Subterranean movement inferred by temporary emigration in Barton Springs salamanders (Eurycea sosorum).
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ABSTRACT:
SUBMITTER: Bendik NF
PROVIDER: S-EPMC8074841 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description: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.
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Project description: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.
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Project description:Insights into the ecology and natural history of the neotenic salamander, Eurycea tonkawae, are provided from eight years of capture-recapture data from 10,041 captures of 7,315 individuals at 16 sites. Eurycea tonkawae exhibits seasonal reproduction, with peak gravidity occurring in the fall and winter. Size frequency data indicated recruitment occurred in the spring and summer. Open-population capture-recapture models revealed a similar seasonal pattern at two of three sites, while recruitment was dependent on flow at the third site. Females can reach sexual maturity within one year, and oviposition likely takes place below ground. The asymptotic body length of 1,290 individuals was estimated as 31.73 mm (at ca. two years of age), although there was substantial heterogeneity among growth trajectories. Longevity was approximately eight years, and the median age for a recaptured adult was 2.3 years. Abundance estimated from closed-population and robust-design capture-recapture models varied widely within and among sites (range 41-834), although, surprisingly, dramatic changes in abundance were not observed following prolonged dry periods. Seasonal migration patterns of second-year and older adults may help explain lower ratios of large individuals and higher temporary emigration during the latter half of the year, but further study is required. Low numbers of captures and recaptures precluded the use of open-population models to estimate demographic parameters at several sites; therefore, closed-population (or robust-design) methods are generally recommended. Based on observations of their life history and population demographics, E. tonkawae seems well adapted to conditions where spring flow is variable and surface habitat periodically goes dry.
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Project description:BACKGROUND:Body shape can be both a consequence and cause of a species' evolution and ecology. There are many examples of phenotypes associated with specific ecological niches, likely as a result of specific selective regimes. A classic example of this is the phenotypic change associated with colonization of caves, including body and limb elongation. However, studies explicitly testing for differences in body shape between cave-dwelling and non-cave-dwelling lineages have been limited and so the role of the cave environment in determining morphological characteristics is still not completely understood. Here we examine variation in body shape among 405 individuals representing 20 species in the salamander genus Eurycea (Plethodontidae) and select outgroups exhibiting great diversity in morphology, ecological niche, and life history. RESULTS:After analyzing morphometric data in a phylogenetic context using phylogenetic MANOVA and examination of the phylomorphospace, we found significant differences in body shape among cave-dwelling and non-cave-dwelling species and between aquatic and terrestrial species. Notably, limb elongation and reduced body and tail size characterized cave-dwelling species. Terrestrial species also exhibited elongation of the limbs and digits. We also observed differences in shape variance among paedomorphic and biphasic species. Our results suggest that the functional limitations imposed by habitat and life history played a key role in the evolution of body shape in this group in the context of their phylogenetic history.
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Project description:The complete mitochondrial genome of the southern two-lined salamanders (Eurycea cirrigera) was determined in this study. The complete mitogenome sequence of E. cirrigera is 16,759bp in length and contains 37 genes (13 protein coding genes (PGCs), two ribosomal RNA, 22 transfer RNA genes and one control region). This is the first time of the mitochondrial genome sequencing for E. cirrigera.
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Project description:Geothermal energy has been harnessed and used for domestic heating in Iceland. In wells that are typically drilled to a depth of 1,500 to 2,000 m, the temperature of the source water is 50 to 130 degrees C. The bottoms of the boreholes can therefore be regarded as subterranean hot springs and provide a unique opportunity to study the subterranean biosphere. Large volumes of geothermal fluid from five wells and a mixture of geothermal water from 50 geothermal wells (hot tap water) were sampled and concentrated through a 0.2-microm-pore-size filter. Cells were observed in wells RG-39 (91.4 degrees C) and MG-18 (71.8 degrees C) and in hot tap water (76 degrees C), but no cells were detected in wells SN-4, SN-5 (95 to 117 degrees C), and RV-5 (130 degrees C). Archaea and Bacteria were detected by whole-cell fluorescent in situ hybridization. DNAs were extracted from the biomass, and small-subunit rRNA genes (16S rDNAs) were amplified by PCR using primers specific for the Archaea and Bacteria domains. The PCR products were cloned and sequenced. The sequence analysis showed 11 new operational taxonomic units (OTUs) out of 14, 3 of which were affiliated with known surface OTUs. Samples from RG-39 and hot tap water were inoculated into enrichment media and incubated at 65 and 85 degrees C. Growth was observed only in media based on geothermal water. 16S rDNA analysis showed enrichments dominated with Desulfurococcales relatives. Two strains belonging to Desulfurococcus mobilis and to the Thermus/Deinococcus group were isolated from borehole RG-39. The results indicate that subsurface volcanic zones are an environment that provides a rich subsurface for novel thermophiles.
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Project description:Removal sampling data are the primary source of monitoring information for many populations (e.g., invasive species, fisheries). Population dynamics, temporary emigration, and imperfect detection are common sources of variation in monitoring data and are key parameters for informing management. We developed two open robust-design removal models for simultaneously modeling population dynamics, temporary emigration, and imperfect detection: a random walk linear trend model (estimable without ancillary information), and a 2-age class informed population model (InfoPM, closely related to integrated population models) that incorporated prior information for age-structured vital rates and relative juvenile availability. We applied both models to multiyear, removal trapping time-series of a large invasive lizard (Argentine black and white tegu, Salvator merianae) in three management areas of South Florida to evaluate the effectiveness of management programs. Although estimates of the two models were similar, the InfoPMs generally returned more precise estimates, partitioned dynamics into births, deaths, net migration, and provided a decision support tool to predict population dynamics under different effort scenarios while accounting for uncertainty. Trends in tegu superpopulation abundance estimates were increasing in two management areas despite generally high removal rates. However, tegu abundance appeared to decline in the Core management area, where trapping density was the highest and immigration the lowest. Finally, comparing abundance predictions of no-removal scenarios to those estimated in each management area suggested significant population reductions due to management. These results suggest that local tegu population control via systematic trapping may be feasible with high enough trap density and limited immigration; and highlights the value of these trapping programs. We provided the first estimates of tegu abundance, capture probabilities, and population dynamics, which is critical for effective management. Furthermore, our models are applicable to a wide range of monitoring programs (e.g., carcass recovery or removal point-counts).
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Project description: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.
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Project description:Detectability of individual animals is highly variable and nearly always < 1; imperfect detection must be accounted for to reliably estimate population sizes and trends. Hierarchical models can simultaneously estimate abundance and effective detection probability, but there are several different mechanisms that cause variation in detectability. Neglecting temporary emigration can lead to biased population estimates because availability and conditional detection probability are confounded. In this study, we extend previous hierarchical binomial mixture models to account for multiple sources of variation in detectability. The state process of the hierarchical model describes ecological mechanisms that generate spatial and temporal patterns in abundance, while the observation model accounts for the imperfect nature of counting individuals due to temporary emigration and false absences. We illustrate our model's potential advantages, including the allowance of temporary emigration between sampling periods, with a case study of southern red-backed salamanders Plethodon serratus. We fit our model and a standard binomial mixture model to counts of terrestrial salamanders surveyed at 40 sites during 3-5 surveys each spring and fall 2010-2012. Our models generated similar parameter estimates to standard binomial mixture models. Aspect was the best predictor of salamander abundance in our case study; abundance increased as aspect became more northeasterly. Increased time-since-rainfall strongly decreased salamander surface activity (i.e. availability for sampling), while higher amounts of woody cover objects and rocks increased conditional detection probability (i.e. probability of capture, given an animal is exposed to sampling). By explicitly accounting for both components of detectability, we increased congruence between our statistical modeling and our ecological understanding of the system. We stress the importance of choosing survey locations and protocols that maximize species availability and conditional detection probability to increase population parameter estimate reliability.
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Project description:T cells leave the thymus at a specific time during differentiation and do not return despite elaboration of known T cell chemoattractants by thymic stroma. We observed differentiation stage-restricted egress of thymocytes from an artificial thymus in which vascular structures or hemodynamics could not have been playing a role. Hypothesizing that active movement of cells away from a thymic product may be responsible, we demonstrated selective reduction in emigration from primary thymus by inhibitors of active movement down a concentration gradient (chemofugetaxis). Immature intrathymic precursors were insensitive to an emigration signal, whereas mature thymocytes and peripheral blood T cells were sensitive. Thymic stroma was noted to elaborate at least two proteins capable of inducing emigration, one of which was stromal cell-derived factor-1. Thymic emigration is mediated, at least in part, by specific fugetaxis-inducing factors to which only mature cells respond.
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