Salamander Larvae Research Articles

Enhanced recruitment of larger predators in the presence of large prey.

Most carnivores undergo diet shift from smaller to larger prey items during ontogeny. The trophic relationship between a growing carnivore and larger prey is representative of a size-structured predator-prey interaction. The strength of this interaction is, in part, determined by the recruitment of individuals from smaller predatory size classes into larger predatory size classes. Therefore, it is interesting to investigate how larger prey alter the recruitment of smaller predator size classes into larger predator size classes, since this can affect their own future predation risk. Past empirical studies have exclusively documented that large prey reduce predator recruitment by decreasing growth and/or survival of the smaller predators. In this study, we provide empirical evidence of the contrasting pattern: large prey enhance the recruitment of smaller predators into larger predators even though they increase cannibalism mortality of the smaller predators. We have done this here by studying the trophic interaction between predatory salamander larvae Hynobius retardatus and the frog tadpoles Rana pirica that represent their large prey. In a field experiment in which salamander hatchlings were exposed to the presence or absence of large frog tadpoles, we found that more giant salamanders emerged in the presence of frog tadpoles than in their absence. Reassignment of frog tadpoles (to both treatments) in the subsequent experimental period showed that the enhanced emergence of giant salamanders in the presence of frog tadpoles leads to the intensification of salamander predation on the frog tadpoles. In an additional laboratory experiment, to better understand the underlying mechanisms, we manipulated both the presence of frog tadpoles and the occurrence of cannibalism between salamander hatchlings. This experiment revealed that frog tadpoles intensify the cannibalism of salamander larvae during their hatchling stage, thus allowing more salamander larvae to become large-sized predators. Our results suggest that frog tadpoles can inadvertently intensify their own future predation risk by intensifying cannibalistic interactions among predatory salamander hatchlings, thereby enhancing the degree of predator recruitment to a larger size class. Hence, large prey can enhance the recruitment of individuals from small predator size classes into larger predator size classes.

Prospective interspecies interaction between Siberian and Ezo salamander larvae

AbstractSpecies habitat range is partly determined by interspecies interactions between phylogenetically related species. Siberian salamanders are widely distributed across the Eurasian continent and occupy various habitats, but in Hokkaido island, Japan, it is restricted to only two regions. For the restricted habitat range of Siberian salamanders in Hokkaido, we hypothesized that Ezo salamander, whose larvae heavily consume amphibian larvae, excludes Siberian salamander from their range by the predation during the larval period. Here, we investigated the potential interaction between Siberian and Ezo salamander larvae in an aquarium experiment. As expected, in the cases where they cohabit, all Siberian salamander larvae were immediately killed by Ezo salamander larvae through predation. Although the predation enhanced individual growth of Ezo salamander larvae, it may not merely increase the fitness of Ezo salamander larvae. Interestingly, in the presence of Siberian salamanders, cannibalism occurred more frequently in Ezo salamanders, even though it only occurred in limited replications, probably as a result of improving growth and increasing size variation among Ezo salamander larvae.

Developmental costs of yellow colouration in fire salamanders and experiments to test the efficiency of yellow as a warning colouration

Abstract Warning colouration reduces predation risk by signalling or mimicking the unpleasantness of prey and therefore increases survival. We tested in two experiments the evolutionary costs and benefits of the yellow colour pattern in fire salamanders (Salamandra salamandra), which display a yellow/black colour pattern usually associated with toxic alkaloids. Our first experiment aimed to test whether the development of colouration is condition dependent and thus related to developmental costs, i.e. influenced by resource availability during the developmental process. Therefore, we reared fire salamander larvae under different nutritional conditions and compared the relative amount of yellow they developed after metamorphosis. Fire salamander larvae reared under limited food conditions had a lower proportion of yellow following metamorphosis than control larvae reared under superior food conditions. In a second experiment we tested whether the proportion of yellow has an impact on the risk of being attacked using artificial models. We tested, in salamander-free and salamander-occupied natural habitats, whether artificial clay models with different proportions of yellow and black receive different attack rates from potential predators (birds, mammals, insects). In clay models the proportion of yellow and the site had a significant effect on predation risk. Models with larger amounts of yellow had fewer bite marks from predators such as carabid beetles and birds, but only in sympatry with salamanders. In conclusion, the early expression of conspicuous colouration seems to be condition dependent and therefore potentially costly. Furthermore, the yellow colouration of fire salamanders act as a signal that potentially reduces their risk of being attacked by predators. Thus, the yellow colouration of fire salamanders seems to represent an adaptive trait that reduces the risk of predation, which can be expressed in higher quantity by individuals of a certain condition.

Circumventing surface tension: tadpoles suck bubbles to breathe air.

The surface tension of water provides a thin, elastic membrane upon which many tiny animals are adapted to live and move. We show that it may be equally important to the minute animals living beneath it by examining air-breathing mechanics in five species (three families) of anuran (frog) tadpoles. Air-breathing is essential for survival and development in most tadpoles, yet we found that all tadpoles at small body sizes were unable to break through the water's surface to access air. Nevertheless, by 3 days post-hatch and only 3 mm body length, all began to breathe air and fill the lungs. High-speed macrovideography revealed that surface tension was circumvented by a novel behaviour we call 'bubble-sucking': mouth attachment to the water's undersurface, the surface drawn into the mouth by suction, a bubble 'pinched off' within the mouth, then compressed and forced into the lungs. Growing tadpoles transitioned to air-breathing via typical surface breaching. Salamander larvae and pulmonate snails were also discovered to 'bubble-suck', and two insects used other means of circumvention, suggesting that surface tension may have a broader impact on animal phenotypes than hitherto appreciated.

A first record of the antioxidant defense and selected trace elements in Salamandra salamandra larvae on Mt. Avala and Mt. Vrsacki Breg (Serbia)

We investigated the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR) and the phase II biotransformation enzyme glutathione S-transferase (GST) in the whole body of fire salamander larvae (Salamandra salamandra) from two localities on Mt. Avala (AVS and ABP) and one locality on Mt. Vrsacki Breg (VSB), Serbia. We also determined the total glutathione (GSH) and sulfhydryl group (SH) contents, as well as the concentrations of manganese (Mn), copper (Cu), zinc (Zn), selenium (Se), arsenic (As), cadmium (Cd), lead (Pb) and uranium (U). The obtained results show that animals from VSB had significantly lower weights and lengths than animals from AVS and ABP. The activities of all investigated enzymes were significantly higher, while the SH content was significantly lower in animals from VSB compared to those from AVS and ABP. No correlations between trace-element concentrations in water and animal tissue were observed. We concluded that the obtained results were more likely a consequence of the combination of developmental differences and the effects of different habitat conditions, environmental and anthropogenic influences than of concentrations of trace elements in the water alone.

Water-borne and plasma corticosterone are not correlated in spotted salamanders.

Water‐borne hormone measurement is a noninvasive method suitable for amphibians of all sizes that are otherwise difficult to sample. For this method, containment‐water is assayed for hormones released by the animal. Originally developed in fish, the method has expanded to amphibians, but requires additional species‐specific validations. We wanted to determine physiological relevance of water‐borne corticosterone in spotted salamanders (Ambystoma maculatum) by comparing concentrations to those taken using established corticosterone sampling methods, such as plasma. Using a mixture of field and laboratory studies, we compared water‐borne corticosterone levels to other traditional methods of sampling corticosterone for spotted salamander larvae, metamorphs, and adults. Despite multiple attempts, and detecting differences between age groups, we found no correlations between water‐borne and plasma corticosterone levels in any age group. Water‐borne sampling measures a rate of release; whereas plasma is the concentration circulating in the blood. The unique units of measurement may inherently prevent correlations between the two. These two methods may also require different interpretations of the data and the physiological meaning. We also note caveats with the method, including how to account for differences in body size and life history stages. Collectively, our results illustrate the importance of careful validation of water‐borne hormone levels in each species in order to understand its physiological significance.

The Role of Plasticity and Adaptation in the Incipient Speciation of a Fire Salamander Population.

Phenotypic plasticity and local adaptation via genetic change are two major mechanisms of response to dynamic environmental conditions. These mechanisms are not mutually exclusive, since genetic change can establish similar phenotypes to plasticity. This connection between both mechanisms raises the question of how much of the variation observed between species or populations is plastic and how much of it is genetic. In this study, we used a structured population of fire salamanders (Salamandra salamandra), in which two subpopulations differ in terms of physiology, genetics, mate-, and habitat preferences. Our goal was to identify candidate genes for differential habitat adaptation in this system, and to explore the degree of plasticity compared to local adaptation. We therefore performed a reciprocal transfer experiment of stream- and pond-originated salamander larvae and analyzed changes in morphology and transcriptomic profile (using species-specific microarrays). We observed that stream- and pond-originated individuals diverge in morphology and gene expression. For instance, pond-originated larvae have larger gills, likely to cope with oxygen-poor ponds. When transferred to streams, pond-originated larvae showed a high degree of plasticity, resembling the morphology and gene expression of stream-originated larvae (reversion); however the same was not found for stream-originated larvae when transferred to ponds, where the expression of genes related to reduction-oxidation processes was increased, possibly to cope with environmental stress. The lack of symmetrical responses between transplanted animals highlights the fact that the adaptations are not fully plastic and that some level of local adaptation has already occurred in this population. This study illuminates the process by which phenotypic plasticity allows local adaptation to new environments and its potential role in the pathway of incipient speciation.

Larval Prey Preference of Pond-breeding salamander Hynobius tokyoensis Living in a Stream

Habitats for pond-breeding salamanders are declining as a result of land development and management abandonment. In that context, a pond-breeding salamander Hynobius tokyoensis has recently been known to breed in small streams. However, little is known about the ecology of pond-breeding salamander larvae, such as food, in small streams. Here, to gain insight into foraging ecology of Hynobius tokyoensis larvae in small steams, we investigated the potential prey items in nine small streams running through secondary forests in Hachiouji City, Tokyo, Japan. In addition, we hypothesized that H. tokyoensis larvae preferentially predate active prey invertebrates over less-active prey because they are generalist, sit-and-wait predators. To test this hypothesis, we experimentally examined predation frequencies by H. tokyoensis larvae on the two major arthropod species (isopods and Plecoptera larvae) and activity (i.e., movement frequencies and distances) of the potential prey. As a result, isopods (Asellus hilgendorfii) and Plecoptera (Nemouridae larvae) are the two dominant aquatic invertebrates in small streams inhabited by H. tokyoensis, larval salamanders consumed more isopods than Plecoptera larvae and isopods are more active than Plecoptera larvae. Taken together, we concluded that isopods should be the main prey for salamander larvae inhabiting small streams due to their high abundance and conspicuous activities.

Safe as a cave? Intraspecific aggressiveness rises in predator-devoid and resource-depleted environments

Intraspecific aggressiveness can be affected by multiple environmental pressures. In several cases, aggressiveness can grade into full-scale cannibalism, particularly when resources are scarce. However, limited information exists on how intraspecific aggressiveness varies among populations experiencing different environmental pressures, and on the role intraspecific predation plays for the exploitation of harsh habitats. The fire salamander, Salamandra salamandra, is an excellent model species to study factors affecting intraspecific aggressiveness, because of its ability to breed in habitats with contrasting food resources and predation pressure. Here, we evaluated the influence of predation risk and habitat of origin on aggressive interactions. To this extent, we reared larvae from cave (scarce resources; nearly-absent predators) and surface (abundant resources and predators) populations under different risk conditions and measured aggressive behavior towards conspecifics. During behavioral trials, larvae were exposed to different combinations of predator and wounded conspecific chemical cues. Intraspecific aggressiveness increased in large and late-development larvae. Larvae from all the populations significantly reduced aggressiveness under both typologies of risk experienced during rearing (constant presence of predator; pulses of high predation risk), and also when stimulated by predator cues. However, larvae from cave populations exhibited a more pronounced aggressiveness, especially when exposed to wounded conspecific cues. Intraspecific aggressiveness can be modulated by the complex interaction between multiple variables, and both behavioral plasticity and local adaptations can determine its variation across populations. Our findings reveal that aggressive interactions are favored in cave environment, suggesting intraspecific predation can play a key role in the exploitation of resource-depleted habitats. In this study, we investigated how intraspecific aggressiveness of salamander larvae is shaped under predation risk in populations originating from contrasting environments, such as cave and surface habitats. Larvae experiencing predator presence during their development or exposed to predator cues significantly reduced their aggressive interactions, both in cave and surface populations. Interestingly, cave-originating individuals reacted to wounded conspecific cues by increasing the frequency of their aggressive displays, suggesting cannibalistic behavior is locally enhanced in populations from resource-depleted habitats. The present study offers new insights on the importance of intraspecific aggressiveness for the adaptation to harsh environments.

Do scavengers prevent or promote disease transmission? The effect of invertebrate scavenging on Ranavirus transmission

Abstract Host–parasite interactions are shaped by the broader web of community interactions, from interspecific competition to predator–prey dynamics. Heterospecific scavengers might also affect parasite transmission from infectious carcasses, which can be an important source of infections for some wildlife diseases. A robust scavenger community can quickly remove carcasses and tissue and thus prevent secondary transmission by necrophagy or contact with infectious carcasses. Alternatively, by spreading infectious particles and tissues throughout the environment, scavengers may increase rates of casual contact with pathogens and thus overall transmission. However, there has been little empirical consideration of the contrasting roles that scavengers might play in infectious disease dynamics. We carried out a series of studies to determine the efficiency with which scavenging invertebrates remove carcasses of Long‐toed Salamander (Ambystoma macrodactylum) larvae and their role in the transmission of frog virus 3 (Genus: Ranavirus, Family: Iridoviridae) from carcasses. We then estimated the functional response of one efficient invertebrate scavenger (Family: Dytiscidae) to increasing carcass densities in field conditions in order to determine the capacity of scavenging invertebrates to consume large amounts of carcass tissue, as may be present at high prevalence sites. We found that removal of infectious carcasses by scavengers strongly reduced transmission to naïve larvae. Scavengers were as effective at reducing transmission from a carcass as a physical barrier preventing contact with the carcass. There was little evidence that scavenging released sufficient infectious tissues into the water column to rival direct contact as a route of infection. Moreover, while scavenging rates saturated at increasing carcass densities, consistent with a type II functional response, there were sufficient densities of dytiscid larvae, not to mention other scavenging invertebrates, in a surveyed pond to theoretically prevent transmission from carcasses. Our results suggest that at least in systems in which conspecific necrophagy is common, the scavenger community can play an important role in reducing transmission. A plain language summary is available for this article.

Habitat Characteristics in Created Vernal Pools Impact Spotted Salamander Water-Borne Corticosterone Levels

Spotted salamanders (Ambystoma maculatum) require vernal pools for breeding habitat. Limited protection and preservation of vernal pools makes suitable habitat creation important. Differences in corticosterone levels, a hormone associated with growth, development, and stress in amphibians, could indicate population health and habitat quality. Our objective was to determine if habitat characteristics in created vernal pools influence corticosterone levels of spotted salamander larvae. In May and June of 2015 and 2016, we sampled water-borne corticosterone levels of larval spotted salamanders in 34 created vernal pools constructed 1–5 years earlier. Using multiple regression, we determined the best model predicting corticosterone levels included larval total length, pool-water temperature, year sampled, and pool diameter. Pool-water pH, depth, and age; percent cover; and predator presence were not significant predictors. Annual variation in corticosterone levels and habitat characteristics, and positive associations with water temperature and salamander body size highlighted the importance of controlling for external influences. The negative association between pool diameter and corticosterone indicated that larvae in larger pools (up to 12.75-m maximum diameter) were less stressed and potentially healthier. These results indicate that pool diameter contributes to habitat quality and may be important when constructing vernal pools for spotted salamanders.

Warming-induced shifts in amphibian phenology and behavior lead to altered predator-prey dynamics.

Climate change-induced phenological variation in amphibians can disrupt time-sensitive processes such as breeding, hatching, and metamorphosis, and can consequently alter size-dependent interactions such as predation. Temperature can further alter size-dependent, predator-prey relationships through changes in species' behavior. We thus hypothesized that phenological shifts due to climate warming would alter the predator-prey dynamic in a larval amphibian community through changes in body size and behavior of both the predator and prey. We utilized an amphibian predator-prey system common to the montane wetlands of the U.S. Pacific Northwest: the long-toed salamander (Ambystoma macrodactylum) and its anuran prey, the Pacific chorus frog (Pseudacris regilla). We conducted predation trials to test if changes in predator phenology and environmental temperature influence predation success. We simulated predator phenological shifts using different size classes of the long-toed salamander representing an earlier onset of breeding while using spring temperatures corresponding to early and mid-season larval rearing conditions. Our results indicated that the predator-prey dynamic was highly dependent upon predator phenology and temperature, and both acted synergistically. Increased size asymmetry resulted in higher tadpole predation rates and tadpole tail damage. Both predators and prey altered activity and locomotor performance in warmer treatments. Consequently, behavioral modifications resulted in decreased survival rates of tadpoles in the presence of large salamander larvae. If predators shift to breed disproportionately earlier than prey due to climate warming, this has the potential to negatively impact tadpole populations in high-elevation amphibian assemblages through changes in predation rates mediated by behavior.

Calour: an Interactive, Microbe-Centric Analysis Tool.

Microbiome analyses can be challenging because microbial strains are numerous, and often, confounding factors in the data set are also numerous. Many tools reduce, summarize, and visualize these high-dimensional data to provide insight at the community level. However, they lose the detailed information about each taxon and can be misleading (for example, the well-known horseshoe effect in ordination plots). Thus, multiple methods at different levels of resolution are required to capture the full range of microbial patterns. Here we present Calour, a user-friendly data exploration tool for microbiome analyses. Calour provides a study-centric data model to store and manipulate sample-by-feature tables (with features typically being operational taxonomic units) and their associated metadata. It generates an interactive heatmap, allowing visualization of microbial patterns and exploration using microbial knowledge databases. We demonstrate the use of Calour by exploring publicly available data sets, including the gut and skin microbiota of habitat-switched fire salamander larvae, gut microbiota of Trichuris muris-infected mice, skin microbiota of different human body sites, gut microbiota of various ant species, and a metabolome study of mice exposed to intermittent hypoxia and hypercapnia. In these cases, Calour reveals novel patterns and potential contaminants of subgroups of microbes that are otherwise hard to find. Calour is open source under the Berkeley Software Distribution (BSD) license and available from https://github.com/biocore/calour. IMPORTANCE Calour allows us to identify interesting microbial patterns and generate novel biological hypotheses by interactively inspecting microbiome studies and incorporating annotation databases and convenient statistical tools. Calour can be used as a first-step tool for microbiome data exploration.

Detection of elusive fire salamander larvae (Salamandra salamandra) in streams via environmental DNA

Abstract In the face of the global biodiversity crisis, the monitoring of species richness and diversity is experiencing an increased demand entailing a raise in cost and time investment. The analysis of species-specific DNA fragments in environmental samples (eDNA) such as from water or soil, facilitate the molecular detection of species without the specific sampling of individuals. The invasive chytrid fungus Batrachochytrium salamandrivorans (Bsal) is infecting natural fire salamander populations (Salamandra salamandra) and causes chytridiomycosis resulting in infrequent regional extinctions of populations across Central Europe. With regard to the expanding distribution of Bsal over the last years, cost-effective monitoring of fire salamanders is important for the conservation of this species. Based on a real-time quantitative PCR (qPCR) assay, we developed a new protocol to detect S. salamandra larvae in streams via eDNA, using species-specific primers of the mitochondrial control region (D-loop). We tested the efficiency of qPCR primer sets for six combinations of DNA extraction kits coupled with subsequent PCR inhibitor removal kits for obtaining qPCR-detectable S. salamandra eDNA from water filters, that were taken both from natural streams and artificial water tanks in the laboratory as positive controls. We found that the DNeasy Blood & Tissue Kit in combination with the DNeasy PowerClean CleanUp Kit performed best for detecting salamander larvae from natural streams. Our experimental protocol paves the way for resource-saving approaches to monitor S. salamandra larvae, but also confirms the limits to this eDNA approach in that it requires optimized laboratory protocols.

Think of what lies below, not only of what is visible above, or: a comprehensive zoological study of invertebrate communities of spring habitats

Springs are interface habitats between the surface and subterranean environments, often neglected by zoological studies and generally regarded only from a surface perspective. Springs are also often collected and managed by humans: catching buildings that collect spring water may provide an accessible window over groundwaters. With this paper, we aim to assess the determinants of invertebrates’ occurrence in springs using a comprehensive approach and considering the role of catching buildings and of predator occurrence. During 2017 and 2018, we performed six repeated surveys in 44 springs of N-Italy. We distinguished between collected and natural springs, assessed the springs morphological features and recorded the occurrence of predator Salamandra salamandra (Linnaeus, 1758) larvae and of four invertebrate taxa corresponding to strictly spring-dwelling, groundwater-dwelling and stream-dwelling groups, such as the gastropod Graziana alpestris (Frauenfeld, 1863), the amphipods Niphargus thuringius Schellenberg, 1934 and Gammarus balcanicus Schäferna, 1922 and dipterans larvae of the family Tipulidae. We used a constrained redundancy analysis to evaluate the relative role of fire salamander occurrence and of springs features on the occurrence of the invertebrate taxa surveyed. Spring typology and fire salamander larvae were the major determinants of spring invertebrates’ occurrence. G. alpestris was positively related to artificial catching structures. Fire salamander was related to the occurrence of N. thuringius, G. balcanicus and Tipulidae larvae. Our results provide evidence that catching spring structures can significantly favour the detection of strictly spring-dwelling species; moreover, we reveal that the breeding of semi-aquatic predators like salamanders may play important roles on the community of invertebrates occurring in the spring habitats.

Damage to <i>Salamandra infraimmaculata</i> Populations by Human Activity in Creating Water Pits Is a Death Trap in Semi-Arid Habitats

The different breeding sites of Salamandra infraimmaculata on the southern border of its distribution were examined and mapped in order to estimate the damage caused by water holes that could represent death traps for salamanders in xeric habitats. Among the various types of breeding sites (springs, streams, water holes, winter pools and reservoirs), the larvae of salamanders were detected in high numbers in springs and streams (503) and water holes (48), and in relatively low numbers in winter pools. Two water holes were examined in detail to estimate the damage caused to S. infraimmaculata where breeding places are limited. During the winter, both males and females enter a water hole for breeding. The percentage of males in and around the water hole was 42% and that of females 29%. After the salamanders’ oviposition in the water, they try to return to terrestrial habitats, but are unable to do so and lose weight and die. The body mass index (BMI) of salamanders decreases from winter (December) after they move to the water hole to spring (April), when they are found in the water hole. The estimation of potential damage is about 300 mature salamanders annually.

Foraging traits of native predators determine their vulnerability to a toxic alien prey

Abstract Vulnerability to toxic alien prey varies among native predator species, depending on their toxin resistance. Although foraging traits relating to the intake of prey are also likely to influence predator vulnerability to toxic alien prey, these traits have received little attention. To address this issue, we studied the toxic impacts of an alien prey species (Bufo japonicus formosus toad hatchlings) on a carnivorous and an omnivorous native amphibian species (Hynobius retardatus salamander larvae and Rana pirica frog tadpoles, respectively) that both feed on alien B. japonicus formosus toad hatchlings. First, we designed a mesocosm and an aquarium experiment to evaluate the impact of B. japonicus formosus on the survival of native amphibians under various alien prey densities and predation regimes. Second, we performed several additional laboratory experiments to clarify specific processes of native amphibian mortality in the presence of the alien B. japonicus formosus toad hatchlings. We found that both native amphibian species were impacted by the alien B. japonicus formosus toad hatchlings. Interestingly, R. pirica frog tadpoles were more affected than H. retardatus salamander larvae, partly due to their lower toxin resistance and their higher toad consumption rate. Most importantly, omnivorous foraging traits (i.e., food sharing and carcass consumption) demonstrated by R. pirica frog tadpoles, but not by the strictly carnivorous H. retardatus salamander larvae, rendered the former particularly vulnerable to the toxic B. japonicus formosus toad hatchlings. This is the first study suggesting that species‐specific foraging traits such as food‐sharing and carcass consumption can determine predator vulnerability to toxic alien prey. This study emphasises the importance of investigating a wider array of predator traits as factors that determine their vulnerability to toxic alien prey. By doing so, we can understand what types of native species are strongly impacted by toxic alien prey and predict the ecological consequences of toxic species invasion.

Larval salamanders are as effective at short-term mosquito predation as mosquitofish

Biological control of mosquitoes can have unintended ecological consequences. One example is the introduction of the genus Gambusia Poey, 1854 into ponds and wetlands. Gambusia spp. are invasive in many parts of the world and have the potential to alter ecosystems by changing trophic interactions and extirpating amphibians. We sought to determine whether larval amphibians are capable of consuming larval mosquitoes as effectively as Gambusia spp. We tested the predation ability of larval Spotted Salamanders (Ambystoma maculatum (Shaw, 1802); n = 13), Southern Leopard Frog (Rana sphenocephala Cope, 1886; n = 12) tadpoles, and western mosquitofish (Gambusia affinis (Baird and Girard, 1853); n = 13) across a range of body sizes in laboratory experiments. Our results showed that over a 24 h period, salamander larvae (mean ± SE; 238 ± 14) and mosquitofish (195 ± 17) consumed a statistically equivalent number of mosquito larvae, whereas tadpoles consumed a large number (113 ± 14) but significantly less. All species had significant (or marginally significant) positive relationships between body size and rate of mosquito consumption. Further studies into the ability of native larval amphibians to consume mosquito larvae are needed to assess whether amphibians can be successful at mosquito control instead of introducing nonnative species to new areas.

High mortality in aquatic predators of mosquito larvae caused by exposure to insect repellent.

In the face of mosquito-borne disease outbreaks, effective mosquito control is a primary goal for public health. Insect repellents, containing active compounds such as DEET and picaridin, are a first defence against biting insects. Owing to widespread use and incomplete sewage treatment, these compounds are frequently detected in surface waters, but their effects on aquatic taxa such as mosquito larvae or their naturally occurring aquatic predators are poorly understood. We investigated the effects of environmentally realistic concentrations of commercial products containing DEET and picaridin on survivorship of mosquito larvae, and their potential indirect effects on survival of larval salamanders, a major predator of mosquito larvae. Larval mosquitos were not affected by exposure to repellents containing DEET or picaridin. We found no larval salamander mortality in control and DEET treatments, but mortality rates in picaridin treatments ranged from 45 to 65% after 25 days of exposure. Salamander larvae exposed to repellents containing picaridin began to display tail deformities and impaired development four days after the experiment began. Our findings suggest the possibility that environmentally realistic concentrations of picaridin-containing repellents in surface waters may increase the abundance of adult mosquitos owing to decreased predation pressure.

The Effect of Salinity on the Survival and Growth of Anderson's Salamander Ambystoma andersoni Larvae

AbstractEggs and larvae of axolotls are susceptible to fungal infections in culture, producing high mortalities that could be prevented by the use of saline media. Newly hatched larvae of Anderson's salamander Ambystoma andersoni were exposed to seven salinities (0, 5, 10, 15, 20, 25, and 30‰) to observe the effect on survival. Newly hatched larvae did not tolerate more than 10‰ salinity during short‐term exposure. Survival and growth of newly hatched larvae were then assessed at 0, 5, and 10‰ over a 6‐week period. Larval survival and growth were greater at 5‰ than in the 0‰ control. Survival, growth, and proximate composition of 60‐d‐old juveniles were compared between 0‰ and 5‰. The 60‐d‐old juveniles performed better in 0‰, and there was no significant difference in proximate analysis between treatments. This work shows that salinity can be used to improve survival and growth in Anderson's salamander larvae, as they can tolerate up to 10‰ immediately after hatching, and 2‐month‐old larvae survive and grow well in salinities of up to 5‰.