Reproductive endpoints of Rhinella arenarum (Anura, Bufonidae): Populations that persist in agroecosystems and their use for the environmental health assessment

Anuran responses to urbanization: evaluating life history traits of Rhinella arenarum in urban wetlands

Wetlands are unique ecological environments capable of harboring high biodiversity. However, urbanization can degrade, eliminate, or transform these habitats. Although amphibians utilize habitats created by humans in urban landscapes, few studies have investigated the influence of the habitat quality on the life history of anurans. We assessed life history traits such as snout-vent length (SVL), body condition, and reproductive investment in the South American common toad Rhinella arenarum, to determine whether urbanization is harmful or beneficial to this species. We sampled wetlands with different levels of urbanization in Río Cuarto city, Córdoba, Argentina. We recorded males with lower SVL in medium urbanized wetlands and those with the highest SVL in both low and high urbanization categories, similar to what was found for body conditions with males with low body conditions inhabiting wetlands with a medium degree of urbanization. In females, lower SVL was recorded in medium urbanization and highest SVL in high and low urbanization. It is observed that females recorded in highly urbanized wetlands have a very low body condition. The reproductive investment parameters were not significantly different, but we observed an association between a greater number of eggs and clutch size with wetlands of low urbanization. These results show a variability of responses of R. arenarum to urbanization, which could be due to phenotypic plasticity in its life history parameters, allowing it to inhabit urban areas. Continuous monitoring of the species in these wetlands is needed to determine if these biological responses are temporary or persistent.

Effects of mifepristone, a model compound with anti-progestogenic activity, on the reproduction of African clawed frog (Xenopus laevis)

This is the first study on how a substance with anti-progestogenic activity affects amphibian reproduction. Mifepristone, a synthetic anti-progestin used in abortion pills, was chosen as model compound. African clawed frog (Xenopus laevis) females were exposed to four mifepristone concentrations (0.7, 9, 120, and 1380 ng∙L-1) for 30 days. A control group was also included. Egg-laying during the experiment was significantly less at the highest concentration. At the experiment's end, mifepristone-exposed and control females were randomly mated with sexually mature males. Breeding rate for females exposed to 1380 ng∙L-1 mifepristone was only 50 %. Histology revealed no significant changes in gonads, thyroid, or liver. Females exposed to 1380 ng∙L-1 mifepristone had lower estradiol levels in plasma, lower mRNA expression of lh and fsh in brain-pituitary complex, and p450scc in ovaries. In liver, mRNA level of npr was significantly increased in females exposed to 120 ng∙L-1 mifepristone. mRNA expression of mpr, erβ, dio2, and dio3 were upregulated in animals exposed to 9 ng∙L-1 and 120 ng∙L-1 mifepristone, whereas vtg expression was significantly downregulated in females exposed to 1380 ng∙L-1 mifepristone. All these findings show that exposure to compounds with anti-progestogenic activity affects the hypothalamus-pituitary-gonad axis and decreases reproductive success.

Nuclear abnormalities and DNA damage indicate different genotoxic stress responses of marsh frogs (Pelophylax ridibundus, Pallas 1771) to industrial and agricultural water pollution in South Bulgaria

Amphibians are continuously exposed to pollutants and anthropogenic stressors in their natural habitats, representing a significant challenge to their survival. This study aimed to quantify the extent of DNA damage caused by chronic industrial and agrochemical surface water pollution in wild populations of the marsh frog (Pelophylax ridibundus). The observed genotoxic effects on the marsh frog DNA, manifesting as abnormalities in erythrocyte nuclei, micronuclei, and DNA strand breaks, demonstrate a clear cause-and-effect relationship with surface water parameters, heavy metals, metalloids, and pesticides. The most prevalent nuclear abnormalities observed were notched and blebbed nuclei and nuclear buds, indicative of chromosomal instability. The significant correlation between cadmium, lead, and copper contamination and the increased frequency of DNA breakage in the marsh frogs from the industrial site indicates that heavy metal contamination has a higher genotoxic potential than pesticide contamination. These findings underscore the vulnerability of amphibians inhabiting heavy metal-contaminated wetlands to genotoxic stress due to their lower tolerance to environmental genotoxins. Therefore, using in situ assays to detect erythrocyte nuclear abnormalities and DNA damage in P. ridibundus could serve as a reliable indicator of environmental quality and provide early detection of anthropogenic pollution.

Impacts of horticultural environments on Rhinella arenarum (Anura, Bufonidae) populations: exploring genocytotoxic damage and demographic life history traits

Horticulture poses a significant ecological risk, as agrochemicals are applied more frequently and in larger quantities per unit of production compared to extensive crop fields. The native amphibian Rhinella arenarum serves as a reliable bioindicator of environmental health. This study aimed to assess genocytotoxic damage and demographic life history traits of R. arenarum inhabiting horticultural environments. Sampling was conducted in suburban sites in central Argentina: H1 and H2 (sites associated with horticultural activity) and a reference site, RS. Environmental parameters were recorded, and the frequency of micronuclei (Mn), nuclear abnormalities (ENA), and indicators of cytotoxic damage were determined in tadpoles and adults. Demographic variables (age at maturity, longevity, potential reproductive lifespan, size at maturity, modal lifespan) were calculated. The highest nitrate and phosphate values, along with low dissolved oxygen values, were recorded at sites H1 and H2. Organisms inhabiting horticultural environments exhibited higher frequencies of Mn and ENA, surpassing those recorded in previous studies on tadpoles from sites with extensive crop production. Size at maturity and age at maturity of females, as well as size at maturity, longevity, mean age, and mean adult SVL of males, were lower in horticultural sites. The results support the hypothesis that anuran populations inhabiting horticultural environments demonstrate a diminished health status attributed to subpar environmental quality. Monitoring endpoints at different biological levels provides information on the ecotoxicological risk for amphibians and human populations inhabiting nearby areas.

Toxicity of the neonicotinoid insecticides thiamethoxam and imidacloprid to tadpoles of three species of South American amphibians and effects of thiamethoxam on the metamorphosis of Rhinella arenarum

The present study examined the acute and chronic toxicity of the neonicotinoid insecticides imidacloprid (IMI) and thiamethoxam (TIA) on the neotropical amphibian species Rhinella arenarum, Rhinella fernandezae and Scinax granulatus. The median lethal concentration after 96 hr exposure (96 hr-LC₅₀) ranged between 11.28 and >71.2 mg/L amongst all species and development stages tested, indicating that these pesticides are not likely to produce acute toxicity in the wild. The subchronic toxicity was also low, with 21 day-LC₅₀ values ranging between 27.15 and >71.2 mg/L. However, tadpoles of Rhinella arenarum exposed to thiamethoxam from stage 27 until completion of metamorphosis presented a significantly lower metamorphic success rate together with a smaller size at metamorphosis, starting from the lowest concentration tested. Although a number of studies previously examined the effects of neonicotinoids on amphibian tadpoles, these investigations focused on the time to metamorphosis and reported a variety of results including retardation, acceleration or lack of effect. Here, data demonstrated that thiamethoxam predominantly impacts metamorphosis through reduction of the transformation success and body weight, rather than by affecting the timings of metamorphosis. By closely monitoring progression of tadpoles through the different stages, impairment of metamorphosis was demonstrated to occur during the transition from stage 39 to 42, suggesting an effect on the thyroid system. An asymmetry in the length of the arms was also observed in metamorphs treated with thiamethoxam. Overall, these results indicate that thiamethoxam, and conceivably other neonicotinoids, have the potential to significantly impair metamorphosis of amphibians and diminish their performance and survival in the wild.

Bioaccumulation of pesticides and genotoxicity in anurans from southern Brazil

The expansion of agricultural activities causes habitat loss and fragmentation and the pollution of natural ecosystems through the intense use of pesticides, which may affect the populations of amphibian anurans that inhabit agricultural areas. The present study evaluated the in situ bioaccumulation of pesticides in a population of Leptodactylus luctator that occupies farmland in southern Brazil. We also compared the genotoxicity of L. luctator populations from farmland and forested areas in the same region. We analyzed the micronuclei and nuclear abnormalities of 34 adult anurans, 19 from farmland, and 15 from the forested area. We also assessed the presence of 32 pesticides in liver samples obtained from 18 farmland-dwelling anurans, using chromatographic analysis. We recorded significantly higher rates of nuclear abnormalities in the individuals from the farmland, in comparison with the forest. We detected nine pesticides in the liver samples, of which, deltamethrin was the most common and carbosulfan was recorded at the highest concentrations. The bioaccumulation of pesticides and the higher levels of genotoxic damage found in the anurans from agricultural areas, as observed in the present study, represent a major potential problem for the conservation of these vertebrates, including the decline of their populations and the extinction of species.

Concentration of current-use pesticides in frogs from the Pampa region and correlation of a mixture toxicity index with biological effects

Contamination with current-use pesticides is frequently mentioned as a key factor in global amphibian declines although a limited number of studies have examined the mixture of pesticides accumulated by free-living frogs. This study examined the presence of 46 different pesticide residues in the muscle and kidney tissues of two frog species living in close association with row crops in the Pampa region of Argentina: The terrestrial Leptodactylus latinasus and the semi-aquatic Leptodactylus latrans. A total of 20 different pesticides were identified in frog tissues; chlorpyrifos-methyl, pirimiphos-methyl and acetochlor being the most frequently detected molecules. Overall, one or more pesticide residues (up to 12 in a single frog) were detected in 40-57 % of L. latrans. L. latinasus was found to present more pesticide detections than L. latrans. Interestingly, frog sampled in a natural reserve where no pesticides are applied presented an equivalent frequency of detections as frogs living near a crop. In L. latrans, the calculation of a pesticide toxicity index (PTI) permitted to highlight the existence of a strong positive correlation between PTI and liver GSH contents of females whereas, in males, PTI was negatively correlated with the perimeter of testicular seminiferous tubules. Males also presented near significant negative correlations between PTI and both body condition and the scaled fat index. These results indicate that frogs inhabiting agricultural regions are exposed to a complex and diffuse contamination by pesticide mixtures which is likely responsible for a number of biological effects that may be relevant at the population level.

Lurking in the depth: Pond depth predicts microhabitat selection by Rhinella icterica (Anura: Bufonidae) tadpoles at two different sampling scales

Habitat selection has long been a central theme in ecology and has historically considered both physiological responses and ecological factors affecting species establishment. Investigating habitat selection patterns at different scales can provide important information on the relative roles of the environmental factors influencing the organisms’ abilities to use their surrounding habitat. This work aimed at investigating which environmental factors determine habitat selection by Rhinella icterica tadpoles, and also took the opportunity to investigate how the scale in which tadpoles and environmental data are sampled might influence the habitat selection results. A total of 2.240 tadpoles were counted in the whole sampling area, and while substrate cover and depth were the variables that better explained the abundance of tadpoles at the larger scale (plot level), depth and water turbidity better explained tadpoles’ abundance at the smaller scale (subplot level). The results suggest that avoiding predation by matching the background color is a likely process explaining tadpoles’ occupancy at both scales. Depth is known to influence tadpole habitat use in the tropics, and although its combination with turbidity and substrate cover varied between scales, our study suggests that sampling at different scales might not affect the inferred ecological processes driving habitat selection. This information might also be useful to predict tadpoles’ responses to micro-environmental perturbations and help in guiding the choice of parameters that should be taken into account when analyzing the effects of habitat degradation in Atlantic Forest amphibian populations.

Pesticide exposure affects reproductive capacity of common toads (Bufo bufo) in a viticultural landscape

Amphibian populations are declining worldwide at alarming rates. Among the large variety of contributing stressors, chemical pollutants like pesticides have been identified as a major factor for this decline. Besides direct effects on aquatic and terrestrial amphibian stages, sublethal effects like impairments in reproduction can affect a population. Therefore, we investigated the reproductive capacity of common toads (Bufo bufo) in the pesticide-intensive viticultural landscape of Palatinate in Southwest Germany along a pesticide gradient. In a semi-field study, we captured reproductively active common toad pairs of five breeding ponds with different pesticide contamination level and kept them in a net cage until spawning. Toads from more contaminated ponds showed an increased fecundity (more eggs) but decreased fertilization rates (fewer hatching tadpoles) as well as lower survival rates and reduced size in Gosner stage 25, suggesting that the higher exposed populations suffer from long-term reproductive impairments. In combination with acute toxicity effects, the detected sublethal effects, which are mostly not addressed in the ecological risk assessment of pesticides, pose a serious threat on amphibian populations in agricultural landscapes.

Superfrogs in the city: 150 year impact of urbanization and agriculture on the European Common Frog

Despite growing pressure on biodiversity deriving from increasing anthropogenic disturbances, some species successfully persist in altered ecosystems. However, these species' characteristics and thresholds, as well as the environmental frame behind that process are usually unknown. We collected data on body size, fluctuating asymmetry (FA), as well as nitrogen stable isotopes (δ¹⁵ N) from museum specimens of the European Common Frog, Rana temporaria, all originating from the Berlin-Brandenburg area, Germany, in order to test: (a) if specimens have changed over the last 150 years (1868-2018); and (b) if changes could be attributed to increasing urbanization and agricultural intensity. We detected that after the Second World War, frogs were larger than in pre-war Berlin. In rural Brandenburg, we observed no such size change. FA analysis revealed a similar tendency with lower levels in Berlin after the war and higher levels in Brandenburg. Enrichment of δ¹⁵ N decreased over time in both regions but was generally higher and less variable in sites with agricultural land use. Frogs thus seem to encounter favorable habitat conditions after pollution in postwar Berlin improved, but no such tendencies were observable in the predominantly agricultural landscape of Brandenburg. Urbanization, characterized by the proportion of built-up area, was not the main associated factor for the observed trait changes. However, we detected a relationship with the amount of urban greenspace. Our study exemplifies that increasing urbanization must not necessarily worsen conditions for species living in urban habitats. The Berlin example demonstrates that public parks and other urban greenspaces have the potential to serve as suitable refuges for some species. These findings underline the urgency of establishing, maintaining, and connecting such habitats, and generally consider their importance for future urban planning.

Lethal toxicity of the herbicides acetochlor, ametryn, glyphosate and metribuzin to tropical frog larvae

Despite the high amphibian biodiversity and increasing pesticide use in tropical countries, knowledge on the sensitivity of tropical amphibians to pesticides remains limited. The aim of this study was to evaluate the acute toxicity of the active ingredients of four of the main herbicides used in Brazilian sugarcane production to tadpoles of two tropical frog species: Physalaemus cuvieri and Hypsiboas pardalis. The calculated 96 h-LC50 (median lethal concentration; in mg a.s./L) values for P. cuvieri and H. pardalis were 4.4 and 7.8 (acetochlor); 15 and <10 (ametryn); 115 and 106 (glyphosate); and 85 and 68 (metribuzin), respectively. These toxicity values demonstrated little interspecies variation and the toxicity of the herbicides appeared to be at least partly related with the respective octanol-water coefficient. Published acute toxicity data of fish and amphibians for herbicides were also compiled from the US-EPA ECOTOX database. These data indicated little difference in herbicide sensitivity between tropical amphibians and both non-tropical amphibians and fish. These findings indicate that temperate (fish and amphibian) herbicide toxicity data are also protective for tropical amphibians. Constraints in such extrapolations and indications for future research are discussed.

Effect of parasitism of Lernaea cyprinacea on tadpoles of the invasive species Lithobates catesbeianus

The introduction of invasive species is one of the greatest threats currently faced by natural ecosystems, causing ecological imbalances between native populations and transmission of a variety of diseases. We reported the interaction between two exotic species given by the parasitic infestation of the copepod Lernaea cyprinacea in the early stages of the development of the American bullfrog Lithobates catesbeianus in the central area of Argentina. In this paper we analysed the leukocyte profile of parasitized and non-parasitized tadpoles of L. catesbeianus with L. cyprinacea and their body condition (BC) as biomarkers of the health status of organisms. A total of 27 tadpoles of L. catesbeianus were analysed (12 non-parasitized and 15 parasitized). The lower BC recorded in parasitized organisms show a lower health status in these tadpoles, which could be affecting the metamorphosis and therefore impact at the population level. Leukocyte response of L. catesbeianus tadpoles to the parasitism of L. cyprinacea was found. Mature and immature lymphocyte frequencies and hematocrit were higher in parasitized compared to non-parasitized tadpoles, which is a typical response to the presence of parasites. However, eosinophils and monocytes were recorded at high frequencies in not parasitized tadpoles, which could be due to the important role played by these leucocytes in the metamorphosis of frogs. The results of this study constitute a first antecedent on leukocyte profile in aquatic stages of anurans during an ectoparasitosis and its possible implications for environmental health. The parasitism of L. cyprinacea influences the biology of the American bullfrog at both the individual and population levels. Parasitized individuals are not killed directly by the parasite, but they can create conditions for secondary infections, growth retardation, behavioral changes and, ultimately, reduce populations.

Evaluation in situ of genotoxic and cytotoxic response in the diploid/polyploid complex Odontophrynus (Anura: Odontophrynidae) inhabiting agroecosystems

Polyploidization has been documented across a wide range of vertebrates. Gene duplication could promote better adaptation to environmental changes and to chronic injury or stress. We investigated if genotoxic and cytotoxic responses to agricultural impact are affected by ploidy. We evaluate syntopic populations of the cryptic diploid/polyploid complex Odontophrynus cordobae/O. americanus breeding in an agroecosystem from Central Argentina. The blood of 72 adult anurans was analysed. We used erythrometry to distinguish Odontophrynus individuals with different ploidy levels. We calculated micronucleus frequencies (Mn) and erythrocytic nuclear abnormalities (ENAs) as genotoxic effects and enucleated, mitotic, pyknotic and immature erythrocytes as cytotoxic endpoints (CYT). Mn, ENAs and CYT frequencies were significantly different between diploid and polyploid organisms. The higher frequencies of Mn and CYT were recorded in polyploid organisms, and the higher frequency of ENAs was recorded in diploids. These results indicate that stress response, as indicated by most genotoxic and cytotoxic endpoints, was higher in polyploids respect to diploids. Polyploidy could provide greater genetic flexibility increasing buffering against exogenous DNA-damaging agents and thus confer an advantage over diploids under certain environmental conditions.