Bifenthrin induces changes in clinical poisoning symptoms, oxidative stress, DNA damage, histological characteristics, and transcriptome in Chinese giant salamander (Andrias davidianus) larvae

Bifenthrin (BF) is a broad-spectrum insecticide that has gained widespread use due to its high effectiveness. However, there is limited research on the potential toxic effects of bifenthrin pollution on amphibians. This study aimed to investigate the 50 % lethal concentration (LC50) and safety concentration of Chinese giant salamanders (CGS) exposed to BF (at 0, 6.25,12.5,25 and 50 μg/L BF) for 96 h. Subsequently, CGS were exposed to BF (at 0, 0.04, and 4 μg/L BF) for one week to investigate its toxic effects. Clinical poisoning symptoms, liver pathology, oxidative stress factors, DNA damage, and transcriptome differences were observed and analyzed. The results indicate that exposure to BF at 4 μg/L significantly decreased the adenosine-triphosphate (ATP), superoxide dismutase (SOD), glutathione (GSH), and catalase (CAT) contents in the brain, liver, and kidney of CGS. Additionally, the study found that the malondialdehyde (MDA), reactive oxygen species (ROS), and 8-hydroxydeoxyguanosine (8-OHdG) contents were increased. The liver tissue exhibited significant inflammatory reactions and structural malformations. RNA-seq analysis of the liver showed that BF caused abnormal antioxidant indices of CGS. This affected molecular function genes such as catalytic activity, ATP-dependent activity, metabolic processes, signaling and immune system processes, behavior, and detoxification, which were significantly upregulated, resulting in the differential genes significantly enriched in the calcium signaling pathway, PPARα signaling pathway and NF-kB signaling pathway. The results suggest that BF induces the abnormal production of free radicals, which overwhelms the body's self-defense system, leading to varying degrees of oxidative stress. This can result in oxidative damage, DNA damage, abnormal lipid metabolism, autoimmune diseases, clinical poisoning symptoms, and tissue inflammation. This work provides a theoretical basis for the rational application of bifenthrin and environmental risk assessment, as well as scientific guidance for the conservation of amphibian populations.

Linear and Nonlinear Behaviors of the Photoreceptor Coupled Network

Photoreceptors are electrically coupled to one another, and the spatiotemporal properties of electrical synapses in a two-dimensional retinal network are still not well studied, because of the limitation of the single electrode or pair recording techniques which do not allow simultaneously measuring responses of multiple photoreceptors at various locations in the retina. A multiple electrode recording system is needed. In this study, we investigate the network properties of the two-dimensional rod coupled array of the salamander retina (both sexes were used) by using the newly available multiple patch electrode system that allows simultaneous recordings from up to eight cells and to determine the electrical connectivity among multiple rods. We found direct evidence that voltage signal spread in the rod-rod coupling network in the absence of I h (mediated by HCN channels) is passive and follows the linear cable equation. Under physiological conditions, I h shapes the network signal by progressively shortening the response time-to-peak of distant rods, compensating the time loss of signal traveling from distant rods to bipolar cell somas and facilitating synchronization of rod output signals. Under voltage-clamp conditions, current flow within the coupled rods follows Ohm's law, supporting the idea that nonlinear behaviors of the rod network are dependent on membrane voltage. Rod-rod coupling is largely symmetrical in the 2D array, and voltage-clamp blocking the next neighboring rod largely suppresses rod signal spread into the second neighboring rod, suggesting that indirect coupling pathways play a minor role in rod-rod coupling.

Immunohematological Parameters of Ectothermal Amphibians of the Fauna of the Middle Urals: Siberian Salamander Salamandrella Keyserlingii Dybovsky, 1870 (Caudata) and Lake Frog Pelophylax Ridibundus Pallas, 1771 (Anura)

A comparative analysis of hematological parameters was for the first time performed in two ectothermal amphibians of the Middle Ural fauna, the Siberian salamander Salamandrella keyserlingii and lake frog Pelophylax ridibundиs. Species specificity of immune defense was demonstrated with respect to granulocyte and agranulocyte counts (p < 0.001). A high lymphocyte content (73.3-76.1%) of provides for the activation of acquired adaptive immunity mechanisms in the thermophilic lake frog. The Siberian salamander is adapted to low negative temperatures and has a set of nonspecific leukocytes (39.3-44.4%). Innate immunity is better developed in the Siberian salamander compared with the lake frog.

Pre-breeding androgen and glucocorticoid profiles in the eastern hellbender salamander (Cryptobranchus alleganiensis alleganiensis)

Seasonally breeding species exhibit cyclical changes in circulating steroid hormone profiles that correspond with changes to their reproductive behavior and ecology. Such information is critical to the conservation of imperiled and data-deficient species, such as the eastern hellbender salamander (Cryptobranchus alleganiensis alleganiensis). We determined changes in plasma testosterone (T), dihydrotestosterone (DHT), 11-ketotestosterone (11-KT), 11-ketoandrostenedione (11-KA), dehydroepiandrosterone (DHEA), cortisol, corticosterone, and progesterone (P₄) during a four-month period preceding breeding in adult male and female eastern hellbenders. This pre-breeding period is characterized by increased diel movement and aggression by both sexes, follicular development and yolk production in females, and sperm production, territoriality, and nest site establishment in males. In both males and females, we observed a progressive increase in circulating T and DHT during the pre-reproductive season, both peaking in August (17 days before breeding), but concentrations of both hormones were higher in males. Conversely, 11-KT was higher in females, but did not vary significantly by date. These results suggest that T and DHT are the predominant androgens in eastern hellbenders and are likely important regulators of reproductive processes in both males and females. The detection of significant quantities of DHT and 11-KT in females is particularly interesting, considering that unlike T, neither of these androgens can be converted to estrogens. Therefore, it seems possible that aggression or some aspect of reproduction in the female eastern hellbender may be directly mediated by androgen signaling. Baseline cortisol did not vary throughout the pre-breeding period but was higher in females than males, and also became highly variable in females leading up to breeding. Progesterone, 11-KA, DHEA, and corticosterone were rarely or never detected, and thus, do not appear to be important during the pre-reproductive season. This study provides a physiological framework for future studies of hellbender reproductive biology, which could ultimately be important for their conservation.

Towards comparative analyses of salamander limb regeneration

Among tetrapods, only salamanders can regenerate their limbs and tails throughout life. This amazing regenerative ability has attracted the attention of scientists for hundreds of years. Now that large, salamander genomes are beginning to be sequenced for the first time, omics tools and approaches can be used to integrate new perspectives into the study of tissue regeneration. Here we argue the need to move beyond the primary salamander models to investigate regeneration in other species. Salamanders at first glance come across as a phylogenetically conservative group that has not diverged greatly from their ancestors. While salamanders do present ancestral characteristics of basal tetrapods, including the ability to regenerate limbs, data from fossils and data from studies that have tested for species differences suggest there may be considerable variation in how salamanders develop and regenerate their limbs. We review the case for expanded studies of salamander tissue regeneration and identify questions and approaches that are most likely to reveal commonalities and differences in regeneration among species. We also address challenges that confront such an initiative, some of which are regulatory and not scientific. The time is right to gain evolutionary perspective about mechanisms of tissue regeneration from comparative studies of salamander species.

Terrestrial Salamanders Maintain Habitat Suitability under Climate Change despite Trade-Offs between Water Loss and Gas Exchange

Physiological acclimation has the potential to improve survival during climate change by reducing sensitivity to warming. However, acclimation can produce trade-offs due to links between related physiological traits. Water loss and gas exchange are intrinsically linked by the need for respiratory surfaces to remain moist. As climates warm and dry, organisms may attempt to lower desiccation risk by limiting water loss but at a cost of inhibiting their ability to breathe. Here we used laboratory experiments to evaluate the trade-off between water loss and gas exchange in a fully terrestrial, lungless salamander (Plethodon metcalfi). We measured acclimation of resistance to water loss and metabolic rates in response to long-term exposure to temperature and humidity treatments. We then integrated the trade-off into a simulation-based species distribution model to determine the consequences of ignoring physiological trade-offs on energy balance and aerobic scope under climate change. In the laboratory, we found a close association between acclimation of resistance to water loss and metabolic rates indicative of a trade-off. After incorporating the trade-off into our simulations, we found that energy balance and aerobic scope were reduced by 49.7% and 34.3%, respectively, under contemporary climates across their geographic range. Under future warming scenarios, incorporating the trade-off lowered the number of sites predicted to experience local extirpation by 52.2% relative to simulations without the trade-off; however, the number of sites capable of supporting the energetic requirements for reproduction declined from 44.6% to 32.6% across the species' geographic range. These experiments and simulations suggest that salamanders can maintain positive energy balance across their geographic range under climate change despite the costs associated with trade-offs between water loss and gas exchange.

What the salamander eye has been telling the vision scientist's brain

Salamanders have been habitual residents of research laboratories for more than a century, and their history in science is tightly interwoven with vision research. Nevertheless, many vision scientists - even those working with salamanders - may be unaware of how much our knowledge about vision, and particularly the retina, has been shaped by studying salamanders. In this review, we take a tour through the salamander history in vision science, highlighting the main contributions of salamanders to our understanding of the vertebrate retina. We further point out specificities of the salamander visual system and discuss the perspectives of this animal system for future vision research.

Experimental methodologies can affect pathogenicity of Batrachochytrium salamandrivorans infections

Controlled experiments are one approach to understanding the pathogenicity of etiologic agents to susceptible hosts. The recently discovered fungal pathogen, Batrachochytrium salamandrivorans (Bsal), has resulted in a surge of experimental investigations because of its potential to impact global salamander biodiversity. However, variation in experimental methodologies could thwart knowledge advancement by introducing confounding factors that make comparisons difficult among studies. Thus, our objective was to evaluate if variation in experimental methods changed inferences made on the pathogenicity of Bsal. We tested whether passage duration of Bsal culture, exposure method of the host to Bsal (water bath vs. skin inoculation), Bsal culturing method (liquid vs. plated), host husbandry conditions (aquatic vs. terrestrial), and skin swabbing frequency influenced diseased-induced mortality in a susceptible host species, the eastern newt (Notophthalmus viridescens). We found that disease-induced mortality was faster for eastern newts when exposed to a low passage isolate, when newts were housed in terrestrial environments, and if exposure to zoospores occurred via water bath. We did not detect differences in disease-induced mortality between culturing methods or swabbing frequencies. Our results illustrate the need to standardize methods among Bsal experiments. We provide suggestions for future Bsal experiments in the context of hypothesis testing and discuss the ecological implications of our results.

Modeling of the neural mechanism underlying the terrestrial turning of the salamander

In order to explore the neural mechanism underlying salamander terrestrial turning, an improved biomechanical model is proposed by modifying the forelimb structure of the existing biomechanical model. Based on the proposed improved biomechanical model, a new spinal locomotor network model is constructed which contains the interneuron networks and motoneuron pool. Control methods are also developed for the new model which increase its transient response speed, control the initial swing order of the forelimbs, and generate different walking turning gait and turning on the spot (turning without moving forward). The simulation results show that the biomechanical model controlled by the new spinal locomotor network model can generate different walking turning and turning on the spot, and can control posture and the initial swing order of the forelimbs. Moreover, the transient response speed of the proposed model is very rapid. This paper thus provides a useful tool for exploring the operational mechanism of the spinal circuitry of the salamander. In addition, the research results presented here may inspire the construction of artificial spinal control networks for bionic robots.

A salamander that chews using complex, three-dimensional mandible movements

Most non-mammal tetrapods have a hinge-like jaw operation restricted to vertical opening and closing movements. Many mammal jaw joints, by contrast, operate in more complex, three-dimensional (3D) ways, involving not only vertical but also propalinal (rostro-caudal) and transverse (lateral) movements. Data on intraoral food processing in lissamphibians and sauropsids has prompted a generally accepted view that these groups mostly swallow food unreduced, and that in those cases where lissamphibians and sauropsids chew, they mostly use simple vertical jaw movements for food processing. The exception to this generally accepted view is the occurrence of some propalinal chewing in sauropsids. We combined 3D kinematics and morphological analyses from biplanar high-speed video fluoroscopy and micro-computed tomography to determine how the paedomorphic salamander Siren intermedia treats captured food. We discovered not only that S. intermedia uses intraoral food processing but also that the elaborated morphology of its jaw joint facilitates mandibular motions in all three planes, resulting in complex 3D chewing. Thus, our data challenge the commonly held view that complex 3D chewing movements are exclusive to mammals, by suggesting that such mechanisms might have evolved early in the tetrapod evolution.

Salamanders and other amphibians are aglow with biofluorescence

Biofluorescence is the absorption of electromagnetic radiation (light) at one wavelength followed by its reemission at a lower energy and longer wavelength by a living organism. Previous studies have documented the widespread presence of biofluorescence in some animals, including cnidarians, arthropods, and cartilaginous and ray-finned fishes. Many studies on biofluorescence have focused on marine animals (cnidarians, cartilaginous and ray-finned fishes) but we know comparatively little about the presence of biofluorescence in tetrapods. We show for the first time that biofluorescence is widespread across Amphibia, with a focus on salamanders (Caudata), which are a diverse group with a primarily Holarctic distribution. We find that biofluorescence is not restricted to any particular family of salamanders, there is striking variation in their fluorescent patterning, and the primary wavelengths emitted in response to blue excitation light are within the spectrum of green light. Widespread biofluorescence across the amphibian radiation is a previously undocumented phenomenon that could have significant ramifications for the ecology and evolution of these diverse and declining vertebrates. Our results provide a roadmap for future studies on the characterization of molecular mechanisms of biofluorescence in amphibians, as well as directions for investigations into the potential impact of biofluorescence on the visual ecology and behavior of biofluorescent amphibians.

Translucent in air and iridescent in water: structural analysis of a salamander egg sac

Females of some Asian salamanders of the genus Hynobius deposit in streams their eggs embedded in a translucent envelope called an 'egg sac'. The edges of the envelope exhibit a spectacular blue-to-yellow iridescent glow, which instantaneously disappears when the sac is removed from water. First, our scanning electron microscopy analyses reveal that the inner surface of the 100 μm-thick envelope displays striations (length scale of about 3 μm), which are themselves covered by much smaller (190 ± 30 nm) and quasi-periodic corrugations. The latter could constitute a surface diffraction grating generating iridescence by light interference. Second, our transmission electron microscopy and focused-ion-beam scanning electron microscopy analyses show that the bulk of the egg sac wall is composed of meandering fibres with a quasi-periodic modulation of 190 ± 60 nm along the thickness of the envelope, generating a photonic crystal. Third, Fourier power analyses of 450 electron microscopy images with varying incident angles indicate that changing the surrounding medium from water to air shifts most of the backscattered power spectrum to the ultraviolet range, hence, explaining that the egg sac loses visible iridescence when removed out of the water. Fourth, the results of our photography and optical spectroscopy experiments of submerged and emerged egg sacs rule out the possibility that the iridescence is due to a thin film or a multilayer, whereas the observed non-specular response is compatible with the backscattering expected from surface diffraction gratings and volumetric photonic crystals with spatial 1D modulation. Finally, although we mention several potential biological functions of the egg sac structural colours and iridescence, we emphasise that these optical properties might be the by-products of the envelope material internal structure selected during evolution for its mechanical properties.

'Mainland-island' population structure of a terrestrial salamander in a forest-bocage landscape with little evidence for in situ ecological speciation

Adaptation to different ecological environments can, through divergent selection, generate phenotypic and genetic differences between populations, and eventually give rise to new species. The fire salamander (Salamandra salamandra) has been proposed to represent an early stage of ecological speciation, driven by differential habitat adaptation through the deposition and development of larvae in streams versus ponds in the Kottenforst near Bonn (Germany). We set out to test this hypothesis of ecological speciation in an area different from the one where it was raised and we took the opportunity to explore for drivers of genetic differentiation at a landscape scale. A survey over 640 localities demonstrated the species' presence in ponds and streams across forests, hilly terrain and areas with hedgerows ('bocage'). Genetic variation at 14 microsatellite loci across 41 localities in and around two small deciduous forests showed that salamander effective population sizes were higher in forests than in the bocage, with panmixia in the forests (Fst < 0.010) versus genetic drift or founder effects in several of the small and more or less isolated bocage populations (Fst > 0.025). The system fits the 'mainland-island' metapopulation model rather than indicating adaptive genetic divergence in pond versus stream larval habitats. A reanalysis of the Kottenforst data indicated that microsatellite genetic variation fitted a geographical rather than an environmental axis, with a sharp transition from a western pond-breeding to an eastern, more frequently stream-breeding group of populations. A parallel changeover in mitochondrial DNA exists but remains to be well documented. The data support the existence of a hybrid zone following secondary contact of differentiated lineages, more so than speciation in situ.

Decentralized control with cross-coupled sensory feedback between body and limbs in sprawling locomotion

Quadrupeds achieve rapid and highly adaptive locomotion owing to the coordination between their legs and other body parts such as their trunk, head, and tail, i.e. body-limb coordination. Therefore, a better understanding of the mechanism underlying body-limb coordination could provide informative insights into the improvement of legged robot mobility. Sprawling locomotion is a walking gait with lateral bending exhibited in primitive legged vertebrates such as salamanders and newts. Because primitive animals are anticipated to possess the essence of quadruped motor control, their locomotion helps better understand body-limb coordination mechanisms. Previous studies modeled neural networks in salamanders and employed it to control robots and investigate and emulate sprawling locomotion. However, these models predefined the relationship between the legs and the trunk, such that how body-limb coordination is attained is largely unknown. In this article, we demonstrate that sensory feedback facilitates body-limb coordination in sprawling locomotion and improves mobility through mathematical modeling and robot simulations. Our proposed model has cross-coupled sensory feedback, that is, bidirectional feedback from body to limb and limb to body, which leads to an appropriate relationship between the legs and the trunk without any predefined relationship. Resulting gaits are similar to the sprawling locomotion of salamanders and achieve high speed and energy efficiency that are at the same level as those of a neural network model, such as conventional models, optimizing the relationship between the legs and the trunk. Furthermore, sensory feedback contributes to the adaptability toward leg failure, and the bidirectionality of feedback facilitates parameter tuning for stable locomotion. These results suggest that cross-coupled sensory feedback facilitates sprawling locomotion and potentially plays an important role in the body-limb coordination mechanism.

Climate change-based models predict range shifts in the distribution of the only Asian plethodontid salamander: Karsenia koreana

Populations see their range fluctuate in relation to environmental variations, including climate change, and their survival is linked to the maintenance of large enough populations and broad enough distributions during these variations. Most amphibian populations are threatened by numerous ecological and anthropogenic variables acting in synergy with climate change. Accumulating basic ecological data such as range enables the development of population and range dynamics, themselves resulting on adequate conservation plans. Karsenia koreana is the only known Asian plethodontic salamander, occurring in a very restricted area only. Based on presence data, we created an ecological model using six bioclimatic factors with low multicollinearity to define the adequate habitat of the species, and we modelled the predicted suitability of the Korean landscape following four Representative Concentration Pathways (RCPs) predicting climate change scenarios based on CO2 concentrations in 2050 and 2070. The maximum entropy model for the current distribution produced a landscape suitability considerably wider than the current known distribution. The projected ranges for each RCP indicated marked increases, decreases and shifts in areas with suitable landscapes due to climate change. The lowest RCP prediction resulted in an increase in suitable area, although potentially without connectivity with current populations, while the highest RCP predictions resulted in a decrease. Our results highlight the potential negative impact of climate change, thus requiring updates in conservation plans for K. koreana. The methods used here can be replicated with any land-dwelling species, and our results reflect expected range shifts for most amphibians of the northern hemisphere.

[Effects of tourism disturbance on the habitat and water quality for Andrias davidianus in Zhangjiajie, Hunan, China]

To understand the effects of tourism disturbance on the habitat and water quality for Chinese giant salamander (Andrias davidianus, CGS), the interference and characteristics of habitat for CGS under different tourism intensity (high, medium, and low) were investigated, and the physicochemical and microbial index of water were analyzed in Zhangjiajie City, Hunan Province, China from 2014 to 2016. The results showed that high tourism disturbance (>0.5 million per year) significantly increased noise and reduced the number of dens, decreased dissolved oxygen levels, increased total nitrogen, total phosphorus, and microbial abundance in water, especially that of Escherichiacoli. Under high disturbance, the characteristics of habitat and water quality still could meet the requirements of the growth of CGS. According to the National ground water class 2 standard based on the demands of E. coli in the surface water (2000 ind·L^-1), the theoretical threshold of tourist numbers was 26.0471 million per year. The intensity of tourism interference should be effectively reduced by declining tourist numbers and tourism facilities, for the protection of the habitat quality of the CGS and the promotion of tourism development.

Effects of chronic γ-irradiation on growth and sexual maturation of the Tohoku hynobiid salamander, Hynobius lichenatus

There are still considerable gaps in knowledge regarding the biological effects of chronic ionising radiation exposure in amphibians. To fill these gaps, Tohoku hynobiid salamanders, Hynobius lichenatus (Amphibia, Caudata), were chronically irradiated with ¹³⁷Cs γ-rays from embryonic to adult stages over 1954 days, and the effects on their growth and sexual maturation were examined under laboratory conditions. Irradiation at a dose rate of 33 μGy h^-1 had some stimulatory effects on growth (body weight increase) of H. lichenatus, while growth was temporarily or permanently suppressed at 150 or 510 μGy h^-1, respectively. On day 1802, secondary sexual characteristics (a tubercle at the anterior angle of the cloacal vent for males and ovisac development for females) were observed in 91% of the salamanders irradiated at 33 μGy h^-1, and in a similar percentage of non-irradiated controls. At 150 and 510 μGy h^-1, secondary sexual characteristics were not observed in any individuals. These results suggest that the derived consideration reference level (DCRL) of the International Commission on Radiological Protection (ICRP) for Reference Frog, i.e. 40-400 μGy h^-1, is applicable for the protection of H. lichenatus, and that growth and sexual maturation of this salamander may not have been adversely affected even in the most severely contaminated area in Fukushima, where the highest dose rate to salamanders was estimated to be 50 μGy h^-1. However, observations in the contaminated area are required to confirm this conclusion, considering the possible confounding factors which may make this salamander more sensitive to radiation in the natural environment than under laboratory conditions.

A new model of the spinal locomotor networks of a salamander and its properties

A salamander is an ideal animal for studying the spinal locomotor network mechanism of vertebrates from an evolutionary perspective since it represents the transition from an aquatic to a terrestrial animal. However, little is known about the spinal locomotor network of a salamander. A spinal locomotor network model is a useful tool for exploring the working mechanism of the spinal networks of salamanders. A new spinal locomotor network model for a salamander is built for a three-dimensional (3D) biomechanical model of the salamander using a novel locomotion-controlled neural network model. Based on recent experimental data on the spinal circuitry and observational results of gaits of vertebrates, we assume that different interneuron sets recruited for mediating the frequency of spinal circuits are also related to the generation of different gaits. The spinal locomotor networks of salamanders are divided into low-frequency networks for walking and high-frequency networks for swimming. Additionally, a new topological structure between the body networks and limb networks is built, which only uses the body networks to coordinate the motion of limbs. There are no direct synaptic connections among limb networks. These techniques differ from existing salamander spinal locomotor network models. A simulation is performed and analyzed to validate the properties of the new spinal locomotor networks of salamanders. The simulation results show that the new spinal locomotor networks can generate a forward walking gait, a backward walking gait, a swimming gait, and a turning gait during swimming and walking. These gaits can be switched smoothly by changing external inputs from the brainstem. These properties are consistent with those of a real salamander. However, it is still difficult for the new spinal locomotor networks to generate highly efficient turning during walking, 3D swimming, nonrhythmic movements, and so on. New experimental data are required for further validation.

Differences between microhabitat and broad-scale patterns of niche evolution in terrestrial salamanders

The extent to which closely related species share similar niches remains highly debated. Ecological niches are increasingly analysed by combining distribution records with broad-scale climatic variables, but interactions between species and their environment often occur at fine scales. The idea that macroscale analyses correctly represent fine-scale processes relies on the assumption that average climatic variables are meaningful predictors of processes determining species persistence, but tests of this hypothesis are scarce. We compared broad- and fine-scale (microhabitat) approaches by analyzing the niches of European plethodontid salamanders. Both the microhabitat and the macroecological approaches identified niche differences among species, but the correspondence between micro- and macroecological niches was weak. When exploring niche evolution, the macroecological approach suggested a close relationship between niche and phylogenetic history, but this relationship did not emerge in fine-scale analyses. The apparent pattern of niche evolution emerging in broad-scale analyses likely was the by-product of related species having closely adjacent ranges. The environment actually experienced by most of animals is more heterogeneous than what is apparent from macro-scale predictors, and a better combination between macroecological and fine-grained data may be a key to obtain robust ecological generalizations.

Plasticity reveals hidden resistance to extinction under climate change in the global hotspot of salamander diversity

Extinction rates are predicted to rise exponentially under climate warming, but many of these predictions ignore physiological and behavioral plasticity that might buffer species from extinction. We evaluated the potential for physiological acclimatization and behavioral avoidance of poor climatic conditions to lower extinction risk under climate change in the global hotspot of salamander diversity, a region currently predicted to lose most of the salamander habitat due to warming. Our approach integrated experimental physiology and behavior into a mechanistic species distribution model to predict extinction risk based on an individual's capacity to maintain energy balance with and without plasticity. We assessed the sensitivity of extinction risk to body size, behavioral strategies, limitations on energy intake, and physiological acclimatization of water loss and metabolic rate. The field and laboratory experiments indicated that salamanders readily acclimatize water loss rates and metabolic rates in ways that could maintain positive energy balance. Projections with plasticity reduced extinction risk by 72% under climate warming, especially in the core of their range. Further analyses revealed that juveniles might experience the greatest physiological stress under climate warming, but we identified specific physiological adaptations or plastic responses that could minimize the lethal physiological stress imposed on juveniles. We conclude that incorporating plasticity fundamentally alters ecological predictions under climate change by reducing extinction risk in the hotspot of salamander diversity.

Heterogeneous responses of temperate-zone amphibian populations to climate change complicates conservation planning

The pervasive and unabated nature of global amphibian declines suggests common demographic responses to a given driver, and quantification of major drivers and responses could inform broad-scale conservation actions. We explored the influence of climate on demographic parameters (i.e., changes in the probabilities of survival and recruitment) using 31 datasets from temperate zone amphibian populations (North America and Europe) with more than a decade of observations each. There was evidence for an influence of climate on population demographic rates, but the direction and magnitude of responses to climate drivers was highly variable among taxa and among populations within taxa. These results reveal that climate drivers interact with variation in life-history traits and population-specific attributes resulting in a diversity of responses. This heterogeneity complicates the identification of conservation 'rules of thumb' for these taxa, and supports the notion of local focus as the most effective approach to overcome global-scale conservation challenges.

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

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

Accessories to Limb Regeneration

In a recent issue of Nature, Nacu et al. (2016) identified FGF and HH ligands as interacting molecular influences that are necessary and sufficient to induce the formation of supernumerary limbs from blastemal tissue in axolotl salamanders.

Importance of demographic surveys and public lands for the conservation of eastern hellbenders Cryptobranchus alleganiensis alleganiensis in southeast USA

Comparisons of recent and historic population demographic studies of eastern hellbenders Cryptobranchus alleganiensis alleganiensis have identified significant population declines and extirpations associated with habitat degradation, poor water quality and disease, leading to nomination as a candidate for listing under the Endangered Species Act. However, populations in the southern Appalachian region of the range have received less attention despite relatively high levels of watershed protection due to the establishment of federally protected National Forest and National Park public lands. These watersheds likely represent some of the best remaining available habitat, yet the lack of published studies make assessment of population stability and viability very difficult. Our objectives were to (1) conduct a capture-mark-recapture (CMR) demographic study and a point transect survey on the Hiwassee River in Tennessee which is designated a National Scenic River, and is largely contained within the Cherokee National Forest, (2) quantify the size structure of the population, (3) compare abundance, survival and recruitment with historic and contemporary hellbender populations across the range, (4) assess the importance of this population and the significance of National Forest and National Park lands in the context of hellbender population conservation in the southeastern United States. We detected all age classes present, with larval hellbenders comprising 21.5% of captures. Using a combination of static life table and CMR methods, we determined that survival rates during the first year were low (~10%), but were high (68–94%) for taggable sized hellbenders. Density of hellbenders at the study site was very high (84 taggable sized hellbenders per 100m of river) compared to recent demographic studies conducted in other regions of the range. We detected hellbenders over ~28 km of river, with a mean density of 23 taggable sized hellbenders per 100m of river, and a total population estimate of 6440 taggable hellbenders. National Forest and National Park lands are likely to continue to play a particularly important role in providing suitable habitat for hellbenders in the southern Appalachians. In fact, only six of 21 known hellbender locations in Tennessee appear to show consistent larval recruitment, all of which are located within or adjacent to National Forest or National Park land.

Testing the immunocompetence handicap hypothesis: Testosterone manipulation does not affect wound healing in male salamanders

In vertebrates, a bidirectional relationship exists between the immune system and the hypothalamic-pituitary-gonadal axis. In addition, sexual dimorphism in immunity has been documented in many vertebrates as well as some invertebrates, and males are generally less immunocompetent than their female counterparts. A possible explanation for this is described by the immunocompetence handicap hypothesis (ICHH), which proposes that elevated testosterone (T) levels direct resources towards the promotion of secondary sexual characteristics at a cost to immune function. To further test the ICHH, we examined the effects of T on cutaneous wound healing, an integrative measure of immunity, using male Allegheny Mountain dusky salamanders; a species that has sexually dimorphic courtship glands and testosterone-dependent mating behavior. We did this via two methods: surgical manipulation and transdermal delivery of T. In both experiments, elevated plasma T did not delay wound healing. Interestingly, intact animals healed more slowly than animals that had undergone prior invasive surgery, suggesting that the prior surgery had an immune-priming effect that enhanced healing of a second wound.

Olfactory effects of a hypervariable multicomponent pheromone in the red-legged salamander, Plethodon shermani

Chemical communication via chemosensory signaling is an essential process for promoting and modifying reproductive behavior in many species. During courtship in plethodontid salamanders, males deliver a mixture of non-volatile proteinaceous pheromones that activate chemosensory neurons in the vomeronasal epithelium (VNE) and increase female receptivity. One component of this mixture, Plethodontid Modulating Factor (PMF), is a hypervariable pheromone expressed as more than 30 unique isoforms that differ between individual males-likely driven by co-evolution with female receptors to promote gene duplication and positive selection of the PMF gene complex. Courtship trials with females receiving different PMF isoform mixtures had variable effects on female mating receptivity, with only the most complex mixtures increasing receptivity, such that we believe that sufficient isoform diversity allows males to improve their reproductive success with any female in the mating population. The aim of this study was to test the effects of isoform variability on VNE neuron activation using the agmatine uptake assay. All isoform mixtures activated a similar number of neurons (>200% over background) except for a single purified PMF isoform (+17%). These data further support the hypothesis that PMF isoforms act synergistically in order to regulate female receptivity, and different putative mechanisms are discussed.

Diversity of Guilds of Amphibian Larvae in North-Western Africa

The composition and diversity of biotic assemblages is regulated by a complex interplay of environmental features. We investigated the influence of climate and the aquatic habitat conditions on the larval traits and the structure of amphibian larval guilds in north-western Africa. We classified the species into morphological groups, based on external traits: body shape, size, and the relative positions of the eyes and oral apparatus. We characterized the guild diversity based on species richness and interspecific phylogenetic/functional relationships. The larvae of the urodeles were classified as typical of either the stream or pond type, and the anurans as typical of either the lentic-benthic or lentic-nektonic type. The variations in the body shapes of both urodeles and anurans were associated with the type of aquatic habitat (lentic vs lotic) and the types of predators present. Most of the urodele guilds (98.9%) contained a single species, whereas the anuran guilds were usually more diverse. Both the phylogenetic and functional diversity of the anuran guilds were positively influenced by the size of the aquatic habitat and negatively by aridity. In anurans, the benthic and nektonic morphological types frequently co-occurred, possibly influenced by their opportunistic breeding strategies.

Ultrasonography: a method used for pregnancy imaging of the fire salamander (Salamandra salamandra)

Ultrasound imaging has more frequently been used in veterinary medicine of amphibians and reptiles. In this study, we have verified the usefulness of ultrasound imaging in pregnancy determination of the fire salamander Salamandra salamandra. We have also undertaken to estimate the number of larvae and their developmental stage directly in the oviducts. Three gravid females from Lower Silesia (southern Poland) were examined. Due to the small size of the scanned animals, and the particular arrangement of embryos in the oviducts and ultrasound beams dispersal, the method proved to be inaccurate. Therefore, the minimum number of well-visualized larvae was determined. The maximum number of larvae was established on the basis of the visible fragments of embryos. After birth, we found that the number of larvae born was included in the "min-max" range in only one case. In the remaining two salamanders the number of larvae was higher than estimated in 3 to 7 individuals. The results showed that ultrasound imaging allows the minimum number of larvae in salamander; oviducts to be specified. However, total length measurements were possible only for single and clearly visible embryos.

Physiological Responses to Fasting and Estivation for the Three-Toed Amphiuma (Amphiuma tridactylum)

Species of Amphiuma enter a state of subterranean estivation with the drying of their aquatic habitat. Characteristic of amphibian fasting and estivation is an initial depression of metabolism and tissue mass and function with fasting, followed by a more pronounced adaptive decrease in metabolism and tissue function with estivation. We hypothesized that Amphiuma likewise experiences a two-stage set of responses to estivation. Therefore, we examined the physiological responses of the three-toed amphiuma (Amphiuma tridactylum) to fasting and estivation treatments. Recently fed A. tridactylum served as controls for fasting treatments of 1, 3, and 6 mo (in water) and estivation treatments of 3 and 6 mo (buried in dried substrate). After a 1-mo fast, A. tridactylum experienced no further depression of metabolic rate following 3 or 6 mo of fasting or estivation. For all fasting and estivation trials, A. tridactylum maintained blood chemistry homeostasis, with the exception of an increase in blood urea following 6 mo of estivation. Compared with fed controls, the mass of most organs did not vary even after 6 mo of fasting and estivation. Only the small intestine (decreasing) and the full gall bladder (increasing) experienced significant changes in mass with fasting or estivation. The fasting decrease in small intestinal mass was in part due to enterocyte atrophy, which resulted in a decrease in mucosa/submucosa thickness. In contrast to many estivating anurans and the ecologically convergent sirens, A. tridactylum does not surround itself in a cocoon of dried skin or mucus during estivation. The thickness and architecture of their skin remains unchanged even after 6 mo of estivation. Following months of fasting or estivation, individuals still maintain gastric acid production, pancreatic enzyme activity, and intestinal enzyme and transporter activities. Contrary to our hypothesis that A. tridactylum experiences two stages of metabolic depression and tissue downregulation, first with fasting and second with estivation, we observed a relatively modest single-stage response to both. Rather than becoming dormant and engaging in mechanisms to depress metabolism and tissue performance with estivation, A. tridactylum employs an alternative strategy of remaining alert and possibly eating to survive extended periods when their aquatic habitats become dry.

Interactive effects of temperature and glyphosate on the behavior of blue ridge two-lined salamanders (Eurycea wilderae)

The objective of the present study was to evaluate the potential interactive effects of stream temperatures and environmentally relevant glyphosate-based herbicide concentrations on movement and antipredator behaviors of larval Eurycea wilderae (Blue Ridge two-lined salamander). Larval salamanders were exposed to 1 of 4 environmentally relevant glyphosate concentrations (0.00 µg acid equivalent [a.e.]/L, 0.73 µg a.e./L, 1.46 µg a.e./L, and 2.92 µg a.e./L) at either ambient (12 °C) or elevated (23 °C) water temperature. Behaviors observed included the exploration of a novel habitat, use of refuge, habitat selection relative to a potential predator, and burst movement distance. In the absence of glyphosate, temperature consistently affected movement and refuge-use behavior, with individuals moving longer distances more frequently and using refuge less at warm temperatures; however, when glyphosate was added, the authors observed inconsistent effects of temperature that may have resulted from differential toxicity at various temperatures. Larval salamanders made shorter, more frequent movements and demonstrated reduced burst distance at higher glyphosate concentrations. The authors also found that lower glyphosate concentrations sometimes had stronger effects than higher concentrations (i.e., nonmonotonic dose responses), suggesting that standard safety tests conducted only at higher glyphosate concentrations might overlook important sublethal effects on salamander behavior. These data demonstrate that sublethal effects of glyphosate-based herbicides on natural behaviors of amphibians can occur with short-term exposure to environmentally relevant concentrations. Environ Toxicol Chem 2016;35:2297-2303. © 2016 SETAC.

A Novel Cysteine Knot Protein for Enhancing Sperm Motility That Might Facilitate the Evolution of Internal Fertilization in Amphibians

Internal fertilization ensures successful reproduction of tetrapod vertebrates on land, although how this mode of reproduction evolved is unknown. Here, we identified a novel gene encoding sperm motility-initiating substance (SMIS), a key protein for the internal fertilization of the urodele Cynops pyrrhogaster by Edman degradation of an isolated protein and subsequent reverse transcription polymerase chain reaction. The SMIS gene encoded a 150 amino-acid sequence including the cysteine knot (CK) motif. No gene with substantial similarity to the SMIS was in the data bank of any model organisms. An active site of the SMIS was in the C-terminal region of the 2nd loop of CK motif. A synthetic peptide including the active site sequence bound to the midpiece and initiated/enhanced the circular motion of C. pyrrhogaster sperm, which allows penetration of the egg jelly specialized for the internal fertilization of this species. The synthetic peptide bound to whole sperm of Rhacophorus arboreus and enhanced the rotary motion, which is adapted to propel the sperm through egg coat matrix specialized for arboreal reproduction, while it bound to the tip of head and tail of Bufo japonicus sperm, and enhanced the vibratory motion, which is suited to sperm penetration through the egg jelly specialized for the reproduction of that species in freshwater. The polyclonal antibody against the active site of the SMIS specifically bound to egg coat matrix of R. arboreus. These findings suggest that diversification of amphibian reproductive modes accompanies the specialization of egg coat and the adaptation of sperm motility to penetrate the specialized egg coat, and SMIS acts as the sperm motility enhancer of anurans and urodeles that might facilitate to adaptively optimize sperm motility for allowing the establishment of internal fertilization.

Reintroduction and Post-Release Survival of a Living Fossil: The Chinese Giant Salamander

Captive rearing and reintroduction / translocation are increasingly used as tools to supplement wild populations of threatened species. Reintroducing captive-reared Chinese giant salamanders may help to augment the declining wild populations and conserve this critically endangered amphibian. We released 31 captive-reared juvenile giant salamanders implanted with VHF radio transmitters at the Heihe River (n = 15) and the Donghe River (n = 16) in the Qinling Mountains of central China. Salamanders were monitored every day for survival from April 28^th 2013 to September 3^rd 2014. We attempted to recapture all living individuals by the end of the study, measured their body mass and total body length, and checked for abnormalities and presence of external parasites. Two salamanders at the Heihe River and 10 animals at the Donghe River survived through the project timeline. Nine salamanders were confirmed dead, while the status of the other 10 animals was undetermined. The annual survival rate of giant salamanders at the Donghe River (0.702) was 1.7-fold higher than that at the Heihe River (0.405). Survival increased as individuals were held longer following surgery, whereas body mass did not have a significant impact on survival rate. All salamanders recaptured from the Donghe River (n = 8) increased in mass (0.50 ± 0.13 kg) and length (5.5 ± 1.5 cm) after approximately 11 months in the wild, and they were only 7% lighter than wild animals of the same length (mean residual = -0.033 ± 0.025). Our results indicate that captive-reared Chinese giant salamanders can survive in the wild one year after release and adequate surgical recovery time is extremely important to post-release survival. Future projects may reintroduce older juveniles to achieve better survival and longer monitoring duration.

Invasive Asian Earthworms Negatively Impact Keystone Terrestrial Salamanders

Asian pheretimoid earthworms (e.g. Amynthas and Metaphire spp.) are invading North American forests and consuming the vital detrital layer that forest floor biota [including the keystone species Plethodon cinereus (Eastern Red-backed Salamander)], rely on for protection, food, and habitat. Plethodon cinereus population declines have been associated with leaf litter loss following the invasion of several exotic earthworm species, but there have been few studies on the specific interactions between pheretimoid earthworms and P. cinereus. Since some species of large and active pheretimoids spatially overlap with salamanders beneath natural cover objects and in detritus, they may distinctively compound the negative consequences of earthworm-mediated resource degradation by physically disturbing important salamander activities (foraging, mating, and egg brooding). We predicted that earthworms would exclude salamanders from high quality microhabitat, reduce foraging efficiency, and negatively affect salamander fitness. In laboratory trials, salamanders used lower quality microhabitat and consumed fewer flies in the presence of earthworms. In a natural field experiment, conducted on salamander populations from “non-invaded” and “pheretimoid invaded” sites in Ohio, salamanders and earthworms shared cover objects ~60% less than expected. Earthworm abundance was negatively associated with juvenile and male salamander abundance, but had no relationship with female salamander abundance. There was no effect of pheretimoid invasion on salamander body condition. Juvenile and non-resident male salamanders do not hold stable territories centered beneath cover objects such as rocks or logs, which results in reduced access to prey, greater risk of desiccation, and dispersal pressure. Habitat degradation and physical exclusion of salamanders from cover objects may hinder juvenile and male salamander performance, ultimately reducing recruitment and salamander abundance following Asian earthworm invasion.

Extreme negative temperatures and body mass loss in the Siberian salamander (Salamandrella keyserlingii, amphibia, hynobiidae)

Frozen Siberian salamander safely tolerates long (45 days) stay at-35°C. Short-term (3 days) cooling down to-50°C was tolerable for 40% of adult individuals; down to-55°C, for 80% of the underyearlings. Generally, the salamanders lose about 28% of the body mass during the pre-hibernating period (before winter, at temperatures as low as 0°C) and during the process of freezing (as low as-5°C). The body weight remained constant upon further cooling (to-35°C). The frozen salamanders have no physiological mechanisms protecting from sublimation.

Physiological and morphological characterization of ganglion cells in the salamander retina

Retinal ganglion cells (RGCs) integrate visual information from the retina and transmit collective signals to the brain. A systematic investigation of functional and morphological characteristics of various types of RGCs is important to comprehensively understand how the visual system encodes and transmits information via various RGC pathways. This study evaluated both physiological and morphological properties of 67 RGCs in dark-adapted flat-mounted salamander retina by examining light-evoked cation and chloride current responses via voltage-clamp recordings and visualizing morphology by Lucifer yellow fluorescence with a confocal microscope. Six groups of RGCs were described: asymmetrical ON-OFF RGCs, symmetrical ON RGCs, OFF RGCs, and narrow-, medium- and wide-field ON-OFF RGCs. Dendritic field diameters of RGCs ranged 102-490 μm: narrow field (<200 μm, 31% of RGCs), medium field (200-300 μm, 45%) and wide field (>300 μm, 24%). Dendritic ramification patterns of RGCs agree with the sublamina A/B rule. 34% of RGCs were monostratified, 24% bistratified and 42% diffusely stratified. 70% of ON RGCs and OFF RGCs were monostratified. Wide-field RGCs were diffusely stratified. 82% of RGCs generated light-evoked ON-OFF responses, while 11% generated ON responses and 7% OFF responses. Response sensitivity analysis suggested that some RGCs obtained separated rod/cone bipolar cell inputs whereas others obtained mixed bipolar cell inputs. 25% of neurons in the RGC layer were displaced amacrine cells. Although more types may be defined by more refined classification criteria, this report is to incorporate more physiological properties into RGC classification.

Ecological equivalency as a tool for endangered species management

The use of taxon substitutes for extinct or endangered species is a controversial conservation measure. We use the example of the endangered California tiger salamander (Ambystoma californiense; CTS), which is being replaced by hybrids with the invasive barred tiger salamander (Ambystoma mavortium), to illustrate a strategy for evaluating taxon substitutes based on their position in a multivariate community space. Approximately one-quarter of CTS's range is currently occupied by "full hybrids" with 70% nonnative genes, while another one-quarter is occupied by "superinvasives" where a specific set of 3/68 genes comprising 4% of the surveyed genome is nonnative. Based on previous surveys of natural CTS breeding ponds, we stocked experimental mesocosms with field-verified, realistic densities of tiger salamander larvae and their prey, and used these mesocosms to evaluate ecological equivalency between pure CTS, full hybrids, and superinvasives in experimental pond communities. We also included a fourth treatment with no salamanders present to evaluate the community effects of eliminating Ambystoma larvae altogether. We found that pure CTS and superinvasive larvae were ecologically equivalent, because their positions in the multivariate community space were statistically indistinguishable and they did not differ significantly along any univariate community axes. Full hybrids were ecologically similar, but not equivalent, to the other two genotypes, and the no-Ambystoma treatment was by far the most divergent. We conclude that, at least for the larval stage, superinvasives are adequate taxon substitutes for pure CTS and should probably be afforded protection under the Endangered Species Act. The proper conservation status for full hybrids remains debatable.

Regeneration versus scarring in vertebrate appendages and heart

Injuries to complex human organs, such as the limbs and the heart, result in pathological conditions, for which we often lack adequate treatments. While modern regenerative approaches are based on the transplantation of stem cell-derived cells, natural regeneration in lower vertebrates, such as zebrafish and newts, relies predominantly on the intrinsic plasticity of mature tissues. This property involves local activation of the remaining material at the site of injury to promote cell division, cell migration and complete reproduction of the missing structure. It remains an unresolved question why adult mammals are not equally competent to reactivate morphogenetic programmes. Although organ regeneration depends strongly on the proliferative properties of cells in the injured tissue, it is apparent that various organismic factors, such as innervation, vascularization, hormones, metabolism and the immune system, can affect this process. Here, we focus on a correlation between the regenerative capacity and cellular specialization in the context of functional demands, as illustrated by appendages and heart in diverse vertebrates. Elucidation of the differences between homologous regenerative and non-regenerative tissues from various animal models is essential for understanding the applicability of lessons learned from the study of regenerative biology to clinical strategies for the treatment of injured human organs.

Evaluating Multi-Level Models to Test Occupancy State Responses of Plethodontid Salamanders

Plethodontid salamanders are diverse and widely distributed taxa and play critical roles in ecosystem processes. Due to salamander use of structurally complex habitats, and because only a portion of a population is available for sampling, evaluation of sampling designs and estimators is critical to provide strong inference about Plethodontid ecology and responses to conservation and management activities. We conducted a simulation study to evaluate the effectiveness of multi-scale and hierarchical single-scale occupancy models in the context of a Before-After Control-Impact (BACI) experimental design with multiple levels of sampling. Also, we fit the hierarchical single-scale model to empirical data collected for Oregon slender and Ensatina salamanders across two years on 66 forest stands in the Cascade Range, Oregon, USA. All models were fit within a Bayesian framework. Estimator precision in both models improved with increasing numbers of primary and secondary sampling units, underscoring the potential gains accrued when adding secondary sampling units. Both models showed evidence of estimator bias at low detection probabilities and low sample sizes; this problem was particularly acute for the multi-scale model. Our results suggested that sufficient sample sizes at both the primary and secondary sampling levels could ameliorate this issue. Empirical data indicated Oregon slender salamander occupancy was associated strongly with the amount of coarse woody debris (posterior mean = 0.74; SD = 0.24); Ensatina occupancy was not associated with amount of coarse woody debris (posterior mean = -0.01; SD = 0.29). Our simulation results indicate that either model is suitable for use in an experimental study of Plethodontid salamanders provided that sample sizes are sufficiently large. However, hierarchical single-scale and multi-scale models describe different processes and estimate different parameters. As a result, we recommend careful consideration of study questions and objectives prior to sampling data and fitting models.

Salamanders increase their feeding activity when infected with the pathogenic chytrid fungus Batrachochytrium dendrobatidis

Immune function is a costly line of defense against parasitism. When infected with a parasite, hosts frequently lose mass due to these costs. However, some infected hosts (e.g. highly resistant individuals) can clear infections with seemingly little fitness losses, but few studies have tested how resistant hosts mitigate these costly immune defenses. We explored this topic using eastern red-backed salamanders Plethodon cinereus and the fungal pathogen Batrachochytrium dendrobatidis (Bd). Bd is generally lethal for amphibians, and stereotypical symptoms of infection include loss in mass and deficits in feeding. However, individuals of P. cinereus can clear their Bd infections with seemingly few fitness costs. We conducted an experiment in which we repeatedly observed the feeding activity of Bd-infected and non-infected salamanders. We found that Bd-infected salamanders generally increased their feeding activity compared to non-infected salamanders. The fact that we did not observe any differences in mass change between the treatments suggests that increased feeding might help Bd-infected salamanders minimize the costs of an effective immune response.

Life history differences influence the impacts of drought on two pond-breeding salamanders

Drought is a strong density-independent environmental filter that contributes to population regulation and other ecological processes. Not all species respond similarly to drought, and the overall impacts can vary depending on life histories. Such differences can necessitate management strategies that incorporate information on individual species to maximize conservation success. We report the effects of a short-term drought on occupancy and reproductive success of two pond-breeding salamanders that differ in breeding phenology (fall vs. spring breeder) across an active military base landscape in Missouri, USA: We surveyed ~200 ponds for the presence of eggs, larvae, and metamorphs from 2011 to 2013. This period coincided with before, during, and after a severe drought that occurred in 2012. The two species showed contrasting responses to drought, where high reproductive failure (34% of ponds) was observed for the spring breeder during a single drought year. Alternatively, the fall breeder only showed a cumulative 8% failure over two years. The number of breeding ponds available for use in the fall decreased during the drought due to pond drying and/or a lack of re-filling. Estimates of occupancy probability declined for the fall-breeding salamander between 2012 and 2013, whereas occupancy probability estimates of the spring breeder increased post-drought. The presence of fish, hydroperiod, the amount of forest cover surrounding ponds, and canopy cover were all found to affect estimates of occupancy probabilities of each species. Pond clustering (distance to nearest pond and the number of ponds within close proximity), hydroperiod, forest cover, and canopy cover influenced both estimates of colonization and extinction probabilities. Our results show life history variation can be important in determining the relative susceptibility of a species to drought conditions, and that sympatric species experiencing the same environmental conditions can respond differently. Consideration of the spatial network and configuration of habitat patches that act as refuges under extreme environmental conditions will improve conservation efforts, such as the placement of permanent ponds for aquatic organisms. A better awareness of species-specific tolerances to environmental filters such as drought can lead to improved management recommendations to conserve and promote habitat for a greater diversity of species across landscapes of spatially connected populations.

Predator cannibalism can intensify negative impacts on heterospecific prey

Although natural populations consist of individuals with different traits, and the degree of phenotypic variation varies among populations, the impact of phenotypic variation on ecological interactions has received little attention, because traditional approaches to community ecology assume homogeneity of individuals within a population. Stage structure, which is a common way of generating size and developmental variation within predator populations, can drive cannibalistic interactions, which can affect the strength of predatory effects on the predator's heterospecific prey. Studies have shown that predator cannibalism weakens predatory effects on heterospecific prey by reducing the size of the predator population and by inducing less feeding activity of noncannibal predators. We predict, however, that predator cannibalism, by promoting rapid growth of the cannibals, can also intensify predation pressure on heterospecific prey, because large predators have large resource requirements and may utilize a wider variety of prey species. To test this hypothesis, we conducted an experiment in which we created carnivorous salamander (Hynobius retardatus) populations with different stage structures by manipulating the salamander's hatch timing (i.e., populations with large or small variation in the timing of hatching), and explored the resultant impacts on the abundance, behavior, morphology, and life history of the salamander's large heterospecific prey, Rana pirica frog tadpoles. Cannibalism was rare in salamander populations having small hatch-timing variation, but was frequent in those having large hatch-timing variation. Thus, giant salamander cannibals occurred only in the latter. We clearly showed that salamander giants exerted strong predation pressure on frog tadpoles, which induced large behavioral and morphological defenses in the tadpoles and caused them to metamorphose late at large size. Hence, predator cannibalism arising from large variation in the timing of hatching can strengthen predatory effects on heterospecific prey and can have impacts on various, traits of both predator and prey. Because animals commonly broaden their diet as they grow, such negative impacts of predator cannibalism on the heterospecific prey may be common in interactions between predators and prey species of similar size.

An Experimental Test of Buffer Utility as a Technique for Managing Pool-Breeding Amphibians

Vegetated buffers are used extensively to manage wetland-dependent wildlife. Despite widespread application, buffer utility has not been experimentally validated for most species. To address this gap, we conducted a six-year, landscape-scale experiment, testing how buffers of different widths affect the demographic structure of two amphibian species at 11 ephemeral pools in a working forest of the northeastern U.S. We randomly assigned each pool to one of three treatments (i.e., reference, 100m buffer, 30m buffer) and clearcut to create buffers. We captured all spotted salamanders and wood frogs breeding in each pool and examined the impacts of treatment and hydroperiod on breeding-population abundance, sex ratio, and recapture rate. The negative effects of clearcutting tended to increase as forest-buffer width decreased and be strongest for salamanders and when other stressors were present (e.g., at short-hydroperiod pools). Recapture rates were reduced in the 30m, but not 100m, treatment. Throughout the experiment for frogs, and during the first year post-cut for salamanders, the predicted mean proportion of recaptured adults in the 30m treatment was only 62% and 40%, respectively, of that in the reference treatment. Frog sex ratio and abundance did not differ across treatments, but salamander sex ratios were increasingly male-biased in both cut treatments. By the final year, there were on average, only about 40% and 65% as many females predicted in the 100m and 30m treatments, respectively, compared to the first year. Breeding salamanders at short-hydroperiod pools were about 10% as abundant in the 100m versus reference treatment. Our study demonstrates that buffers partially mitigate the impacts of habitat disturbance on wetland-dependent amphibians, but buffer width and hydroperiod critically mediate that process. We provide the first experimental evidence showing that 30-m-wide buffers may be insufficient for maintaining resilient breeding populations of pool-dependent amphibians, at least during the first six years post-disturbance.

3D bite modeling and feeding mechanics of the largest living amphibian, the Chinese giant salamander Andrias davidianus (Amphibia:Urodela)

Biting is an integral feature of the feeding mechanism for aquatic and terrestrial salamanders to capture, fix or immobilize elusive or struggling prey. However, little information is available on how it works and the functional implications of this biting system in amphibians although such approaches might be essential to understand feeding systems performed by early tetrapods. Herein, the skull biomechanics of the Chinese giant salamander, Andrias davidianus is investigated using 3D finite element analysis. The results reveal that the prey contact position is crucial for the structural performance of the skull, which is probably related to the lack of a bony bridge between the posterior end of the maxilla and the anterior quadrato-squamosal region. Giant salamanders perform asymmetrical strikes. These strikes are unusual and specialized behavior but might indeed be beneficial in such sit-and-wait or ambush-predators to capture laterally approaching prey. However, once captured by an asymmetrical strike, large, elusive and struggling prey have to be brought to the anterior jaw region to be subdued by a strong bite. Given their basal position within extant salamanders and their "conservative" morphology, cryptobranchids may be useful models to reconstruct the feeding ecology and biomechanics of different members of early tetrapods and amphibians, with similar osteological and myological constraints.

Questioning the use of an amphibian colour morph as an indicator of climate change

The effects of recent climate changes on earth ecosystems are likely among the most important ecological concerns in human history. Good bioindicators are essential to properly assess the magnitude of these changes. In the last decades, studies have suggested that the morph proportion of the eastern red-backed salamander (Plethodon cinereus), one of the most widely distributed and abundant vertebrate species in forests of eastern North America, could be used as a proxy for monitoring climate changes. Based on new discoveries in the northern areas of the species' range and on one of the largest compilation ever made for a vertebrate in North America (236 109 observations compiled from 1880 to 2013 in 1148 localities), we demonstrate however that climatic and geographic variables do not influence the colour morph proportions in P. cinereus populations. Consequently, we show that the use of colour morph proportions of this species do not perform as an indicator of climate change. Our findings indicate that bioindicator paradigms can be significantly challenged by new ecological research and more representative databases.

Widespread rapid reductions in body size of adult salamanders in response to climate change

Reduction in body size is a major response to climate change, yet evidence in globally imperiled amphibians is lacking. Shifts in average population body size could indicate either plasticity in the growth response to changing climates through changes in allocation and energetics, or through selection for decreased size where energy is limiting. We compared historic and contemporary size measurements in 15 Plethodon species from 102 populations (9450 individuals) and found that six species exhibited significant reductions in body size over 55 years. Biophysical models, accounting for actual changes in moisture and air temperature over that period, showed a 7.1-7.9% increase in metabolic expenditure at three latitudes but showed no change in annual duration of activity. Reduced size was greatest at southern latitudes in regions experiencing the greatest drying and warming. Our results are consistent with a plastic response of body size to climate change through reductions in body size as mediated through increased metabolism. These rapid reductions in body size over the past few decades have significance for the susceptibility of amphibians to environmental change, and relevance for whether adaptation can keep pace with climate change in the future.

Handed behavior in hagfish--an ancient vertebrate lineage--and a survey of lateralized behaviors in other invertebrate chordates and elongate vertebrates

Hagfish represent an ancient lineage of boneless and jawless vertebrates. Among several curious behaviors they exhibit, solitary individuals in one dominant genus of hagfish (Eptatretus spp.) regularly rest in a tightly coiled posture. We present the first systematic treatment of this distinctive behavior. Individual northeastern Pacific hagfish (E. stoutii) exhibited significant handedness (preferred orientation of coiling). However, right-coiling and left-coiling individuals were equally common in the population. Individual hagfish likely develop a preference for one direction by repeating the preceding coiling direction. We also revisit classical accounts of chordate natural history and compare the coiling behavior of Eptatretus with other handed or lateralized behaviors in non-vertebrate chordates, lampreys, and derived vertebrates with elongate bodies. Handed behaviors occur in many of these groups, but they likely evolved independently. In contrast to vertebrates, morphological asymmetries may bias lateralized larval behaviors toward one side in cephalochordates and tunicates. As a consequence, no known handed behavior can be inferred to have existed in the common ancestor of vertebrates.

Adaptation to changes in higher-order stimulus statistics in the salamander retina

Adaptation in the retina is thought to optimize the encoding of natural light signals into sequences of spikes sent to the brain. While adaptive changes in retinal processing to the variations of the mean luminance level and second-order stimulus statistics have been documented before, no such measurements have been performed when higher-order moments of the light distribution change. We therefore measured the ganglion cell responses in the tiger salamander retina to controlled changes in the second (contrast), third (skew) and fourth (kurtosis) moments of the light intensity distribution of spatially uniform temporally independent stimuli. The skew and kurtosis of the stimuli were chosen to cover the range observed in natural scenes. We quantified adaptation in ganglion cells by studying linear-nonlinear models that capture well the retinal encoding properties across all stimuli. We found that the encoding properties of retinal ganglion cells change only marginally when higher-order statistics change, compared to the changes observed in response to the variation in contrast. By analyzing optimal coding in LN-type models, we showed that neurons can maintain a high information rate without large dynamic adaptation to changes in skew or kurtosis. This is because, for uncorrelated stimuli, spatio-temporal summation within the receptive field averages away non-gaussian aspects of the light intensity distribution.

Effects of fine-scale forest habitat quality on movement and settling decisions in juvenile pond-breeding salamanders

A better understanding of how individuals respond to variation in habitat quality while moving through heterogeneous habitats is needed to predict ecological phenomena at larger scales, such as local population and metapopulation dynamics. We sought to identify how fine-scale habitat quality affects the decisions of juvenile pond-breeding salamanders (Ambystoma maculatum and A. annulatum) to cease dispersive movements away from their natal pond, select a refuge, and settle. Because of the acute susceptibility of juvenile amphibians to evaporative water loss in terrestrial habitats, we predicted that they possess mechanisms for adjusting their behavior in response to variations in fine-scale habitat quality. We used experimental field enclosures to isolate the effects of habitat quality on settling behavior and employed generalized linear mixed models to examine how manipulations in canopy cover (closed or open) and microhabitat (control, compacted soils, high coarse woody debris, high burrow density), along with environmental variables (rainfall and air temperature), affect the individual's probability of settling. Our results indicated that A. maculatum and A. annulatum had a 10% and 30% decreased probability of settling in open-canopy clearcut habitat, respectively, compared to closed-canopy forest habitat. In addition, A. annulatum were 24% less likely to settle in compacted soil treatments. Although the settlement probability of A. annulatum did not depend on refuge availability, A. maculatum were 18% and 25% more likely to settle under conditions of high burrow density and high coarse woody debris, respectively. These findings make a unique contribution to our understanding of amphibian movement ecology by demonstrating how the interplay of external factors and individual behavior produce observed patterns of movement and habitat selection.

Effects of red-backed salamanders on ecosystem functions

Ecosystems provide a vast array of services for human societies, but understanding how various organisms contribute to the functions that maintain these services remains an important ecological challenge. Predators can affect ecosystem functions through a combination of top-down trophic cascades and bottom-up effects on nutrient dynamics. As the most abundant vertebrate predator in many eastern US forests, woodland salamanders (Plethodon spp.) likely affect ecosystems functions. We examined the effects of red-backed salamanders (Plethodon cinereus) on a variety of forest ecosystem functions using a combined approach of large-scale salamander removals (314-m(2) plots) and small-scale enclosures (2 m(2)) where we explicitly manipulated salamander density (0, 0.5, 1, 2, 4 m(-2)). In these experiments, we measured the rates of litter and wood decomposition, potential nitrogen mineralization and nitrification rates, acorn germination, and foliar insect damage on red oak seedlings. Across both experimental venues, we found no significant effect of red-backed salamanders on any of the ecosystem functions. We also found no effect of salamanders on intraguild predator abundance (carabid beetles, centipedes, spiders). Our study adds to the already conflicting evidence on effects of red-backed salamander and other amphibians on terrestrial ecosystem functions. It appears likely that the impact of terrestrial amphibians on ecosystem functions is context dependent. Future research would benefit from explicitly examining terrestrial amphibian effects on ecosystem functions under a variety of environmental conditions and in different forest types.

Searching for collective behavior in a large network of sensory neurons

Maximum entropy models are the least structured probability distributions that exactly reproduce a chosen set of statistics measured in an interacting network. Here we use this principle to construct probabilistic models which describe the correlated spiking activity of populations of up to 120 neurons in the salamander retina as it responds to natural movies. Already in groups as small as 10 neurons, interactions between spikes can no longer be regarded as small perturbations in an otherwise independent system; for 40 or more neurons pairwise interactions need to be supplemented by a global interaction that controls the distribution of synchrony in the population. Here we show that such "K-pairwise" models--being systematic extensions of the previously used pairwise Ising models--provide an excellent account of the data. We explore the properties of the neural vocabulary by: 1) estimating its entropy, which constrains the population's capacity to represent visual information; 2) classifying activity patterns into a small set of metastable collective modes; 3) showing that the neural codeword ensembles are extremely inhomogenous; 4) demonstrating that the state of individual neurons is highly predictable from the rest of the population, allowing the capacity for error correction.