Rhyacotriton Variegatus Research Articles

TERRESTRIAL MOVEMENT BY THE SOUTHERN TORRENT SALAMANDER (RHYACOTRITON VARIEGATUS)

Southern Torrent Salamanders (Rhyacotriton variegatus) are a cold, headwater-inhabiting amphibian native to the Pacific Northwest. This genus of salamanders is considered highly aquatic, even in postmetamorphic stages, although instances of terrestrial movement have been observed. This note reports our opportunistic field observations for terrestrial movement in R. variegatus, which primarily occurred in the vicinity of Marys Peak, Benton County, Oregon.

OCCURRENCE OF A SUITE OF STREAM-OBLIGATE AMPHIBIANS IN TIMBERLANDS OF MENDOCINO COUNTY, CALIFORNIA, EXAMINED USING ENVIRONMENTAL DNA

Stream-obligate amphibians are important indicators of ecosystem health in the Pacific Northwest, but distributional information to improve forest management is lacking in many regions. We analyzed archived DNA extracted from water samples in 60 pools in streams on private timberlands in Mendocino County, California, for 3 California Species of Special Concern—Coastal Tailed Frogs (Ascaphus truei), Foothill Yellow-legged Frogs (Rana boylii), and Southern Torrent Salamanders (Rhyacotriton variegatus)—to better understand their distributions in the region. Detection probabilities for eDNA of Foothill Yellow-legged Frogs and Coastal Tailed Frogs were positively influenced by water temperature. eDNA occurrence for both frogs was affected by whether silt or organic matter was a dominant substrate in the sampled pool, and Foothill Yellow-legged Frog eDNA occurrence was also affected by water temperature. Foothill Yellow-legged Frog eDNA occurrence had a strong, positive association with water temperature, with occurrence unlikely below 14°C and very likely above 16°C, and a positive association with silt or organic substrates in pools, which was likely an indicator of higher-order stream reaches. In contrast, Coastal Tailed Frogs had a negative association with silt or organic substrates. Historical visual detections were generally congruent with findings using eDNA, but differences highlight important areas for further study. We did not detect Southern Torrent Salamanders using eDNA at any sites. Our study reinforces that ecological relationships of these species are varied, and shows the importance of maintaining the integrity of streams with diverse characteristics for conserving stream amphibians.

Metrics of disturbance in a redwood forest ecosystem: responses of stream amphibians to repeated sediment infusions

AbstractDisturbances are part of the natural dynamics of Earth's ecosystems, with these events more common now in the Anthropocene. Yet metrics for calibrating these impacts and measuring an ecosystem's capacity to recover are lacking. Highway construction in 1989 to bypass Prairie Creek Redwoods State Park in California resulted in storm‐driven infusion of exposed sediments into five streams; five nearby streams that were not intersected by the bypass construction were not affected by this event and served as controls for a natural experiment. A second large storm event in 1995 contributed sediment loads into all ten streams resulting in a disturbance gradient that allowed us to examine the effects of repeated sediment disturbances. We evaluated the impacts of these stresses on three resident stream amphibian species in 1990 and again in 1996. In 1990, the impacted streams had sixfold higher pool sediment loads and significantly lower larval tailed frog (Ascaphus truei) densities and lower densities of coastal giant salamanders (Dicamptodon tenebrosus) and southern torrent salamanders (Rhyacotriton variegatus) compared with the un‐impacted streams. During the six years between these storm events, pool bowl sediment loads increased 14‐fold in the previously un‐impacted streams and threefold in the previously impacted streams. Larval tailed frogs and torrent salamanders further declined in both sets of streams in 1996 although non‐significantly. In contrast, giant salamander densities increased in both stream sets. Of the three species, giant salamanders appeared the most resistant to the depositional events, while the other two species appeared to decline relative to the intensity of the sediment disturbances but still persist. We believe these results demonstrate the usefulness of these three amphibians as metrics for measuring the effects of this common disturbance type on the ecological resilience of stream networks in this and other temperate northwest forest ecosystems.

Comparative landscape genetics of two endemic torrent salamander species, Rhyacotriton kezeri and R. variegatus: implications for forest management and species conservation

Comparative landscape genetic studies provide insights into whether relationships between landscape features and patterns of spatial genetic structure differ among populations, species, habitat types, and regions. For species with fragmented distributions, especially when management practices contribute to fragmentation, tests of the factors structuring population connectivity are particularly important for understanding continued risks. We determined levels of genetic diversity and tested the relationships of landscape-scale vegetative, geographic, and climate variables with genetic distance in two congeneric, endemic salamander species with status of concern. Using microsatellite data for 326 Rhyacotriton kezeri and 557 Rhyacotriton variegatus individuals collected from 17 to 29 localities, respectively, we implemented a model of landscape resistance based on circuit theory. The northernmost portions of each species’ range is more fragmented than areas to the south, leading to the prediction that these areas would have relatively lower genetic diversity in response. Due to reliance of both species upon cold-water habitats, we predicted that landscape variables maintaining cool, moist microhabitats would be correlated with gene flow. Genetic structure was high overall and trended toward increasing with the proportion of the forested landscape. Based on maximum likelihood population effects models across genetic clusters and species, land cover and roads were the best predictors of genetic distance, even though the degree of fragmentation differed across each species’ geographic range. Our results suggest that forest cover is essential for dispersal in these salamanders, indicating negative effects of fragmentation resulting from timber harvest and other forest disturbances.

Landscape genetics and genetic structure of the southern torrent salamander, Rhyacotriton variegatus

Landscape genetic methods can be used to identify the most effective conservation measures to maintain functional connectivity among populations. Analyses of habitat factors that facilitate or restrict gene flow are particularly useful for species with specific habitat requirements and low dispersal rates. Rhyacotriton variegatus is a salamander species with low desiccation tolerance and a restricted geographic range, limited to the Pacific Northwest. Thus, we predicted that genetic distance would be positively correlated with climate and landscape variables that increase risk of desiccation. Two genetic distance measures, pairwise FST and proportion of shared alleles (DPS), suggested that gene flow was low among 19 sampling localities (367 total individuals) and genetic structure was high overall (DPS = 0.636 ± 0.010, FST = 0.330 ± 0.011; mean ± SD). Using both least-cost path and Circuitscape models of landscape resistance, we found that low stream cover, low canopy cover, high heat-load index, and short frost-free period all restricted gene flow among populations. We suggest that the conservation status of this species be revisited given this evidence of high genetic structure within the species, the level of habitat fragmentation in their range, and their reliance on dense canopy cover for dispersal. Maintaining stream corridors with buffers of dense canopy cover may maximize connectivity despite the pressures of timber harvest and urbanization.

Characterization of 10 microsatellite markers for the southern torrent salamander (Rhyacotriton variegatus)

Rhyacotriton variegatus is an endemic salamander species with specific habitat requirements and a restricted geographic range in the northwestern United States. Although not currently listed at the state or federal level, R. variegatus is vulnerable to habitat loss from timber harvest. We isolated and characterized 10 polymorphic microsatellite loci among 367 individuals from across the species’ range. The number of alleles per locus ranged from 7 to 16, observed heterozygosity ranged from 0.16 to 0.58, and expected heterozygosity ranged from 0.53 to 0.87. These new loci will assist in examining the genetic diversity and structure of R. variegatus and potentially related species.

Identifying Shared Genetic Structure Patterns among Pacific Northwest Forest Taxa: Insights from Use of Visualization Tools and Computer Simulations

BackgroundIdentifying causal relationships in phylogeographic and landscape genetic investigations is notoriously difficult, but can be facilitated by use of multispecies comparisons.Methodology/Principal FindingsWe used data visualizations to identify common spatial patterns within single lineages of four taxa inhabiting Pacific Northwest forests (northern spotted owl: Strix occidentalis caurina; red tree vole: Arborimus longicaudus; southern torrent salamander: Rhyacotriton variegatus; and western white pine: Pinus monticola). Visualizations suggested that, despite occupying the same geographical region and habitats, species responded differently to prevailing historical processes. S. o. caurina and P. monticola demonstrated directional patterns of spatial genetic structure where genetic distances and diversity were greater in southern versus northern locales. A. longicaudus and R. variegatus displayed opposite patterns where genetic distances were greater in northern versus southern regions. Statistical analyses of directional patterns subsequently confirmed observations from visualizations. Based upon regional climatological history, we hypothesized that observed latitudinal patterns may have been produced by range expansions. Subsequent computer simulations confirmed that directional patterns can be produced by expansion events.Conclusions/SignificanceWe discuss phylogeographic hypotheses regarding historical processes that may have produced observed patterns. Inferential methods used here may become increasingly powerful as detailed simulations of organisms and historical scenarios become plausible. We further suggest that inter-specific comparisons of historical patterns take place prior to drawing conclusions regarding effects of current anthropogenic change within landscapes.

Concerns regarding the use of amphibians as metrics of critical biological thresholds: a comment on Welsh & Hodgson (2008)

Summary1. Welsh & Hodgson (2008) argued that stream‐associated amphibians (Ascaphus truei, Dicamptodon tenebrosus and Rhyacotriton variegatus) are reliable indicators of ecosystem health in the Pacific Northwest (PNW), U.S.A. We demonstrate that their assertions rely on circular reasoning as well as logical and empirical assumptions that have not received rigorous evaluation.2. Welsh & Hodgson (2008) based their arguments on data collected in northwestern California, U.S.A. However, all three taxa occur across a wide range of environmental gradients in the PNW, and other research results suggest that the taxa respond differentially to environmental perturbations across their geographical distribution. Hence, differences in abundance are not always reliable indicators of the state of an ecosystem, as population numbers can be influenced by factors that may not be associated with habitat quality (e.g. predation and disease).3. Welsh & Hodgson (2008) present indices (rather than estimates) of abundance, which contain an unquantifiable amount of uncertainty not reliably attributable to either environmental or management factors. Evaluating parameters such as reproductive success and survival are more likely to provide strong inference about factors influencing population size than correlative studies that associate some measure of relative abundance with individual habitat features.4. We argue that direct measurement of physical features (water temperature, sediment and wood), for which Welsh & Hodgson (2008) suggest using amphibians as surrogates, is more accurate, efficient and cost effective compared with monitoring cryptic species with methods that are unable to quantify spatial and temporal uncertainty in biological responses.5. Headwater streams are critical components of catchments in the PNW, and all three amphibian taxa show strong associations with low‐order streams. However, we think research and monitoring of headwater streams should be guided by hypotheses that evaluate causal mechanisms, rather than relying on descriptive patterns that are limited in geographical scope and which support only weak inference about ecosystem processes. Other studies provide direct links between physical features and responses of target populations (i.e. fish). Adding a second correlative link (i.e. amphibians) provides no added benefit, and increases uncertainty in the association between management actions and changes in population size.

Amphibians as metrics of critical biological thresholds in forested headwater streams of the Pacific Northwest, U.S.A.

Summary1. Amphibians are recognized both for their sensitivity to environmental perturbations and for their usefulness as cost‐effective biometrics of ecosystem integrity (=system health).2. Twenty‐three years of research in headwater streams in the Klamath‐Siskiyou and North Coast Bioregions of the Pacific Northwest, U.S.A., showed distinct patterns in the distribution of amphibians to variations in water temperature, % fine sediments and the amount of large woody debris (LWD).3. Here, we review seven studies that demonstrate connections between species presence and abundance and these three in‐stream variables. These data were then used to calculate realized niches for three species, the southern torrent salamander, the larval coastal tailed frog and the larval coastal giant salamander, relative to two of these environmental stressors (water temperature and % fine sediments). Moreover, multivariate generalized additive models were used to predict the presence of these three amphibians when these three stressors act in concert.4. Stream‐dwelling amphibians are shown to be extremely sensitive to changes in water temperature, amounts of fine sediment and LWD, and specific thresholds and ranges for a spectrum of animal responses can be used to manage for headwater tributary ecosystem integrity.5. Consequently, amphibians can provide a direct metric of stream ecosystem integrity acting as surrogates for the ability of a stream network to support other stream‐associated biota, such as salmonids, and their related ecological services.

Low thermal tolerances of stream amphibians in the Pacific Northwest: Implications for riparian and forest management

Temperature has a profound effect on survival and ecology of amphibians. In the Pacific Northwest, timber harvest is known to increase peak stream temperatures to 24 ◦ C or higher, which has potential to negatively impact cold-water stream amphibians. I determined the Critical Thermal Maxima (CTmax) for two salamanders that are endemic to the Pacific Northwest. Rhyacotriton variegatus larvae acclimated at 10 ◦ C had mean CTmax of 26.7 ± 0. 7S D ◦ C and adults acclimated at 11 ◦ C had mean CTmax of 27.9 ± 1.1 ◦ C. These were among the lowest known values for any amphibian. Values were significantly higher for larval Dicamptodon tenebrosus acclimated at 14 ◦ C ( ¯ x = 29.1 ± 0.2 ◦ C). Although the smallest R. variegatus had some of the lowest values, size of larvae and adults did not influence CTmax in this species. Current forest practices retain riparian buffers along larger fish-bearing streams; however, such buffers along smaller headwaters and non-fish bearing streams may provide favorable habitat conditions for coldwater-associated species in the Pacific Northwest. The current study lends further evidence to the need for protection of Northwest stream amphibians from environmental perturbations. Forest guidelines that include riparian buffer zones and configurations of upland stands should be developed, while monitoring amphibian responses to determine their success.

Phylogeography and Spatial Genetic Structure of the Southern Torrent Salamander: Implications for Conservation and Management

The Southern torrent salamander (Rhyacotriton variegatus) was recently found not warranted for listing under the US Endangered Species Act due to lack of information regarding population fragmentation and gene flow. Found in small-order streams associated with late-successional coniferous forests of the US Pacific Northwest, threats to their persistence include disturbance related to timber harvest activities. We conducted a study of genetic diversity throughout this species' range to 1) identify major phylogenetic lineages and phylogeographic barriers and 2) elucidate regional patterns of population genetic and spatial phylogeographic structure. Cytochrome b sequence variation was examined for 189 individuals from 72 localities. We identified 3 major lineages corresponding to nonoverlapping geographic regions: a northern California clade, a central Oregon clade, and a northern Oregon clade. The Yaquina River may be a phylogeographic barrier between the northern Oregon and central Oregon clades, whereas the Smith River in northern California appears to correspond to the discontinuity between the central Oregon and northern California clades. Spatial analyses of genetic variation within regions encompassing major clades indicated that the extent of genetic structure is comparable among regions. We discuss our results in the context of conservation efforts for Southern torrent salamanders.

Life History of the Southern Torrent Salamander (Rhyacotriton variegatus) in Coastal Northern California

Southern Torrent Salamanders (Rhyacotriton variegatus) range widely from north coastal Oregon to northern California but are a patchily distributed inhabitant of forested seeps and headwater springs. We collected bimonthly samples of this species from managed forest sites in the Mad River watershed, Humboldt County. Larvae were measured, marked, and released, but a limited number of transformed individuals were preserved for laboratory analyses. North coastal R. variegatus breeds annually and has an extended courtship and egg-laying period. Cloacal spermatophores were present in gravid females from February through June, and oviposition likely occurs spring through fall. A prolonged larval period (hatching to metamorphosis) lasts 2–2.5 yr; transformed females require another 1.5–2 yr until first breeding, and clutch size averages 7.5 eggs. Adult sizes, size at metamorphosis, and developmental times were comparable to north coastal Oregon R. variegatus, suggesting that a simple north-south, harsh-mild environmental cline does not influence developmental time for coastal populations. Unexpectedly, clutch size and size-fecundity relationships for the California population of R. variegatus were more similar to Rhyacotriton cascadae, an inland, northern species with longer larval periods and larger sizes at metamorphosis, than to R. variegatus in north coastal Oregon. Rhyacotriton variegatus has limited rates of population increase because of long generation times and low fecundities and could be highly sensitive to frequent disturbances that impact numbers.

Ultrastructure of the annual cycle of female sperm storage in spermathecae of the torrent salamander, Rhyacotriton variegatus (Amphibia: Rhyacotritonidae).

This study is the first report on the ultrastructure of the sperm storage glands (spermathecae) in the salamander Rhyacotriton variegatus. The population studied is associated with cold-water, rocky streams of the redwood (Sequoia) zone in northern California. Males possess sperm in their vasa deferentia and undergo spermiation throughout the year, but mating is seasonal. Most females with large, vitellogenic follicles (2.0-3.9 mm mean dia.) collected from February-June contain sperm in their spermathecae, although some females with large follicles lack sperm. Other mature-size females collected during this period have small ovarian follicles (0.9-1.2 mm mean dia.) and lack stored sperm. All females collected from September-November have small follicles (0.6-1.6 mm mean dia.) and lack sperm, except in one instance in which a female collected in November had a small amount of degraded sperm, apparently retained from the previous breeding season. The spermathecae consist of simple tubulo-alveolar glands in which the neck tubules produce a mucoid secretory product, and the distal bulbs, where sperm are stored, contain secretory vacuoles of uniform density that stain positively for glycosaminoglycans. In specimens containing sperm, some bulbs have abundant sperm and others lack sperm, but the ultrastructure is similar in both conditions. The acini contain columnar epithelial cells with wide intercellular canaliculi, and a merocrine process releases the secretion. Spermiophagy occurs. In specimens from spring and summer with small ovarian follicles, the neck tubules are similar to those of breeding females, but the distal bulbs are reduced to cords of cells lacking a discernible lumen. Secretory activity in the distal bulbs is initiated in the fall. Spermathecae of R. variegatus are most similar to those of a stream-dwelling plethodontid, Eurycea cirrigera.

Sperm Aggregations in the Spermathecae of Southern Torrent Salamanders, Rhyacotriton variegatus

Female salamanders in the suborder Salamandroidea store sperm in cloacal glands called spermathecae. Scanning electron microscopy was used to study these glands in females of the Southern Torrent Salamander, Rhyacotriton variegatus (Rhyacotritonidae), from northern California. Sperm initially enter the cloaca in a tangled mass from the spermatophore cap, but within the spermathecal tubules, small groups become aligned along their long axes. Sperm nuclei typically are embedded in apical microvilli of the secretory cells forming the distal acini of the spermathecae. Junctional complexes between apices of adjacent epithelial cells are occasionally broached or otherwise absent, and sperm can be found in the intercellular canaliculi between such cells. Spermathecae of R. variegatus are simple glands that branch off a tube extending dorsally into cloacal tissue. This spermathecal anatomy is in-between that of the Plethodontidae, which have a compound tubuloaveolar gland as the single spermatheca, and other salamandroids, in which sperm storage occurs in numerous simple tubular glands, each one a spermatheca. Sperm associations in the simple spermathecae of R. variegatus, however, are most similar to those reported for plethodontids.

Three New Nests of the Columbia Torrent Salamander, Rhyacotriton kezeri, in Oregon with Observations of Nesting Behavior

mander (R. kezeri) in Tillamook County, Oregon, and another in Wahkiakum County, Washington. Karraker (1999) recently documented a southern torrent salamander (R. variegatus) nest in Humboldt County, California. Here we provide new information on the nesting behavior of Rhyacotriton kezeri, including 3 new nest site descriptions for R. kezeri in Oregon and the 1st report of adult female Rhyacotriton associated with nests.

Sensitivity to urea fertilization in three amphibian species.

Forest fertilization with granular urea is a well-established management practice in many forested regions of the world. We hypothesize that chemical forest fertilizers may be affecting forest-dwelling wildlife. In the laboratory, we studied the effects of fertilization doses of granular urea on three species of forest-dwelling amphibians (Plethodon vehiculum, Rhyacotriton variegatus, and Taricha granulosa). In avoidance experiments, the three species avoided a substrate treated with a dose of 225 kg N/ha urea. In toxicity experiments, we exposed amphibians to urea at doses of 225 kg N/ha and 450 kg N/ha for 4 days. The observed effects increased with time and dose, and there were significant differences in sensitivity among the species. Both treatment levels had an acute effect on survival of P. vehiculum and R. variegatus. At 24 h, mortality at the highest dose was 67% for P. vehiculum, and 47% for R. variegatus. In contrast, there was no mortality for T. granulosa at these concentrations. We suggest that environmental levels of urea could be affecting behavior and survival of some amphibians species in fertilized forests.

STREAM AMPHIBIANS AS INDICATORS OF ECOSYSTEM STRESS:A CASE STUDY FROM CALIFORNIA’S REDWOODS

Road construction of the Redwood National Park highway bypass resulted in a large accidental infusion of fine sediments into pristine streams in Prairie Creek State Park, California, during an October 1989 storm event. This incident provided a natural experiment where we could measure, compare, and evaluate native stream amphibian densities as indicators of stream ecosystem stress. We employed a habitat-based, stratified sampling design to assess the impacts of these sediments on the densities of aquatic amphibians in five impacted streams by comparing them with densities in five adjacent, unimpacted (control) streams. Three species were sampled in numbers sufficient to be informative: tailed frogs (Ascaphus truei, larvae), Pacific giant salamanders (Dicamptodon tenebrosus, paedomorphs and larvae), and southern torrent salamanders (Rhyacotriton variegatus, adults and larvae). Densities of amphibians were significantly lower in the streams impacted by sediment. While sediment effects were species specific,...

Chemical Alarm Signalling in Terrestrial Salamanders: Intra‐ and Interspecific Responses

AbstractChemical alarm cues are known to be important in mediating predator avoidance in a variety of taxonomic groups. The purpose of this study was to test whether three species of salamanders that co‐occur in the coastal mountains of Oregon utilize chemical alarm cues in predator avoidance. In laboratory experiments, Western redback salamanders, Plethodon vehiculum, and Southern torrent salamanders, Rhyacotriton variegatus, exhibited an avoidance response to stimuli from injured conspecifics, while Dunn's salamanders, Plethodon dunni did not. Additional experiments demonstrated interspecific alarm responses. P. vehiculum and R. variegatus responded to each other's alarm cues but did not respond to the alarm cues of allotopic long‐toed salamanders, Ambystoma macrodactylum. For R. variegatus, this is despite the fact that they are more closely related to the allotopic species (A. macrodactylum) than to the syntopic species (P. vehiculum). Thus phylogeny alone may not explain patterns of cross‐species alarm responses. Instead, interspecific alarm responses may occur between syntopic species that belong to the same prey guild (i.e. those species that co‐occur spatially and temporally and are exposed to the same suite of predators).

Habitat Correlates of the Southern Torrent Salamander, Rhyacotriton variegatus (Caudata: Rhyacotritonidae), in Northwestern California

Asystematic stratified sampling design was used to quantify the habitat relationships of the southern torrent salamander, Rhyacotriton variegatus, in northwestern California. We sampled 53 first to third order streams, each surrounded by at least 5-7 ha of relatively homogeneous forest or harvested forest habitat. Measurements of 121 attributes of the forest and stream environment were recorded in conjunction with area-constrained aquatic sampling for salamanders. A subset of 68 variables, grouped into 11 ecological components including attributes at the landscape, macrohabitat, and microhabitat scales, was used in a hierarchical analysis of habitat associations. Results from discriminant and regression analyses indicated that this species occurs within a relatively narrow range of physical and microclimatic conditions and is associated with cold, clear headwater to low-order streams with loose, coarse substrates (low sedimentation), in humid forest habitats with large conifers, abundant moss, and HO% canopy closure. Thus, the southern torrent salamander demonstrates an ecological dependence on conditions of microcli- mate and habitat structure that are typically best created, stabilized, and maintained within late seral forests in northwestern California.

Distribution and Habitat of Rhyacotriton variegatus in Managed, Young Growth Forests in North Coastal California

We examined the distribution and habitat of Rhyacotriton variegatus in streams of managed forests in north coastal California. We found 1475 salamanders from 220 streams from 1990-1994 through surveys of randomly selected first and second order streams and incidental searches. Of 71 headwater streams randomly selected to relate landscape variables to the presence/absence of R. variegatus, 57 (80.3%) contained salamanders. Geological formation was the only landscape variable that predicted the presence of R. variegatus in a stepwise logistic regression model. A second survey was conducted to determine which habitat variables of stream reaches were related to the presence/absence of R. variegatus. Thirty- one of 64 stream reaches contained salamanders and stream slope (gradient) was the only variable of 20 measured that entered a stepwise logistic regression model to predict the presence of R. variegatus. Pairwise comparisons indicated that reaches with salamanders had significantly higher slope, more small boulders, and less sand. No other variables, including canopy closure and water temperatures, were significant. An additional survey to further define the microhabitat for R. variegatus showed that abundance was positively related to stream slope and that this species was found more often than expected in high gradient riffles. The preferred substrate was gravel with smaller amounts of silt/clay, sand, and cobble. We discuss the past and future impacts of timber harvest on this species in north coastal California. Results of studies in Douglas-fir (Pseudotsuga