Instrumental appetitive extinction involves the reduction of a previously reinforced response when its occurrence is no longer rewarded. Two experiments with terrestrial toads (Rhinella arenarum) tested whether the occurrence of a nonreinforced response is necessary for response extinction by varying the time of exposure to nonrewarded goal-box stimuli across groups. In Experiment 1, toads that received the same acquisition training (15 sessions, 1 session/day, 300 s of access to water in the goal box) were randomly assigned to two groups. In Group 600 (n=12), animals spent 600 s in the goal box in 8 daily extinction sessions (water present but inaccessible). In Group 0 (n=11), toads performed the runway response (i.e., walking from the start to the goal box) but were removed as soon as they entered the goal box, thus having minimal exposure to nonrewarded goal-box stimuli. The runway response was weakened in Group 600 across extinction trials, but exhibited little change in Group 0. In Experiment 2, toads were randomly assigned to two groups after the same acquisition training. Group 0 (n=7) was treated the same as Group 0 in the previous experiment. In Group RI (retention interval, n=7), toads remained in their home cage for 13 days. Finally, all animals received 4 extinction sessions with 300 s in the empty goal box. There was little behavioral change in Group 0 during the 13 sessions with minimal exposure to the goal box. In extinction, both groups reduced their runway response at similar rates. Although the procedures were instrumental, extinction of the runway response in toads can be accounted for in terms of a Pavlovian approach response to stimuli paired with reward and nonreward in the goal box.

UNASSIGNED: Skin secretions of toads are widely used in medicine all over the world for their antiviral, anti-infective, and cardiotonic properties. Because these secretions are mostly employed to combat blood parasite infection, it is important to understand their potential toxic effects on human erythrocytes. Therefore, the objective of the current investigation was to elucidate the effects of Duttaphrynus melanostictus (Schneider) skin extracts on the physiology of human erythrocytes.
UNASSIGNED: Toads captured from their natural habitat were separated into three groups according to their body size. Hydroalcoholic extracts of toad skin were prepared by reflux heating. These extracts were then evaluated for their hemolytic and hemoglobin denaturation potential. The effects of the extracts on cytosolic and membrane-bound enzymes of human erythrocytes were assessed.
UNASSIGNED: The hemolysis and hemoglobin denaturation caused by these extracts correlated positively with the respective toad sizes. Extracts from medium and large toads led to increased osmotic fragility even at near iso-osmotic concentrations. Biochemical analysis of hemolysate showed that the treatment induced a shift of metabolic flux toward the glutathione pathway. Analysis of membrane-bound enzymes revealed a significant decrease in the activity of Na+/K+ ATPase and acetylcholinesterase. SDS-PAGE analysis of the erythrocyte membrane did not show the band of tropomodulin for the cells treated with 1000 𝜇g/ml extract from large toads.
UNASSIGNED: In conclusion, the present study demonstrates that the toxicity of toad skin secretions aggravates with the size of the animal and interferes with the physiology of human erythrocytes, leading to their membrane disruption and rapid lysis.

Amphibians are widely known as a prolific source of bioactive metabolites. In this work, we isolated and characterized compounds with antiparasitic activity from the oocytes of the toad Rhinella alata collected in Panama. Bio-guided isolation and structural elucidation were carried out using chromatographic and spectroscopic techniques, respectively. The organic extract was subjected to solid phase extraction followed by HPLC purification of the fraction with in vitro activity against Trypanosoma cruzi trypomastigotes. Seven steroids (1-7) of the bufadienolide family were isolated, and their structures were determined using NMR and MS analyses; of these 19-formyl-dyscinobufotalin, (3) is reported as a new natural product. Compounds 1 and 3-7 resulted in a good anti-trypanosomal activity profile. Among these, 16β-hydroxyl-hellebrigenin (1) and bufalin (7) showed significant selectivity values of >5 and 2.69, respectively, while the positive control benznidazole showed a selectivity of 18.81. Furthermore, molecular docking analysis showed compounds 1, 3 and 7 interact through H-bonds with the amino acid residues GLN-19, ASP-158, HIS-159 and TRP-177 from cruzipain at the catalytic site. Given the lack of therapeutic options to treat American trypanosomiasis, this work can serve as the basis for further studies that aim for the development of bufadienolides or their derivatives as drugs against Chagas disease.

The outcomes of species interactions can vary by life stage, year, and surrounding environmental conditions. Amphibian species are expected to compete most strongly during their tadpole stage when they exist in the highest densities. Changes in arrival timing, surrounding aquatic communities, and yearly conditions could all affect the outcome of larval competition. In Long Point, Ontario, the Fowler\'s toad (Anaxyrus fowleri) is at the northern edge of its range and overlaps with the more common American toad (Anaxyrus americanus). Both species breed in ponds that encounter high inter-annual variation. To determine whether these species compete strongly, and if this effect was replicated across multiple years, we raised both species as tadpoles together and, apart, in mesocosms in 2018 and 2021. We measured survivorship to, weight at, and time to metamorphosis for both species in both years. We determined that the presence of American toad tadpoles consistently had a detrimental effect on Fowler\'s toad tadpoles, even though this effect presented itself differently across years. Our study suggests that competitive exclusion by American toads could be occurring at the edge of the Fowler\'s toad\'s range. This study further demonstrates the importance of studying communities across multiple years to understand the full scope of species interactions.

Amphibians are more threatened than any other vertebrate class, yet evidence for many threats is missing. The Cape lowland fynbos (endemic scrub biome) is threatened by habitat loss, and natural temporary freshwater habitats are removed in favour of permanent impoundments. In this study, we determine amphibian assemblages across different freshwater habitat types with special attention to the presence of invasive fish. We find that anuran communities differ primarily by habitat type, with permanent water habitats having more widespread taxa, while temporary water bodies have more range restricted taxa. Invasive fish are found to have a significant impact on frogs with toads most tolerant of their presence. Temporary freshwater habitats are a conservation priority in the area, and their amphibian assemblages represent endemic taxa that are intolerant of invasive fish. Conservation of a biodiverse amphibian assemblage in lowland fynbos areas will rely on the creation of temporary freshwater habitats, rather than a northern hemisphere pond based solution.

This review summarizes the role of environmental factors on amphibian microbiotas at the organismal, population, community, ecosystem, and biosphere levels. At the organismal-level, tissue source, disease status, and experimental manipulations were the strongest predictors of variation in amphibian microbiotas. At the population-level, habitat quality, disease status, and ancestry were commonly documented as drivers of microbiota turnover. At the community-level, studies focused on how species\' niche influence microbiota structure and function. At the ecosystem-level, abiotic and biotic reservoirs were important contributors to microbiota structure. At the biosphere-level, databases, sample banks, and seminatural experiments were commonly used to describe microbiota assembly mechanisms among temperate and tropical amphibians. Collectively, our review demonstrates that environmental factors can influence microbiotas through diverse mechanisms at all biological scales. Importantly, while environmental mechanisms occurring at each of the different scales can interact to shape microbiotas, the past 10 years of research have mostly been characterized by targeted approaches at individual scales. Looking forward, efforts considering how environmental factors at multiple organizational levels interact to shape microbiota diversity and function are paramount. Generating opportunities for meaningful cross-disciplinary interactions and supporting infrastructure for research that spans biological scales are imperative to addressing this gap.

High-elevation adaptation provides an excellent system for examining adaptive evolution, and adaptive variations may manifest at gene expression or any other phenotypic levels. We examined gene expression profiles of Asiatic toads (Bufo gargarizans) along an elevational gradient from both wild and common-garden acclimated populations. Asiatic toads originated from high altitudes have distinctive gene expression patterns. We identified 18 fixed differentially expressed genes (DEGs), which are different in both wild and acclimated samples, and 1217 plastic DEGs, which are different among wild samples. The expression levels of most genes were linearly correlated with altitude gradient and down-regulated in high-altitude populations. Expression variations of several genes associated with metabolic process are fixed, and we also identified a co-expression module that is significantly different between acclimated populations and has functions related to DNA repair. The differential expression of the vast majority genes, however, are due to phenotypic plasticity, revealing the highly plastic nature of gene expression variations. Expression modification of some specific genes related to metabolism and response to UV radiation play crucial role in adaptation to high altitude for Asiatic toads. Common-garden experiments are essential for evaluating adaptive evolution of natural populations.

The medial pallium (MP) of amphibians is the homologue of the mammalian hippocampus, and previous research has implicated MP for locating a using the boundary geometry of an environment. MP-lesioned, sham-operated and intact control terrestrial toads, Rhinella arenarum, were trained to locate a goal in a rectangular arena with a visual feature cue placed on one of the short walls. Whereas the sham-operated and intact subjects successfully learned to locate the goal, the MP-lesioned toads showed no evidence of learning. The data support the hypothesis that the amphibian MP is involved when the boundary geometry of an environment is used to locate a goal, which is consistent with evidence from other vertebrate groups. Curious, however, is that the MP lesions also resulted in the toads\' inability to locate the goal based on the visual feature cue. This result supports previous research and suggests that, in contrast to the hippocampal homologue of amniotes, the amphibian medial pallium plays a broader role in spatial learning processes.

Prior research with terrestrial toads (Rhinella arenarum) in a water-reinforced instrumental situation indicated a direct relationship between acquisition rate and reward magnitude. However, a reward downshift produced a gradual adjustment of instrumental performance and a rapid adjustment of consummatory performance, rather than the abrupt and transient deterioration of behavior typical of a successive negative contrast effect. In Experiment 1, using a two-chamber box, a downshift from deionized water (which supports maximal rehydration) to 250-mM sodium chloride solution (which supports a lower rehydration), also yielded a gradual adjustment of instrumental behavior. In this experiment, animals received one trial per day and were allowed 300 s of access to the reward in the goal box. Experiment 2 used the same procedure, except that animals were allowed access to the solution in the goal box for 600 s. Under these conditions, reward downshift led to longer latencies (instrumental) and lower rehydration levels (consummatory) than those of unshifted controls, providing evidence for successive negative contrast. Unlike in similar experiments with mammals, the effect was not transient, but persisted relatively unmodified over twelve daily postshift trials. In this case, the possibility of adaptation of the peripheral mechanisms for water uptake is considered. The comparative relevance of these results is discussed in terms of habit formation versus expectancy-guided behavior in vertebrate learning.

To date, there has been no published investigation on the trophic diversity in any tepui summit vertebrate. In this paper, we analyzed the dietary composition of a tepui summit endemic toad, Oreophrynella quelchii from Roraima-tepui, and compared it with that of O. nigra from Kukenán-tepui, to examine to what extent diet differs between these two sister species across isolated, although neighboring, tepui tops. The digestive tracts of a total of 197 toads were dissected: 111 from O. quelchii and 86 from O. nigra. The diet composition of O. quelchii was relatively diverse, with 13 major prey categories; mites (Acari, 36.5%) and beetles (Coleoptera, 21.0%) numerically dominated its diet. Despite occurring on two different tepui summits, O. quelchii and O. nigra exhibited a similar diet composition, although in O. nigra mites (Acari, 42.4%) and hymenopterans (especially ants, 16.9%) numerically dominated the diet. The present data suggest that tepui summit Oreophrynella species are flexible in their diet and are active foragers that also feed on aquatic arthropods, successful strategies in tepui competitive environments.