Anuran Larvae Research Articles

Predators like it hot: Thermal mismatch in a predator-prey system across an elevational tropical gradient.

Climate change may have dramatic consequences for communities through both direct effects of peak temperatures upon individual species and through interspecific mismatches in thermal sensitivities of interacting organisms which mediate changes in interspecific interactions (i.e. predation). Despite this, there is a paucity of information on the patterns of spatial physiological sensitivity of interacting species (at both landscape and local scales) which could ultimately influence geographical variation in the effects of climate change on community processes. In order to assess where these impacts may occur, we first need to evaluate the spatial heterogeneity in the degree of mismatch in thermal tolerances between interacting organisms. We quantify the magnitude of interspecific mismatch in maximum (CTmax ) and minimum (CTmin ) thermal tolerances among a predator-prey system of dragonfly and anuran larvae in tropical montane (242-3,631m) and habitat (ponds and streams) gradients. To compare thermal mismatches between predator and prey, we coined the parameters maximum and minimum predatory tolerance margins (PTMmax and PTMmin ), or difference in CTmax and CTmin of interacting organisms sampled across elevational and habitat gradients. Our analyses revealed that: (a) predators exhibit higher heat tolerances than prey (~4°C), a trend which remained stable across habitats and elevations. In contrast, we found no differences in minimum thermal tolerances between these groups. (b) Maximum and minimum thermal tolerances of both predators and prey decreased with elevation, but only maximum thermal tolerance varied across habitats, with pond species exhibiting higher heat tolerance than stream species. (c) Pond-dwelling organisms from low elevations (0-1,500m a.s.l.) may be more susceptible to direct effects of warming than their highland counterparts because their maximum thermal tolerances are only slightly higher than their exposed maximum environmental temperatures. The greater relative thermal tolerance of dragonfly naiad predators may further increase the vulnerability of lowland tadpoles to warming due to potentially enhanced indirect effects of higher predation rates by more heat-tolerant dragonfly predators. However, further experimental work is required to establish the individual and population-level consequences of this thermal tolerance mismatch upon biotic interactions such as predator-prey. ​.

INSERT HOST IN THE LIFE CYCLE OF ALARIA ALATA (TREMATODA, STRIGEIDIDA) IN THE NATURAL ENVIRONMENT OF THE CENTRAL BLACK-EARTH ZONE

Currently, an increase in cases of infection of wild and domestic carnivores with the trematode Alaria alata (Trematoda, Strigeidida) is currently recorded in the Central Black-Earth Zone. The trematode A. alata has a complex life cycle involving intermediate, insert and reservoir hosts. We obtained new data on the realization of the life cycle of A. alata in the natural environment of the Central Black-Earth Zone. The moor frog (Rana arvalis), green toad (Bufotes viridis) and spade-footed toad (Pelobates fuscus) are recorded as insert hosts. Infection with mesocercarias A. alata of the moor frog is 20% (the prevalence) and 23 specimens (infection intensity). The moor frog is the most numerous species among amphibians and is characterized by high in-touch capabilities with carnivorous mammals. The moor frog is the main insert host in the circulation of A. alata in natural biocenoses. We have identified the localization of the Alaria mesocercarias in the moor frog, namely, the pericardium and subcutaneous tissue of the intermaxillary space. We determined the distribution of mesocercarias in moor frogs of this year's brood: 71% in the head; 25.8% in the hind legs; 22.6% in the trunk; and 3.2% in the front legs. The green toad and spade-footed toad were also classified as insert hosts of A. alata (prevalence of infection was less than 10%; and infection intensity was 4.0 specimens). Mesocercarias were found in frog larvae (24.6%; 2.6 sp.).

Larval anurans follow predictions of stoichiometric theory: implications for nutrient storage in wetlands

AbstractEcological stoichiometry provides a framework to predict how animals regulate nutritional balances within their tissue and, as a result, how animal biomass affects ecosystem processes through nutrient cycling. However, most interspecific and developmental stoichiometric studies in animals focus on invertebrates, and the few vertebrate studies are largely fish‐centric. Larval anurans are ideal vertebrates to test predictions of developmental and interspecific stoichiometry as they undergo a complex development, exhibit broad arrays of life‐history traits, and can constitute high animal biomass in wetlands, implying major roles in wetland nutrient storage and cycling. We examined (1) patterns of body stoichiometry across larval developmental stages within multiple anuran species, (2) whether key predictors of stoichiometric change, specifically body size, developmental period, and breeding season, influence interspecific stoichiometric variation, and (3) natural magnitudes and fluctuations of larval anuran nutrient storage in geographically isolated wetlands (GIWs). We measured carbon (C), nitrogen (N), and phosphorus (P) tissue content in larval anurans across five developmental stages within 11 species collected from four GIWs to examine patterns of developmental and interspecific stoichiometry. Within species, we found broad developmental stoichiometric patterns in which later developmental stages were lower in %N, but higher in %P than earlier stages. Patterns in %C were inconsistent but were generally lower in later stages, while tissue C:N ratios increased, and C:P and N:P decreased in later developmental stages. Interspecific stoichiometric variation was partially explained by body size and developmental period which positively affected %C and C:N ratios. We observed spatial and temporal fluctuations in species‐specific biomass which dictated nutrient storage patterns within larval anuran assemblages, though stoichiometric identity played a major role. Our estimated magnitudes of larval anuran areal nutrient storage also greatly exceeded that of other wetland fauna with the maximum estimated areal P storage reaching over 200 times that of a similar‐density co‐occurring invertebrate group. These results highlight stoichiometric patterns of development and interspecific variation in a diverse group of amphibians while providing critical baseline information for elucidating the role of anurans in wetland nutrient dynamics.

Novel brain gene-expression patterns are associated with a novel predaceous behaviour in tadpoles.

Novel behaviours can spur evolutionary change and sometimes even precede morphological innovation, but the evolutionary and developmental contexts for their origins can be elusive. One proposed mechanism to generate behavioural innovation is a shift in the developmental timing of gene-expression patterns underlying an ancestral behaviour, or molecular heterochrony. Alternatively, novel suites of gene expression, which could provide new contexts for signalling pathways with conserved behavioural functions, could promote novel behavioural variation. To determine the relative contributions of these alternatives to behavioural innovation, I used a species of spadefoot toad, Spea bombifrons. Based on environmental cues, Spea larvae develop as either of two morphs: 'omnivores' that, like their ancestors, feed on detritus, or 'carnivores' that are predaceous and cannibalistic. Because all anuran larvae undergo a natural transition to obligate carnivory during metamorphosis, it has been proposed that the novel, predaceous behaviour in Spea larvae represents the accelerated activation of gene networks influencing post-metamorphic behaviours. Based on comparisons of brain transcriptional profiles, my results reject widespread heterochrony as a mechanism promoting the expression of predaceous larval behaviour. They instead suggest that the evolution of this trait relied on novel patterns of gene expression that include components of pathways with conserved behavioural functions.

Effects of Desiccation on Metamorphic Climax in Bombina variegata: Changes in Levels and Patterns of Oxidative Stress Parameters.

Simple SummaryGlobal warming alters patterns of precipitation and drought, which are important factors in the survival of amphibian populations. Metamorphosis is affected by environmental changes; this is especially true of metamorphic climax, the crucial stage of amphibian development that is accompanied by significant morphological, physiological and behavioral adaptations necessary for the transition to a terrestrial habitat. This study investigated naturally occurring changes in the cellular oxidative status (antioxidant system and oxidative damage) of yellow-bellied toad larvae during this phase, and how exposure to exogenous factors such as desiccation affected them. Our results revealed clear changes in the antioxidant system’s (AOS) response and the levels of oxidative damage during metamorphic climax, with the highest response and damage observed at the end stage. Decreasing water levels during larval development altered the components of the AOS and increased oxidative damage, resulting in increased oxidative stress. The knowledge gained from this study could contribute to a better understanding of the oxidative stress that larvae experience during this critical stage of development, and the consequences of global warming—such as water loss—on amphibians.In this paper, we examined how the oxidative status (antioxidant system and oxidative damage) of Bombina variegata larvae changed during the metamorphic climax (Gosner stages: 42—beginning, 44—middle and 46—end) and compared the patterns and levels of oxidative stress parameters between individuals developing under constant water availability (control) and those developing under decreasing water availability (desiccation group). Our results revealed that larvae developing under decreasing water availability exhibited increased oxidative damage in the middle and end stages. This was followed by lower levels of glutathione in stages 44 and 46, as well as lower values of catalase, glutathione peroxidase, glutathione S-transferase and sulfhydryl groups in stage 46 (all in relation to control animals). Comparison between stages 42, 44 and 46 within treatments showed that individuals in the last stage demonstrated the highest intensities of lipid oxidative damage in both the control and desiccation groups. As for the parameters of the antioxidant system, control individuals displayed greater variety in response to changes induced by metamorphic climax than individuals exposed to desiccation treatment. The overall decrease in water availability during development led to increased oxidative stress and modifications in the pattern of AOS response to changes induced by metamorphic climax in larvae of B. variegata.

Effects of two pesticides on northern leopard frog (Lithobates pipiens) stress metrics: Blood cell profiles and corticosterone concentrations

Amphibians are declining globally. Exposure to pesticides has been implicated in decreasing amphibian immune function, thus increasing their susceptibility to parasites and disease and thereby negatively affecting individuals and populations. Amphibians are likely exposed to neonicotinoids because these widely used insecticides are highly soluble in water and because amphibian freshwater habitats are often embedded in agroecosystems. Herein, we investigate the effects of long-term exposure to two individual neonicotinoids (clothianidin or thiamethoxam) at either low or high concentrations (2.5 or 250 µg/L) on northern leopard frog (Lithobates pipiens) blood cell profiles and concentrations of corticosterone, an energy-mediating hormone associated with stress. Larval frogs from Gosner stage 25 to 46 were exposed to pesticide and control treatments in outdoor mesocosms. Corticosterone concentrations were measured after 6 d of exposure, and blood cell profiles were assessed once frogs reached Gosner stage 46 (following 8 w of exposure). No significant changes were found in erythrocyte counts, leukocyte counts, monocyte to leukocyte ratios or corticosterone concentrations between treatments. However, exposure to either 2.5 or 250 µg/L of clothianidin, or 250 µg/L of thiamethoxam decreased neutrophil to lymphocyte ratios and neutrophil to leukocyte ratios, and exposure to 2.5 µg/L of clothianidin or 250 µg/L of thiamethoxam decreased eosinophil to leukocyte ratios. Our results indicate that long-term exposure to neonicotinoids can alter leukocyte profiles, indicative of a stress response. Future studies should investigate whether chronic exposure to neonicotinoids affect multiple measures of stress differently or influences the susceptibility of amphibians to parasites and pathogens. Our work underscores the importance of continued use of multiple measures of stress for different amphibian species when undertaking ecotoxicological assessments.

Warmer temperature increases toxicokinetic elimination of PCBs and PBDEs in Northern leopard frog larvae (Lithobates pipiens).

We studied the temperature dependence of accumulation and elimination of two polychlorinated biphenyls (PCBs; PCB-70 and PCB-126) and a commercial mixture of congeners of polybrominated diphenyl ethers (PBDEs; DE-71™)) in Northern leopard frog (Lithobates pipiens) tadpoles. We reared tadpoles at 18, 23, or 27 °C for 5.3 or up to 13.6 weeks (longer at cooler temperature where development is slower) on diets containing the toxicants, each at several different toxicant concentrations, and compared tissue concentrations as a function of food concentration and rearing temperature. Following > 1 month of accumulation, tissue concentrations of all three toxicants in exposed tadpoles were linearly related to dietary concentrations as expected for first order kinetics, with no significant effect of rearing temperature.We also raised free-swimming L. pipiens tadpoles for 14 days on foods containing either toxicant at 18 or 27 °C during an accumulation phase, and then during depuration (declining toxicant) phase of 14 days we provided food without toxicants and measured the decline of toxicants in tadpole tissue. All the congeners were eliminated faster at warmer rearing temperature, as expected. Using Arrhenius' equation, we calculated that the apparent activation energy for elimination of both PCB congeners by tadpoles was 1.21eV (95% confidence interval 0.6-1.8eV). We discuss how this value was within the range of estimates for metabolic reactions generally (range 0.2 - 1.2eV), which might include metabolic pathways for biotransformation and elimination of PCBs. Furthermore, we discuss how the lack of an effect of rearing temperature on tadpole near-steady-state tissue residue levels suggests that faster elimination at the warmer temperature was balanced by faster uptake, which is plausible considering the similar temperature sensitivities (i.e., activation energies) of all these processes. Although interactions between toxicants and temperature can be complex and likely toxicant-dependent, it is plausible that patterns observed in tadpoles might apply to other aquatic organisms. Published data on depuration in 11 fish species eliminating 8 other organic toxicants indicated that they also had similar apparent activation energy for elimination (0.82±0.12eV; 95% confidence interval 0.56 - 1.08eV), even though none of those studied toxicants were PCBs or PBDEs. Additional research on toxicant-temperature interactions can help improve our ability to predict toxicant bioaccumulation in warming climate scenarios.

GENETIC STRUCTURE NOT DETECTED IN NORTHERN IDAHO AND NORTHEAST WASHINGTON WESTERN TOAD (ANAXYRUS BOREAS) POPULATIONS

Western Toads (Anaxyrus boreas) are widely considered to be of conservation concern, and have high genetic variability both continentally and locally. Previous research has identified 3 major genetic clades of Western Toads in North America. We collected tissue samples from 47 larval toads representing 16 different collection sites in northern Idaho and northeastern Washington. For each sample we sequenced a 269 base-pair section of the mitochondrial cytochrome c oxidose I (COI) gene. We also downloaded COI sequences from GenBank, which had been used in a previous study to identify geographic clades. We used PAUP to build phylogenies in which our samples did not align geographically with each other or form distinct clades within the continental phylogeny. Our samples did, however, group in the expected Northwestern clade which was identified in a previous study. The toads examined in our study area show no evidence of cryptic diversity within the section of COI we examined and our data support the current taxonomic assignment to Anaxyrus boreas.

Breeding Effort and Hydroperiod Indicate Habitat Quality of Small, Isolated Wetlands for Amphibians Under Climate Extremes

The distribution and function of small, temporarily ponded wetlands such as vernal pools are driven by climate variation, especially precipitation. These wetland ecosystems provide important habitat for amphibians, whose breeding effort (egg deposition) is often used to characterize pool habitat quality. However, whether breeding effort consistently predicts larval survival, juvenile production, and overall reproductive output—key indicators of habitat quality for amphibians in a varying environment—remains unclear. We assessed the occurrence of spotted salamander (Ambystoma maculatum) and wood frog (Lithobates sylvaticus) larvae in 71 vernal pools in New York, USA during the spring and summer of 2016 and 2017—the fifth driest and third wettest years in regional history, respectively—to better understand the relationship between breeding effort and metamorph production under environmental extremes. Breeding effort was an important predictor of whether late-stage larvae occurred in pools for both species. However, occurrence of late-stage larvae was substantially lower for both species during 2016, i.e., the drought year, when pools dried rapidly. These outcomes suggest that, in the face of an increasingly variable climate, prioritizing clusters of pools that encompass a range of hydroperiods and include high-productivity pools would help maintain populations of vernal-pool dependent amphibians.

Stream Restoration Is Influenced by Details of Engineered Habitats at a Headwater Mine Site

A lack of information regarding which ecological factors influence restoration success or failure has hindered scientifically based restoration decision-making. We focus on one headwater site to examine factors influencing divergent ecological outcomes of two post-mining stream restoration projects designed to improve instream conditions following 70 years of mining impacts. One project was designed to simulate natural stream conditions by creating a morphologically complex channel with high habitat heterogeneity (HH-reach). A second project was designed to reduce contaminants and sediment using a sand filter along a straight, armored channel, which resulted in different habitat characteristics and comparatively low habitat heterogeneity (LH-reach). Within 2 years of completion, stream habitat parameters and community composition within the HH-reach were similar to those of reference reaches. In contrast, habitat and community composition within the LH-reach differed substantially from reference reaches, even 7–8 years after project completion. We found that an interaction between low gradient and high light availability, created by the LH-reach design, facilitated a Chironomid-Nostoc mutualism. These symbionts dominated the epilithic surface of rocks and there was little habitat for tailed frog larvae, bioavailable macroinvertebrates, and fish. After controlling for habitat quantity, potential colonizing species’ traits, and biogeographic factors, we found that habitat characteristics combined to facilitate different ecological outcomes, whereas time since treatment implementation was less influential. We demonstrate that stream communities can respond quickly to restoration of physical characteristics and increased heterogeneity, but “details matter” because interactions between the habitats we create and between the species that occupy them can be complex, unpredictable, and can influence restoration effectiveness.

Variation in upper thermal tolerance among 19 species from temperate wetlands.

Communities usually possess a multitude of interconnected trophic interactions within food webs. Their regulation generally depends on a balance between bottom-up and top-down effects. However, if sensitivity to temperature varies among species, rising temperatures may change trophic interactions via direct and indirect effects. We examined the critical thermal maximum (CTmax) of 19 species from temperate wetlands (insect predators, amphibian larvae, zooplankton and amphipods) and determined if they vary in their sensitivity to warming temperatures. CTmax differed between the groups, with predatory insects having higher CTmax than amphibians (both herbivorous larval anurans and predatory larval salamanders), amphipods and zooplankton. In a scenario of global warming, these differences in thermal tolerance may affect top-down and bottom-up processes, particularly considering that insect predators are more likely to maintain or improve their performance at higher temperatures, which could lead to increased predation rates on the herbivores in the food web. Further studies are needed to understand how the energy flows through communities, how species' energy budgets may change and whether other physiological and behavioral responses (such as phenotypic plasticity and thermoregulation) can buffer or increase these changes in the top-down regulation of wetland food webs.

Competition induces silver spoon effects in developing anuran larvae

Early life conditions can have lifelong impacts on survival and fitness. Silver spoon effects occur when favorable early life conditions provide advantages through adulthood, even if conditions worsen. Alternatively, compensatory growth allows organisms initially reared in unfavorable conditions to grow more quickly than expected should conditions improve. We examined these possibilities in the American Toad, Anaxyrus americanus, by rearing larvae in low and high competition environments and then transferring them to either high- or low-resource levels. We measured growth one-week post-transfer and toadlet size after metamorphosis. We also dissected larvae and toadlets from each treatment to examine effects on organ size. Before transfer, larvae reared with low competition grew significantly faster than those reared with high competition. Consistent with the silver spoon hypothesis, these larvae ate significantly more food, continued to grow faster post-transfer, and metamorphosed into larger toadlets with smaller livers and larger guts than those initially reared with high competition, despite having the same food availability within a resource level. Overall, our study demonstrates that larvae initially reared in favorable conditions maintain a growth advantage through metamorphosis even if resource levels decline. Future studies should explore the effects of this advantage post-metamorphosis and into adulthood.

The effect of water extract from bentonite on embryonic and larval development of the green toad (bufoviridis) with different phenotypes

Ontogenesis is a complex process of morphophysiological transformations. Embryonic and postembryonic development is continuously affected by both endogenous and environmental factors, which lead to variability in morphometric parameters. The research was conducted in the laboratory of ecological embryology of the Federal State Budgetary Educational Institution of Higher Education of the North Osetian Federal University (Vladikavkaz). The results showed that under the influence of bentonite extract, the morphological parameters of green toad larvae with a brown phenotype are more variable than in larvae with an olive green phenotype in both the control and experimental groups. Thus, the embryos and larvae of the green toad with the olive green phenotype are more stable than the larvae that had the brown phenotype, both in natural circumstances and under the influence of bentonite clay extracts.

Attraction to conspecifcs in Rhinella icterica and R. ornata tadpoles (Anura: Bufonidae)

Abstract: Tadpoles are able to perceive and discriminate signals from environment and they may use this ability in behaviors and ecological processes. Recognition mechanisms may be involved in schooling by means of attraction among individuals, characterizing a social process. By means of laboratory experiments the present study investigated the presence or absence of attraction to conspecifics in tadpoles of Rhinella icterica and R. ornata, two sympatric species from the Atlantic Forest of southeastern Brazil. We collected eggs of these two species in the field and reared them in laboratory according to two different methods (isolated or in groups of siblings). Tadpoles were submitted to experiments of choice between conspecifics, heterospecifics, and an empty compartment. Rhinella icterica tadpoles preferred to associate with conspecifics rather than R. ornata tadpoles, and we verified this is an innate behavior. Rhinella ornata tadpoles failed to discriminate between conspecifics and R. icterica tadpoles. When submitted to choice between a group of tadpoles of the other species and an empty compartment, R. icterica tadpoles presented random distribution, while R. ornata tadpoles preferred to associate with heterospecifics. Our results indicate R. icterica tadpoles have preference to associate with conspecifics, while R. ornata tadpoles may school indiscriminately. This study contributes for a better understanding of larval anuran social behavior.

Larval anatomy of monotypic painted ant nest frogs Lithodytes lineatus reveals putative homoplasies with the Leptodactylus pentadactylus group (Anura: Leptodactylidae)

The morphological diversity of anuran larvae made them an important source of information for evolutionary and systematic studies. For the monotypic frog genus Lithodytes, which has an interesting taxonomic history, including its past synonymizing with Adenomera and its placement as a subgenus of Leptodactylus, the information provided from its larvae can help to understand its systematics interrelationships and also provide insights about its evolutionary trajectories. Herein, we provide a detailed description of the larval morphology of Lithodytes lineatus, including novel data of internal morphology (buccopharyngeal cavity and skeleton), and discuss some morphological and evolutionary aspects in relation to other members of the subfamily Leptodactylinae. Despite the overall similar larval morphology with others members of the subfamily, we identified four autapomorphic traits for Lithodytes and seven purported homoplastic traits with a subclade of the Leptodactylus pentadactylus species group that likely evolved convergently. Some of these traits have been previously associated with a carnivorous diet. Putative homoplastic and autapomorphic characters served as additional diagnostic traits for Lithodytes, supporting its recognition as a distinct genus within Leptodactylidae.

Comparative analysis of the chondrocranium and hyobranchial skeleton of bromeliad arboreal frog larvae of the genus Phyllodytes Wagler, 1830 (Anura, Hylidae).

The genus Phyllodytes comprises 15 species, ten of them having their tadpole external morphology described in the literature. However, there are few descriptive studies on chondrocranium and hyobranchial skeleton. In this work, we describe the chondrocranium and hyobranchial skeleton of Phyllodytes larvae and discuss shared features and interspecific variation. Our findings suggest that the skeletal morphology is mostly conserved in the genus, with common features including a single suprarostral cartilage, short infrarostral cartilages, and overall short trabecular horns. Main intrageneric variations include the arrangement of the ascending process, the presence of larval otic process, and the configuration of the crista parotica. These variations are not correlated with the phylogenetic structure of the genus. Some distinctive aspects of P. praeceptor and P. gyrinaethes are also described in tadpoles of Osteopilus ocellatus, and could be related to oophagous habits in these tadpoles.

Olfactory subsystems in the peripheral olfactory organ of anuran amphibians.

Anuran amphibians (frogs and toads) typically have a complex life cycle, involving aquatic larvae that metamorphose to semi-terrestrial juveniles and adults. However, the anuran olfactory system is best known in Xenopus laevis, an animal with secondarily aquatic adults. The larval olfactory organ contains two distinct sensory epithelia: the olfactory epithelium (OE) and vomeronasal organ (VNO). The adult organ contains three: the OE, the VNO, and a "middle cavity" epithelium (MCE), each in its own chamber. The sensory epithelia of Xenopus larvae have overlapping sensory neuron morphology (ciliated or microvillus) and olfactory receptor gene expression. The MCE of adults closely resembles the OE of larvae, and senses waterborne odorants; the adult OE is distinct and senses airborne odorants. Olfactory subsystems in other (non-pipid) anurans are diverse. Many anuran larvae show a patch of olfactory epithelium exposed in the buccal cavity (bOE), associated with a grazing feeding mode. And other anuran adults do not have a sensory MCE, but many have a distinct patch of epithelium adjacent to the OE, the recessus olfactorius (RO), which senses waterborne odorants. Olfaction plays a wide variety of roles in the life of larval and adult anurans, and some progress has been made in identifying relevant odorants, including pheromones and feeding cues. Increased knowledge of the diversity of olfactory structure, of odorant receptor expression patterns, and of factors that affect the access of odorants to sensory epithelia will enable us to better understand the adaptation of the anuran olfactory system to aquatic and terrestrial environments.

Trade‐offs affect the adaptive value of plasticity: stronger cannibal‐induced defenses incur greater costs in toad larvae

AbstractAdaptive developmental plasticity allows individuals to match their phenotype with their environment, increasing fitness where threats are inconsistently present. However, despite clear advantages of plasticity, adaptive traits are not ubiquitously nor infinitely plastic. Trade‐offs between benefits and costs or limits are therefore theoretically necessary to constrain the evolution of plastic responses. Systems in which extreme risk can be reliably detected are ideal for investigating trade‐offs, as even costly responses may be adaptive where risk is severe. Cane toads (Rhinella marina) are abundant in Australia and produce large clutches (frequently >10,000 eggs), but asynchronous breeding and rapid development result in variable larval densities within breeding pools. In the field, we found that cannibalism by older cohorts often reduces the survival of conspecific eggs and newly hatched pre‐feeding larvae (“hatchlings”) by >99%, as feeding larvae (“tadpoles”) use chemical cues from the relatively immobile hatchlings to locate and consume them. After hatchlings become free‐swimming, however, they cannot be cannibalized. Hatchlings can reduce this period of vulnerability by accelerating development when they detect cannibal cues. However, this developmental acceleration decreases initial tadpole mass, reduces subsequent survival, growth, and development, affects behavior, and compromises feeding structures. Reaction norms differ among clutches, and greater developmental acceleration is followed by greater impairment of larval function in plastic clutches, whereas nonresponsive clutches are unaffected by cue exposure. More plastic clutches ultimately exhibit both poorer performance and greater variation among siblings in exposed and (to a lesser degree) control treatments. Variation among clutches in tadpole viability is driven by differences in plasticity rather than phenotype; fitness reductions are linked to developmental acceleration, not rapid development per se. Clutches with intrinsically slow pre‐feeding developmental rates exhibit stronger acceleration (i.e., steeper reaction norms), but clutches with intrinsically rapid development reach invulnerable stages more quickly than those that accelerate development. As a result, high cannibalism risk may favor canalized rapid development rather than facultative developmental acceleration. Cannibalism plays an important role in the recruitment of this invasive species, and hatchling defenses against this threat demonstrate how the limits and costs associated with an inducible defense can favor canalized defenses over phenotypic plasticity.

Shifts in the developmental rate of spadefoot toad larvae cause decreased complexity of post-metamorphic pigmentation patterns

Amphibian larvae are plastic organisms that can adjust their growth and developmental rates to local environmental conditions. The consequences of such developmental alterations have been studied in detail, both at the phenotypic and physiological levels. While largely unknown, it is of great importance to assess how developmental alterations affect the pigmentation pattern of the resulting metamorphs, because pigmentation is relevant for communication, mate choice, and camouflage and hence influences the overall fitness of the toads. Here we quantify the variation in several aspects of the pigmentation pattern of juvenile spadefoot toads experimentally induced to accelerate their larval development in response to decreased water level. It is known that induced developmental acceleration comes at the cost of reduced size at metamorphosis, higher metabolic rate, and increased oxidative stress. In this study, we show that spadefoot toads undergoing developmental acceleration metamorphosed with a less complex, more homogeneous, darker dorsal pattern consisting of continuous blotches, compared to the more contrasted pattern with segregated blotches and higher fractal dimension in normally developing individuals, and at a smaller size. We also observed a marked effect of population of origin in the complexity of the pigmentation pattern. Complexity of the post-metamorphic dorsal pigmentation could therefore be linked to pre-metamorphic larval growth and development.

Multiple Cases of Hypomelanism in Wood Frog Larvae (Rana sylvatica) Associated with Developmental Retardation and Mortality

Hypomelanism in natural populations is rare and has been anecdotally associated with developmental retardation and mortality when present in anuran larvae. We report multiple, recent cases of hypomelanism across 5 populations in 2 counties in Connecticut. We also experimentally confirm that this phenotype is associated with extremely delayed metamorphosis and increased mortality.