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Normal tables of development are essential for studies of embryogenesis, serving as an important resource for model organisms, including the frog Xenopus laevis. Xenopus has long been used to study developmental and cell biology, and is an increasingly important model for human birth defects and disease, genomics, proteomics and toxicology. Scientists utilize Nieuwkoop and Faber's classic 'Normal Table of Xenopus laevis (Daudin)' and accompanying illustrations to enable experimental reproducibility and reuse the illustrations in new publications and teaching. However, it is no longer possible to obtain permission for these copyrighted illustrations. We present 133 new, high-quality illustrations of X. laevis development from fertilization to metamorphosis, with additional views that were not available in the original collection. All the images are available on Xenbase, the Xenopus knowledgebase (http://www.xenbase.org/entry/zahn.do), for download and reuse under an attributable, non-commercial creative commons license. Additionally, we have compiled a 'Landmarks Table' of key morphological features and marker gene expression that can be used to distinguish stages quickly and reliably (https://www.xenbase. org/entry/landmarks-table.do). This new open-access resource will facilitate Xenopus research and teaching in the decades to come. [ABSTRACT FROM AUTHOR]

Diet quality and predation are two critical factors in determining the growth and development of organisms. Various anurans are susceptible to phenotypic changes influenced by these factors. Yet, few studies examined prey diet quality as potential influence over predator-induced traits. Using wood frog tadpoles (Lithobates sylvaticus) as a model species, we investigated the effects of three diet compositions (plant-based, animal-based, omnivorous) crossed with presence or absence of chemical cues from predatory dragonfly larvae (Aeshnidae). After 35 days, we recorded 11 morphological measurements, Gosner stage, and intestinal length of tadpoles to assess phenotypic changes under the six different experimental conditions. Our results showed the additive effects of both diet quality and predator chemical cue without detection of interactions between the two. Tadpoles receiving the omnivorous diet grew and developed faster with wider denticle rows than those receiving the plant or animal diets. The growth and development of tadpoles receiving only the animal diet were significantly hindered. These results emphasize the importance of diet quality in the growth and development of larval wood frogs. Chemical cues from predators significantly reduced tadpole body size but, in contrast to previous findings, did not affect tail size. Our experimental procedure of providing water containing predator and injured conspecific chemical cues on a weekly basis likely provided relatively weak predation risk perceived by tadpoles compared to previous studies using caged predators. The predator environment in our experiment, however, represents one ecologically relevant scenario in which predation risk is not urgent. [ABSTRACT FROM AUTHOR]

Amphibians are highly vulnerable and diverse vertebrates for which we still have modest genomic resources. Amphibian larvae are key components of continental wetlands, where they have strong influences on energy fluxes, nutrient cycling, and community structure. Amphibian larvae are highly sensitive to environmental conditions and can often alter their physiology, behavior and even morphology in response to the local conditions experienced, although we still know relatively little about the transcriptomic changes that enable such plasticity. Here we contribute the larval transcriptomes of two spadefoot toad species with divergent developmental rates and degree of developmental plasticity in response to pond drying.

Metamorphs of the yellow-bellied toad, Bombina variegata, vary widely in size at metamorphosis in the field. We performed a replicated outdoor mesocosm study to simulate the environmental factor combinations in permanent and ephemeral breeding sites and to quantify their effects on tadpole development (duration of the larval period, metamorph size and body condition). Looking for potential carry-over effects of the larval environment, we quantified locomotor performance of all metamorph phenotypes originating from the mesocosms immediately after metamorphosis under controlled conditions. In contrast to the prediction of life-history theory, tadpoles were unable to adjust developmental rate to water availability, but metamorphs originating from the ephemeral pond treatment were smaller and had a lower body condition than those from the permanent pond treatment. Size-dependent carry-over effects included the length of the first jump following tactile stimulation, burst performance (total length of spontaneous jumps) and endurance (total distance covered in 10 forced jumps). A size-independent effect of larval environment was the prolonged locomotor effort to escape (5.7 consecutive jumps following initial stimulus) of metamorphs from the ephemeral pond treatment compared to same-sized ones (3.7 jumps) from the permanent pond treatment. Thus, we demonstrate that carry-over effects of larval environment on metamorph phenotype and behaviour cause a considerable variation in fitness in the early terrestrial stage of B. variegata. Informed conservation management of endangered populations in the northern range should therefore include the provision of small permanent breeding ponds promoting larger and fitter metamorphs. [ABSTRACT FROM AUTHOR]

Abstract Octylphenol (OP), a class of endocrine disrupting chemicals (EDCs), could produce adverse effects on developmental process of animals. Thyroid hormone is one of the important hormones involved in animal development. To determine whether OP affect the growth and development of amphibian larvae via interfering the thyroid function, Rana chensinensis larvae at Gosner stage 29 were exposed to 10−8, 10−7 and 10−6 mol/L OP in the present study. Results demonstrated that OP could decrease the body length and mass and retard the development of tadpoles. The histologic evaluation showed microscopic structures of thyroid gland were changed in 10−7 and 10−6 mol/L OP treated groups on day 40. The expression levels of Dio2 , Dio3 , TRα and TRβ mRNA in the liver, brain, skin and tail of tadpoles were detected by qRT-PCR, when treated with OP for 20, 30, 40 and 50 day, respectively. The results of qRT-PCR showed OP could affect the expressions of Dio2 , Dio3 , TRα and TRβ mRNA in the four tissues, and then influence the activity and function of THs, further affecting the growth and development of the tadpoles. Highlights • OP could decrease the body length and weight of Rana chensinensis tadpoles. • OP could induce increased colloid and follicles in the thyroid gland of Rana chensinensis tadpoles. • OP could affect the expressions of Dio2 , Dio3 , TRα and TRβ mRNA in the liver, brain, skin, and tail of Rana chensinensis tadpoles. [ABSTRACT FROM AUTHOR]

Trichlorfon is an organophosphate insecticide widely used in aquaculture and agriculture. Little is known about the effects of long‐term of low doses trichlorfon exposure on amphibians. In this study, we investigated the effects of low doses trichlorfon on Rana chensinensis tadpoles after exposure to 0.01, 0.1, and 1.0 mg/L trichlorfon for 2 and 4 weeks. Survival, growth, development and mortality were monitored regularly over the course of exposure. The results showed that trichlorfon led to a decrease in tadpole survival. Reductions in growth and disruptions to the development of tadpoles were observed in trichlorfon treatments. Morphological abnormalities of affected tadpoles included axial flexures, skeletal malformations and lateral kinks. Trichlorfon increased the frequency of micronucleus (MN) formation in circulating erythrocytes of tadpoles exposed for 2 weeks to 0.1 and 1.0 mg/L trichlorfon. At all concentrations, an enhanced frequency of MN formation was observed in tadpoles exposed for 4 weeks. Exposure to trichlorfon induced other nuclear abnormalities such as lobed and notched nuclei only in tadpoles exposed to 1.0 mg/L trichlorfon for 4 weeks. In addition, exposure to trichlorfon within the 0.01‐1.0 mg/L range increased the genetic damage index in hepatic tissues in all treatments. Apoptosis‐associated DNA fragmentation in hepatic tissues occurred in a weak ladder‐like pattern. This study presents evidence of low doses trichlorfon effects on amphibians, highlighting the properties of this organophosphate insecticide that jeopardize nontarget species exposed to trichlorfon. [ABSTRACT FROM AUTHOR]

Amphibians are seasonal breeders living in seasonal environments having time constraints to achieve their annual life history states. Their survival is strongly dependent on successful timing of certain critical life history decisions. Larval amphibian development, growth, and metamorphosis are strongly time-limited due to variations in the seasonal factors. Photoperiod influences wide range of physiological processes in seasonal breeder. Being ectothermic, temperature may also play critical role in development of amphibian larvae. Food also acts as an ultimate factor in many organisms. Most studies of rearing conditions on growth, development, and metamorphosis of amphibian’s tadpoles have been focused on laboratory species; genus Xenopus. Less is known about other seasonally breeding amphibians. In present study, we addressed the effects of photic (light quality) and non-photic cues (temperature and food quality) on growth, development and metamorphosis of giant tree frog (Rhacophorus maximus). Three experiments have been performed. In experiment one effect of light quality (light wavelength), in experiment two effect of food quality and in experiment three effect of temperature on growth, development, and metamorphosis of giant tree frog tadpoles were studied. Our results suggest that light and food quality and high temperature promotes faster growth, development, and metamorphosis in R. maximus tadpoles. [ABSTRACT FROM AUTHOR]

The effects of illumination on the early development of four amphibian species -- Lissotriton vulgaris (Linnaeus, 1758), Triturus cristatus (Laurenti, 1768), Rana arvalis (Nilsson, 1842), and R. temporaria (Linnaeus, 1758) -- have been studied. In general, the rate of their early development is rather independent of illumination. The eggs of tailless amphibians develop almost similarly under any illumination conditions, whereas the eggs of tailed amphibians better develop at an illumination of 700 lx. Illumination mainly influences the survival rate of embryos and prolarvae, which increases at low light intensities and decreases in the dark. Possible mechanisms and causes underlying the observed facts are discussed. [ABSTRACT FROM AUTHOR]

Early life-stages of amphibians rely on the innate immune system for defense against pathogens. While thyroid hormones (TH) are critical for metamorphosis and later development of the adaptive immune system, the role of TH in innate immune system development is less clear. An integral part of the innate immune response are pro-inflammatory cytokines – effector molecules that allow communication between components of the immune system. The objective of this study was to characterize the expression of key pro-inflammatory cytokines, tumor necrosis factor-α (TNFα), interleukin-1β (IL-1β) and interferon-γ (IFN-γ), throughout amphibian development and determine the impacts of thyroidal modulation on their expression. Xenopus laevis were sampled at various stages of development encompassing early embryogenesis to late prometamorphosis and cytokine expression was measured by real-time PCR. Expression of TNFα and IL-1β were transient over development, increasing with developmental stage, while IFN-γ remained relatively stable. Functionally athyroid, premetamorphic tadpoles were exposed to thyroxine (0.5 and 2 μg/L) or sodium perchlorate (125 and 500 μg/L) for seven days. Tadpoles demonstrated characteristic responses of advanced development with thyroxine exposure and delayed development (although to a lesser extent) and increased thyroid gland area and follicular cell height with sodium perchlorate exposure. Exposure to thyroxine for two days resulted in decreased expression of IL-1β in tadpole trunks. Sodium perchlorate had negligible effects on cytokine expression. Overall, these results demonstrate that cytokine transcript levels vary with stage of tadpole development but that their ontogenic regulation is not likely exclusively influenced by thyroid status. Understanding the direct and indirect effects of altered hormone status may provide insight into potential mechanisms of altered immune function during amphibian development. [ABSTRACT FROM AUTHOR]

The rise in pesticides application has increased the need for better understanding of their ecological impacts. The global amphibian declines, for example, have been positively correlated with pesticides use. The differential susceptibility in the developmental stages of amphibians to chemical substances are still largely unknown. We examined the 96-h differential toxicity responses of embryos, premetamorphic and transitional larval stage of Xenopus laevis, to six formulated aquatic herbicide products containing the active ingredients of diquat dibromide (Midstream), glufosinate ammonium (Basta), imazapyr (Arsenal), and three glyphosate formulations (Roundup, Kilo Max, and Environ Glyphosate). The results showed the premetamorphic stage as the most sensitive to the herbicides toxicity. This study confirmed that the developmental stage at which amphibian are exposed to contaminants is critical to their survival and that the chemical contamination hypothesis of the global decline of amphibians should continue to be considered. This establishment of the premetamorphic larval as sensitive toxicity representative for all developmental stages of X. laevis means that this stage could be used more extensively in pesticides toxicity assessments. [ABSTRACT FROM AUTHOR]

Thyroid hormone (TH) orchestrates amphibian metamorphosis. Thus, this developmental phase is often used to study TH-dependent responses in specific tissues. However, TH signaling appears early in development raising the question of the control of TH availability in specific cell types prior to metamorphosis. TH availability is under strict temporal and tissue-specific control by deiodinases. We examined the expression of the TH-inactivating enzyme, deiodinase type 3 (D3), during early retinal development. To this end we created a Xenopus laevis transgenic line expressing GFP from the Xenopus dio3 promoter region (pdio3) and followed pdio3–GFP expression in pre-metamorphic tadpoles. To validate retinal GFP expression in the transgenic line as a function of dio3 promoter activity, we used in situ hybridization to compare endogenous dio3 expression to reporter-driven GFP activity. Retinal expression of dio3 increased during pre-metamorphosis through stages NF41, 45 and 48. Both sets of results show dio3 to have cell-specific, dynamic expression in the pre-metamorphic retina. At stage NF48, dio3 expression co-localised with markers for photoreceptors, rods, Opsin-S cones and bipolar neurons. In contrast, in post-metamorphic juveniles dio3 expression was reduced and spatially confined to certain photoreceptors and amacrine cells. We compared dio3 expression at stages NF41 and NF48 with TH-dependent transcriptional responses using another transgenic reporter line: THbZIP-GFP and by analyzing the expression of T3-regulated genes in distinct TH availability contexts. At stage NF48, the majority of retinal cells expressing dio3 were negative for T3 signaling. Notably, most ganglion cells were virtually both dio3-free and T3-responsive. The results show that dio3 can reduce TH availability at the cellular scale. Further, a reduction in dio3 expression can trigger fine-tuned T3 action in cell-type specific maturation at the right time, as exemplified here in photoreceptor survival in the pre-metamorphic retina. [ABSTRACT FROM AUTHOR]

Fish endpoints measured in early life stage toxicity tests are often used as representative of larval amphibian sensitivity in Ecological Risk Assessment (ERA). This application potentially overlooks the impact of developmental delays on amphibian metamorphosis, and thereby reduced survival, in amphibian populations constrained by habitat availability. Likewise, the effects of reduced productivity or altered sexual development as a result of chemical exposure are not presented in terms of lower population fecundity in these surrogate tests. Translating endpoints measured in toxicity tests to those that are more representative of amphibian ecology and population dynamics provides a means of identifying how developmental effects result in long-term impacts. Here we compare effects of developmental delay on metamorphosis success in six anuran species and simulate population-level impacts of subsequent reductions in larval survival as well as potential reductions in fecundity as a result of developmental impacts. We use deterministic matrix models to compare realistic combinations of amphibian demographic rates and relative impacts of reduced growth on larval survival and subsequently on population growth. Developmental delays are less detrimental in species with longer and less synchronous larval periods. All six species were most sensitive to changes in first-year survival, and damping ratios were generally a good indicator of resilience to perturbations in both larval survival and fecundity. Further identification of species and population-level vulnerabilities can improve the evaluation of sublethal effects in relevant context for ERA. [ABSTRACT FROM AUTHOR]

A hormone-dependent developmental transition from aquatic to terrestrial existence occurs in all tetrapod vertebrates, such as birth, hatching, and metamorphosis. Thyroid hormones (TH) and their receptors (TRs) are key players in the tissue transformations comprising vertebrate developmental transitions. The African clawed frog, Xenopus , is a premier model for the role of TRs in developmental transitions because of the numerous and dramatic TH-dependent tissue transformations during metamorphosis and because of the endocrine, molecular, and genomic resources available. TRs are nuclear receptors that repress TH-response genes when plasma TH is minimal and that activate those same genes to induce tissue-specific gene regulation cascades when TH plasma levels increase. Tissue-specific TR expression levels help determine tissue sensitivity and responsivity to TH thereby regulating the initiation and rate of developmental change in TH-sensitive tissues which govern the tissue developmental asynchrony observed during metamorphosis. This review highlighting Xenopus presents the key experimental findings underpinning the roles TRs play in control of vertebrate developmental transitions. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the adverse effects of lead (Pb) exposure on Bufo gargarizans embryos. The 96 h-LC of Pb for B. gargarizans embryos was determined to be 26.6 mg L after an acute test. In the chronic test, B. gargarizans embryos at Gosner stage 3 were exposed to 10~2000 μg Pb L during embryogenesis. Total length, weight, developmental stage, and malformation were monitored. In addition, the transcript levels of type II and type III iodothyronine deiodinase ( Dio2 and Dio3) and thyroid hormone receptors ( TRα and TRβ) were determined to assess the thyroid-disrupting effects of Pb. Slightly increased growth and development of B. gargarizans embryos were observed at low concentrations of Pb (10, 50, and 100 μg L), while retarded growth and development were found at high concentrations of Pb (1000 and 2000 μg L). In addition, Pb exposure induced morphological abnormalities, which were characterized by edema at tail, wavy fin, abdominal edema, stunted growth, hyperplasia, and axial flexures in B. gargarizans embryos. Furthermore, our results showed that exposure to 2000 μg Pb L decreased the transcript levels of Dio2, TRα, and TRβ, but it increased Dio3 mRNA level. In contrast, exposure to 50 μg Pb L increased TRα mRNA level and decreased Dio3 mRNA level. These results suggested that Pb might have thyroid-disrupting effects, leading to the disruption of growth and development in B. gargarizans embryos. [ABSTRACT FROM AUTHOR]

When anuran tadpoles are treated with vitamin A after tail amputation, hindlimb-like structures can be generated instead of the lost tail part at the amputation site. This homeotic transformation was initially expected to be a key to understanding the body plan of vertebrates. Unfortunately, homeotic limb formation has been reproduced in only some Indian frog species and a European species, but not in experimental anurans such as Xenopus laevis or Rana catesbeiana. Consequently, this fascinating phenomenon has not been well analyzed, especially at the molecular level. In addition, the initial processes of ectopic limb development are also unclear because morphological changes in the early phases have not been analyzed in detail. In this study, we report the induction of homeotic transformation using Japanese brown frogs and present a detailed morphological analysis. Unexpectedly, the ectopic limbs developed not only at the ventral sites, but also at the dorsal sites of the tail regenerates of vitamin A-treated tadpoles. The relationship between position and axial orientation of ectopic limbs suggested the double duplication of positional value order along the rostral-caudal axis and the dorsal-ventral axis of the tail regenerates. [ABSTRACT FROM AUTHOR]

Increased pesticide use in rice agricultural ecosystems may alter competitive interactions between invasive and native amphibian species. We conducted an experiment with two rice paddy amphibians found in Luzon, Philippines, the invasive cane toad ( Rhinella marina) and the endemic Luzon wart frog ( Fejervarya vittigera), to determine whether exposure to a common herbicide, butachlor, drives competitive interactions in favor of the invasive amphibian. Our results revealed that competition had a strong effect on the development of both species, but in opposing directions; Luzon wart frog tadpoles were smaller and developed slower than when raised alone, whereas cane toad tadpoles were larger and developed faster. Contrary to our predictions, development and survival of endemic wart frog tadpoles was not affected by butachlor, whereas invasive cane toad tadpoles were affected across several endpoints including gene expression, body size, and survival. We also observed an interaction between pesticide exposure and competition for the cane toad, where survival declined but body size and expression of thyroid sensitive genes increased. Taken together, our findings indicate that the success of the cane toad larvae in rice fields may be best explained by increased rates of development and larger body sizes of tadpoles in response to competition with native Luzon wart frog tadpoles rather than lower sensitivity to a common pesticide. Our results for the cane toad also provide evidence that butachlor can disrupt thyroid hormone mediated development in amphibians, and further demonstrate that important species interactions such as competition can be affected by pesticide exposure in aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Abstract: The linking of research data from evolutionary biology and palaeontology is shedding new light on the origin and development of amphibians. For scientists working in this area, salamanders are a fascinating object of study – from the unusual development of their extremities to the regeneration of entire limbs. [ABSTRACT FROM AUTHOR]

The presence of predators can induce changes in both the morphology and behaviour of Anuran larvae, affecting both their size and developmental stage at metamorphosis and, consequently, the fitness of adult individuals. Tadpoles have been shown to be capable of finely tuning their defensive responses according to the actual risk perceived, which is expected to vary according to the prey-to-predator size ratio. In this study, we exposed common frog ( Rana temporaria) tadpoles (Gosner stages 28-30), for a period of 2 weeks, to the non-lethal presence of dragonfly larvae ( Anax imperator) and backswimmers ( Notonecta glauca). In such a narrow window of time, we expected behavioural responses to be similar for both predators and exposure to predation risk to have negligible effects on tadpole development and weight. Overall, tadpoles increased hiding behaviour and were less active when predators were present in the experimental mesocosms, but behavioural responses were constrained to the early phase of the ontogeny and were no longer used when tadpoles reached a threshold size. Developmental rate slightly slowed down for predator treatments in comparison to controls, possibly as a consequence of energetic investment in unrecorded morphological defences. Although variation in laboratory conditions and protocols makes it hard to compare the results of different experiments, our results contribute to verify the consistency of behavioural responses in Anuran larvae. [ABSTRACT FROM AUTHOR]

The hydroperiod of breeding habitats imposes a strong selection on amphibians and pond-breeding species usually exhibit a high degree of plasticity in the duration of larval period. However, the potential for phenotypic plasticity in fast developing species was investigated only in a small number of anurans, and the specific response to environmental cues such as low water versus decreasing water level, as well as the effects of such cues on particular developmental stages, are even less understood. In this context, we investigated the plastic response to pond desiccation in a neotropical species ( Ceratophrys stolzmanni) by raising tadpoles in three water level treatments: constant high, constant low, and decreasing. The growth rates were the highest reported for amphibian tadpoles (up to 0.3 g day−1) and the time to metamorphosis was short in all treatments, with the fastest developing tadpole metamorphosing in only 16 days after egg deposition. Individuals from the constant high water level treatment had a higher growth rate than those in the other two treatments, whereas decreasing and constant low water levels had similar effects on development, speeding up metamorphosis. In turn, this involved a cost as these tadpoles had a lower body size and mass at metamorphosis than the ones raised in constant high water levels. The final stages of metamorphosis, when tadpoles are the most vulnerable, were shorter in tadpoles exposed to a decreasing water level, allowing them to leave water quickly. Our experiment demonstrates that phenotypic plasticity is maintained even in environments devoid of permanent aquatic habitats. Ceratophryd tadpoles are able to shorten their developmental time when they perceive a risk of desiccation and react similarly to cues coming from the two unfavorable water conditions showing their adaptation to ephemeral and unpredictable breeding habitats. [ABSTRACT FROM AUTHOR]

Hatching is an essential and often behaviourally mediated process. Many animals can hatch at different developmental stages, and embryos time hatching based on cues indicating threats to eggs or opportunities outside them. However, specific mechanisms enabling such responses, and how their ontogenies combine to determine when environmentally cued hatching is possible, are largely unknown. Many embryos use hatching cues in multiple sensory modalities. Thus, comparing response onset across cue types can distinguish shared ontogenetic constraints, such as hatching ability, from modality-specific constraints, such as sensor development. The arboreal embryos of red-eyed treefrogs, Agalychnis callidryas , hatch rapidly in response to physical disturbance in predator attacks and hypoxia if flooded. Prior research documented both responses beginning at age 4 days. Because embryos orient in oxygen gradients long before this, we hypothesized the onset of hypoxia-cued hatching is limited by development of hatching ability. The onset of mechanosensory-cued hatching might share this constraint or be limited by a later-developing sensory mechanism. We tested developmental series for hypoxia-cued hatching, by submerging eggs in degassed water to impose strong hypoxia, and for mechanosensory-cued hatching, by manually jiggling eggs as a simulated attack. We identified morphological markers to distinguish developmental stages across the onset of hatching. Hatching competence begins substantially earlier than previously reported. Across sibships, hypoxia-cued hatching began at a smaller size and less developed stage, and on average 8 h earlier than mechanosensory-cued hatching. Both responses increased from 0% to 100% over just a few hours. Latency to hatch after stimulation was longer in hypoxia-cued hatching and uncorrelated with stage, whereas latency in mechanosensory-cued hatching decreased with development. Hypoxia-cued hatching appears constrained by the development of hatching ability, while mechanosensory-cued hatching appears constrained by mechanosensor development. Hatching ability is not the sole constraint on the onset of escape-hatching responses to attacks. [ABSTRACT FROM AUTHOR]

Determining the extent of reproductive isolation in cryptic species with dynamic geographic ranges can yield important insights into the processes that generate and maintain genetic divergence in the absence of severe geographic barriers. We studied mating patterns, propensity to hybridize in nature and subsequent fertilization rates, as well as survival and development of hybrid F1 offspring for three nominal species of the Engystomops petersi species complex in Yasuní National Park, Ecuador. We found at least two species in four out of six locations sampled, and 14.3% of the wild pairs genotyped were mixed-species (heterospecific) crosses. We also found reduced fertilization rates in hybrid crosses between E. petersi females and E. “magnus” males, and between E. “magnus” females and E. “selva” males but not in the reciprocal crosses, suggesting asymmetric reproductive isolation for these species. Larval development times decreased in F1 hybrid crosses compared to same species (conspecific) crosses, but we did not find significant reduction in larval survival or early metamorph survival. Our results show evidence of post-mating isolation for at least two hybrid crosses of the cryptic species we studied. The general decrease in fertilization rates in heterospecific crosses suggests that sexual selection and reinforcement might have not only contributed to the pattern of call variation and behavioral isolation we see between species today, but they may also contribute to further signal divergence and behavioral evolution, especially in locations where hybridization is common and fertilization success is diminished. [ABSTRACT FROM AUTHOR]

Teratogenic effects, which were remarkably similar to those induced by retinoic acids, have been seen in wild frogs indicating possible source of retinoids in the environment. Recent studies indicate that some cyanobacterial species can contain teratogenic retinoic acids (RAs) and their analogues. Retinoids are known to regulate important processes such as differentiation, development, and embryogenesis. The study investigated the effects of exudates (extracellular compounds) of two cyanobacteria species with retinoic-like activity and one algae species on embryonic development of amphibians. The retinoid-like activity determined by in vitro reporter gene assay reached 528 ng retinoid equivalents (REQ)/L and 1000 ng REQ/L in exudates of Cylindrospermopsis raciborskii and Microcystis aeruginosa , respectively, while algal exudates showed no detectable activity. Total mean of retinoid-like copounds into exudate was 35.6 ng ATRA/mil.cells for M.aeruginosa and 6.71 ng ATRA/mil.cells for C.raciborskii , respectively. Toxicity tests with amphibian embryos up to 96 h of development were carried out according to the standard guide for the Frog Embryo Teratogenesis Assay Xenopus. Lowest observed effect concentrations (LOEC) of malformations (2.5–2.6 µg/L REQ) were two times lower than LOEC for ATRA (5 µg/L). The exudates of both cyanobacteria were indeed provoking diverse teratogenic effects ( e.g. tail, gut and eyes deformation) and interference with growth in frogs embryos, while such effects were not observed for the algae. Xenopus embryos were also exposed to all- trans retinoic acid (ATRA) in concentration range (1−40 µg/L) equivalent to the REQs detected in cyanobacterial exudates. ATRA (10 µg/L) caused similar teratogenic phenotypes at corresponding REQs as cyanobacterial exudates. The study confirms the ability of some species of cyanobacteria to produce retinoids naturally and excrete them directly into the environment at concentrations which might have adverse influence on the development of amphibians. [ABSTRACT FROM AUTHOR]

Pharmaceuticals are widely used for the treatment of various physical and psychological ailments. Due to incomplete removal during sewage treatment many pharmaceuticals are frequently detected in aquatic waterways at trace concentrations. The diversity of pharmaceutical contaminants and potential for complex mixtures to occur makes it very difficult to predict the toxicity of these compounds on wildlife, and robust methods are therefore needed to explore sub-lethal effects. Metabolic syndrome is one of the most widespread health concerns currently facing the human population, and various drugs, including anti-diabetic medications and lipid- and cholesterol-lowering fibrates and statins, are widely prescribed as treatment. In this study, we exposed striped marsh frog ( Limnodynastes peronii ) tadpoles to a mixture of the drugs metformin, atorvastatin and bezafibrate at 0.5, 5, 50 and 500 μg/L to explore possible effects on growth and development, energy reserves (triglycerides and cholesterol), and profiles of small polar metabolites extracted from hepatic tissues. It was hypothesised that exposure would result in a general reduction in energy reserves, and that this would subsequently correspond with reduced growth and development. Responses differed from expected outcomes based on the known mechanisms of these compounds in humans, with no changes to hepatic triglycerides or cholesterol and a general increase in mass and condition with increasing exposure concentration. Deviation from the expected response patterns may be explained by differences in the receptivity or uptake of the compounds in non-mammalian species. Proton nuclear magnetic resonance ( 1 H NMR) spectroscopy revealed evidence of broad metabolic dysregulation in exposed animals, and possible interaction between the solvent and mixture. Specifically, increased lactic acid and branched-chain amino acids were observed, with responses tending to follow a non-monotonic pattern. Overall, results demonstrate that a mixture of drugs commonly prescribed to treat human metabolic syndrome is capable of eliciting physiological and developmental effects on larval amphibians. Importantly, outcomes further suggest that it may not be possible to predict toxicological effects in non-target wildlife based on our knowledge of how these compounds act in humans. [ABSTRACT FROM AUTHOR]

Several photographs of amphibians living in temperate environments, displaying their compensatory responses in a period of adverse conditions are presented including Moor frog hatchlings, predatory dragonfly larvae and geometric morphometric analyses on shape changes of Moor frog tadpoles.

The retinotectal circuit is the major component of the amphibian visual system. It is comprised of the retinal ganglion cells (RGCs) in the eye, which project their axons to the optic tectum and form synapses onto postsynaptic tectal neurons. The retinotectal circuit is relatively simple, and develops quickly: Xenopus tadpoles begin displaying retinotectal-dependent visual avoidance behaviors by approximately 7–8 days post-fertilization, early larval stage. In this review we first provide a summary of the dynamic development of the retinotectal circuit, including the microcircuitry formed by local tectal–tectal connections within the tectum. Second, we discuss the basic visual avoidance behavior generated specifically by this circuit, and how this behavior is being used as an assay to test visual system function. [ABSTRACT FROM AUTHOR]

Vestibulo-ocular reflexes (VOR) ensure gaze stability during locomotion and passively induced head/body movements. In precocial vertebrates such as amphibians, vestibular reflexes are required very early at the onset of locomotor activity. While the formation of inner ears and the assembly of sensory-motor pathways is largely completed soon after hatching, angular and translational/tilt VOR display differential functional onsets and mature with different time courses. Otolith-derived eye movements appear immediately after hatching, whereas the appearance and progressive amelioration of semicircular canal-evoked eye movements is delayed and dependent on the acquisition of sufficiently large semicircular canal diameters. Moreover, semicircular canal functionality is also required to tune the initially omnidirectional otolith-derived VOR. The tuning is due to a reinforcement of those vestibulo-ocular connections that are co-activated by semicircular canal and otolith inputs during natural head/body motion. This suggests that molecular mechanisms initially guide the basic ontogenetic wiring, whereas semicircular canal-dependent activity is required to establish the spatio-temporal specificity of the reflex. While a robust VOR is activated during passive head/body movements, locomotor efference copies provide the major source for compensatory eye movements during tailand limb-based swimming of larval and adult frogs. The integration of active/passive motion-related signals for gaze stabilization occurs in central vestibular neurons that are arranged as segmentally iterated functional groups along rhombomere 1-8. However, at variance with the topographic maps of most other sensory systems, the sensory-motor transformation of motion-related signals occurs in segmentally specific neuronal groups defined by the extraocular motor output targets. [ABSTRACT FROM AUTHOR]

As a widely used herbicide, atrazine (AZ) has been extensively studied for its adverse effects on the reproductive system, especially feminization in male animals. However, the relationship of gene expression changes and associated toxicological endpoints remains unclear. In this study, developing Xenopus laevis tadpoles were exposed to concentration of AZ at 0.1, 1, 10 or 100 μg/L continuously. Compared with froglets in the control group, there were no significant differences in body length, body weight, liver weight and hepatosomatic index (HSI) of males in groups treated with AZ for 90 d. At 100 μg/L AZ treatment caused a significant reduction of gonad weight and gonadosomatic index (GSI) of males ( p < 0.01). In addition, AZ at all dose levels caused testicular degeneration, especially in froglets from the groups with 0.1 and 100 μg/L which exhibited U-shaped dose-response trend. We further investigated the gene expression changes associated with the testicular degeneration induced by AZ. We found that the expression of 1165 genes was significantly altered with 616 upregulated and 549 downregulated compared to the expression profile of the control animals. KEGG analysis showed that genes which were significantly affected by AZ are mainly involved in arginine and proline metabolism, cell cycle, riboflavin metabolism, spliceosome, base excision repair and progesterone-mediated oocyte maturation pathway. Our results show that AZ may affect reproductive and immune systems by interference with the related gene expression changes during the male X. laevis development. The findings may help to clarify the feminization mechanisms of AZ in male X. laevis . [ABSTRACT FROM AUTHOR]

Natural selection is predicted to favor the evolution of life history plasticity in response to differences in mortality risk between life stages, such that the duration of the more dangerous stage is reduced. I report a meta-analysis of 29 published tests of this hypothesis involving 20 amphibian species, in which exposure of embryos to predation risk was experimentally manipulated. The results confirm that amphibians are sensitive to risk during the embryonic stage, but the predictions of theory were only weakly upheld. Amphibians hatch at a less advanced developmental stage (0.24 SD units) and smaller body size (0.10 SD units) when exposed to predator species that consume eggs, but the expected decline in age at hatching (0.16 SD units) was not significant. Predators that consume larvae did not significantly delay hatching (0.19 SD units) or influence any other response. [ABSTRACT FROM AUTHOR]

Amphibians are undergoing a global decline. One poorly investigated reason could be the pollution of aquatic habitats by endocrine disrupting compounds (EDCs). We tested the susceptibility to the synthetically stabilized estrogen 17α-ethinylestradiol (EE2) in three deeply diverged anuran species, differing in sex determination systems, types of gonadogenesis and larval ecologies. To understand whether data from the amphibian model Xenopus laevis (Pipidae) are analogous and applicable to only distantly related non-model amphibians, tadpoles of X. laevis , Hyla arborea (Hylidae) and Bufo viridis (Bufonidae) were simultaneously exposed to 50, 500 and 5000 ng/L EE2 from hatching until completion of metamorphosis, using a flow-through-system under identical experimental conditions. Comparing molecularly established genetic with histologically assessed phenotypic sex in all species, we have recently shown that EE2 provoked numerous genetic-male-to-phenotypic-female sex reversals and mixed sex individuals, confirming overall its expected feminizing effect. In the present study, we focus on the influence of EE2 on gonadal and somatic development. Anatomy and histology revealed several species-specific effects. In both non-model species, H. arborea and B. viridis , high numbers of anatomically impaired gonads were observed. In H. arborea , exposed to 5000 ng/L EE2, numerous underdeveloped gonads were detected. Whereas EE2 did not alter snout-to-vent length and body weight of X. laevis metamorphs, H. arborea showed a treatment-dependent decrease, while B. viridis exhibited an increase in body weight and snout-to-vent length. Apart from a concentration-dependent occurrence of yellowish skin color in several H. arborea , no organ-specific effects were detected. Since EE2 ubiquitously occurs in many aquatic ecosystems and affects sexual and somatic development, among EDCs, it may indeed contribute to amphibian decline. The inter-species variation in developmental EE2-effects corroborates species-specific vulnerability differences towards EDCs between deeply diverged amphibian groups. [ABSTRACT FROM AUTHOR]

In the vertebrate blastula and gastrula the Nodal pathway is essential for formation of the primary germ layers and the organizer. Nodal autoregulatory feedback potentiates signaling activity, but mechanisms limiting embryonic Nodal ligand transcription are poorly understood. Here we describe a transcriptional switch mechanism mediated by FoxH1, the principle effector of Nodal autoregulation. FoxH1 contains a conserved engrailed homology (EH1) motif that mediates direct binding of groucho-related gene 4 (Grg4), a Groucho family corepressor. Nodal-dependent gene expression is suppressed by FoxH1, but enhanced by a FoxH1 EH1 mutant, indicating that the EH1 motif is necessary for repression. Grg4 blocks Nodal-induced mesodermal gene expression and Nodal autoregulation, suggesting that Grg4 limits Nodal pathway activity. Conversely, blocking Grg4 function in the ectoderm results in ectopic expression of Nodal target genes. FoxH1 and Grg4 occupy the Xnr1 enhancer, and Grg4 occupancy is dependent on the FoxH1 EH1 motif. Grg4 occupancy at the Xnr1 enhancer significantly decreases with Nodal activation or Smad2 overexpression, while FoxH1 occupancy is unaffected. These results suggest that Nodal-activated Smad2 physically displaces Grg4 from FoxH1, an essential feature of the transcriptional switch mechanism. In support of this model, when FoxH1 is unable to bind Smad2, Grg4 occupancy is maintained at the Xnr1 enhancer, even in the presence of Nodal signaling. Our findings reveal that FoxH1 mediates both activation and repression of Nodal gene expression. We propose that this transcriptional switch is essential to delimit Nodal pathway activity in vertebrate germ layer formation. [ABSTRACT FROM AUTHOR]

Learning is crucial to the survival of organisms across their life span, including during embryonic development. We set out to determine when learning becomes possible in amphibian development by exposing spotted salamander ( Ambystoma maculatum) embryos to chemical stimuli from a predator ( Ambystoma opacum), nonpredator ( Lithobates clamitans), or control at developmental stages 16-21 or 36-38 (Harrison ). Once exposures were completed and embryos hatched, we recorded the number of movements and time spent moving of individuals in both groups and all treatments. There was no significant difference in number of movements or time spent moving among any of the treatments. The groups that were exposed to predator stimuli and a blank control at stages 36-38 were also tested to determine whether there was a difference in refuge preference or difference in survivorship when exposed to a predator (marbled salamander). There was no difference in survival or refuge preference between individuals; however, all individuals preferred vegetated over open areas regardless of treatment type. We discuss hypotheses for the absence of embryonic learning in this species and suggest it may be the result of the intensity of the predator-prey interaction between the predator, large marbled salamander larvae, and the prey, spotted salamander larvae. [ABSTRACT FROM AUTHOR]

Organismal performance can be significantly affected by the nutritional conditions experienced during different life-stages. The Silver Spoon Hypothesis predicts that individuals will always perform better as adults when they experience advantageous conditions during development. In contrast, the Environmental Matching Hypothesis predicts that individuals will perform better if they experience similar conditions during development and adulthood. Past tests of these hypotheses have focussed on the effect of food quantity on growth and development, with little attempt to investigate the effect of individual nutrients on behavioural traits. This study aimed to test the predictions of the Environmental Matching and Silver Spoon Hypotheses by investigating the influence of carotenoid supplementation at different life-stages on the foraging performance of Pseudophryne corroboree . To assess foraging performance, adults were presented with prey in either a cryptic or conspicuous foraging matrix. There was no effect of diet treatment on time to first movement towards prey, number of stalking events, time spent actively foraging, proportion of successful strikes, proportion of prey consumed or number of pedal luring events. These findings indicate that carotenoid supplementation at different life-stages does not influence the foraging performance of P. corroboree , providing no support for either the Silver Spoon or Environmental Matching Hypotheses. [ABSTRACT FROM AUTHOR]

The present study examined the adverse effects of fluoride exposure on embryos and larvae of Rana chensinensis . Survival, morphological abnormalities, growth and development, time to metamorphosis and size at metamorphic climax of R. chensinensis were examined. Our results showed that embryos malformation occurred in all fluoride treatments. Morphological abnormalities of embryos are characterized by axial flexures, the extrusion of fin axis, edema, and ruffled dorsal and ventral fin. Additionally, 4.1 mg F − /L and above could significantly inhibit embryos growth and development. On day 15, total length and weight of tadpole were significantly lower in 19.6 and 42.4 mg F − /L treatments compared to control. However, significant reductions in total length and weight were observed only at 42.4 mg F − /L on day 30. Moreover, significant metamorphic delay and decrease in the size at metamorphic climax were found in larvae exposed to 42.4 mg F − /L. Taken together, embryos of R. chensinensis are more vulnerable to fluoride exposure than their tadpoles. Our results suggested that the presence of high concentrations fluoride might increase mortality risk and a reduction in juvenile recruitment in the field by increasing embryos malformation, delaying metamorphosis and decreasing size at metamorphosis. [ABSTRACT FROM AUTHOR]

The Neotropical frog genera Ceratophrys, Chacophrys and Lepidobatrachus form the monophyletic family Ceratophryidae. Although in- and out-group relationships are not fully resolved, the monophyly of the three genera is well supported by both morphological and molecular data. Much is known about the morphology of the ceratophryids, but there is little comparative information on how modification of a common ancestral developmental pathway played a role in shaping their particular body plans. Herein, we review morphological variation during ceratophryid ontogeny in order to explore the role of development in their evolution. The ceratophryids are collectively characterized by rapid larval development with respect to other anurans, yet the three genera difer in their postmetamorphic growth rates to sexual maturity. Derived traits in the group can be divided into many homoplastic features that evolved in parallel with those of anurans with fossorial/burrowing behaviors in semiarid environments, and apomorphies. Morphological novelties have evolved in their feeding mechanism, which makes them capable of feeding on exceptional large prey. Lepidobatrachus is unusual in having reduced the ecomorphological differences between its larvae and adults. As a result, both the larvae and the frog are similarly able to capture large prey underwater. Some unique features in Lepidobatrachus are differentiated in the tadpole and then exaggerated in the adult (e.g., the posterior displaced jaw articulation) in a manner unobserved in any other anurans. [ABSTRACT FROM AUTHOR]

Chinese toad ( Bufo gargarizans ) tadpoles were exposed to copper (1, 6.4, 32 and 64 μg L −1 copper) from the beginning of larval period through completion of metamorphosis. We examined the effects of chronic copper exposure on mortality, growth, time to metamorphosis, tail resorption time, body size at the metamorphic climax (Gs 42) and completion of metamorphosis (Gs 46) and thyroid gland histology. In addition, type 2 and 3 iodothyronine deiodinase ( Dio2 and Dio3 ), thyroid hormone receptors (TRα and TRβ) mRNA levels were also measured to assess disruption of TH synthesis. Our result showed that 6.4–64 μg L −1 copper concentration increased the mortality and inhibited the growth of B. gargarizans tadpoles. In addition, significant reduction in size at Gs 42 and a time delay to Gs 42 were observed at 6.4–64 μg L −1 copper treatments. Moreover, histological examinations have clearly revealed that 64 μg L −1 copper caused follicular cell hyperplasia in thyroid gland. According to real-time PCR results, exposure to 32 and 64 μg L −1 copper significantly up-regulated mRNA expression of Dio3, but down-regulated mRNA expression of TRα and TRβ mRNA level. We concluded that copper delayed amphibian metamorphosis through changing mRNA expression of Dio3, TRα and TRβ, which suggests that copper might have the endocrine-disrupting effect. [ABSTRACT FROM AUTHOR]

Environmental conditions during early development in ectothermic vertebrates can lead to variation in vertebral number among individuals of the same species. It is often seen that individuals of a species raised at cooler temperatures have more vertebrae than individuals raised at warmer temperatures, although the functional consequences of this variation in vertebral number on swimming performance are relatively unclear. To investigate this relationship, we tested how vertebral number in axolotls ( Ambystoma mexicanum ) affected performance of aquatic escape responses (C-starts). Axolotls were reared at four temperatures (12–24 °C) encompassing their natural thermal range and then transitioned to a mean temperature (18 °C) three months before C-starts were recorded. Our results showed variation in vertebral number, but that variation was not significantly affected by developmental temperature. C-start performance among axolotls was significantly correlated with caudal vertebral number, and individuals with more caudal vertebrae were able to achieve greater curvature more quickly during their responses than individuals with fewer vertebrae. However, our results show that these individuals did not achieve greater displacements or velocities, and that developmental temperature did not have any effect on C-start performance. We highlight that the most important aspects of escape swim performance (i.e., how far individuals get from a threat and how quickly they move the most important parts of the body away from that threat) are consistent across individuals regardless of developmental temperature and morphological variation. [ABSTRACT FROM AUTHOR]

Numerous endocrine disrupting chemicals can affect the growth and development of amphibians. We investigated the effects of a targeted disruption of the endocrine axes modulating development and somatic growth. Wood frog ( Lithobates sylvaticus ) tadpoles were exposed for 2 weeks (from developmental Gosner stage (Gs) 25 to Gs30) to sodium perchlorate (SP, thyroid inhibitor, 14 mg/L), estradiol (E 2 , known to alter growth and development, 200 nM) and a reduced feeding regime (RF, to affect growth and development in a chemically-independent manner). All treatments experienced developmental delay, and animals exposed to SP or subjected to RF respectively reached metamorphic climax (Gs42) approximately 11(±3) and 17(±3) days later than controls. At Gs42, only SP-treated animals showed increased weight and snout-vent length ( P < 0.05) relative to controls. Tadpoles treated with SP had 10-times higher levels of liver igf1 mRNA after 4 days of exposure (Gs28) compared to controls. Tadpoles in the RF treatment expressed 6-times lower levels of liver igf1 mRNA and 2-times higher liver igf1r mRNA ( P < 0.05) at Gs30. Tadpoles treated with E 2 exhibited similar developmental and growth patterns as controls, but had increased liver igf1 mRNA levels at Gs28, and tail igf1r at Gs42. Effects on tail trβ mRNA levels were detected in SP-treated tadpoles at Gs42, 40 days post-exposure, suggesting that the chemical inhibition of thyroid hormone production early in development can have long-lasting effects. The growth effects observed in the SP-exposed animals suggest a relationship between TH-dependent development and somatic growth in L. sylvaticus tadpoles. [ABSTRACT FROM AUTHOR]

Temporary ponds, where many amphibians from temperate regions breed, show an annual cycle with a maximum water volume in spring followed by a progressive desiccation throughout late spring and summer. This desiccation leads to a decrease in dissolved oxygen and an increase in nitrogen levels, which can additionally increase because of anthropogenic sources such as chemical fertilizers. We analyzed the toxicity posed by environmentally relevant levels of a common nitrogenous fertilizer, ammonium nitrate, at different conditions of oxygen availability to Bufo calamita tadpoles, which typically develop in ephemeral ponds. Ammonium nitrate (90.3 mg N-NONH/l) and hypoxic conditions (initial dissolved oxygen 4.53 ± 0.40 mg/l) caused significant lethal effects after 7 and 12 days of exposure, respectively. At the end of experiment (16 days), mortality rates were 32.5 % in individuals exposed to the fertilizer and 15 % in those growing under hypoxic conditions. When both stressors were combined, they showed an additive effect on tadpole survival. Malformations, such as oedemas and spinal curvatures, and locomotory abnormalities, were detected after 12 days of experiment in >90 % of individuals exposed to 45.2 mg N-NONH/l under hypoxic conditions, whereas none of these stressors by separate related to abnormality rates >35 %. Delayed development was also observed in tadpoles exposed to ammonium nitrate with hypoxia affecting developmental rate only after 12 days of exposure. The results are discussed in terms of potential mechanisms linking negative effects of both factors as well as in terms of potential alterations of the ecological plasticity that often allows amphibians to survive in unpredictable environments. [ABSTRACT FROM AUTHOR]

Understanding skeletal diversification involves knowing not only how skeletal rudiments are shaped embryonically, but also how skeletal shape changes throughout life. The pharyngeal arch ( PA) skeleton of metamorphosing amphibians persists largely as cartilage and undergoes two phases of development (embryogenesis and metamorphosis) and two phases of growth (larval and post-metamorphic). Though embryogenesis and metamorphosis produce species-specific features of PA cartilage shape, the extents to which shape and size change during growth and metamorphosis remain unaddressed. This study uses allometric equations and thin-plate spline, relative warp and elliptic Fourier analyses to describe shape and size trajectories for the ventral PA cartilages of the frog Xenopus laevis in tadpole and frog growth and metamorphosis. Cartilage sizes scale negatively with body size in both growth phases and cartilage shapes scale isometrically or close to it. This implies that most species-specific aspects of cartilage shape arise in embryogenesis and metamorphosis. Contributions from growth are limited to minor changes in lower jaw (LJ) curvature that produce relative gape narrowing and widening in tadpoles and frogs, respectively, and most cartilages becoming relatively thinner. Metamorphosis involves previously unreported decreases in cartilage size as well as changes in cartilage shape. The LJ becomes slightly longer, narrower and more curved, and the adult ceratohyal emerges from deep within the resorbing tadpole ceratohyal. This contrast in shape and size changes suggests a fundamental difference in the underlying cellular pathways. The observation that variation in PA cartilage shape decreases with tadpole growth supports the hypothesis that isometric growth is required for the metamorphic remodeling of PA cartilages. It also supports the existence of shape-regulating mechanisms that are specific to PA cartilages and that resist local adaptation and phenotypic plasticity. [ABSTRACT FROM AUTHOR]

The focus of evolutionary behavioural ecologists has recently turned towards understanding the causes and consequences of behavioural consistency, manifesting either as animal personality (consistency in a single behaviour) or behavioural syndrome (consistency across more behaviours). Behavioural type (mean individual behaviour) has been linked to life-history strategies, leading to the emergence of the integrated pace-of-life syndrome (POLS) theory. Using Rana dalmatina tadpoles as models, we tested if behavioural consistency and POLS could be detected during the early ontogenesis of this amphibian. We targeted two ontogenetic stages and measured activity, exploration and risk-taking in a common garden experiment, assessing both individual behavioural type and intra-individual behavioural variation. We observed that activity was consistent in all tadpoles, exploration only became consistent with advancing age and risk-taking only became consistent in tadpoles that had been tested, and thus disturbed, earlier. Only previously tested tadpoles showed trends indicative of behavioural syndromes. We found an activity-age at metamorphosis POLS in the previously untested tadpoles irrespective of age. Relative growth rate correlated positively with the intra-individual variation of activity of the previously untested older tadpoles. In previously tested older tadpoles, intra-individual variation of exploration correlated negatively and intra-individual variation of risk-taking correlated positively with relative growth rate. We provide evidence for behavioural consistency and POLS in predator- and conspecific-naive tadpoles. Intra-individual behavioural variation was also correlated to life history, suggesting its relevance for the POLS theory. The strong effect of moderate disturbance related to standard behavioural testing on later behaviour draws attention to the pitfalls embedded in repeated testing. [ABSTRACT FROM AUTHOR]

We investigated the interaction between larvae of two anuran amphibian species ( Rana temporaria and Bufo bufo) to test models of two-species competition. The study had a response surface experimental design with four replicates, each consisting of 24 density combinations. Larval performance-and, by assumption, change in population size-was defined by a linear combination of survival, growth, and development. We fit six competition models from the literature and discovered that density dependence was strongly non-linear, with the highest support for the Hassel-Comins model. Rana temporaria was competitively superior to B. bufo; the impacts of both species on growth and development were about five- to tenfold greater than those on survival. Isocline analysis predicted a stable configuration, which agrees with the observation that these two species are syntopic in nature. The results of this study confirm competition theory by identifying a model structure that agrees with data and making predictions that are broadly supportive of the observations. [ABSTRACT FROM AUTHOR]

Amphibians vary in the degree of pre-metamorphic developmental plasticity in response to risk of predation. Changes in hatching time and development rate can increase egg or tadpole survival respectively by shortening the duration of the more vulnerable stages. The intensity of predator induced developmental response and its direction, i.e. delayed, accelerated, or none, varies considerably between amphibian and predator species. We surveyed freshly deposited clutches of the European common frog Rana temporaria in a population in Braunschweig, Germany and found that 62% (N = 20) of the clutches contained planarians (Schmidtea nova), with an average of 3.94 ± 0.79 and a maximum of 13 planarians per clutch. A laboratory predation experiment confirmed that this planaria preys on R. temporaria eggs and early embryos. We further exposed freshly laid egg masses to either free, caged, or no planarians treatments using floating containers within a breeding pond where the two species co-occur. After 10 days exposure, embryos showed developmental stages 14-25 along the Gosner scale with statistically significant positive effects of both predator treatments. The observed effect was rather slight as predator-exposed individuals showed an increase by a single Gosner stage relative to those raised without planarians. The detected trend suggests that direct and indirect cues from flatworms, rarely considered as anuran predators, might induce a developmental response in R. temporaria early developmental stages. [ABSTRACT FROM AUTHOR]

One widely documented phenological response to climate change is the earlier occurrence of spring-breeding events. While such climate change-driven shifts in phenology are common, their consequences for individuals and populations have rarely been investigated. I addressed this gap in our knowledge by using a multi-year observational study of six wood frog ( Rana sylvatica) populations near the southern edge of their range. I tested first if winter temperature or precipitation affected the date of breeding and female fecundity, and second if timing of breeding affected subsequent larval development rate, mass at metamorphosis, date of metamorphosis, and survival. Warmer winters were associated with earlier breeding but reduced female fecundity. Winter precipitation did not affect breeding date, but was positively associated with female fecundity. There was no association between earlier breeding and larval survival or mass at metamorphosis, but earlier breeding was associated with delayed larval development. The delay in larval development was explained through a counterintuitive correlation between breeding date and temperature during larval development. Warmer winters led to earlier breeding, which in turn was associated with cooler post-breeding temperatures that slowed larval development. The delay in larval development did not fully compensate for the earlier breeding, such that for every 2 days earlier that breeding took place, the average date of metamorphosis was 1 day earlier. Other studies have found that earlier metamorphosis is associated with increased postmetamorphic growth and survival, suggesting that earlier breeding has beneficial effects on wood frog populations. [ABSTRACT FROM AUTHOR]

Sex in many reptiles is determined by temperature during development (temperature-dependent sex determination; TSD) rather than by an individual's genotype (genotypic sex determination; GSD). TSD has numerous ecological and evolutionary implications, and whether or not species display TSD is of conservation concern because substantial habitat and climate change have the potential to skew sex ratios. It is therefore important to describe the means by which sex is determined in reptile species. To date, the sex determination mechanism is not known for any species within the Anguidae, a diverse lizard family that is globally distributed. I used controlled incubation experiments to test the hypothesis that Southern Alligator Lizards ( Elgaria multicarinata) display TSD. Offspring sex was assessed by direct examination of the gonads after incubation in one of five constant-temperature treatments (24°, 26°, 28°, 30°, and 32°C). Developmental temperature did not affect offspring sex, indicating that E. multicarinata does not display a strict form of TSD. Rather, my results indicate that E. multicarinata displays GSD, as is most common in vertebrates, although I cannot rule out the possibility that sex determination is somewhat thermally sensitive. Further work with additional samples and other anguid species is clearly needed. [ABSTRACT FROM AUTHOR]

Amphibian population declines are widespread; the main causal factors are human related and include habitat fragmentation due to agriculture, mining, fires, and urban development. Brazil is the richest country in species of amphibians, and the Brazilian regions with the greatest amphibian diversity are experiencing relatively high rates of habitat destruction, but there are presently relatively few reports of amphibian declines. It is thus important to develop research methods that will detect deterioration in population health before severe declines occur. We tested the use of measurements of fluctuating asymmetry (FA) taken on amphibian larvae to detect anthropogenic stress. We hypothesized that greater human occupancy in the landscape might result in more stressful conditions for amphibians. We conducted this study at the Espinhaço mountain range in southeastern Brazil, using as a model an endemic species (Bokermannohyla saxicola, Hylidae). We chose two tadpole denticle rows and eye-nostril distance as traits for FA measurement. We measured percent cover of human-altered habitats in the landscape around tadpole sampling points and measured FA levels in sampled tadpoles. We found FA levels to differ among localities but found no relationship between human modification of the landscape and tadpole FA levels. Levels of FA in the traits we examined may not be strongly affected by environmental conditions, or may be affected by local variables that were not captured by our landscape-scale measures. Alternatively, populations may be genetically differentiated, affecting how FA levels respond to stress and obscuring the effects of anthropogenic disturbance. [ABSTRACT FROM AUTHOR]

Every living organism on earth has developed and evolved in unit gravity (1G) conditions. It is likely that any deviation from earth's standard gravity will influence development, particularly at early stages. Previous reports from this lab showed that total length is reduced and that ventricle size is increased during development at 7G. The objective of the present study was to investigate the effect of increasing levels of hypergravity on the development of the ventricular myocardial wall and the neuromuscular responsiveness of Xenopus laevis. At early gastrulation, embryos were placed in a centrifuge simulating 7G, 10G, 15G or 17G until they reached stage 45 (feeding tadpole stage, approximately 72 hours from initiation of gastrulation). Mortality was low and only the 17G exposure induced significant mortality. Immediately following centrifugation, the embryos were stimulated by touching with a probe to test neuromuscular responsiveness. With increasing G forces, responsiveness to this test was incrementally reduced. A quarter of the embryos were fixed and their body dimensions were measured. One group of remaining live embryos, those exposed to 7G, was maintained and swimming behavior was observed during daily 5-minute periods for 52 days. Overall, abnormal swimming behavior was found in 33% of 7G embryos and in 2% of controls during this time. These embryos were later subjected to an orientation-swimming test. Hypergravity-exposed embryos required, on average, one second longer (9% of time required) to become oriented. From the embryos exposed to increasing G levels and then fixed, we found that total length was reduced successively at increasing hypergravity levels, but the snout-vent proportion of total length increased. Stained sections of the fixed embryos revealed that the thickness of the ventricle wall was increased, especially the interior ridge component (trabeculae/papillary muscles). The data demonstrates that hypergravity has persistent effects on the development of the ventricular myocardial wall, neuromuscular responsiveness, and equilibrium organs. [ABSTRACT FROM AUTHOR]

Urodele amphibians have remarkable organ regeneration capability, and their limb regeneration capability has been investigated as a representative phenomenon. In the early 19th century, nerves were reported to be an essential tissue for the successful induction of limb regeneration. Nerve substances that function in the induction of limb regeneration responses have long been sought. A new experimental system called the accessory limb model (ALM) has been established to identify the nerve factors. Skin wounding in urodele amphibians results in skin wound healing but never in limb induction. However, nerve deviation to the wounded skin induces limb formation in ALM. Thus, nerves can be considered to have the ability to transform skin wound healing to limb formation. In the present study, co-operative Bmp and Fgf application, instead of nerve deviation, to wounded skin transformed skin wound healing to limb formation in two urodele amphibians, axolotl ( Ambystoma mexicanum ) and newt ( Pleurodeles waltl ). Our findings demonstrate that defined factors can induce homeotic transformation in postembryonic bodies of urodele amphibians. The combination of Bmp and Fgf(s) may contribute to the development of novel treatments for organ regeneration. [ABSTRACT FROM AUTHOR]

ABSTRACT Despite their divergent morphology, extant and extinct amphibians share numerous features in the timing and spatial patterning of dermal skull elements. Here, I show how the study of these features leads to a deeper understanding of morphological evolution. Batrachians (salamanders and frogs) have simplified skulls, with dermal bones appearing rudimentary compared with fossil tetrapods, and open cheeks resulting from the absence of other bones. The batrachian skull bones may be derived from those of temnospondyls by truncation of the developmental trajectory. The squamosal, quadratojugal, parietal, prefrontal, parasphenoid, palatine, and pterygoid form rudimentary versions of their homologs in temnospondyls. In addition, failure to ossify and early fusion of bone primordia both result in the absence of further bones that were consistently present in Paleozoic tetrapods. Here, I propose a new hypothesis explaining the observed patterns of bone loss and emargination in a functional context. The starting observation is that jaw-closing muscles are arranged in a different way than in ancestors from the earliest ontogenetic stage onwards, with muscles attaching to the dorsal side of the frontal, parietal, and squamosal. The postparietal and supratemporal start to ossify in a similar way as in branchiosaurids, but are fused to neighboring elements to form continuous attachment areas for the internal adductor. The postfrontal, postorbital, and jugal fail to ossify, as their position is inconsistent with the novel arrangement of adductor muscles. Thus, rearrangement of adductors forms the common theme behind cranial simplification, driven by an evolutionary flattening of the skull in the batrachian stem. J. Exp. Zool. (Mol. Dev. Evol.) 322B: 619-630, 2014. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]