Ensatina Research Articles

Wildfires disturb the natural skin microbiota of terrestrial salamanders.

Environmental change can disturb natural associations between wildlife and microbial symbionts, in many cases to the detriment of host health. We used a North American terrestrial salamander system to assess how the skin microbiota of amphibians responds to wildfires. In northern California's redwood/oak forests, we assessed how recent wildfires affected the skin microbiota of three different salamander species (Taricha sp., Batrachoseps attenuatus, and Ensatina eschscholtzii) over two different sampling seasons in 2018 and 2021. We found species-specific responses to wildfire disturbance on the alpha diversity of the skin microbiota of terrestrial salamanders, although burning in general altered the composition of the skin microbiota. The effect of burning on alpha diversities and body condition indices varied by sampling season, suggesting an additional effect of annual climatic conditions on body condition and skin microbiota response. We tested all salamanders for Batrachochytrium dendrobatidis and found four infected individuals in 2018 and none in 2021. Our study documents correlations in the skin microbiota response to an increasing source of disturbance in western North American ecosystems. In addition, our results highlight the need to consider the effects of increased wildfire regimes/intensities and longitudinal effects on wildlife-associated microbiota and animal health.

Characterizing lift, drag, and pressure differences across wandering salamanders (Aneides vagrans) with computational fluid dynamics to investigate aerodynamics.

Wandering salamanders (Aneides vagrans), known to occupy the crowns of old growth coast redwood trees, have recently been found to decelerate and engage in controlled, nonvertical descent while falling. Closely related, nonarboreal species with seemingly minor morphological differences exhibit far less behavioral control while falling; however, the influence of salamander morphology on aerodynamics remains to be tested. Here, we examine differences in morphology and aerodynamics of two salamander species, A. vagrans and the nonarboreal ensatina salamander (Ensatina eschscholtzii), using a combination of traditional and contemporary techniques. Specifically, we compare morphometrics statistically, then use computational fluid dynamics (CFD) to characterize predicted airflow and pressure over digitally reconstructed models of the salamanders. While similar in body and tail lengths, A. vagrans are more dorsoventrally flattened with longer limbs and greater surface area of the foot relative to body size than the nonarboreal E. eschscholtzii. CFD results show dorsoventral pressure gradients differ between the two digitally reconstructed salamanders resulting in lift coefficients of approximately 0.02 and 0.00, and lift:drag ratios of approximately 0.40 and 0.00 for A. vagrans and E. eschscholtzii, respectively. We conclude that the morphology of A. vagrans is better suited for controlled descent than that of the closely related E. eschscholtzii and highlight the importance of subtle morphological features, such as dorsoventral flatness, foot size, and limb length, for aerial control. That our simulation reports align with real-world performance data underscores the benefits of CFD for studying the link between morphology and aerodynamics in other taxa.

Evidence for ephemeral ring species formation during the diversification history of western fence lizards (Sceloporus occidentalis).

Divergence is often ephemeral, and populations that diverge in response to regional topographic and climatic factors may not remain reproductively isolated when they come into secondary contact. We investigated the geographical structure and evolutionary history of population divergence within Sceloporus occidentalis (western fence lizard), a habitat generalist with a broad distribution that spans the major biogeographical regions of Western North America. We used double digest RAD sequencing to infer population structure, phylogeny and demography. Population genetic structure is hierarchical and geographically structured with evidence for gene flow between biogeographical regions. Consistent with the isolation-expansion model of divergence during Quaternary glacial-interglacial cycles, gene flow and secondary contact are supported as important processes explaining the demographic histories of populations. Although populations may have diverged as they spread northward in a ring-like manner around the Sierra Nevada and southern Cascade Ranges, there is strong evidence for gene flow among populations at the northern terminus of the ring. We propose the concept of an "ephemeral ring species" and contrast S.occidentalis with the classic North American ring species, Ensatina eschscholtzii. Contrary to expectations of lower genetic diversity at northern latitudes following post-Quaternary-glaciation expansion, the ephemeral nature of divergence in S.occidentalis has produced centres of high genetic diversity for different reasons in the south (long-term stability) vs. the north (secondary contact).

Experimental evidence indicates variable responses to forest disturbance and thermal refugia by two plethodontid salamanders

Understanding how natural and anthropogenic disturbances affect sensitive species is critical to support conservation programs as land use activities and climatic conditions change. Forest management provides a range of ecosystem services to expanding human populations including production of substantial amounts of woody biomass, thereby reducing area under management and increasing opportunity for conservation designations. However, relatively little experimental information is available to describe how manipulating habitat at multiple scales may affect spatial and temporal variation in populations of climate-sensitive forest taxa. We conducted a Before-After Control-Impact experiment over seven years to evaluate responses of two species of Plethodontid salamanders in operational treatment (harvest, replanting, and herbicide application) and control units, Oregon, USA. In addition, we capitalized on existing variation in downed wood size and accounted for potential behavioral responses to evaluate the thermal refugia hypothesis. For Oregon slender salamanders (Batrachoseps wrighti), mean plot-level occupancy (90% CRI) was increased an estimated 11% (1.11; 0.62–2.1) and estimated mean abundance reduced 16% (0.84; 0.54–1.4) post-harvest. For Ensatina (Ensatina eschscholtzii), mean occupancy was reduced an estimated 80% (0.20; 0.08–0.47) and estimated mean abundance reduced 63% (0.37; 0.22–0.65) post-harvest. We found strong evidence of positive associations for both species with downed wood amount. As predicted, we found ambient temperatures to be higher in harvest than control units. Also, internal downed wood temperatures were warmer in harvested units, suggesting these structures may not have provided adequate thermal refugia. Application of an experimental framework provided evidence about both stand and structure level responses to active management. Habitat structures did not appear to buffer against substantial variation in local climate but evidence was equivocal about importance of these structures to population retention. Monitoring of recruitment and retention of downed wood through subsequent rotations can provide critical information to reduce trade-offs between wood production and conservation of climate sensitive taxa.

Cling performance and surface area of attachment in plethodontid salamanders.

Plethodontid salamanders inhabit terrestrial, scansorial, arboreal and troglodytic habitats in which clinging and climbing allow them to access additional food and shelter as well as escape from unfavorable temperature and moisture conditions and ground-dwelling predators. Although salamanders lack claws and toe pads found in other taxa, they successfully cling to and climb on inclined, vertical and inverted substrates in nature. Maximum cling angle was tested on smooth acrylic, and the relationship between cling angle, body mass and surface area of attachment (contact area) was investigated. This study found that many salamander species can cling fully inverted using only a portion of their ventral surface area to attach. Salamanders fall into three functional groups based on mass and maximum cling angle: (1) high-performing, very small salamanders, (2) moderately high performing small and medium-sized salamanders and (3) low-performing large salamanders. They show significant differences in maximum cling angle, even between species of similar mass. In species of similar mass experiencing significantly different detachment stress (resulting from significantly different contact area), differences in morphology or behavior affect how much body surface is attached to the substrate. High performance in some species, such as Desmognathus quadramaculatus, is attributable to large contact area; low performance in a similarly sized species, Ensatina eschscholtzii, is due to behavior that negatively impacts contact area. There was no clear evidence of scaling of adhesive strength with increasing body size. Salamander maximum cling angle is the result of morphology and behavior impacting the detachment stresses experienced during clinging.

Skin Microbiomes of California Terrestrial Salamanders Are Influenced by Habitat More Than Host Phylogeny.

A multitude of microorganisms live on and within plant and animal hosts, yet the ecology and evolution of these microbial communities remains poorly understood in many taxa. This study examined the extent to which environmental factors and host taxonomic identity explain microbiome variation within two salamander genera, Ensatina and Batrachoseps, in the family Plethodontidae. In particular, we assessed whether microbiome differentiation paralleled host genetic distance at three levels of taxonomy: genus and high and low clade levels within Ensatina eschscholtzii. We predicted that more genetically related host populations would have more similar microbiomes than more distantly related host populations. We found that salamander microbiomes possess bacterial species that are most likely acquired from their surrounding soil environment, but the relative representation of those bacterial species is significantly different on the skin of salamanders compared to soil. We found differences in skin microbiome alpha diversity among Ensatina higher and lower clade groups, as well as differences between Ensatina and Batrachoseps. We also found that relative microbiome composition (beta diversity) did vary between Ensatina lower clades, but differences were driven by only a few clades and not correlated to clade genetic distances. We conclude this difference was likely a result of Ensatina lower clades being associated with geographic location and habitat type, as salamander identity at higher taxonomic levels (genus and Ensatina higher clades) was a weak predictor of microbiome composition. These results lead us to conclude that environmental factors are likely playing a more significant role in salamander cutaneous microbiome assemblages than host-specific traits.

Dynamics and thermal sensitivity of ballistic and non-ballistic feeding in salamanders.

Low temperature reduces the performance of muscle-powered movements, but in movements powered by elastic recoil mechanisms, this effect can be mitigated and performance can be increased. To better understand the morphological basis of high performance and thermal robustness of elastically powered movements, we compared feeding dynamics at a range of temperatures (5-25°C) in two species of terrestrial plethodontid salamanders, Plethodon metcalfi and Ensatina eschscholtzii, which differ in tongue muscle architecture and the mechanism of tongue projection. We found that Ensatina is capable of ballistic projection with a mean muscle mass-specific power of 2100 W kg(-1), revealing an elastic mechanism. Plethodon, in contrast, projected its tongue non-ballistically with a mean power of only 18 W kg(-1), indicating it is muscle powered. Ensatina projected its tongue significantly farther than Plethodon and with dynamics that had significantly lower thermal sensitivity at temperatures below 15°C. These performance differences were correlated with morphological differences, namely elongated collagenous aponeuroses in the projector muscle of Ensatina as compared with Plethodon, which are likely the site of energy storage, and the absence in Ensatina of projector muscle fibers attaching to the tongue skeleton that allows projection to be truly ballistic. These findings demonstrate that, in these otherwise similar species, the presence in one species of elaborated connective tissue in series with myofibers confers not only 10-fold greater absolute performance but also greater thermal robustness of performance. We conclude that changes in muscle and connective tissue architecture are sufficient to alter significantly the mechanics, performance and thermal robustness of musculoskeletal systems.

Slow Lives in the Fast Landscape: Conservation and Management of Plethodontid Salamanders in Production Forests of the United States

Intensively-managed forest (IMF) ecosystems support environmental processes, retain biodiversity and reduce pressure to extract wood products from other forests, but may affect species, such as plethodontid salamanders, that are associated with closed canopies and possess limited vagility. We describe: (1) critical aspects of IMF ecosystems; (2) effectiveness of plethodontid salamanders as barometers of forest change; (3) two case studies of relationships between salamanders and coarse woody debris (CWD); and (4) research needs for effective management of salamanders in IMF ecosystems. Although plethodontid salamanders are sensitive to microclimate changes, their role as ecological indicators rarely have been evaluated quantitatively. Our case studies of CWD and salamanders in western and eastern forests demonstrated effects of species, region and spatial scale on the existence and strength of relationships between plethodontid species and a “critical” microhabitat variable. Oregon slender salamanders (Batrachoseps wrighti) were more strongly associated with abundance of CWD in managed second growth forests than ensatina salamanders (Ensatina eschscholtzii). Similarly, CWD was not an important predictor of abundance of Appalachian salamanders in managed hardwood forest. Gaining knowledge of salamanders in IMF ecosystems is critical to reconciling ecological and economic objectives of intensive forest management, but faces challenges in design and implementation.

Responses of the woodland salamander Ensatina eschscholtzii to commercial thinning by helicopter in late-seral Douglas-fir forest in northwest California

We examined responses of the woodland salamander Ensatina (Ensatina eschscholtzii) to commercial thinning by helicopter in late-seral Douglas-fir forest in northwestern California, USA, using a before-after control-impact (BACI) design. We employed passive pitfall traps on eight (four each treatment and control) 100 trap grids over eight years (1996–2003), three years pre- and five years post-treatment. We conducted 3–11 weekly site visits within each of 10 trap periods depending upon weather over two spring and eight fall periods for a total of 50 visits to test for differences in surface counts and body condition. We standardized data to captures/1000 trap nights. Surface counts over the eight years were highly variable with less surface activity in spring compared to fall. Although the BACI design allows for initial differences among pre-treatment grids there were none. However, in the three years post-treatment (1999–2001) mean counts on treatment grids were significantly lower than on control grids. By 2002 and 2003, post-treatment counts on control and treatment grids both declined substantially, such that despite 47% more salamanders on control grids, variability was sufficient to preclude statistical significance. Recapture rates averaged 23.3% for three years pre-treatment, but increased to 51.4% for the five years post-treatment. Pre-treatment population estimates increased on control grids post-treatment, however, surface density estimates declined. On treatment grids both population and density estimates declined following treatment. Body condition analyses indicated no significant differences between controls and treatments for either sex prior to or post-treatment. The three years of significant differences in surface counts between controls and treatments post-treatment, followed by no differences in the last two years of the study, combined with no differences in BCIs, lead us to conclude that the surface activity of Ensatina on treatments grids was only temporarily impacted by the thinning. Declining population estimates on treatment grids also indicated at least a temporary reduction in those populations. We unexpectedly found declines in counts and density estimates on both sets of grids over the eight years, suggesting a wider effect may be causing reductions in the surface activity of these salamanders, and possibly in their populations.

The trophic role of a forest salamander: impacts on invertebrates, leaf litter retention, and the humification process

Woodland (Plethodontid) salamanders are the most abundant vertebrates in North American forests, functioning as predators on invertebrates and prey for higher trophic levels. We investigated the role of Ensatina (Ensatina eschscholtzii) in regulating invertebrate numbers and leaf litter retention in a northern California forest. Our objective was to examine how salamander predation on invertebrates affects leaf litter retention and the amount available for soil‐building and carbon capture at the litter‐soil interface. We used field enclosures to quantify the effects of Ensatina on invertebrates and litter retention over two wet seasons, using moisture as a covariate. In the first year Ensatina reduced Coleoptera (beetles) and Diptera (flies) larvae >2 mm, adult Coleoptera, Collembola (springtails), and Formicidae (ants), and increased Oribatid mites, larvae <2 mm (Diptera and Coleoptera), Diplopoda (millipedes), and Aranaea (spiders) <2 mm by reducing their competitors and predators. A single Ensatina in a 1.5m2 enclosure increased litter retention by 13.3% ± 3.6% (mean ± SE) compared to controls, facilitating the capture of 200 kg/ha of carbon. At a similar density range‐wide this would equate to 72.3 metric tons/yr of carbon in one season potentially sequestered in forest soil rather than entering the atmosphere. In the second year invertebrate densities doubled in response to early rains such that while salamanders reduced the numbers of the same taxa, effect sizes were lower compared to year one, producing biological effects that failed to achieve statistical significance. However, three taxa did significantly increase in year two (Annelida [worms], Psocoptera [barklice], and Chelonethida [pseudoscorpions]). Litter retention in year two was greater on treatment plots by 5.6% ± 4.6%; however, high variability across plots precluded statistical significance. Ensatina suppressed some invertebrate taxa, released others, increased leaf litter retention, and facilitated greater carbon capture in both years; however, the strength of the effects were modulated by the bottom‐up effects of the timing and amount of precipitation in year two.

Woodland salamanders as metrics of forest ecosystem recovery: a case study from California's redwoods

Woodland (Plethodontid) salamanders occur in huge numbers in healthy forests in North America where the abundances of many species vary along successional gradients. Their high numbers and trophic role as predators on shredder and decomposer arthropods influence nutrient and carbon pathways at the leaf litter/soil interface. Their extreme niche conservatism and low vagility offer further advantages to the use of these salamanders as metrics of forest ecosystem condition. Mill Creek is a 103 km2 commercially logged redwood forest watershed acquired as parkland where original primary forest is being restored. This study evaluated woodland salamanders as metrics of seral recovery at Mill Creek. Surface counts and body condition were examined in four sets of stands, two early seral, one mature, and one of primary forest (never harvested old‐growth). Later seral sites were closer to the coast where fog increased available moisture; younger sites were further inland at higher elevations where fog was reduced. We distinguished the effects of geography and succession using ANCOVA with a PCA‐derived landscape covariate. Both geography and succession increased counts of California Slender Salamanders (Batrachoseps attenuatus); advancing succession alone indicated increased counts of Ensatina (Ensatina eschscholtzii). Means and variances in body condition of these two species were lower in older stands; for the Del Norte salamander (Plethodon elongatus) only the means were lower. Coastal proximity increased mean body condition in E. eschscholtzii, but with P. elongatus it was the opposite. We modeled surface counts and body condition along environmental gradients associated with succession. The counts and body condition in two of three species when taken together suggested that the increased structural complexity in late‐seral forest stands supported larger populations that appeared to be competing for limited resources and, thus, likely have greater population fitness than those in younger forests. B. attenuatus and E. eschscholtzii proved to be viable metrics of advancing succession with their numbers and body condition providing readily quantifiable measures of ecosystem recovery at Mill Creek.

Temporal changes in the relative abundance of amphibians relative to riparian buffer width in western Washington, USA

In certain regions of Canada and the United States, amphibians have been shown to be sensitive to forest management and the short-term adverse effects of timber harvesting on terrestrial amphibians have been well documented in the literature. However, the effects of silvicultural treatments on amphibians may not be realized until many years after treatment. Manipulative forest management experiments with pre- and post-treatment data, random assignment of replicates to treatments, and analyses over a large spatial scale are rare in the literature. Furthermore, even studies with pre- and post-treatment data can be affected by ecological time lags; the longevity of some species may mean that it could take several years to observe a treatment effect. Riparian areas in forested landscapes of the Pacific Northwest have been recognized for high species richness of amphibians yet little is known about the persistence of amphibians in mature forest fragments such as unharvested riparian buffers surrounded by clearcuts. Our study investigated the efficacy, 2 and 10 years post-logging, of two different riparian management zone prescriptions established around third- and fourth-order streams in western Washington to mitigate the effects of upland timber harvest on amphibians. Our findings suggest that there is no global response by terrestrial amphibians to logging or to the retention of riparian management zones. Rather, species showed individual responses that varied over time and between treatments and transects. Specifically Coastal Tailed Frogs (Ascaphus truei) declined in clearcut upland habitats 2- and 10-years following logging while Western Red-backed Salamander (Plethodon vehiculum) and Ensatina (Ensatina eschscholtzii) appear to benefit from the recommended riparian management zone width. The influence of site effects was evident for some species, whereas for others there is some suggestion of treatment effects, but the analyses were confounded by patterns of natural population change at both local and regional scales, which were evident 2 years following logging. Our results exemplify the need for longer-term studies to ensure that potentially confounding factors, such as natural population fluctuation, are considered when interpreting the results of time series data.

Ring distributions leading to species formation: a global topographic analysis of geographic barriers associated with ring species

BackgroundIn the mid 20th century, Ernst Mayr and Theodosius Dobzhansky championed the significance of circular overlaps or ring species as the perfect demonstration of speciation, yet in the over 50 years since, only a handful of such taxa are known. We developed a topographic model to evaluate whether the geographic barriers that favor processes leading to ring species are common or rare, and to predict where other candidate ring barriers might be found.ResultsOf the 952,147 geographic barriers identified on the planet, only about 1% are topographically similar to barriers associated with known ring taxa, with most of the likely candidates occurring in under-studied parts of the world (for example, marine environments, tropical latitudes). Predicted barriers separate into two distinct categories: (i) single cohesive barriers (< 50,000 km2), associated with taxa that differentiate at smaller spatial scales (salamander: Ensatina eschscholtzii; tree: Acacia karroo); and (ii) composite barriers - formed by groups of barriers (each 184,000 to 1.7 million km2) in close geographic proximity (totaling 1.9 to 2.3 million km2) - associated with taxa that differentiate at larger spatial scales (birds: Phylloscopus trochiloides and Larus (sp. argentatus and fuscus)). When evaluated globally, we find a large number of cohesive barriers that are topographically similar to those associated with known ring taxa. Yet, compared to cohesive barriers, an order of magnitude fewer composite barriers are similar to those that favor ring divergence in species with higher dispersal.ConclusionsWhile these findings confirm that the topographic conditions that favor evolutionary processes leading to ring speciation are, in fact, rare, they also suggest that many understudied natural systems could provide valuable demonstrations of continuous divergence towards the formation of new species. Distinct advantages of the model are that it (i) requires no a priori information on the relative importance of features that define barriers, (ii) can be replicated using any kind of continuously distributed environmental variable, and (iii) generates spatially explicit hypotheses of geographic species formation. The methods developed here - combined with study of the geographical ecology and genetics of taxa in their environments - should enable recognition of ring species phenomena throughout the world.

Asymmetric reproductive isolation between terminal forms of the salamander ring species Ensatina eschscholtzii revealed by fine-scale genetic analysis of a hybrid zone

BackgroundRing species, exemplified by salamanders of the Ensatina eschscholtzii complex, represent a special window into the speciation process because they allow the history of species formation to be traced back in time through the geographically differentiated forms connecting the two terminal forms of the ring. Of particular interest is the nature and extent of reproductive isolation between the geographically terminal forms, in this case E. e. eschscholtzii and E. e. klauberi. Previous studies have documented infrequent hybridization at the end of the ring. Here, we report the first fine-scale genetic analysis of a hybrid zone between the terminal forms in southern California using individual-based Bayesian analyses of multilocus genetic data to estimate levels and direction of hybridization and maximum-likelihood analysis of linkage disequilibrium and cline shape to make inferences about migration and selection in the hybrid zone.ResultsThe center of the hybrid zone has a high proportion of hybrids, about half of which were classified as F1s. Clines are narrow with respect to dispersal, and there are significant deviations from Hardy-Weinberg equilibrium as well as nonrandom associations (linkage disequilibria) between alleles characteristic of each parental type. There is cytonuclear discordance, both in terms of introgression and the geographic position of mitochondrial versus nuclear clines. Genetic disequilibrium is concentrated on the eschscholtzii side of the zone. Nearly all hybrids possess klauberi mtDNA, indicating that most hybrids are formed from female klauberi mating with male eschscholtzii or male hybrids (but not vice versa).ConclusionsOur results are consistent with a tension zone trapped at an ecotone, with gene combinations characteristic of klauberi showing up on the eschscholtzii side of the zone due to asymmetric hybridization. We suggest that the observed asymmetry is best explained by increased discriminatory power of eschscholtzii females, or asymmetric postzygotic isolation. The relatively high frequency of hybrids, particularly F1s, contrasts with other contacts between the terminal forms, and with other contacts between other divergent Ensatina lineages, highlighting the diverse outcomes of secondary contact within a single species complex.

GENETIC LEAKAGE AFTER ADAPTIVE AND NONADAPTIVE DIVERGENCE IN THEENSATINA ESCHSCHOLTZIIRING SPECIES

The salamander Ensatina eschscholtzii is an example of a ring species in which extant intermediate stages of terminal forms have a nearly continuous range, offering replicated interactions at several stages of divergence. We employ a greatly expanded allozyme database and individual-based analyses to separate the effects of divergence time and gene flow to evaluate how gradual divergence of populations around the ring contributes to the development of reproductive isolation. Despite the high degree of genetic (D<or= 0.39) and ecomorphological divergence observed in secondary contacts around the ring, reproductive isolation or rare hybridization is observed only at the terminus of the ring. Instead, in the secondary contacts sampled around the ring, hybrids are common and reproductively successful, enabling genetic leakage between parental genomes and the potential for genetic merger. Nevertheless, genetic admixture is geographically broad (<100 km) only in contacts between ecomorphologically similar populations (within subspecies). When divergence is accompanied by alternative patterns of adaptive divergence (between subspecies), zones of intergradation are narrower and affect populations only locally (>8 km). Diversification and consequent genetic interactions in Ensatina reveal a continuum between populations, ecological races, and species, where polytypic traits and high genetic differentiation are maintained without reproductive isolation.

Isolation and characterization of 15 polymorphic microsatellites in the Plethodontid salamander Ensatina eschscholtzii

We developed 15 new polymorphic microsatellites for the plethodontid salamander Ensatina eschscholtzii. Loci were isolated from a genomic library from Ensatina eschscholtzii xanthoptica enriched for (AAAG)(n) repetitive elements. The number of alleles per locus ranged from 4 to 20 (mean 9) in the sampled population. Observed heterozygosity ranged from 0.37 to 1. None of the loci deviated from Hardy-Weinberg equilibrium or showed significant linkage disequilibrium after a Bonferroni correction for multiple comparisons. All loci amplified in the six other subspecies of the Ensatina eschscholtzii complex. These new markers will prove useful in measuring gene flow and population structure as well as patterns of mating and sperm use in Ensatina.

Closing the ring: historical biogeography of the salamander ring species Ensatina eschscholtzii

AbstractAim The salamander Ensatina eschscholtzii Gray is a classic example of a ring species, or a species that has expanded around a central barrier to form a secondary contact characterized by species‐level divergence. In the original formulation of the ring species scenario, an explicit biogeographical model was proposed to account for the occurrence of intraspecific sympatry between two subspecies in southern California (the ‘southern closure’ model). Here we develop an alternative ring species model that is informed by the geomorphological development of the California Coast Ranges, and which situates the point of ring closure in the Monterey Bay region of central coastal California (the ‘Monterey closure’ model). Our study has two aims. The first is to use phylogenetic methods to evaluate the two competing biogeographical models. The second is to describe patterns of phylogeographical diversity throughout the range of the Ensatina complex, and to compare these patterns with previously published molecular systematic data.Location Western North America, with a focus on the state of California, USA.Methods We obtained mitochondrial DNA sequence data from 385 individuals from 224 populations. A phylogeny was inferred using Bayesian techniques, and the geographical distributions of haplotypes and clades were mapped. The two biogeographical ring species models were tested against our Bayesian topology, including the associated Bayesian 95% credible set of trees.Results High levels of phylogeographical diversity were revealed, especially in central coastal and northern California. Our Bayesian topology contradicts the Monterey closure model; however, 0.08% of the trees in our Bayesian 95% credible set are consistent with this model. In contrast, the classic ring species biogeographical model (the southern closure model) is consistent with our Bayesian topology, as were 99.92% of the trees in our 95% credible set.Main conclusions Our Bayesian phylogenetic analysis most strongly supports the classic ring species model, modified to accommodate an improved understanding of the complex geomorphological evolution of the California Coast Ranges. In addition, high levels of phylogeographical diversity in central and northern California were identified, which is consistent with the striking levels of allozymic differentiation reported previously from those regions.

Pronounced phylogeographic structure on a small spatial scale: Geomorphological evolution and lineage history in the salamander ring species Ensatina eschscholtzii in central coastal California

The salamander Ensatina eschscholtzii is a classic example of a ring species, and has an intricate biogeographic history. Within a part of the ring distribution, earlier work using allozymes disclosed high levels of genetic structure in central coastal California, where the subspecies oregonensis, xanthoptica, and eschscholtzii meet. We used mitochondrial cytochrome b sequences to further examine patterns of divergence in this area, including data from 155 localities (309 individuals). Our focus is on the documentation of population-level haplotype lineages. We show that oregonensis is represented by two unrelated, phenotypically similar clades, both of which possess substantial substructure of their own. The subspecies xanthoptica includes two lineages that differ in phenotype, one of which has colonized the foothills of the Sierra Nevada. The subspecies eschscholtzii occurs mainly to the south, but some populations from a northern lineage extend into the Monterey Bay region, where they approach xanthoptica geographically. In sum, populations in the central coastal California region form a distributional patchwork, including three subspecies, three clades (which differ from the three subspecies), and ten haplotype lineages. We conclude that such striking levels of phylogeographic structure reflect interspersed episodes of spatial fragmentation, in part driven by the complex geomorphological evolution of the California Coast Range system.

Distribution and Conservation Of Plethodon Salamanders On Federal Lands In Siskiyou County, California

The Northwest Forest Plan is a large-scale ecosystem management plan that establishes a system of federal reserves interspersed with matrix forestlands where timber and other commodity production are given priority. Generally, management on reserved lands attempts to protect species associated with older forests. Whereas management in matrix lands emphasizes timber production, it maintains some protections for species associated with older forests. We conducted surveys at randomly selected points within the range of the Scott Bar Salamander (Plethodon asupak) and the southern portion of the range of the Siskiyou Mountains Salamander (P. stormi). We conducted surveys on both reserved and matrix lands to assess the relative role that these allocations play in the long-term persistence of Plethodon salamanders in this region. At low elevations (<1219 m), the proportion of sample points with captures of Plethodon spp. was significantly higher in matrix lands than on reserved lands. However, the number of Plethodon spp. captured at matrix and reserved land points was similar. Matrix land mitigations may be essential to provide protection for salamanders with small ranges and limited dispersal abilities. Oregon Ensatina (Ensatina eschscholtzii), the 2nd most commonly encountered amphibian, was more evenly distributed across the landscape than Plethodon spp. and was not associated with either reserved nor matrix lands.

Influence of Headwater Site Conditions and Riparian Buffers on Terrestrial Salamander Response to Forest Thinning

Abstract Although thinning of young, even-aged forests may accelerate the development of characteristics associated with mature forests, in the short term it may negatively affect some taxa, including terrestrial salamanders. Preexisting site conditions, including down wood, and forest management measures, such as riparian buffers, may moderate these effects, but these relationships are poorly understood. To explore whether down wood and riparian buffer widths might influence short-term responses to thinning, we sampled salamanders using ground searches before and during the first 2 years after experimental thinning at two 45- to 65-year-old headwater forest sites in western Oregon that differed in down wood volume. Prethinning distributions of terrestrial salamanders overlapped one- and two-tree height riparian buffers, and except for red-backed salamanders, overlapped very little with narrower streamside or variable-width buffers. At the site where down wood volume was low, captures of ensatina (Ensatina eschscholtzii Gray) and western red-backed salamanders (Plethodon vehiculum Cooper) both declined by 40% in thinned areas. In contrast, captures of ensatina and Oregon slender salamanders (Batrachoseps wrighti Bishop) were not significantly affected by thinning at the site where down wood volume was high. Our results suggest that site conditions, such as down wood volume, and riparian buffers may influence the effect of thinning on terrestrial salamanders, and demonstrate the tight linkage among management of aquatic, riparian, and upslope resources in headwater forests.