Laevis Larvae Research Articles

Visual input regulates melanophore differentiation.

Developmental processes continue in organisms in which sensory systems have reached functional maturity, however, little research has focused on the influence of sensory input on cell and tissue development. Here, we explored the influence of visual system activity on the development of skin melanophores in Xenopus laevis. Melanophore number was measured in X. laevis larvae after the manipulation of visual input through eye removal (enucleation) and/or incubation on a white or black substrate at the time when the visual system becomes functional (stage 40). To determine the developmental process impacted by visual input, migration, proliferation and differentiation of melanophores was assessed. Finally, the role of melatonin in driving melanophore differentiation was explored. Enucleating, or maintaining stage 40 larvae on a black background, results in a pronounced increase in melanophore number in the perioptic region within 24 h. Time lapse analysis revealed that in enucleated larvae new melanophores appear through gradual increase in pigmentation, suggesting unpigmented cells in the perioptic region differentiate into mature melanophores upon reduced visual input. In support, we observed increased expression of melanization genes tyr, tyrp1, and pmel in the perioptic region of enucleated or black background-reared larvae. Conversely, maintaining larvae in full light suppresses melanophore differentiation. Interestingly, an extra-pineal melatonin signal was found to be sufficient and necessary to promote the transition to differentiated melanophores. In this study, we found that at the time when the visual system becomes functional, X. laevis larvae possess a population of undifferentiated melanophores that can respond rapidly to changes in the external light environment by undergoing differentiation. Thus, we propose a novel mechanism of environmental influence where external sensory signals influence cell differentiation in a manner that would favor survival.

Combined toxic effects of fluxapyroxad and multi-walled carbon nanotubes in Xenopus laevis larvae

Carbon nanomaterials rarely exist in isolation in the natural environment, and their combined effects cannot be ignored. Multi-walled carbon nanotubes (MWCNTs) have shown tremendous potential applications in diverse fields, including pollution remediation, biomedicine, energy, and smart agriculture. However, the combined toxicities of MWCNTs and pesticides on non-target organisms, particularly amphibians, are often overlooked. Fluxapyroxad (FLX), a significant succinate dehydrogenase inhibitor fungicide, has been extensively utilized for the protection of food and cash crops and control of fungi. This raises the possibility of coexistence of MWCNTs and FLX. The objective of this study was to explore the individual and combined toxic effects of FLX and MWCNTs on the early life stages of Xenopus laevis. Embryos were exposed to varying concentrations of FLX (0, 5, and 50 μg/L) either alone or in combination with MWCNTs (100 μg/L) for a duration of 17 days. The findings indicated that co-exposure to FLX and MWCNTs worsened the inhibition of growth, liver damage, and dysregulation of enzymatic activity in tadpoles. Liver transcriptomic analysis further revealed that the presence of MWCNTs exacerbated the disturbances in glucose and lipid metabolism caused by FLX. Additionally, the combined exposure groups exhibited amplified alterations in the composition and function of the gut microflora. Our study suggests that it is imperative to pay greater attention to the agricultural applications, management and ecological risks of MWCNTs in the future, considering MWCNTs may significantly enhance the toxicity of FLX.

Comparative effects of polyvinyl chloride microplastics on the brittle star Ophiactis virens and the amphibian Xenopus laevis

In this study, we investigated the effects of PVC microplastics (PVC-MPs) using two different animal models: the brittle star Ophiactis virens, and the African clawed frog Xenopus laevis. This is the first study using an environmental relevant sample of PVC-MPs obtained through mechanical fragmentation of a common PVC plumbing pipe. Exposure experiments on brittle star were performed on the adult stage for a duration of 14 days, while those on African clawed frog were performed on the embryogenic developmental stage according to the standardized FETAX protocol (Frog Embryo Teratogenesis Assay-Xenopus). For both models, different endpoints were analysed: mortality, developmental parameters, behavioural assays and histological analyses on target organs by optical and electronic microscopy. Results showed that the concentration of 0.1 μg mL−1 PVC do not cause any adverse effects in both models (common NOEC concentration), while exposure to 1 μg mL−1 PVC adversely affected at least one species (common LOEC concentration). In particular arm regeneration efficiency was the most affected parameters in O. virens leading to a significantly lower differentiation pattern at 1 μg mL−1 PVC. On the contrary, in X. laevis larvae histopathological analyses and behavioural tests were the most susceptible endpoints, exhibiting several abnormal figures and different swimming speed at 10 μg mL−1 PVC. Histopathological analyses revealed a higher abundance of degenerating cells, pyknotic nuclei and cellular debris in the gut of exposed larvae in respect to control. The comparative analyses performed in this work allowed to characterize the specificity of action of the PVC-MPs on the two species, underlining the importance of exploring a large spectrum of endpoints to offer adequate protection in the emerging fields of microplastic research.

The olfactory network of larval Xenopus laevis regenerates accurately after olfactory nerve transection.

Across vertebrate species, the olfactory epithelium (OE) exhibits the uncommon feature of lifelong neuronal turnover. Epithelial stem cells give rise to new neurons that can adequately replace dying olfactory receptor neurons (ORNs) during developmental and adult phases and after lesions. To relay olfactory information from the environment to the brain, the axons of the renewed ORNs must reconnect with the olfactory bulb (OB). In Xenopus laevis larvae, we have previously shown that this process occurs between 3 and 7 weeks after olfactory nerve (ON) transection. In the present study, we show that after 7 weeks of recovery from ON transection, two functionally and spatially distinct glomerular clusters are reformed in the OB, akin to those found in non-transected larvae. We also show that the same odourant response tuning profiles observed in the OB of non-transected larvae are again present after 7 weeks of recovery. Next, we show that characteristic odour-guided behaviour disappears after ON transection but recovers after 7-9 weeks of recovery. Together, our findings demonstrate that the olfactory system of larval X. laevis regenerates with high accuracy after ON transection, leading to the recovery of odour-guided behaviour.

Comparing the effects and potencies of perchlorate and nitrate on amphibian metamorphosis using a modified amphibian metamorphosis assay (AMA).

A modified amphibian metamorphosis assay was performed in which Nieuwkoop and Faber (NF) stage 47 Xenopus laevis larvae were exposed to different concentrations of either perchlorate (ClO4 -) or nitrate (NO3 -) for 32 days. Larvae were exposed to 0.0 (control), 5, 25, 125, 625, and 3125 μg/L ClO4 -, or 0 (control), 23, 71, 217, 660, and 2000 mg/L NO3 -. The primary endpoints were survival, hind limb length (HLL), forelimb emergence and development, developmental stage (including time to NF stage 62 [MT62]), thyroid histopathology, wet weight, and snout-vent length (SVL). Developmental delay as evidenced by altered stage distribution and increased MT62, a higher degree of thyroid follicular cell hypertrophy, and an increase in the prevalence of follicular cell hyperplasia was observed at concentrations ≥125 μg/L ClO4 -. The no observed effect concentration (NOEC) for developmental endpoints was 25.0μg/L ClO4 - and the NOEC for growth endpoints was 3125 μg/L ClO4 -. Exposure to nitrate did not adversely affect MT62, but a decreasing trend in stage distribution and median developmental stage at ≥217 mg/L NO3 - was observed. No histopathologic effects associated with nitrate exposure were observed. An increasing trend in SVL-normalized HLL was observed at 2000 mg/L NO3 -. Nitrate did not alter larval growth. The NOEC for developmental endpoints was 71 mg/L NO3 -, and 2000 mg/L NO3 - for growth endpoints. The present study provided additional evidence that the effects and potency of nitrate and perchlorate on metamorphosis and growth in X.laevis are considerably different.

Inefficacy of dietary test substance administration in Amphibian Metamorphosis Assay (AMA) studies.

Traditionally, the Amphibian Metamorphosis Assay (AMA; OECD TG 231) is performed by exposing Xenopus laevis tadpoles to test substances dissolved in laboratory water. Recently, the use of dietary administration has been proposed to combat poorly soluble test substances in ecotoxicologically-based regulatory endocrine disruption (ED) studies, specifically the AMA warranting an investigation into the efficacy of dietary administration. An efficacy study comprised of two phases: 1) evaluation of the physical influence of the loading process via solvent and 10, 1, and 0.1 mg/l test substance or surrogate (sunflower oil, SFO) on the Sera® Micron Nature (SMN) diet, and 2) performance of a modified AMA in which Nieuwkoop and Faber (NF) stage 51 X. laevis larvae were exposed to dechlorinated tap water using one concentration of the SFO in the diet for 21 days, was performed. In phase 1, the addition of acetone or acetone with bis(2-propylheptyl) phthalate (DPHP) or SFO to SMN with subsequent solvent purge altered the diet reducing the density of the liquified diet and dietary pellet size following centrifugation indicative of alteration of the physical properties of the diet. Treatments used in the modified AMA were acetone alone and 0.1 mg/l SFO dissolved in acetone. These treatments were evaluated against an SMN benchmark using standard AMA endpoints. Both the acetone-treated SMN and 0.1 mg/l SFO-treated diets significantly reduced survival rates, 67 and 70% relative to the SMN benchmark (100%), decreased developmental stage distribution and snout-vent length-normalized hind limb length relative to the SMN benchmark, and slightly increased the prevalence and severity of thyroid follicular cell hypertrophy. Although the acetone-treated diets may have impacted the hypothalamo-pituitary-thyroid axis, clinical signs of gastrointestinal impaction and tail flexure were also observed in the acetone-treated diets, but not the SMN diet alone. Ultimately, test substance exposure via the diet in an AMA study can produce results that may confound data interpretation, which suggests that the traditional aqueous exposure route is generally more appropriate.

A biologically based computational model for the hypothalamic-pituitary-thyroid (HPT) axis in Xenopus laevis larvae

A biologically based computational model was developed to describe the hypothalamic-pituitary-thyroid (HPT) axis in developing Xenopus laevis larvae. The goal of this effort was to develop a tool that can be used to better understand mechanisms of thyroid hormone-mediated metamorphosis in X. laevis and predict organismal outcomes when those mechanisms are perturbed by chemical toxicants. In this report, we describe efforts to simulate the normal biology of control organisms. The structure of the model borrows from established models of HPT axis function in mammals. Additional features specific to X. laevis account for the effects of organism growth, growth of the thyroid gland, and developmental changes in regulation of thyroid stimulating hormone (TSH) by circulating thyroid hormones (THs). Calibration was achieved by simulating observed changes in stored and circulating levels of THs during a critical developmental window (Nieuwkoop and Faber stages 54–57) that encompasses widely used in vivo chemical testing protocols. The resulting model predicts that multiple homeostatic processes, operating in concert, can act to preserve circulating levels of THs despite profound impairments in TH synthesis. Represented in the model are several biochemical processes for which there are high-throughput in vitro chemical screening assays. By linking the HPT axis model to a toxicokinetic model of chemical uptake and distribution, it may be possible to use this in vitro effects information to predict chemical effects in X. laevis larvae resulting from defined chemical exposures.

Amphibian Metamorphosis Assay: Investigation of the potential effects of five chemicals on the hypothalamic-pituitary thyroid axis of Xenopus laevis

2-Ethylhexyl 4-hydroxybenzoate (2-EHHB), 4-tert-octylphenol (4-OP), 4-nonylphenol-branched (4-NP), benzyl butyl phthalate (BBP) and dibutyl phthalate (DBP) were evaluated using a 21-day Amphibian Metamorphosis Assay (AMA). Xenopus laevis larvae were exposed nominally to each chemical at 3.6, 10.9, 33.0, and 100 μg/L, except 4-NP concentrations were 1.8, 5.5, 16.5 and 50 μg/L. Endpoints included mortality, developmental stage, hind limb length (HLL), snout-vent length (SVL), body weight (BW), and thyroid histopathology. BBP and 4-OP accelerated development compared to controls at the mean measured concentration of 3.5 and 39.8 μg/L, respectively. An increase in developmental stage frequency distribution was observed for 4-OP at 39.8 and 103 µg/L, BBP at all concentrations and DBP at 143 µg/L. Normalized HLL was increased on study day (SD) 21 for all tested substances except 4-NP. Histopathology revealed accelerated development and mild thyroid follicular cell hypertrophy at all BBP concentrations, but moderate severity at 105 μg/L. Increased BW occurred for all chemicals except 4-OP. Increased SVL was observed for 4-NP, BBP and DBP on SD 21. There was insufficient evidence that 4-NP and 2-EHHB affected the hypothalamic-pituitary thyroid axis, however, BBP, DBP and 4-OP showed potential effects on amphibian metamorphosis and thyroid activity, albeit through different lines of evidence.

Water Contamination by Nitrates and its Thyroid Disruptive Action. Bioassay on Xenopus Laevis

Background: Groundwater could vehicle substances that have shown to have a thyroid-disrupting action. Amphibians are used as bioassays to analyze changes that these disruptors generate during metamorphosis. Objectives: To assess the thyroid disrupting action of groundwater contaminated with nitrates and arsenic, by means of a bioassay of chronic toxicity in Xenopus laevis larvae. Methods: Three experimental groups immersed in water: Control group (C) (n=13) filtered drinking water, Exposed group (E) groundwater (n=18) and Positive Control group (PC) (n=18) filtered drinking water added with 0,007 mg/l of potassium perchlorate. A water physicochemical analysis was performed. The duration of metamorphosis stages, total body length, mortality per group, weight and height were morphologically evaluated. The colloid volume, degrees of hyperplasia, and height of the follicular epithelium of the thyroid gland were histologically evaluated. At molecular level, NIS thyroid symporter protein expression was measured.

Injury-induced Erk1/2 signaling tissue-specifically interacts with Ca2+ activity and is necessary for regeneration of spinal cord and skeletal muscle

The transition of stem cells from quiescence to proliferation enables tissues to self-repair. The signaling mechanisms driving these stem-cell-status decisions are still unclear. Ca2+ and the extracellular signal-regulated kinase (Erk1/2) are two signaling pathways that have the potential to coordinate multiple signals to promote a specific cellular response. They both play important roles during nervous system development but their roles during spinal cord and muscle regeneration are not fully deciphered. Here we show in Xenopus laevis larvae that both Ca2+ and Erk1/2 signaling pathways are activated after tail amputation. In response to injury, we find that Erk1/2 signaling is activated in neural and muscle stem cells and is necessary for spinal cord and skeletal muscle regeneration. Finally, we show in vivo that Erk1/2 activity is necessary for an injury-induced increase in intracellular store-dependent Ca2+ dynamics in skeletal muscle-associated tissues but that in spinal cord, injury increases Ca2+ influx-dependent Ca2+ activity independent of Erk1/2 signaling. This study suggests that precise temporal and tissue-specific activation of Ca2+ and Erk1/2 pathways is essential for regulating spinal cord and muscle regeneration.

Resolving different presynaptic activity patterns within single olfactory glomeruli of Xenopus laevis larvae

Olfactory sensing is generally organized into groups of similarly sensing olfactory receptor neurons converging into their corresponding glomerulus, which is thought to behave as a uniform functional unit. It is however unclear to which degree axons within a glomerulus show identical activity, how many converge into a glomerulus, and to answer these questions, how it is possible to visually separate them in live imaging. Here we investigate activity of olfactory receptor neurons and their axon terminals throughout olfactory glomeruli using electrophysiological recordings and rapid 4D calcium imaging. While single olfactory receptor neurons responsive to the same odor stimulus show a diversity of responses in terms of sensitivity and spontaneous firing rate on the level of the somata, their pre-synaptic calcium activity in the glomerulus is homogeneous. In addition, we could not observe the correlated spontaneous calcium activity that is found on the post-synaptic side throughout mitral cell dendrites and has been used in activity correlation imaging. However, it is possible to induce spatio-temporal presynaptic response inhomogeneities by applying trains of olfactory stimuli with varying amino acid concentrations. Automated region-of-interest detection and correlation analysis then visually distinguishes at least two axon subgroups per glomerulus that differ in odor sensitivity.

Non-canonical Hedgehog signaling regulates spinal cord and muscle regeneration in Xenopus laevis larvae.

Inducing regeneration in injured spinal cord represents one of modern medicine's greatest challenges. Research from a variety of model organisms indicates that Hedgehog (Hh) signaling may be a useful target to drive regeneration. However, the mechanisms of Hh signaling-mediated tissue regeneration remain unclear. Here, we examined Hh signaling during post-amputation tail regeneration in Xenopus laevis larvae. We found that while Smoothened (Smo) activity is essential for proper spinal cord and skeletal muscle regeneration, transcriptional activity of the canonical Hh effector Gli is repressed immediately following amputation, and inhibition of Gli1/2 expression or transcriptional activity has minimal effects on regeneration. In contrast, we demonstrate that protein kinase A is necessary for regeneration of both muscle and spinal cord, in concert with and independent of Smo, respectively, and that its downstream effector CREB is activated in spinal cord following amputation in a Smo-dependent manner. Our findings indicate that non-canonical mechanisms of Hh signaling are necessary for spinal cord and muscle regeneration.

Mcrs1 plays a role in otic and branchial arch gene expression

Branchio-oto-renal (BOR) syndrome presents with inner, middle, and outer ear deformities, hyoid cysts and fistulae, and kidney hypoplasia or absence. Half of BOR cases are caused by mutations in genes encoding the transcription factor SIX1 or its co-factor EYA1. We previously suggested that other Six1 cofactors might be BOR candidates, and subsequently showed that Microspherule 1 (Mcrs1) binds to Six1, reduces Six1-Eya1 transcriptional activation, and during preplacodal development aids to define both the neural plate and preplacodal region. Disruption of Mcrs1 endogenous levels also disrupts otic vesicle gene expression and size. However, the consequences of these changes during larval stages of craniofacial development have yet to be characterized. To alter the levels of Mcrs1 in Xenopus laevis larvae, either mcrs1 mRNA or translation blocking antisense oligonucleotides were microinjected into the neural crest (NC) and cranial placode progenitor blastomeres. Larvae then were assessed by in situ hybridization for changes in gene expression within the otic vesicle (OV) and branchial arches (BA). Increasing Mcrs1 levels did not significantly impact OV or BA gene expression, whereas knockdown of Mcrs1 downregulated key skeletogenesis/NC (dlx5, sox9, tbx1) and cranial placode (six1, irx1) genes in both the OV and BA. In contrast, emx2 expression was upregulated by Mcrs1 knockdown. These results indicate that Mcrs1 is required for the proper level of expression of several OV and BA genes, and is a repressor of emx2, a gene known to regulate proliferation, differentiation, patterning, and migration of cells within the OV. These data indicate that Mcrs1 plays an important role in the development of craniofacial structures that are affected in BOR patients.

Autophagy Induction by HDAC Inhibitors Is Unlikely to bethe Mechanism of Efficacy in Prevention of Retinal Degeneration Caused by P23H Rhodopsin.

We previously found that valproic acid (VPA) and other histone deacetylase inhibitors (HDACis) ameliorate retinal degeneration (RD) caused by P23H rhodopsin in Xenopus laevis larvae and hypothesized that this may be due to enhancement of autophagy. Here we use X. laevis expressing an autophagy marker to assess effects of HDACis on autophagy. We also assess the effects of non-HDACi activators and inducers of autophagy on RD caused by P23H rhodopsin.

Cannibalism or congeneric predation? The African clawed frog, Xenopus laevis (Daudin), preferentially predates on larvae of Cape platannas, Xenopus gilli Rose & Hewitt

AbstractPredators are not limited to prey from other species as they can cannibalise vulnerable individuals within their own population. The African clawed frog, Xenopus laevis (Daudin), is a predator with a broad diet, known to consume multiple prey species, including congeners and conspecifics. African clawed frogs occur in sympatry with the Endangered Cape platanna, Xenopus gilli Rose & Hewitt, which are under threat through competition and predation from X. laevis. We investigated the threat of X. laevis predation on X. gilli using choice and no‐choice experiments to evaluate the relative vulnerability of X. laevis and X. gilli larvae. Results showed that large X. gilli larvae had a significantly higher vulnerability to X. laevis predation compared to small X. gilli larvae. However, the same discrimination was not discerned when offered large and small X. laevis larvae, or mixed larvae of the same size. We report ontogenic shifts in behaviour of X. gilli larvae that may be a factor in contributing to the vulnerability of large X. gilli larvae to adult X. leavis predation. Congeneric predation likely has negative implications for the population structure of the Endangered X. gilli. Our study underlines the call for the removal of X. laevis to conserve populations of X. gilli.

Transfer and Ecotoxicity of Titanium Dioxide Nanoparticles in Terrestrial and Aquatic Ecosystems: A Microcosm Study.

With the advancement in nanotechnology, particularly the use of TiO2 nanoparticles (NPs), there is a need to study their release into the environment and assess the related risk in an environmentally relevant contamination scenario. In the present study, the transfer and toxicity of TiO2 NPs in microcosms mimicking terrestrial and aquatic ecosystems were evaluated. The contaminated soil was prepared by spiking natural soils, with these then used as the basis for all exposure systems including preparation of soil leachates for amphibian exposure. Results demonstrated significant reductions in bacterial (-45%) and archaeal (-36%) nitrifier abundance; significant translocation of Ti to M. truncatula leaves (+422%); significant reductions in plant height (-17%), number of leaves (-29%), and aboveground biomass (-53%); nonsignificant Ti uptake in snail foot and viscera, and excretion in feces; and genotoxicity to X. laevis larvae (+119% micronuclei). Our study highlights a possible risk of engineered TiO2 NPs in the environment in terms of trophic transfer and toxicity in both terrestrial and aquatic environments.

Neuronal degeneration and regeneration induced by axotomy in the olfactory epithelium of Xenopus laevis.

The olfactory epithelium (OE) has the remarkable capability to constantly replace olfactory receptor neurons (ORNs) due to the presence of neural stem cells (NSCs). For this reason, the OE provides an excellent model to study neurogenesis and neuronal differentiation. In the present work, we induced neuronal degeneration in the OE of Xenopus laevis larvae by bilateral axotomy of the olfactory nerves. We found that axotomy induces specific- neuronal death through apoptosis between 24 and 48h post-injury. In concordance, there was a progressive decrease of the mature-ORN marker OMP until it was completely absent 72h post-injury. On the other hand, neurogenesis was evident 48h post-injury by an increase in the number of proliferating basal cells as well as NCAM-180- GAP-43+ immature neurons. Mature ORNs were replenished 21 days post-injury and the olfactory function was partially recovered, indicating that new ORNs were integrated into the olfactory bulb glomeruli. Throughout the regenerative process no changes in the expression pattern of the neurotrophin Brain Derivate Neurotrophic Factor were observed. Taken together, this work provides a sequential analysis of the neurodegenerative and subsequent regenerative processes that take place in the OE following axotomy. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1308-1320, 2017.

Current status and future prospect of FSHD region gene 1.

FSHD region gene 1 (FRG1), as the name suggests, is the primary candidate gene for fascioscapulohumeral muscular dystrophy disease. It seemingly affects muscle physiology in normal individuals but in FSHD, where it is found to be highly upregulated, might be involved in disruption of face, scapula and humeral skeletal muscle. Literature on FRG1, reviewed from 1996 to 2016, reveals that it is primarily associated with muscle development and maintenance. Approximately 75% of FSHD patients also show vascular abnormalities indicating that FRG1 might have some part to play in these abnormalities. Research involving vasculature in X. laevis larvae shows that FRG1 positively affects normal vasculature. Few of the well-established angiogenic regulators seem to get affected by abnormal expression level of FRG1. Its primary localization in sub nuclear structures like Cajal bodies and nuclear speckles indicates regulation of the above-mentioned factors by transcriptional and post-transcriptional machineries, but in-depth studies need to be done to conclude a clear statement. In this review, we have attempted to present all the work done on FRG1, all the lacunas which need to be unraveled, and hypothesized a model for our readers to get an insight into its molecular mechanism.

Surface area of carbon-based nanoparticles prevails on dispersion for growth inhibition in amphibians

The attractive properties of carbon-based nanoparticles such as graphene and its derivatives or carbon nanotubes lead to their use in many application fields, whether they are raw or functionalized, such as oxidized. These particles may finally contaminate the aquatic compartment, which is a major receptacle of pollutants. The study of their impact on aquatic organisms is thus essential. At the nano scale, recent studies have highlighted that specific surface area should be used as the most relevant descriptor of toxicity instead of the conventional mass concentration. By using a dose-response model, this work compares the chronic toxicity observed on Xenopus laevis larvae after 12-day in vivo exposure to raw, oxidized carbon allotropes, or in the presence of chemical dispersant. We show that chemical dispersion does not influence the observed chronic toxicity, whether it is through surface chemistry (oxidation state) or through the addition of a dispersant. The biological hypothesis leading to growth inhibition are discussed. Finally, these results confirm that surface area is the more suited metric unit describing growth inhibition.

Effects of a commonly used glyphosate-based herbicide formulation on early developmental stages of two anuran species.

Environmental contamination, especially due to the increasing use of pesticides, is suggested to be one out of six main reasons for the global amphibian decline. Adverse effects of glyphosate-based herbicides on amphibians have been already discussed in several studies with different conclusions, especially regarding sublethal effects at environmentally relevant concentrations. Therefore, we studied the acute toxic effects (mortality, growth, and morphological changes) of the commonly used glyphosate-based herbicide formulation Roundup® UltraMax on early aquatic developmental stages of two anuran species with different larval types (obligate vs. facultative filtrating suspension feeders), the African clawed frog (Xenopus laevis) and the Mediterranean painted frog (Discoglossus pictus). While X. laevis is an established anuran model organism in amphibian toxicological studies, we aim to establish D. pictus as another model for species with facultative filtrating larvae. A special focus of the present study lies on malformations in X. laevis embryos, which were investigated using histological preparations. In general, embryos and larvae of X. laevis reacted more sensitive concerning lethal effects compared to early developmental stages of D. pictus. It was suggested, that especially the different morphology of their filter apparatus and the higher volume of water pumped through the buccopharynx of X. laevis larvae lead to higher exposure to the formulation. The test substance induced similar lethal effects in D. pictus larvae as it does in the teleost standard test organism used in pesticide approval, the rainbow trout (Oncorhynchus mykiss), whereas embryos of both species are apparently more tolerant and, conversely, X. laevis larvae about two times more sensitive. In both species, early larvae always reacted significantly more sensitive than embryos. Exposure to the test substance increased malformation rates in embryos of both species in a concentration-dependent manner, but not at environmentally relevant concentrations. However, the assumed field safety, based on calculated surface water concentrations of the active ingredient (glyphosate), should be validated with realistic field data and buffer strips have to be urgently regarded to any aquatic amphibian habitat.