Salamander Populations Research Articles

Using stable isotopes to test for trophic niche partitioning: a case study with stream salamanders and fish

Summary1. Stream salamanders and fish often co‐occur even though fish prey on and outcompete salamanders. However, the mechanisms that allow palatable salamanders to coexist with fish are unknown.2. We tested mechanisms in the field that promote coexistence between Idaho giant salamanders (Dicamptodon aterrimus) and stream salmonid fishes in headwater streams. Previous research in this system indicated that salamander dispersal did not promote coexistence with fish. We tested the hypothesis that D. aterrimus shift their diet when they occur with fish, facilitating coexistence through local niche partitioning.3. We used nitrogen and carbon stable isotopes to describe the trophic niche of D. aterrimus and fish in three co‐occurring populations of salamanders and fish and three populations of salamanders without fish. We used two approaches to quantify trophic niche partitioning with stable isotopes: 95% kernel density estimators and isotopic mixing models.4. We found that salamanders and fish were generalists that consumed aquatic invertebrates primarily, but both species were also cannibalistic and predatory on one another. We also found no support for trophic niche partitioning as a coexistence mechanism because there were no differences in the trophic niche metrics among salamander populations with and without fish.5. Although we did not identify mechanisms that facilitate salamander and fish coexistence, our empirical data and use of novel approaches to describe the trophic niche did yield important insights on the role of predator–prey interactions and cannibalism as alternative coexistence mechanisms. In addition, we found that 95% kernel estimators are a simple and robust method to describe population‐level measure of trophic structure.

Current and Historical Drivers of Landscape Genetic Structure Differ in Core and Peripheral Salamander Populations

With predicted decreases in genetic diversity and greater genetic differentiation at range peripheries relative to their cores, it can be difficult to distinguish between the roles of current disturbance versus historic processes in shaping contemporary genetic patterns. To address this problem, we test for differences in historic demography and landscape genetic structure of coastal giant salamanders (Dicamptodon tenebrosus) in two core regions (Washington State, United States) versus the species' northern peripheral region (British Columbia, Canada) where the species is listed as threatened. Coalescent-based demographic simulations were consistent with a pattern of post-glacial range expansion, with both ancestral and current estimates of effective population size being much larger within the core region relative to the periphery. However, contrary to predictions of recent human-induced population decline in the less genetically diverse peripheral region, there was no genetic signature of population size change. Effects of current demographic processes on genetic structure were evident using a resistance-based landscape genetics approach. Among core populations, genetic structure was best explained by length of the growing season and isolation by resistance (i.e. a ‘flat’ landscape), but at the periphery, topography (slope and elevation) had the greatest influence on genetic structure. Although reduced genetic variation at the range periphery of D. tenebrosus appears to be largely the result of biogeographical history rather than recent impacts, our analyses suggest that inherent landscape features act to alter dispersal pathways uniquely in different parts of the species' geographic range, with implications for habitat management.

In Search of Critically Endangered Species: The Current Situation of Two Tiny Salamander Species in the Neotropical Mountains of Mexico

Worldwide, one in every three species of amphibian is endangered, 39 species have gone extinct in the last 500 years and another 130 species are suspected to have gone extinct in recent decades. Of the amphibians, salamanders have the highest portion of their species in one of the risk categories, even higher than the frogs. To date there have been few studies that have used recent field data to examine the status of populations of endangered salamanders. In this study we evaluate the current situation of two tiny salamanders, Parvimolge townsendi and Thorius pennatulus, both of which are distributed at intermediate elevations in the mountains of the northern Neotropics and are considered to be critically endangered; the first has been proposed as possibly extinct. By carrying out exhaustive surveys in both historical and potentially suitable sites for these two species, we evaluated their abundance and the characteristics of their habitats, and we estimated their potential geographic distribution. We visited 22 sites, investing 672 person-hours of sampling effort in the surveys, and found 201 P. townsendi salamanders in 11 sites and only 13 T. pennatulus salamanders in 5 sites. Both species were preferentially found in cloud forest fragments that were well conserved or only moderately transformed, and some of the salamanders were found in shade coffee plantations. The potential distribution area of both species is markedly fragmented and we estimate that it has decreased by more than 48%. The results of this study highlight the importance of carrying out exhaustive, systematic field surveys to obtain accurate information about the current situation of critically endangered species, and help us better understand the crisis that amphibians are facing worldwide.

Ancient DNA Assessment of Tiger Salamander Population in Yellowstone National Park

Recent data indicates that blotched tiger salamanders (Ambystoma tigrinum melanostictum) in northern regions of Yellowstone National Park are declining due to climate-related habitat changes. In this study, we used ancient and modern mitochondrial haplotype diversity to model the effective size of this amphibian population through recent geological time and to assess past responses to climatic changes in the region. Using subfossils collected from a cave in northern Yellowstone, we analyzed >700 base pairs of mitochondrial sequence from 16 samples ranging in age from 100 to 3300 years old and found that all shared an identical haplotype. Although mitochondrial diversity was extremely low within the living population, we still were able to detect geographic subdivision within the local area. Using serial coalescent modelling with Bayesian priors from both modern and ancient genetic data we simulated a range of probable population sizes and mutation rates through time. Our simulations suggest that regional mitochondrial diversity has remained relatively constant even through climatic fluctuations of recent millennia.

Growth, Age at Maturity, and Age-Specific Survival of the Arboreal Salamander (Aneides lugubris) on Southeast Farallon Island, California

Abstract Growth, age at maturity, and survival are life-history parameters that provide important information for understanding population dynamics. We modeled growth and age at maturity for an island population of Arboreal Salamanders, Aneides lugubris, using snout–vent length (SVL) growth intervals from a 4-yr capture–mark–recapture study fit to the von Bertalanffy growth interval model. We estimated annual survival as a function of SVL using a multistate open robust design model, and computed age-specific survival using results from the von Bertalanffy growth model. Arboreal Salamanders have indeterminate growth that slows with age from hatchling size (24.4-mm SVL) to the mean adult (asymptotic) size of 66.0-mm SVL. Age at maturity is 2.69 yr, and average adult age is 8–11 yr. Annual survival increased with age from 0.363 in age 0 to 0.783 in ages >4 yr. Our results provide the first estimates of life-history parameters for this species and indicate similarities to other terrestrial salamanders from lo...

A phylogeny of the Tylototriton asperrimus group (Caudata: Salamandridae) based on a mitochondrial study: suggestions for a taxonomic revision.

A phylogenetic hypothesis for the Asian newts of the Tylototriton asperrimus group was generated using data from two mitochondrial fragments including COI and the ND1-ND2 regions. Four distinct clades (A, B, C, D) were resolved with high nodal support within this monophyletic group. Clade A included T. asperrimus, T. hainanensis, T. notialis, "T. vietnamensis", and two unnamed salamander populations from Vietnam. Clade A, constituted the sister group of clades B + C. Newly identified clade C likely represents a new cryptic species. Clade C was the sister group of T. wenxianensis. The true T. vietnamensis exclusively constituted clade D. Our results bring into question some previous taxonomic decisions, and a revision is required. This study illustrates the necessity to include samples from type localities in taxonomic studies, and highlights the importance of fine-grained geographical sampling.

Iridovirus Infection in Chinese Giant Salamanders, China, 2010

Iridovirus Infection in Chinese Giant Salamanders, China, 2010

Adult Sex Ratio of a Population of the Japanese Salamander, Hynobius tokyoensis (Caudata: Hynobiidae)

Adult sex ratio is considered to be a key factor in understanding sexual selection, mating behavior, life history and population dynamics. Following Fisher (1930), a general consensus was formed that sex ratio tends to be largely balanced. However, gainsaying this, large variations in sex ratio have been reported among populations and species of amphibians. There is little information on sex ratio in natural populations of Japanese hynobiid salamanders. To help fill this gap, we conducted a long-term census of a population of Hynobius tokyoensis from 1976 to 1985 and estimated the adult sex ratio (the proportion of males within the population) at 0.578 from data gathered during eight non-breeding seasons. The bootstrap 95% confidence interval was 0.516–0.641. The study showed that the adult sex ratio was significantly biased toward males in the population studied; it was nearly 1.5:1 (males:females). Age at first reproduction is 1 year later in females, which suggests that the most likely factor driving the unbalanced sex ratio is the differential maturation rate between the sexes.

Genomotype Frequencies and Genetic Diversity in Urban and Protected Populations of Blue-spotted Salamanders (Ambystoma laterale) and Related Unisexuals

Abstract The Blue-spotted Salamander (Ambystoma laterale) and the Jefferson Salamander (Ambystoma jeffersonianum) are both part of the Jefferson complex that also includes unisexuals of various ploidy levels and genome composition, referred to as genomotypes. Female unisexuals reproduce mainly through gynogenesis, but ploidy elevations, translocations, recombinations, intergenomic exchanges, and genome replacement also have been documented. The objective of this study was to obtain information on the geographical distribution of genomotypes and the distribution of genetic diversity in southern Quebec, Canada. To do so, we examined populations of the Jefferson complex from five sites, including one site from a city and the other sites from protected areas. Genetic analysis using mitochondrial DNA and six microsatellite loci were performed. Results revealed that genomotype frequencies vary greatly, because some populations were mainly composed of A. laterale, whereas unisexuals were clearly predominant in o...

The Age Structure of a Breeding Population of Hynobius lichenatus (Amphibia, Caudata)

Abstract: Using the lines of arrested growth (LAGs), we estimated the age structure of a breeding population and individual ages at sexual maturity of a salamander, Hynobius lichenatus, from Sendai, northeastern Japan. No significant sexual differences were detected in either the age structure or the age at maturity, and the breeding individuals ranged from 5 to 14 yrs old, while the age of their maturation ranged from 3 to 7 yrs old. Reasons for this difference in minimal ages remain to be studied. There was no significant correlation between the age and the body size of the salamanders. Hynobius lichenatus does not differ from its close relative H. tokyoensis from Tokyo in age structure, but mature significantly later, with a longer life, than H. tokyoensis from Chiba. These findings suggest that the age structure of these salamander populations is affected at most partially by temperature conditions, and more strongly by other environmental, ecological, or phylogenetic factors.

Effects of organic matter availability on the life history and production of a top vertebrate predator (Plethodontidae: Gyrinophilus palleucus) in two cave streams

Summary 1. Surface ecosystems provide the primary source of organic matter to many cave communities. Variation in the strength of connectivity to the surface suggests that some caves may be more resource-limited than others. To test this, we examined diet, prey availability and production of an obligate cave salamander Gyrinophilus palleucus (Plethodontidae), a top predator, in two south-eastern U.S.A. caves with different levels of organic matter (Tony Sinks cave, 165 g AFDM m−2; Bluff River cave, 62 g AFDM m−2). 2. We quantified density, biomass, growth rate, production and diet of G. palleucus monthly for 21 months. Diet composition, differences in prey communities and seasonal patterns in prey consumption were also analysed. 3. Salamander density, biomass and secondary production were significantly greater in the high organic matter cave (0.10 m−2, 0.18 g AFDM m−2, 0.12 g AFDM m−2 year−1) than in the low organic matter cave (0.03 m−2, 0.03 g AFDM m−2, 0.01 g AFDM m−2 year−1). Although growth rates were not statistically different between the two cave salamander populations, low recaptures probably influenced this result. 4. Isopoda prey were the major contributor to salamander production in the high organic matter cave (69%). In the low organic matter cave, production was provided by isopods (41%) and oligochaetes (20%). The lower number of prey taxa contributing to salamander production in the high organic matter cave suggests the ability to forage more selectively. 5. The differences in foraging strategy, density, biomass and secondary production were probably related to differences in the strength of surface connectivity, which controls organic matter supply. Links between basal resource level and top predator performance show the importance of bottom-up limitation in the food webs of caves and other detritus-based ecosystems.

Survey for the Pathogenic Chytrid Fungus Batrachochytrium dendrobatidis in Southwestern North Carolina Salamander Populations

Batrachochytrium dendrobatidis is a fungal pathogen responsible for a potentially fatal disease of amphibians. We conducted a survey for B. dendrobatidis in the Appalachian Mountains of southwestern North Carolina, USA, from 10 June to 23 July 23 2009. Ventral skin swabs were collected from plethodontid salamanders (n=278) and real-time PCR was performed to test for the presence of B. dendrobatidis. We found no evidence of B. dendrobatidis, suggesting that B. dendrobatidis is absent or present in such low levels that it was undetected. If B. dendrobatidis was present at the time of our sampling, this survey supports evidence of low prevalence of B. dendrobatidis in North American headwater stream salamander populations.

Wolf in sheep's clothing: Effects of predation by small-bodied fish on survival and behaviour of salamander larvae

Fish can affect amphibian larvae directly through consumption or indirectly by eliciting antipredator behaviours that incur fitness costs. Because of predation, long-toed salamanders (Ambystoma macrodactylum) typically show an allotopic distribution with fish. Linnet Lake (Waterton Lakes National Park, Alberta, Canada) represents the unusual situation in which salamanders coexist with a small-bodied cyprinid, lake chub (Couesius plumbeus). However, the salamander population resident to Linnet Lake has declined in recent years. Our objective was to assess the role of lake chub in the decline of this salamander population by combining field observations and laboratory experiments. We used mark-recapture techniques to estimate the size of the 2 populations. We found little evidence of successful salamander reproduction, and the adult population had decreased by 60% in 14 y. In contrast, a large population of lake chub was present. Experiments showed that lake chub between 70 and 100 mm could consume salamander larvae < 40 mm in length. Larvae responded to the presence of lake chub by reducing activity and increasing refuge use, especially during the day. Our study is one of few to document the ability of a native small-bodied fish to consume amphibian larvae. The coexistence of fish and salamanders may result from a dynamic interplay between periodic extirpation of fish by winter hypoxia and of salamanders by predation, punctuated by episodes of re-colonization or strong recruitment.

Sympatry between Two Wide-ranging Salamander Species

Understanding how closely related species coexist remains a central problem in community ecology. Habitat characteristics, presence of predators and competitors, and frequency of disturbance all affect the geographic distribution of a species. Plethodon cinereus and P. electromorphus are two closely related and ecologically similar species that have a large geographic overlap in their distributions. In this study, I had two main goals. First, I wanted to determine how commonly sympatric locations occurred between these two species. To address this goal, I conducted landscape-scale surveys in areas that should contain sympatric locations based on their distributions. My second goal was to determine if the relative number of individuals of each species within sympatric locations was stable over time by monitoring four sympatric locations over three years. In addition, flooding occurred during one year of the study, impacting two of the four monitored sympatric locations; therefore, I wanted to examine whether this disturbance affected the salamander populations at those locations. This flooding event provided a rare opportunity to study the impact of flooding on terrestrial salamanders, a topic about which little is known. I found that sympatric locations occurred less frequently than expected by chance and that some sympatric sites seem to be relatively stable while at others, the relative population size of P. cinereus was increasing — and that this shift might be positively affected by flooding. While this study demonstrated that P. cinereus and P. electromorphus do not occur in sympatry as frequently as expected by chance, the cause for this result is unknown. The most likely factor is that the two species exhibit subtle habitat differences that have not yet been demonstrated. The interactions between P. cinereus and P. electromorphus are complex, and the patterns observed here could have been generated by any number of mechanisms. Further research on this system could clarify some of these remaining questions.

Coexistence in streams: do source–sink dynamics allow salamanders to persist with fish predators?

Theory suggests that source-sink dynamics can allow coexistence of intraguild predators and prey, but empirical evidence for this coexistence mechanism is limited. We used capture-mark-recapture, genetic methods, and stable isotopes to test whether source-sink dynamics promote coexistence between stream fishes, the intraguild predator, and stream salamanders (Dicamptodon aterrimus), the intraguild prey. Salamander populations from upstream reaches without fish were predicted to maintain or supplement sink populations in downstream reaches with fish. We found instead that downstream reaches with fish were not sinks even though fish consumed salamander larvae-apparent survival, recruitment, and population growth rate did not differ between upstream and downstream reaches. There was also no difference between upstream and downstream reaches in net emigration. We did find that D. aterrimus moved frequently along streams, but believe that this is a response to seasonal habitat changes rather than intraguild predation. Our study provides empirical evidence that local-scale mechanisms are more important than dispersal dynamics to coexistence of streams salamanders and fish. More broadly, it shows the value of empirical data on dispersal and gene flow for distinguishing between local and spatial mechanisms of coexistence.

Adult Sex Ratio of a Population of the Japanese Salamander, Hynobius tokyoensis (Caudata: Hynobiidae)

Adult sex ratio is considered to be a key factor in understanding sexual selection, mating behavior, life history and population dynamics. Following Fisher (1930), a general consensus was formed that sex ratio tends to be largely balanced. However, gainsaying this, large variations in sex ratio have been reported among populations and species of amphibians. There is little information on sex ratio in natural populations of Japanese hynobiid salamanders. To help fill this gap, we conducted a long-term census of a population of Hynobius tokyoensis from 1976 to 1985 and estimated the adult sex ratio (the proportion of males within the population) at 0.578 from data gathered during eight non-breeding seasons. The bootstrap 95% confidence interval was 0.516–0.641. The study showed that the adult sex ratio was significantly biased toward males in the population studied; it was nearly 1.5:1 (males:females). Age at first reproduction is 1 year later in females, which suggests that the most likely factor driving the unbalanced sex ratio is the differential maturation rate between the sexes.

The Age Structure of a Breeding Population of Hynobius lichenatus (Amphibia, Caudata)

Using the lines of arrested growth (LAGs), we estimated the age structure of a breeding population and individual ages at sexual maturity of a salamander, Hynobius lichenatus, from Sendai, northeastern Japan. No significant sexual differences were detected in either the age structure or the age at maturity, and the breeding individuals ranged from 5 to 14 yrs old, while the age of their maturation ranged from 3 to 7 yrs old. Reasons for this difference in minimal ages remain to be studied. There was no significant correlation between the age and the body size of the salamanders. Hynobius lichenatus does not differ from its close relative H. tokyoensis from Tokyo in age structure, but mature significantly later, with a longer life, than H. tokyoensis from Chiba. These findings suggest that the age structure of these salamander populations is affected at most partially by temperature conditions, and more strongly by other environmental, ecological, or phylogenetic factors.

Effects of Urbanization on Occupancy of Stream Salamanders

Urban development is the most common form of land conversion in the United States. Using a before-after control-impact study design, we investigated the effects of urbanization on larval and adult stages of southern two-lined salamanders (Eurycea cirrigera) and northern dusky salamanders (Desmognathus fuscus). Over 5 years, we estimated changes in occupancy and probabilities of colonization and survival in 13 stream catchments after urbanization and in 17 catchments that were not urbanized. We also examined effects of proportion of urbanized area in a catchment and distance of the salamander population to the nearest stream on probabilities of colonization and survival. Before urbanization, adult and larval stages of the two salamander species occupied nearly all surveyed streams, with occupancy estimates ranging from 1.0 to 0.78. Four years after urbanization mean occupancy of larval and adult two-lined salamanders had decreased from 0.87 and 0.78 to 0.57 and 0.39, respectively. Estimates of mean occupancy of larval northern dusky salamanders decreased from 1.0 to 0.57 in urban streams 4 years after urbanization; however, adult northern dusky salamander occupancy remained close to 1.0 in urban streams over 5 years. Occupancy estimates in control streams were similar for each species and stage over 5 years. Urbanization was associated with decreases in survival probabilities of adult and larval two-lined salamanders and decreases in colonization probabilities of larval dusky salamanders. Nevertheless, proportion of impervious surface and distance to nearest stream had little effect on probabilities of survival and colonization. Our results imply that in the evaluation of the effects of urbanization on species, such as amphibians, with complex life cycles, consideration of the effects of urbanization on both adult and larval stages is required.

Fine-Scale Spatial Genetic Structure and Genetic Diversity among Clouded Salamander (Hynobius nebulosus) Populations

Abstract: We investigated the genetic structure of 16 populations (from five geographical groups) of clouded salamander (Hynobius nebulosus) in northern Kyushu, Japan, by analyzing the sequence of the mitochondrial DNA control region. A total of 24 haplotypes were found in 199 individuals of the salamander. In the analysis of genetic diversity of the populations, an isolated small population sustained in an urban area had a low level of genetic diversity. This is considered to be due to both the less suitable nature of the habitat and a recent artificial barrier to gene flow. In the analysis of genetic differentiation (FST) among 16 populations, significant differences were detected in 76.7% of all possible population pairs. Analysis of molecular variance (AMOVA) showed that most of the genetic variation was attributed to individual differences within populations, but a significant genetic difference among groups was also detected. This fine-scale genetic differentiation would be formed through genetic is...

The origin of tiger salamander (Ambystoma tigrinum) populations in California, Oregon, and Nevada: introductions or relicts?

Whether intentionally or accidentally introduced, exotic species have the capacity to dramatically disrupt native communities. In central California, tiger salamanders (Ambystoma tigrinum) have been introduced as a by-product of the sport fishing bait industry. Some of these introductions are relatively well known and have resulted in the formation of hybrids with the imperiled native California tiger salamander (A. californiense). Other populations of A. tigrinum, particularly in the northern and eastern parts of the state, remain poorly characterized and are present in regions where relictual amphibian populations of other species have persisted, suggesting that these might be relictual, native A. tigrinum. We used genetic sequence data to determine the provenance of all known extralimital A. tigrinum populations in California and adjacent Oregon and Nevada through comparison with reference samples from the native range of A. tigrinum. Our results suggest that A. tigrinum have been introduced in Northern California, Southern California and the Sierra Nevada, originating from multiple sources across the Great Plains of the US. Furthermore, two populations near the California-Oregon border are most closely related to A. tigrinum populations from Washington and Oregon and may represent native tiger salamander lineages.