Newt Larvae Research Articles

Trophic effects of Bti-based mosquito control on two top predators in floodplain pond mesocosms

Chironomid (Diptera: Chironomidae) larvae play a key role in aquatic food webs as prey for predators like amphibian and dragonfly larvae. This trophic link may be disrupted by anthropogenic stressors such as Bacillus thuringiensis var. israelensis (Bti), a biocide widely used in mosquito control. In a companion study, we recorded a 41% reduction of non-target larval chironomids abundance in outdoor floodplain pond mesocosms (FPMs) treated with Bti. Therefore, we examined the diet of two top predators in the FPMs, larvae of the palmate newt (Salamandridae: Lissotriton helveticus) and dragonfly (Aeshnidae: predominantly Anax imperator), using bulk stable isotope analyses of carbon and nitrogen. Additionally, we determined neutral lipid fatty acids in newt larvae to assess diet-related effects on their physiological condition. We did not find any effects of Bti on the diet proportions of newt larvae and no significant effects on the fatty acid content. We observed a trend in Aeshnidae larvae from Bti-FPMs consuming a higher proportion of large prey (Aeshnidae, newt, damselfly larvae; ~42%), and similar parts of smaller prey (chironomid, mayfly, Libellulidae, and zooplankton), compared to controls. Our findings may suggest bottom-up effects of Bti on aquatic predators but should be further evaluated, for instance, by using compound-specific stable isotope analyses of fatty acids or metabarcoding approaches.

Density Mediates the Predator-Induced Growth and Metamorphic Plasticity of Chinhai Spiny Newt Larvae

Predators significantly influence amphibian larval development. Predator-induced plasticity is often studied independently from conspecific density effects, but these environmental factors may interact. We conducted two-factor factorial experimental design to manipulate conspecific density and predator cues, aiming to investigate the independently or interactive impacts of these two factors on the development of Chinhai spiny newt larvae (Echinotriton chinhaiensis). Our findings reveal that both high and low conspecific densities constrain spiny newt larval growth and predators also limit growth. Interestingly, high conspecific density restricts predator-induced growth plasticity without interacting effects. Only lower density groups exhibit slower growth responses to predators. Our study investigates how density mediates predator-induced plasticity in the endangered Chinhai spiny newt larvae, providing insights into their intricate life history. These results contribute to the understanding of predator-induced plasticity in amphibians and provide insights into the adaptive strategies of endangered species like Chinhai spiny newt. Such knowledge informs the development of effective conservation strategies for their protection.

The presence of predators constrains larval development process by influencing critical developmental windows in the endangered Chinhai spiny newt.

Predators significantly impact the development process and subsequently influence the metamorphic decisions of amphibian larvae. Larvae often exhibit induced growth and metamorphic plasticity in response to the presence of predators. However, growth and development rates are not always perfectly correlated, growth responses can vary throughout ontogeny. It is crucial to consider the stage-specific growth responses induced by predators. Here, we employ a critical windows experimental design and examine development-related growth and metamorphic responses to predators in the endangered Chinhai spiny newt (Echinotriton chinhaiensis). Our findings reveal that predators constrain the development process of spiny newt larvae and also impact survival to metamorphosis. Inducible plasticity predominantly exhibits in the early and middle stages of larval development. Our results also suggest that diverse developmental plasticity has been adopted by larvae in response to predators. The presence of predators during early stage induces larvae to exhibit a same size at metamorphosis but a prolonged time to metamorphosis, while predators present during middle stage induce larvae to exhibit a large size at metamorphosis but a same time to metamorphosis. The presence of predators at the late developmental stage does not induce any plasticity in larval growth and metamorphosis. Moreover, these results also suggest that several stages of larval development are likely critical developmental windows for spiny newt larvae. This study not only provides basic biological information on predator-induced developmental plasticity of the endangered Chinhai spiny newt but also likely provides biological insights for the implementation of insitu conservation and preservation efforts for endangered species.

Larval newts from turbid and transparent waterbodies exhibit different morphological and behavioural traits

Abstract Turbidity represents an obstacle to visual acuity underwater that might entail considerable consequences for multiple faunal traits. Morphology, especially eye size, could be adjusted to cope with reduced visibility in turbid water. Moreover, turbidity could interfere with colour signals or crypsis. Turbid water may simultaneously impair the ability of prey and predators to detect each other, which may cause reduced speed, flight initiation distance, activity time, boldness, and exploratory behaviour by prey. In this work, we compared these traits in larvae of the newt Pleurodeles waltl from transparent and turbid ponds (around 100 and 300 FTU, respectively). Body size did not differ between pond types, but larvae from turbid ponds had smaller eyes, probably because visual acuity is structurally hindered by the environment. Colouration did not differ between transparent and turbid ponds on average, but it was more variable in larvae from transparent than turbid ponds, probably because transparent ponds trigger crypsis towards diverse background colours, whereas turbid ponds promote reduced pigmentation in all cases. In addition, behavioural traits were gauged in larvae from both types of ponds, in tests conducted in either transparent or turbid water. Speed was unaffected by turbidity, but larvae from turbid ponds increased their flight initiation distance when tested in transparent water. In all cases, larvae from transparent ponds were more active, and bolder in transparent water, and all larvae were more exploratory when tested in transparent water (regardless of which pond type they came from). Turbidity could trigger more cautious behaviours, probably because it makes predators harder to track. Alternatively, transparent water could stimulate a more expansive use of space through improved visibility, or it might encourage a more active search for shelter. These results shed light on the role of turbidity as a promotor of morphological and behavioural variability in amphibian larvae. These ecological consequences of water turbidity can be framed in terms of energy allocation and detectability in the context of predator–prey interactions.

Suitability of Wheel Ruts: Characterization of Overlooked Breeding Habitats of Alpine Newts

The Alpine newt (Ichthyosaura alpestris) is sensitive to habitat destruction and alteration, and as a result there has been a decline in their populations across Europe. Due to historical landscape changes, the populations of Alpine newts drawn from lowlands and hilly areas have recently been primarily found in artificial habitats, such as wheel ruts. In some areas inhabited by the Alpine newt range, wheel ruts are the only available habitat for newt breeding, and thus the only one allowing the maintenance of their populations. However, our knowledge about this type of habitat is limited. Therefore, 60 wheel ruts in a hilly forested area in the Czech Republic were checked for the presence of Alpine newt larvae. Their characteristics were measured (conductivity, pH, dissolved oxygen, depth, water coverage, plants, presence of prey, hydroperiod). The presence of larvae was positively associated with higher values of pH, coverage of water plants, and the presence of prey. The strongest predictor was the hydrological stability of wheel ruts, and newts were found to prefer non-drying ruts. From the conservation point of view, this means that the suitability of wheel ruts for Alpine newts can be estimated quite easily. This can essentially be performed on the basis of visual inspection if it is carried out through the breeding season of newts.

Trophic Relationships in Larval California Newts (Taricha torosa)

The larval stage of the California newt (Taricha torosa) has been little studied despite the presence and abundance of the species throughout much of California. During the 2017–2018 time period, the diet and life history characteristics of this cohort of stream-dwelling newt larvae were examined, using gut contents and stable isotopes, in order to better understand the ecological niche and trophic relationships of the life stage. Our results suggest that the newt larvae consume Chironomidae as a major part of their diet and that this reliance decreases as the larvae age. Newt larvae also feed more widely and abundantly as they age. The isotopic data suggest that as larvae get larger, they alter their diet but that the relationships to both carbon source (δC) and trophic level (δN) are complex.

Oxidative Stress Parameters in Goitrogen-Exposed Crested Newt Larvae (Triturus spp.): Arrested Metamorphosis.

Thiourea is an established disruptor of thyroid hormone synthesis and is frequently used as an inhibitor of metamorphosis. The changes caused by thiourea can affect processes associated with the oxidative status of individuals (metabolic rate, the HPI axis, antioxidant system). We investigated the parameters of oxidative stress in crested newt (Triturus spp.) larvae during normal development in late larval stage 62 and newly metamorphosed individuals, and during thiourea-stimulated metamorphosis arrest in individuals exposed to low (0.05%) and high (0.1%) concentrations of thiourea. Both groups of crested newts exposed to thiourea retained their larval characteristics until the end of the experiment. The low activities of antioxidant enzymes and the high lipid peroxidation level pointed to increased oxidative stress in larvae at the beginning of stage 62 as compared to fully metamorphosed individuals. The activities of catalase (CAT) and glutathione-S-transferase (GST) and the concentration of sulfhydryl (SH) groups were significantly lower in larvae reared in aqueous solutions containing thiourea than in newly metamorphosed individuals. The high thiourea concentration (0.1%) affected the antioxidative parameters to the extent that oxidative damage could not be avoided, contrary to a lower concentration. Our results provide a first insight into the physiological adaptations of crested newts during normal development and simulated metamorphosis arrest.

Impacts of predator-induced behavioural plasticity on the temperature dependence of predator-prey activity and population dynamics.

Predation is a key ecological interaction affecting populations and communities. Climate warming can modify this interaction both directly by the kinetic effects of temperature on biological rates and indirectly through integrated behavioural and physiological responses of the predators and prey. Temperature dependence of predation rates can further be altered by predator-induced plasticity of prey locomotor activity, but empirical data about this effect are lacking. We propose a general framework to understand the influence of predator-induced developmental plasticity on behavioural thermal reaction norms in prey and their consequences for predator-prey dynamics. Using a mesocosm experiment with dragonfly larvae (predator) and newt larvae (prey), we tested if the predator-induced plasticity alters the elevation or the slope of the thermal reaction norms for locomotor activity metrics in prey. We also estimated the joint predator-prey thermal response in mean locomotor speed, which determines prey encounter rate, and modelled the effect of both phenomena on predator-prey population dynamics. Thermal reaction norms for locomotor activity in prey were affected by predation risk cues but with minor influence on the joint predator-prey behavioural response. We found that predation risk cues significantly decreased the intercept of thermal reaction norm for total activity rate (i.e. all body movements) but not the other locomotor activity metrics in the prey, and that prey locomotor activity rate and locomotor speed increased with prey density. Temperature had opposite effects on the mean relative speed of predator and prey as individual speed increased with temperature in predators but decreased in prey. This led to a negligible effect of body temperature on predicted prey encounter rates and predator-prey dynamics. The behavioural component of predator-prey interaction varied much more between individuals than with temperature and the presence of predation risk cues in our system. We conclude that within-population variation in locomotor activity can buffer the influence of body temperature and predation risk cues on predator-prey interactions, and further research should focus on the magnitude and sources of behavioural variation in interacting species to predict the impact of climate change on predator-prey interactions and food web dynamics.

The Effect of Shelter on Oxidative Stress and Aggressive Behavior in Crested Newt Larvae (Triturus spp.).

Simple SummaryA lack of adequate refuge, even in the absence of predators, can alter the metabolism, levels of corticosteroids, growth and behavior in various groups of animals. Even though some of those processes (higher metabolic rates and activation of the stress response of the hypothalamic-pituitary-adrenal axis) in animals can result in enhanced reactive species (RS) production and oxidative stress, there is no study examining the effects of shelter on oxidative stress parameters. The results from this study showed that in crested newt larvae the absence of refuges altered their oxidative/antioxidative status and movement, but did not affect their aggressivity/injuries rate. Higher values of catalase, glutathione peroxidase, glutathione S-transferase and glutathione can indicate increased production of hydrogen peroxide in individuals without an adequate hiding place. This boosted antioxidant defense has a certain physiological cost that can be expressed in terms of the consumption of energy needed to maintain it as upregulated.Shelters are important for animal survival. Provision of adequate hiding places allow animals to express their natural sheltering behavior and it can have different positive effects on cortisol levels, physiological processes and mental performance. Although the absence of a refuge activates some stress response, its effect on oxidative stress has not been adequately examined. This study investigated whether the presence/absence of a shelter modifies the oxidative status (the antioxidant system and oxidative damage) and aggressive behavior of crested newt larvae (Triturus macedonicus and its hybrid with T. ivanbureschi). Our results show that individuals reared with shelters had lower values of the tested antioxidant parameters (catalase, glutathione peroxidase, glutathione S-transferase and glutathione), indicating a lower production of reactive species than individuals reared without shelter. The same pattern was observed in both T. macedonicus and its hybrid. Contrary to the activation of some physiological pathways, shelter availability did not significantly affect the rate of intraspecific aggressive behavior. The physiological benefits of shelter use can be manifested as a lower requirement for investment in the energy necessary for the maintenance of the upregulated antioxidant defenses, activation of repair systems and synthesis of endogenous antioxidants. This study highlights the importance of shelter provision, which may be valuable in habitat restoration and animal conservation studies.

Phenotypic Switching Resulting From Developmental Plasticity: Fixed or Reversible?

The prevalent view of developmental phenotypic switching holds that phenotype modifications occurring during critical windows of development are “irreversible” – that is, once produced by environmental perturbation, the consequent juvenile and/or adult phenotypes are indelibly modified. Certainly, many such changes appear to be non-reversible later in life. Yet, whether animals with switched phenotypes during early development are unable to return to a normal range of adult phenotypes, or whether they do not experience the specific environmental conditions necessary for them to switch back to the normal range of adult phenotypes, remains an open question. Moreover, developmental critical windows are typically brief, early periods punctuating a much longer period of overall development. This leaves open additional developmental time for reversal (correction) of a switched phenotype resulting from an adverse environment early in development. Such reversal could occur from right after the critical window “closes,” all the way into adulthood. In fact, examples abound of the capacity to return to normal adult phenotypes following phenotypic changes enabled by earlier developmental plasticity. Such examples include cold tolerance in the fruit fly, developmental switching of mouth formation in a nematode, organization of the spinal cord of larval zebrafish, camouflage pigmentation formation in larval newts, respiratory chemosensitivity in frogs, temperature-metabolism relations in turtles, development of vascular smooth muscle and kidney tissue in mammals, hatching/birth weight in numerous vertebrates,. More extreme cases of actual reversal (not just correction) occur in invertebrates (e.g., hydrozoans, barnacles) that actually ‘backtrack’ along normal developmental trajectories from adults back to earlier developmental stages. While developmental phenotypic switching is often viewed as a permanent deviation from the normal range of developmental plans, the concept of developmental phenotypic switching should be expanded to include sufficient plasticity allowing subsequent correction resulting in the normal adult phenotype.

Larval newts adjust foraging rate to perceived predator and competitor proximity

Foraging is key for most animals, because their energy and matter income depend on food ingestion. However, animals may respond adaptively to perceived competitor and/or predator proximity by modifying their foraging rates. Increased foraging activity is expected to improve the chances of succeeding in competition. However, the benefits of increased foraging activity could be offset by the risks of increased conspicuousness to predators. Plus, starvation may have counteracting or additive effects on foraging behaviour. Here, we test these hypotheses in larval Iberian ribbed newts (Pleurodeles waltl). We estimated foraging rates of individuals haphazardly assigned to either a restricted or an unrestricted-feeding regime, in water with (1) self-odour as control, (2) predator Dytiscus sp. chemical cues, and (3) competitor conspecific larva chemical cues. Treatments were presented in a random sequence. Newt larvae responded to either predator or conspecific chemical cues by increasing foraging rates relative to the control. Conspecific chemical cues increased foraging rates over the other two treatments. Feeding regime did not modify larva response to perceived predator and competitor proximity. Increased foraging rates in the presence of conspecific chemical cues could simultaneously improve larval energetic status to face competition and reduce prey available for the competitor. Intermediate foraging rates in the presence of predator chemical cues suggest a trade-off between the benefits (likely improved energetic status or accelerated metamorphosis) and the costs (likely increased conspicuousness) of increased food ingestion. These results prove that larval newts adjust foraging rates to perceived predator and competitor proximity.

Palatability and Defense of Eastern Newt (Notophthalmus viridescens) Larvae and Metamorphic Juveniles against Predatory Dragonfly Nymphs

We examined the predator–prey relationship between nymphs of the predatory dragonfly Anax junius (Common Green Darner) and larval and metamorphic Notophthalmus viridescens (Eastern Newt), some of which may contain the potent neurotoxin, tetrodotoxin. First, we conducted a palatability study to determine which life-history stages were palatable to dragonflies. We also tested the metamorphosis and survival rates of larval newts when exposed to predatory dragonflies in small microcosms. Finally, we tested the predator avoidance behavior of larval newts in response to chemical cues from a control, food stimulus, and predatory dragonflies. All life-history stages (small and large larvae, and recent metamorphs) were palatable to dragonflies. In microcosm trials, we found that newt larvae had a lower chance of surviving and transforming when dragonflies were present compared to a control. Finally, newt larvae decreased movement significantly when exposed to predatory dragonfly stimulus compared to either a control or food stimulus. These results suggest dragonflies are effective predators of newts from hatching through metamorphosis. However, the larvae do possess behavioral avoidance mechanisms that likely reduce the risk of predation by dragonflies.

Mosquito control based on Bacillus thuringiensis israelensis (Bti) interrupts artificial wetland food chains

The biocide Bacillus thuringiensis israelensis (Bti) has become the most commonly used larvicide to control mosquitoes in seasonal wetlands. Although Bti is considered non-toxic to most aquatic organisms, the non-biting chironomids show high susceptibilities towards Bti. As chironomids are a key element in wetland food webs, major declines in their abundance could lead to indirect effects that may be passed through aquatic and terrestrial food chains. We conducted two mesocosm experiments to address this hypothesis by assessing direct and indirect effects of Bti-modified availability of macroinvertebrate and zooplankton food resources on the predatory larvae of palmate and smooth newts (Urodelans: Lissotriton helveticus, Lissotriton vulgaris). We examined newt survival rates and dietary composition by means of stable isotope (δ15N and δ13C) analysis in the presence of Bti treatment and a predator (Odonata: Aeshna cyanea). We assessed palmate newts' body size at and time to metamorphosis while developing in Bti treated mesocosms. Chironomid larvae were the most severely affected aquatic invertebrates in all Bti treated food chains and experienced abundance reductions by 50 to 87%. Moreover, stable isotope analysis revealed that chironomids were preferred over other invertebrates and comprised the major part in newts' diet (56%) regardless of their availability. The dragonfly A. cyanea decreased survival of newt larvae by 27% in Bti treated mesocosms showing affected chironomid abundances. Increasing intraguild predation is most likely favored by the Bti-induced reduction of alternative prey such as chironomid larvae. The decreased food availability after Bti treatment led to slightly smaller L. helveticus metamorphs while their developmental time was not affected. Our findings highlight the crucial role of chironomids in the food webs of freshwater ecosystems. We are also emphasizing the importance of reconsidering human-induced indirect effects of mosquito control on valuable wetland ecosystems particularly in the context of worldwide amphibian and insect declines.

Does predation risk outweigh the costs of lost feeding opportunities or does it generate a behavioural trade-off? A case study with Iberian ribbed newt larvae

PA was supported by a ‘Ramon y Cajal’ contract (RYC-2011–07670, MINECO). This study was partly funded by the project CGL2014-56416-P (MINECO).

Influence of interspecific competitors on behavioral thermoregulation: developmental or acute plasticity?

Many ectotherms reduce their exposure to changing thermal conditions using behavioral thermoregulation. The effectiveness of behavioral thermoregulation in maintaining ectotherm body temperatures within the target range is influenced not only by environmental (operative) temperatures but also by the presence of other con- and heterospecific individuals. How species’ interactions affect behavioral thermoregulation is largely unknown. Theory predicts that species’ interactions could affect the plasticity of behavioral thermoregulation in two ways, i.e., by developmental plasticity of a preferred temperature range or by an acute shift in body temperatures. Empirical tests of these predictions are scarce. We examined the developmental and acute effects of heterospecific social interactions on the accuracy and effectiveness of thermoregulation in the larvae of two competing species, Ichthyosaura alpestris and Lissotriton vulgaris. The presence of heterospecifics during larval development had no effect on preferred body temperatures but it modified later acute thermoregulatory responses to heterospecifics. Ichthyosaura alpestris larvae from heterospecific tanks increased their thermoregulatory accuracy and effectiveness, while L. vulgaris larvae from conspecific tanks relaxed their thermoregulatory efforts. The thermal dependence of somatic growth suggests that modified behavioral thermoregulation has the potential to accelerate growth in competitively dominant I. alpestris. Acute thermoregulatory responses are affected by heterospecific social interactions in newt larvae, but not conspecific. A developmental plastic response modified body temperatures not the target thermoregulatory range, which shows that the influence of heterospecific social interactions is more complex than predicted by theory. Species interactions complicate estimating an ectotherm’s vulnerability to ongoing climate change. Many ectothermic animals control their body temperature through behavioral thermoregulation. Their thermoregulatory decisions are influenced not only by environmental temperatures, but also by the presence of other species. We show that the current thermoregulatory effort in interacting newt larvae is affected by previous experience with competing species. The influence of heterospecific social interactions is more complex than predicted by theory, which complicates estimating an ectotherm’s vulnerability to ongoing climate change.

No trade-offs in interspecific interference ability and predation susceptibility in newt larvae.

Coexistence of species with similar requirements is allowed, among others, through trade‐offs between competitive ability and other ecological traits. Although interspecific competition is based on two mechanisms, exploitation of resources and physical interference, trade‐off studies largely consider only species’ ability to exploit resources. Using a mesocosm experiment, we examined the trade‐off between interference competition ability and susceptibility to predation in larvae of two newt species, Ichthyosaura alpestris and Lissotriton vulgaris. In the presence of heterospecifics, L. vulgaris larvae slowed somatic growth and developmental rates, and experienced a higher frequency of injuries than in conspecific environments which suggests asymmetrical interspecific interference. During short‐term predation trials, L. vulgaris larvae suffered higher mortality than I. alpestris. Larvae of the smaller species, L. vulgaris, had both lower interference and antipredator performance than the larger I. alpestris, which suggests a lack of trade‐off between interference competition ability and predator susceptibility. We conclude that interference competition may produce a positive rather than negative relationship with predation susceptibility, which may contribute to the elimination of subordinate species from common habitats.

Vital fluorescent staining for non–destructive studies of neuromast topography in urodele amphibians

Neuromasts are mechanosensory organs found in primarily aquatic vertebrates, including many species of amphibians, and are arranged as specific patterns to form the lateral-line system on the head and along the body. We used a hair-cell-specific fluorescent dye, DiASP, to analyze the distributional pattern of neuromasts in the lateral line system of live captive-born larvae of the Italian crested newt, Triturus carnifex (Laurenti, 1768). We confirmed that DiASP presents a safe and accurate alternative method for non-destructive studies of neuromast ontogeny and distribution in live amphibians. All newt larvae subjected to analyses survived and no teratogenic effects of DiASP on their further development were observed. We were able to use these data to completely characterize the distribution of neuromasts in this species and to infer the functional significance of this distribution. Cross-species comparison of general topography points to neuromast arrangement as a conserved trait in urodelans.

Are direct density cues, not resource competition, driving life history trajectories in a polyphenic salamander?

Polyphenisms, where multiple, discrete, environmentally-cued phenotypes can arise from a single genotype, are extreme forms of phenotypic plasticity. Cue acquisition and interpretation are vital for matching phenotypes to varying environments, but can be difficult if cues are unreliable indicators or if multiple cues are present simultaneously. Facultative paedomorphosis, where juvenile traits are retained at sexual maturity, is a density-dependent polyphenism exhibited by many salamanders. Favorable conditions such as low larval densities and stable hydroperiod delay metamorphosis and promote a paedomorphic strategy. We investigated proximate cues affecting facultative paedomorphosis in order to understand how larval newts (Notophthalmus viridescens louisianensis) assess conspecific density. To isolate the effects of density cues from the effects of resources and agonistic behavior, we caged larval newts in mesocosms in a 2 × 2 factorial design that manipulated both background larval newt densities (high or low) and food levels (ambient or supplemented). We found strong effects of both food and density on caged individuals. Under high densities, caged larvae were more likely to become efts, a long-lasting juvenile terrestrial stage, across both food levels, while paedomorphs were more common under low densities. Though food levels increased growth rates, density had strong independent effects on metamorphic timing and phenotype. Competition for food and space are classical density-dependent processes, but density cues themselves may be a mediator of density-dependent effects on polyphenisms and life history responses.

Consistency of Coloration Pattern and Applicability of Photo Identification Method as a Tool to Identify Individuals of the Kaiser’s Mountain Newt, <i>Neurergus kaiseri</i>

In this study, we investigated the use of the dorsal coloration pattern of larval, post-metamorphic and adult Neurergus kaiseri in order to develop a non-invasive photo-identification method to identify individuals of this species. Development of color pattern of larval and post-metamorphic newts until to reach to a pattern constancy was studied by consecutive photography during one year. In all transparent larval newts, we observed that random distributed pigment cells gradually accumulate along dorsal line and midbody lateral line during the first half of the larval period, and following localization in early post metamorphosis remains unchanged thereafter. Also, in a separate experiment we evaluated accuracy (% matching) and efficiency (time required for each matching) of visual judgments (true recognition or matching and false recognition or miss-matching) by naive observers when they recognized 150 individual’s adult newts based on their pattern coloration in colored photographs. In all visual judgments of photographic identification trials based on true and false recognitions in naive observer using different dorsal parts the success rate averaged 99.9 ± 0.3. The mean success rate in false recognition was 99.9% ranging from 99.7 to 100%. Assessment of accuracy of photo-identification method by true recognition yielded 100% success rate.

Noxious newts and their natural enemies: Experimental effects of tetrodotoxin exposure on trematode parasites and aquatic macroinvertebrates

The dermal glands of many amphibian species secrete toxins or other noxious substances as a defense strategy against natural enemies. Newts in particular possess the potent neurotoxin tetrodotoxin (TTX), for which the highest concentrations are found in species within the genus Taricha. Adult Taricha are hypothesized to use TTX as a chemical defense against vertebrate predators such as garter snakes (Thamnophis spp.). However, less is known about how TTX functions to defend aquatic-developing newt larvae against natural enemies, including trematode parasites and aquatic macroinvertebrates. Here we experimentally investigated the effects of exogenous TTX exposure on survivorship of the infectious stages (cercariae) of five species of trematode parasites that infect larval amphibians. Specifically, we used dose-response curves to test the sensitivity of trematode cercariae to progressively increasing concentrations of TTX (0.0 [control], 0.63, 3.13, 6.26, 31.32, and 62.64 nmol L−1) and how this differed among parasite species. We further compared these results to the effects of TTX exposure (0 and 1000 nmolL−1) over 24 h on seven macroinvertebrate taxa commonly found in aquatic habitats with newt larvae. TTX significantly reduced the survivorship of trematode cercariae for all species, but the magnitude of such effects varied among species. Ribeiroia ondatrae – which causes mortality and limb malformations in amphibians – was the least sensitive to TTX, whereas the kidney-encysting Echinostoma trivolvis was the most sensitive. Among the macroinvertebrate taxa, only mayflies (Ephemeroptera) showed a significant increase in mortality following exogenous TTX exposure, despite the use of a concentration 16x higher than the maximum used for trematodes. Our results suggest that maternal investment of TTX into larval newts may provide protection against certain trematode infections and highlight the importance of future work assessing the effects of newt toxicity on both parasite infection success and the palatability of larval newts to invertebrate predators.