Tadpole Morphology Research Articles

Don’t go with the flow: cranial adaptations of stream tadpoles in the Afrobatrachian family Arthroleptidae

Abstract Arthroleptidae are an ecologically diverse group of sub-Saharan frogs. Arthroleptid tadpoles predominately occur in slow flowing to torrent waters. Their musculoskeletal system and the relationship between tadpole morphology and lifestyle are poorly understood. Here, we investigated the cranial morphology of four arthroleptid tadpoles occurring in different microhabitats: Leptopelis parkeri, Astylosternus occidentalis, Trichobatrachus robustus, and Nyctibates corrugatus. The crania of the tadpoles of A. occidentalis, N. corrugatus, and T. robustus are highly modified relative to L. parkeri, with wide and partly or completely fused cornua trabeculae, a fused cartilago labialis superior, as well as several modifications of the palatoquadrate, such as a broad commissura quadratocranialis and a processus ventralis which expands the surface for the origin of the large m. orbitohyoideus. The processus hyoquadratis is an evolutionary novelty, forming a functional unit together with the ceratohyale in the cranium of N. corrugatus. Finally, we compared the cranial morphology of these arthroleptids to other lotic and non-lotic species. Although the processus ventralis is not a generalized feature of the cranium in lotic species, it is not present in lentic species.

Effects of amphibian genetic diversity on ecological communities.

The amount of genetic diversity within a population can affect ecological processes at population, community, and ecosystem levels. However, the magnitude, consistency, and scope of these effects are largely unknown. To investigate these issues, we conducted two experiments manipulating the amount of genetic diversity and environmental factors in larval amphibians. The first experiment manipulated wood frog genetic diversity, the presence or absence of caged predators, and competition from leopard frogs to test whether these factors affected survival, growth, and morphology of wood frogs and leopard frogs. The second experiment manipulated wood frog genetic diversity, the presence or absence of uncaged predators, and resource abundance to test whether these factors affected wood frog traits (survival, morphology, growth, development, and behavior) and other components of the ecological community (zooplankton abundance, phytoplankton, periphyton, and bacterial community structure). Genetic diversity did not affect wood frog survival, growth, and development in either experiment. However, genetic diversity did affect the mean morphology of wood frog tadpoles in the first experiment and the abundance and distribution of zooplankton in the second experiment. It did not affect phytoplankton abundance, periphyton abundance, or bacterial community structure. While effect sizes (Cohen's d) of genetic diversity were approximately half those of environment treatments, the greatest effect sizes were for interaction effects between genetic diversity and environment. Our results indicate that genetic diversity can have a large effect on ecological processes, but the direction of those effects is highly dependent upon environmental conditions, and not easily predicted from simple measures of traits.

Impacts of Exposure to Ultraviolet Radiation and an Agricultural Pollutant on Morphology and Behavior of Tadpoles (Limnodynastes tasmaniensis).

Amphibians are the most threatened vertebrate class globally. Multiple factors have been implicated in their global decline, and it has been hypothesized that interactions between stressors may be a major cause. Increased ultraviolet (UV) radiation, as a result of ozone depletion, has been identified as one such stressor. Exposure to UV radiation has been shown to have detrimental effects on amphibians and can exacerbate the effects of other stressors, such as chemical pollutants. Chemical pollution has likewise been recognized as a major factor contributing to amphibian declines, particularly, endocrine-disrupting chemicals. In this regard, 17β-trenbolone is a potent anabolic steroid used in the agricultural industry to increase muscle mass in cattle and has been repeatedly detected in the environment where amphibians live and breed. At high concentrations, 17β-trenbolone has been shown to impact amphibian survival and gonadal development. In the present study, we investigated the effects of environmentally realistic UV radiation and 17β-trenbolone exposure, both in isolation and in combination, on the morphology and behavior of tadpoles (Limnodynastes tasmaniensis). We found that neither stressor in isolation affected tadpoles, nor did we find any interactive effects. The results from our 17β-trenbolone treatment are consistent with recent research suggesting that, at environmentally realistic concentrations, tadpoles may be less vulnerable to this pollutant compared to other vertebrate classes. The absence of UV radiation-induced effects found in the present study could be due to species-specific variation in susceptibility, as well as the dosage utilized. We suggest that future research should incorporate long-term studies with multiple stressors to accurately identify the threats to, and subsequent consequences for, amphibians under natural conditions. Environ Toxicol Chem 2024;43:1615-1626. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Shape Evolution in Two Acts: Morphological Diversity of Larval and Adult Neoaustraranan Frogs.

Phenotypic traits can evolve independently at different stages of ontogeny, optimizing adaptation to distinct ecological contexts and increasing morphological diversity in species with complex life cycles. Given the relative independence resulting from the profound changes induced by metamorphosis, niche occupation and resource utilization in tadpoles may prompt evolutionary responses that do not necessarily affect the adults. Consequently, diversity patterns observed in the larval shape may not necessarily correspond to those found in the adult shape for the same species, a premise that can be tested through the Adaptive Decoupling Hypothesis (ADH). Herein, we investigate the ADH for larval and adult shape differentiation in Neoaustrarana frogs. Neoaustrarana frogs, particularly within the Cycloramphidae family, exhibit remarkable diversity in tadpole morphology, making them an ideal model for studying adaptive decoupling. By analyzing 83 representative species across four families (Alsodidae, Batrachylidae, Cycloramphidae, and Hylodidae), we generate a morphological dataset for both larval and adult forms. We found a low correlation between larval and adult shapes, species with a highly distinct larval shape having relatively similar shape when adults. Larval morphological disparity is not a good predictor for adult morphological disparity within the group, with distinct patterns observed among families. Differences between families are notable in other aspects as well, such as the role of allometric components influencing shape and morphospace occupancy. The larval shape has higher phylogenetic structure than the adult. Evolutionary convergence emerges as a mechanism of diversification for both larval and adult shapes in the early evolution of neoaustraranans, with shape disparity of tadpoles reaching stable levels since the Oligocene. The widest occupation in morphospace involves families associated with dynamically changing environments over geological time. Our findings support the ADH driving phenotypic diversity in Neoaustrarana, underscoring the importance of considering ontogenetic stages in evolutionary studies.

A hundred-year-old mystery—the reproductive mode and larval morphology of the enigmatic frog genus Allophryne (Amphibia; Anura; Allophrynidae)

Frogs of the Allophrynidae are an enigmatic family from South America. To date, published information is lacking regarding this group’s reproductive biology and larval morphology. Here, we provide the first detailed description of the reproductive mode, developmental mode, and tadpole morphology for Allophryne ruthveni. We developed a captive breeding and rearing protocol for this species and then conducted a series of observations to describe aspects of its reproductive biology. In captivity, this species exhibits aquatic oviposition, where single eggs are laid ungrouped within a simple jelly capsule and are scattered free in the water column before sinking to develop on benthic substrates. We did not observe parental care nor any parental interactions with eggs post-fertilization. Tadpoles are characterized by an oval body, anteroventral oral disc, a labial tooth row formula of 2(2)/3, and a dextral vent tube. The buccopharyngeal cavity is marked by the presence of two pairs of infralabial papilla and four lingual papillae. Cranial morphology is characterized by the presence of the commissura quadratoorbital. This species possesses an additional slip of the m. rectus cervicis and of the m. levator arcuum branchialium III. We discuss our results in comparison with glassfrogs (Centrolenidae).

A new snouted treefrog (Anura, Hylidae, Scinax) from fluvial islands of the Juruena River, southern Brazilian Amazonia.

Southern Amazonia is one of the less-explored regions by anuran taxonomists. We describe a small new species of snouted treefrog, genus Scinax, from this region, from a fluvial archipelago in the Juruena River, state of Mato Grosso, Brazil. The description is based on external morphology of adults and tadpoles, advertisement call and molecular data. The species is phylogenetically related to other snouted treefrogs of the Scinax cruentomma species group and shows the most southeastern distribution in Amazonia among its close relatives. It is distinguished from congeners mainly by its larger adult body size and bilobate vocal sac that reaches the level of the pectoral fold, a reddish-brown horizontal stripe on the iris, dark melanophores or blotches on the vocal sac and the throat of females, and the uniformly brown posterior portion of the thigh. The advertisement call comprises one pulsed note emitted at regular intervals, with a duration of 189-227 ms, 30-35 pulses/note and a dominant frequency of 2,250-2,344 Hz. The type locality is suffering several environmental impacts, including illegal mining, overfishing, unsustainable agriculture, uncontrolled logging and degradation associated with the construction of new hydroelectric dams. Further study of the biology and regional distribution of the new species is required to propose mitigation measures needed for its conservation.

Morphological, acoustic and genetic identification of a reproducing population of the invasive African clawed frog Xenopuslaevis (Anura, Pipidae) recently discovered in Belgium.

Using external morphology of adults and tadpoles, osteology from high-resolution microcomputed tomography, vocalization analysis, and DNA sequence data, the identity of a reproducing Belgian population of invasive Xenopus at the current northernmost edge of the distribution of the genus in Europe was assessed. All data concur to an identification as Xenopus (Xenopus) laevis (Daudin, 1802). Genetically it is most closely related to populations of the Cape region in South Africa. No studies on the natural history of the Belgian Xenopus population and its impact on the local environment have been made to date.

Gut microbiota perturbations during larval stages in Bufo gargarizans tadpoles after Cu exposure with or without the presence of Pb

Cu and Pb are ubiquitous environmental contaminants, but there is limited information on their potential impacts on gut microbiota profile in anuran amphibians at different developmental stages during metamorphosis. In this study, Bufo gargarizans tadpoles were chronically exposed to Cu alone or Cu combined with Pb from Gs26 throughout metamorphosis. Morphology of tadpoles, histological characteristic and bacterial community of intestines were evaluated at three developmental stages: Gs33, Gs36, and Gs42. Results showed that Cu and Cu + Pb exposure caused various degrees of morphological and histological changes in guts at tested three stages. In addition, bacterial richness and diversity in tadpoles especially at Gs33 and Gs42 were disturbed by Cu and Cu + Pb. Beta diversity demonstrated that the bacterial community structures were influenced by both heavy metals exposure and developmental stages. Alterations in taxonomic composition were characterized by increased abundance of Proteobacteria and Firmicutes, reduction of Fusobacteriota, as well as decreased Cetobacterium and increased C39 at all three stages. Overall, response of gut bacterial diversity and composition to Cu stress depends on the developmental stage, while the altered patterns of bacterial community at Cu stress could be modified further by the presence of Pb. Moreover, predicted metabolic disorders were associated with shifts in bacterial community, but needs integrated information from metagenomic and metatranscriptomic analyses. These results contribute to the growing body of research about potential ecotoxicological effects of heavy metals on amphibian gut microbiota during metamorphosis.

Morphological anomalies of tadpoles from a contaminated stream in the state of Tlaxcala, Mexico

The contamination of aquatic systems by anthropogenic activities may impact amphibian populations by causing malformation and death in tadpoles. However, there often needs to be more information regarding environmental pollutants' effects on amphibians, such as contaminated systems from the state of Tlaxcala in Mexico. This study reports on morphological abnormalities observed in Lithobates spectabilis tadpoles found in a stream of three sites monitored in Tlaxcala. The tadpoles presented swollen heads, edema, intestinal hemorrhage, anomalies in the mouth, a deviated tail, and underdeveloped tail fins. We hypothesise that these abnormalities have been caused by exposure to contamination from nearby communities, including garbage and sewage pumped directly into the stream. This research provides the first report on the potential adverse effects of contaminant exposure on tadpole development and morphology in this region. Identifying malformations in tadpoles could help detect contaminants in aquatic systems for further analysis. Keywords: Lithobates spectabilis, pollutants, anthropogenic, edema, abnormalities

Tadpoles of Papurana milleti (Amphibia: Anura): molecular identification and morphological description

Based on molecular identification, we described the tadpole morphology of Dalat forest frog, Papurana milleti. Twenty tadpole specimens of P. milleti (Gosner stage 25–42) were collected from Di Linh plateau, southern Vietnam. Detailed descriptions of external morphological features, morphometric measurements, color patterns in life and in preservation and ecological notes are provided. Tadpoles of P. milleti are distinguished from those of its congeners by having yellowish brown body, LTRF 2(2)/3(1) and single submarginal papillae from the lateral of row P-1 to under row P-3.

Novel predator-induced phenotypic plasticity by hemoglobin and physiological changes in the brain of Xenopus tropicalis.

Organisms adapt to changes in their environment to survive. The emergence of predators is an example of environmental change, and organisms try to change their external phenotypic systems and physiological mechanisms to adapt to such changes. In general, prey exhibit different phenotypes to predators owing to historically long-term prey-predator interactions. However, when presented with a novel predator, the extent and rate of phenotypic plasticity in prey are largely unknown. Therefore, exploring the physiological adaptive response of organisms to novel predators is a crucial topic in physiology and evolutionary biology. Counterintuitively, Xenopus tropicalis tadpoles do not exhibit distinct external phenotypes when exposed to new predation threats. Accordingly, we examined the brains of X. tropicalis tadpoles to understand their response to novel predation pressure in the absence of apparent external morphological adaptations. Principal component analysis of fifteen external morphological parameters showed that each external morphological site varied nonlinearly with predator exposure time. However, the overall percentage change in principal components during the predation threat (24h) was shown to significantly (p < 0.05) alter tadpole morphology compared with that during control or 5-day out treatment (5days of exposure to predation followed by 5days of no exposure). However, the adaptive strategy of the altered sites was unknown because the changes were not specific to a particular site but were rather nonlinear in various sites. Therefore, RNA-seq, metabolomic, Ingenuity Pathway Analysis, and Kyoto Encyclopedia of Genes and Genomes analyses were performed on the entire brain to investigate physiological changes in the brain, finding that glycolysis-driven ATP production was enhanced and ß-oxidation and the tricarboxylic acid cycle were downregulated in response to predation stress. Superoxide dismutase was upregulated after 6h of exposure to new predation pressure, and radical production was reduced. Hemoglobin was also increased in the brain, forming oxyhemoglobin, which is known to scavenge hydroxyl radicals in the midbrain and hindbrain. These suggest that X. tropicalis tadpoles do not develop external morphological adaptations that are positively correlated with predation pressure, such as tail elongation, in response to novel predators; however, they improve their brain functionality when exposed to a novel predator.

Early life experience with predators impacts development, behavior, and post‐translocation outcomes in an endangered amphibian

AbstractPre‐release training is becoming a standard practice in conservation breeding and translocation programs for mammals and birds, but is still relatively neglected for herpetofauna, likely stemming from widespread beliefs that amphibians are “hard‐wired” and are thus predicted to benefit little from experiential learning. However, experience during development can drive both morphological and behavioral modifications that could benefit post‐translocation survival. Here, we developed an anti‐predator training program for the endangered mountain yellow‐legged frog Rana muscosa and evaluated its impact on morphometrics, developmental rates, behavior, and post‐release outcomes. Using a controlled, balanced factorial experimental design, we exposed individuals at two developmental stages (tadpoles and post‐metamorphic) to visual and olfactory cues from one of its principal predators, the two‐striped garter snake Thamnophis hammondii. We found that exposure to predators during the tadpole stage impacted tadpole development, morphology, and behavior. However, we found no evidence that post‐metamorphic behavior or post‐release outcomes were influenced by tadpole predator exposure, either on its own or in interaction with post‐metamorphic training treatments. Training of post‐metamorphic frogs, however, yielded evidence of learning, with downstream effects on behavior and apparent survival after release into the wild. Our findings produce novel insights on the value of anti‐predator training in amphibian conservation translocation programs, bolster recent evidence re‐evaluating the importance of learning and developmental experience for amphibian species, and provide guidance for selecting optimal developmental windows for training.

Man-made check dams alter tadpole growth and activity

Some tadpoles living in the Himalaya were recently discovered to be overwintering in cold stream water. We asked how the modification of these stream habitats by check dams installed for water extraction influences tadpole behaviour and morphology. We found tadpoles living in check dam pools are showing variations in body size and activity pattern from the ones in natural pools.

Rediscovery and phylogenetic position of the glassfrog "Centrolene"acanthidiocephalum (Ruiz-Carranza and Lynch, 1989) (Anura: Centrolenidae)with the description of its advertisement call and comments on clutches and tadpoles.

The lack of basic natural history and distributional data represents a challenge for the conservation of rare and endemic amphibian species. This is the case of "Centrolene" acanthidiocephalum, a poorly known glassfrog endemic to the Cordillera Oriental of the Colombian Andes. This species was formally described in the late 1980s and no records have been reported over the last quarter century. Therefore, little is known about its distributional boundaries, morphological variation, natural history, and evolutionary relationships. Here we report the finding of a population of "Centrolene" acanthidiocephalum from a locality around its historical range and provide additional information on its geographic distribution, clutch size, and adult morphology. We also present for the first time data on tadpole morphology, as well as a description of its advertisement call and a phylogenetic tree based on mitochondrial genetic data corroborating its generic position within Centrolene.

Consumptive and nonconsumptive effects of omnivorous tadpoles on aquatic invertebrate communities

AbstractConsumptive effects (CEs) of predation have been well‐studied in most aquatic systems, but nonconsumptive effects (NCEs) on prey have only recently received limited attention. As aquatic consumers, tadpoles have traditionally been considered strict herbivores, leaving their predatory impacts via CEs and NCEs largely unexplored. We quantified omnivory among wood frog (Lithobates sylvaticus) tadpoles and characterized their CEs and NCEs on invertebrate communities. Tadpoles from natural ponds were dissected to quantify the frequency of omnivory generally, as well as specifically in relation to pond size and tadpole morphology. Additional tadpoles were employed in a mesocosm experiment that manipulated tadpole presence (absent, caged, or free‐swimming) to quantify CEs and NCEs on freshwater zooplankton and macroinvertebrate communities. Over 70% of tadpoles in natural ponds engaged in omnivory, primarily on zooplankton, and tadpoles with wider heads and deeper tails were more likely to be omnivorous. Tadpoles in mesocosms exhibited CEs and NCEs on invertebrate communities, with stronger effects exerted on zooplankton than macroinvertebrates. The NCEs of tadpoles on invertebrates likely included production of predatory chemical cues that influenced invertebrate behavior, abundance, and community composition. Because tadpoles are often the dominant vertebrate predators in ephemeral aquatic ecosystems, this study stresses their ecological importance in structuring aquatic communities.

Frog hatchlings use early environmental cues to produce an anticipatory resource-use phenotype.

Developmental plasticity can occur at any life stage, but plasticity that acts early in development may give individuals a competitive edge later in life. Here, we asked if early (pre-feeding) exposure to a nutrient-rich resource impacts hatchling morphology in Mexican spadefoot toad tadpoles, Spea multiplicata. A distinctive carnivore morph can be induced when tadpoles eat live fairy shrimp. We investigated whether cues from shrimp--detected before individuals are capable of feeding--alter hatchling morphology such that individuals could potentially take advantage of this nutritious resource once they begin feeding. We found that hatchlings with early developmental exposure to shrimp were larger and had larger jaw muscles--traits that, at later stages, increase a tadpole's competitive ability for shrimp. These results suggest that early developmental stages can assess and respond to environmental cues by producing resource-use phenotypes appropriate for future conditions. Such anticipatory plasticity may be an important but understudied form of developmental plasticity.

Tadpole morphology of Jerdon’s Narrow-mouthed Frog Uperodon montanus (Jerdon, 1853) with a range and elevation extension report from Western Ghats, India

The study discusses about the new data on larval description, morphological features, larval ecology of stage 25–40 of the Jerdon’s Narrow-mouthed Frog Uperodon montanus (Jerdon, 1853). Tadpoles were identified up to family and genus level based on the historical literature and the species level confirmation was done with molecular studies. We also present a new northern limit record of this species from the Pushpagiri hill ranges in Karnataka (12.669 N, 75.717 E) and a new highest elevation record of 1,916 m at Vaguvarai, Idukki, Kerala which are outside its currently known distribution and elevation ranges. As per the present work, the distribution range of U. montanus has extended northwards by 130 km and upwards by 216 m. Additionally, the IUCN Red List status for the species is also discussed based on the area of occupancy and extent of occurrence redone considering the new range envelope.

ANOVA of Cerium Chloride on Morphology and Metamorphosis Development in Tadpoles of C. melanogaster

In this experiment, the effects of 0.004 mg·L-1, 0.02 mg·L-1, 0.1 mg·L-1, and 0.5 mg·L-1 cerium chloride solutions on the growth and metamorphosis development of the tadpoles of the black spotted frog were investigated. The experimental results showed that cerium chloride solution at 0.5 mg·L-1significantly reduced the survival rate of tadpoles, which was 6.67% at 168h (7d) in the 0.5 mg·L-1 treatment compared with 93.3% in the blank control (lake water). The growth condition (body weight) at 168h (7d) (0.56 g) was different from that of the blank control (lake water) tadpoles (The growth (mass) of tadpoles at 0.5 mg·L-1 slowed down significantly in early development compared to the blank control (lake water) tadpoles (0.67g ± 0.05g); at the same time, we noticed that the tadpoles at 0.5 mg·L-1 concentration were in a dormant state of growth, and the mass was not significantly different compared to the beginning of the experiment. The metamorphosis time of tadpoles in the high concentration of cerium chloride salt solution (31 ± 5 days) was greater than that of the blank control tadpoles (26 ± 3 days). Tadpoles at concentrations of 0.02 mg·L-1, 0.1 mg·L-1, and 0.5 mg·L-1 were significantly heavier than the blank control tadpoles at metamorphosis. The results of this experiment indicated that moderate concentration levels of cerium chloride (0.004 mg·L-1, 0.02 mg·L-1) could significantly accelerate the growth and promote the metamorphosis development of the tadpoles of C. melanogaster.

Automated multi-sample DNA extraction for genotyping live Xenopus embryos.

Xenopus frogs are used extensively for modeling genetic diseases owing to characteristics such as the abundance of eggs combined with their large size, allowing easy manipulation, and rapid external embryo development enabling the examination of cellular and phenotypic alterations throughout embryogenesis. However, genotyping of mutant animals is currently done either as part of a large group, requiring many embryos, or late in development with welfare effects. Therefore, we adapted the Zebrafish Embryonic Genotyper for rapid genomic DNA extraction from Xenopus tropicalis and Xenopus laevis at early stages. Sufficient and good quality DNA was extracted as early as the Nieuwkoop and Faber stage 19 and, importantly, no detrimental effects of the extraction process on the subsequent tadpole development, behavior, or morphology were observed. Amplicons of up to 800 bp were successfully amplified and used for further analyses such as gel electrophoresis, T7 endonuclease I assay and Sanger sequencing. This method allows rapid genotyping during the early stages of Xenopus development, which enables safe identification of mutants. These can be analyzed at early developmental stages or selected for raising without the need for invasive genotyping later, with resource savings and ethical gains in line with the 3Rs principles.

Filling the knowledge gaps of Paratelmatobius mantiqueira (Anura: Leptodactylidae): tadpole, acoustic repertoire, and life history traits

ABSTRACT We monitored a recently discovered population of Paratelmatobius mantiqueira for 13 months and gathered new data for the species: external morphology of tadpoles, acoustic repertoire, and life history traits. We also collected unprecedented data on behaviours and interactions of adults and tadpoles observed during monitoring. Based on natural markings of P. mantiqueira adults, we estimated the effective population size and estimated their home range. With circular statistics, we tested whether they were seasonally active and evaluated how humidity and temperature influenced the detectability of the species. We found that tadpoles and advertisement calls of P. mantiqueira differed from congeneric species. We also described the release and aggressive calls. We found that the species has a small home range, with probable resident females. Temperature and humidity positively influenced the detectability of P. mantiqueira; encounters varied seasonally. Paratelmatobius mantiqueira is a strictly forest species, found mainly in leaf litter and associated with muddy areas in rocky outcrops of highland forests. Our study provides new data about P. mantiqueira, which may help future integrative taxonomy approaches and contribute to the conservation of this species.