gut contents analysis, gastric lavage) makes them inappropriate for such species. Stable isotope analysis facilitates non-lethal, indirect analysis of animal diet that has unrealized potential in the conservation of endangered organisms, particularly amphibians.Methodology/findingsI determined proportional contributions of aquatic macroinvertebrate prey to the diet of an endangered aquatic salamander Eurycea sosorum over a two-year period using stable isotope analysis of 13/12C and 15/14N and the Bayesian stable isotope mixing model SIAR. I calculated Strauss’ dietary electivity indices by comparing these proportions with changing relative abundance of potential prey species through time. Stable isotope analyses revealed that a previously unknown prey item (soft-bodied planarian flatworms in the genus Dugesia) made up the majority of E. sosorum diet. Results also demonstrate that E. sosorum is an opportunistic forager capable of diet switching to include a greater proportion of alternative prey when Dugesia populations decline. There is also evidence of intra-population dietary variation.Conclusions/significanceEffective application of stable isotope analysis can help circumvent two key limitations commonly experienced by researchers of endangered species: the inability to directly observe these species in nature and the invasiveness or lethality of traditional methods of dietary analysis. This study illustrates the feasibility of stable isotope analysis in identifying preferred prey species that can be used to guide conservation management of both wild and captive food sources for endangered species.

Conservation Physiology of the Plethodontid Salamanders Eurycea nana and E. sosorum: Response to Declining Dissolved Oxygen

Eurycea sosorum and E. nana are plethodontid salamanders endemic to several karst springs in central Texas. Landscapes around these habitats are increasingly urbanized. At the Barton Springs complex, where E. sosorum occurs, average dissolved oxygen (DO) in the main flow is approximately 6.5 mg L−1. However, DO is quite variable, ranging between 2.4 and 10 mg O2 L−1, and recent data suggest a positive relationship between DO and spring discharge in Barton Springs Pool, though this relationship may not be as strong under extreme low-flow conditions. Here we examine sensitivity of a surrogate species, E. nana, to experimental variation in oxygen availability (DO); due to limited availability of E. sosorum, they were examined in only a subset of experiments. A suite of traits was measured on adults: spontaneous activity, metabolic rate, and mortality during 28 days of exposure. A separate experiment examined growth of juveniles across levels of DO during 60 days of exposure. Levels of DO below 3.4 mg O2 L−1 appeared to pose a grave threat to salamander survival over a 28-day study, whereas DO above 4.5 mg O2 L−1 gave no observable effects in any experiment. Between these values is a critical range in which salamanders became progressively compromised. An ambient water quality criterion for DO in lentic systems (5 mg O2 L−1, 24 hour minimum) appears adequate to protect Eurycea.

Individual and seasonal variation in the diet of the endangered Barton Springs Salamander (Eurycea sosorum): An application of stable isotope analysis to the conservation of an endangered species

AbstractIt is well known that many species show strong temporal variation in diet. Long-term dietary trends may be important in assessing the effects of ecological change such as global warming, land use change, or introductions of invasive species. Short-term variation in food sources or prey selection may be crucial for understanding population dynamics in poorly understood species. The Barton Springs Salamander (Eurycea sosorum) is an endangered species endemic to four small spring outflows in downtown Austin, Texas. This species remains aquatic throughout life and inhabits benthic rocky substrate. While little is known about its foraging ecology, E. sosorum is assumed to be a generalist predator with the abundant amphipod Hyalella azteca as its primary food source. The salamander’s secretive behavior and obscure microhabitat make direct foraging observations impossible. Thus, stable isotope applications may be the only feasible means of estimating diet in these animals. Measurements of [delta]^13^C and [delta]^15^N for wild-caught Eurycea sosorum and a suite of potential invertebrate prey (amphipods, chironomids and planarians) were taken in November 2007, February 2008, May 2008 and August 2008. Quantitative invertebrate censuses track seasonal changes in invertebrate relative abundance. A multi-source mixing model is applied to field isotope data, and a distribution of likely prey item contributions to salamander diet is obtained for each season. Measurement of [delta]^13^C and [delta]^15^N from captive-bred E. sosorum raised on a constant diet indicate minimal fractionation of [delta]^13^C (&lt;1‰) and approximately 2.3‰ enrichment in [delta]^15^N per trophic level. Mixing model results show that salamanders feed nearly equally on planarians (53-57% of diet) and amphipods (43-47% of diet) during the course of the study, and that chironomids do not contribute to the diet of E. sororum. The relative isotopic relationship between the three prey items and salamander tissue remains constant over the course of the study. Furthermore, individual variation in salamander diet is large in all seasons (range of 6-8‰ of [delta]^13^C values for individual salamanders), potentially reflecting the highly clumped prey item distributions or individual specialization on different food resources.Stable isotope techniques allow investigation of how diet composition responds to temporal changes in prey availability in field populations and the degree to which intrapopulation diet variation influences overall population diet estimates. This work provides conservation biologists at Barton Springs with essential information on the diet and ecology of E. sosorum, which is being used to improve species management plans that will be applicable to other spring systems.

Individual and seasonal variation in the diet of the endangered Barton Springs Salamander (Eurycea sosorum): An application of stable isotope analysis to the conservation of an endangered species

Individual and seasonal variation in the diet of the endangered Barton Springs Salamander (Eurycea sosorum): An application of stable isotope analysis to the conservation of an endangered species

Detection of Batrachochytrium dendrobatidis in Endemic Salamander Species from Central Texas

A nested PCR protocol was used to analyze five endemic salamander species from Central Texas for the presence of the emerging pathogen, chytrid fungus (Batrachochytrium dendrobatidis). Chytrid fungus was detected from samples of each of the five species sampled: with low abundance, in the Texas salamander (Eurycea neotenes) (1 positive out of 16 individuals tested; 1/16), the Blanco River Springs salamander (E. pterophila) (1/20), the threatened San Marcos salamander (E. nana) (1/17), and the endangered Barton Springs salamander (E. sosorum) (1/7); much higher abundance was obtained for the Jollyville Plateau salamander (E. tonkawae) (6/14), which has recently been petitioned for addition to the USA endangered species list. With one exception, sequences of PCR products were identical to the 5.8S rRNA gene, and nearly so for the flanking internal transcribed spacer (ITS) regions of B. dendrobatidis which confirmed the detection of chytrid fungus, and thus demonstrated the presence of this pathogen in populations of endangered species in Central Texas. These confirmations were obtained from nonconsumptive tail clippings which confirms the applicability of historically collected samples from other studies in the examination of the fungus across time.