Effects of mancozeb on heat Shock protein 70 (HSP70) and its relationship with the thermal physiology of Physalaemus henselii (Peters, 1872) tadpoles (Anura: Leptodactylidae)

Ecological impacts of agrochemical and pharmaceutical antifungals on a non-target aquatic host-parasite model

Agrochemical fungicides and their pharmaceutical counterparts are a major anthropogenic threat to the biodiversity of freshwater ecosystems as they affect non-target organisms (including aquatic fungi) and disrupt the processes in which they intervene. The goal of this work was to assess the effects of four common agricultural fungicides differing in their modes of action (azoxystrobin, carbendazim, folpet, and mancozeb) and an antifungal pharmaceutical (clotrimazole) on a host × parasite experimental model. We conducted 21-day life history experiments with Daphnia magna (the host) in the absence or presence of Metschnikowia bicuspidata (a microparasitic yeast) to evaluate the effect of each fungicide on the outcome of this relationship (disease) and the fitness of both host and parasite. Interactive but context-dependent effects were observed in D. magna life history responses upon concomitant exposure to parasite and toxicant. The parasite had a drastic negative effect on host survival and reproduction. Carbendazim, clotrimazole and folpet significantly decreased host fitness. In some cases (depending on the combination of toxicant and measured endpoint), simultaneous exposure of the host to the parasite and fungicides led to a slight decrease in host reproduction, which was absent when only the fungicide was present. In two other cases, the fungicide interfered with the host-parasite relationship: azoxystrobin had an impact on infection intensity (decreasing spore load per host), whereas clotrimazole demonstrated a strong antiparasitic effect, clearing all signs of infection (0 % prevalence). These findings emphasize the context-dependent nature of the interaction between pollution and disease.

Environmental dynamics of pesticides: sources, impacts on amphibians, nanoparticles, and endophytic microorganism remediation

Pesticides, which are widely used in agriculture, have elicited notable environmental concern because they persist and may be toxic. The environmental dynamics of pesticides were reviewed with a focus on their sources, impacts on amphibians, and imminent remediation options. Pesticides are directly applied in ecosystems, run off into water bodies, are deposited in the atmosphere, and often accumulate in the soil and water bodies. Pesticide exposure is particularly problematic for amphibians, which are sensitive indicators of the environment's health and suffer from physiological, behavioral, and developmental disruption that has "pushed them to the brink of extinction." Finally, this review discusses the nanoparticles that can be used to tackle pesticide pollution. However, nanoparticles with large surface areas and reactivity have the potential to degrade or adsorb pesticide residues during sustainable remediation processes. Symbiotic microbes living inside plants, known as endophytic microorganisms, can detoxify pesticides. Reducing pesticide bioavailability improves plant resilience by increasing the number of metabolizing microorganisms. Synergy between nanoparticle technology and endophytic microorganisms can mitigate pesticide contamination. Results show that Interdisciplinary research is necessary to improve the application of these strategies to minimize the ecological risk of pesticides. Eco-friendly remediation techniques that promote sustainable agricultural practices, while protecting amphibian populations and ecosystem health, have advanced our understanding of pesticide dynamics.

Vulnerability of amphibians to global warming

Amphibians are the most threatened vertebrates, yet their resilience to rising temperatures remains poorly understood1,2. This is primarily because knowledge of thermal tolerance is taxonomically and geographically biased3, compromising global climate vulnerability assessments. Here we used a phylogenetically informed data-imputation approach to predict the heat tolerance of 60% of amphibian species and assessed their vulnerability to daily temperature variations in thermal refugia. We found that 104 out of 5,203 species (2%) are currently exposed to overheating events in shaded terrestrial conditions. Despite accounting for heat-tolerance plasticity, a 4 °C global temperature increase would create a step change in impact severity, pushing 7.5% of species beyond their physiological limits. In the Southern Hemisphere, tropical species encounter disproportionally more overheating events, while non-tropical species are more susceptible in the Northern Hemisphere. These findings challenge evidence for a general latitudinal gradient in overheating risk4-6 and underscore the importance of considering climatic variability in vulnerability assessments. We provide conservative estimates assuming access to cool shaded microenvironments. Thus, the impacts of global warming will probably exceed our projections. Our microclimate-explicit analyses demonstrate that vegetation and water bodies are critical in buffering amphibians during heat waves. Immediate action is needed to preserve and manage these microhabitat features.

Changes in thermal sensitivity of Rhinella arenarum tadpoles (Anura: Bufonidae) exposed to sublethal concentrations of different pesticide fractions (Lorsban® 75WG)

The intensive use of agrochemicals and the rapid increase of global temperatures have modified the thermal conditions of aquatic environments, thus increasing amphibians' vulnerability to global warming and positioning them at great risk. Commercial formulations of chlorpyrifos (COM) are the pesticides most widely used in agricultural activities, with a high toxic potential on amphibians. However, little is known about the separate effects of the active ingredient (CPF) and adjuvants (AD). We studied the thermal sensitivity at different concentrations and pesticide fractions in Rhinella arenarum tadpoles, on thermal tolerance limits (CTmax = Critical thermal maximum and CTmin = Critical thermal minimum), swimming speed (Ss), Optimum temperature (Top), and Thermal breadth 50 (B50). Our results demonstrate that the pesticide active ingredient, the adjuvants, and the commercial formulation of chlorpyrifos differentially impair the thermal sensitivity of R. arenarum tadpoles. The pesticide fractions affected the heat and the cold tolerance (CTmax and CTmin), depending on the concentrations they were exposed to. The locomotor performance (Ss, Top, and B50) of tadpoles also varied among fractions, treatments, and environmental temperatures. In the context of climate change, the outcomes presented are particularly relevant, as mean temperatures are increasing at unprecedented rates, which suggests that tadpoles inhabiting warming and polluted ponds are currently experiencing deleterious conditions. Considering that larval stages of amphibians are the most susceptible to changing environmental conditions and the alarming predictions about environmental temperatures in the future, it is likely that the synergism between high temperatures and pesticide exposure raise the threat of population deletions in the coming years.

A comprehensive database of amphibian heat tolerance

Rising temperatures represent a significant threat to the survival of ectothermic animals. As such, upper thermal limits represent an important trait to assess the vulnerability of ectotherms to changing temperatures. For instance, one may use upper thermal limits to estimate current and future thermal safety margins (i.e., the proximity of upper thermal limits to experienced temperatures), use this trait together with other physiological traits in species distribution models, or investigate the plasticity and evolvability of these limits for buffering the impacts of changing temperatures. While datasets on thermal tolerance limits have been previously compiled, they sometimes report single estimates for a given species, do not present measures of data dispersion, and are biased towards certain parts of the globe. To overcome these limitations, we systematically searched the literature in seven languages to produce the most comprehensive dataset to date on amphibian upper thermal limits, spanning 3,095 estimates across 616 species. This resource will represent a useful tool to evaluate the vulnerability of amphibians, and ectotherms more generally, to changing temperatures.

Does a Moderately Warming Climate Compensate for the Negative Effects of UV-B Radiation on Amphibians at High Altitudes? A Test of Rana kukunoris Living on the Qinghai–Tibetan Plateau

Simple Summary

Both the warming climate and ultraviolet-B radiation are notable environmental factors affecting tadpole development. However, the phenotypes of tadpoles living at high altitudes may be improved by moderately warming temperatures, reducing or eliminating the negative effects of oxidative damage caused by cool temperatures or strong ultraviolet-B radiation. To verify this hypothesis, Rana kukunoris tadpoles, which live at high altitudes, were exposed to ultraviolet-B radiation and ultraviolet-B radiation-free environments at 14 (cool temperature) and 22 °C (warm temperature), respectively. Ultraviolet-B radiation and a warm temperature had opposite influences on several traits of the tadpoles, and the moderate temperature could compensate for or override the negative effects of ultraviolet-B radiation by increasing the tadpoles’ preferred body temperature and critical tolerance temperature, thus enhancing the locomotion ability and thermal sensitivity of their antioxidant systems. The dark skin coloration and aggregation behavior of R. kukunoris tadpoles may also be effective strategies for allowing them to resist ultraviolet-B radiation and helping them to better adapt to a warming environment with stronger ultraviolet-B radiation. Thus, a moderate degree of warming may increase the capacity of living organisms to adapt to environmental changes and thus have positive effects on the development of tadpoles living at high altitudes.

Abstract

Both the warming climate and ultraviolet-B radiation (UVBR) are considered to be notable environmental factors affecting amphibian population decline, with particular effects on tadpole development. However, the phenotypes of tadpoles living at high altitudes may be improved by moderately warming temperatures, reducing or eliminating the negative effects of oxidative damage caused by cool temperatures or strong UVBR at high altitudes. To verify this hypothesis, Rana kukunoris tadpoles, which live at high altitudes, were used to test the effect of the interaction of temperature and UVBR on their development and antioxidant systems in a fully factorial design. The tadpoles were exposed to UVBR and UVBR-free environments at 14 (cool temperature) and 22 °C (warm temperature), respectively. UVBR and a warm temperature had opposite influences on several traits of the tadpoles, including their survival, developmental rate, individual size, preferred body temperature, thermal tolerance temperature, oxidative damage, and enzymatic and nonenzymatic antioxidant systems. The moderate temperature could compensate for or override the negative effects of UVBR by increasing the tadpoles’ preferred body temperature and critical tolerance temperature, thus enhancing the locomotion ability and thermal sensitivity of their antioxidant systems. Furthermore, the dark skin coloration and aggregation behavior of R. kukunoris tadpoles may also be effective strategies for allowing them to resist UVBR and helping them to better adapt to a warming environment with stronger UVBR. Thus, it is possible that a moderate degree of warming may increase the capacity of living organisms to adapt to environmental changes and thus have positive effects on the development of tadpoles living at high altitudes.