Timing and frequency of sublethal exposure modifies the induction and retention of increased insecticide tolerance in wood frogs (Lithobates sylvaticus)

Naïve and induced tolerance of 15 amphibian populations to three commonly applied insecticides

Human impacts on ecological communities are pervasive and species must either move or adapt to changing environmental conditions. For environments polluted by contaminants, researchers have found hundreds of target pest species evolving increased tolerance, but we have substantially fewer cases of evolved tolerance in non-target species. When species do evolve increased tolerance, inducible tolerance can provide immediate protection and favor the evolution of increased tolerance over generations via genetic assimilation. Using a model larval amphibian (wood frogs, Rana sylvatica), we examined the tolerance of 15 populations from western Pennsylvania and eastern New York (USA), when first exposed to no pesticide or sublethal concentrations and subsequently exposed to lethal concentrations of three common insecticides (carbaryl, chlorpyrifos, and diazinon). We found high variation in naïve tolerance among the populations for all three insecticides. We also discovered that nearly half of the populations exhibited inducible tolerance, though the degree of inducible tolerance (magnitude of tolerance plasticity; MoTP) varied. We observed a cross-tolerance pattern of the populations between chlorpyrifos and diazinon, but no pattern of similar MoTP among the pesticides. With populations combined from two regions, increased tolerance was not associated with proximity to agricultural fields, but there were correlations between proximity to agriculture and MoTP. Collectively, these results suggests that amphibian populations possess a wide range of naïve tolerance to common pesticides, with many also being able to rapidly induce increased tolerance. Future research should examine inducible tolerance in a wide variety of other taxa and contaminants to determine the ubiquity of these responses to anthropogenic factors.

Combined effects of landscape composition and agrochemicals on frog communities amid sugarcane-dominated agroecosystems

Global demand for crops will continue increasing over the next few decades to cover both food and biofuel needs. This demand will put further pressure to expand arable land and replace natural habitats. However, we are only beginning to understand the combined effects of agrochemicals and land-use change on tropical freshwater biodiversity. In this study, we analyzed how pond-dwelling anuran larvae responded to pond characteristics, landscape composition, and agrochemical contamination in a sugarcane-dominated agroecosystem in Brazil. Then we used an information theoretical approach with generalized linear models to relate species richness and abundance to predictor variables. The variation in tadpole abundance was associated with both agrochemical concentration (e.g., ametryn, diuron, and malathion) and landscape variables (e.g., percentage of forest, percentage of agriculture, and distance to closest forest). The relationship between species abundance and agrochemicals was species-specific. For example, the abundances of Scinax fuscovarius and Physalaemus nattereri were negatively associated with ametryn, and Dendropsophus nanus was negatively associated with tebuthiuron, whereas that of Leptodactylus fuscus was positively associated with malathion. Conversely, species richness was associated with distance to forest fragments and aquatic vegetation heterogeneity, but not agrochemicals. Although we were unable to assign a specific mechanism to the variation in tadpole abundance based on field observations, the lower abundance of three species in ponds with high concentrations of agrochemicals suggest they negatively impact some frog species inhabiting agroecosystems. We recommend conserving ponds near forest fragments, with abundant stratified vegetation, and far from agrochemical runoffs to safeguard more sensitive pond-breeding species.

Generational sensitivity alteration in Chironomus yoshimatsui to carbamate and pharmaceutical chemicals and the effect on Catalase, CYP450, and hemoglobin gene transcription

To ascertain the tolerance mechanisms of aquatic organisms to artificial chemicals, intergenerational sensitivity changes of Chironomus yoshimatsui to a carbamate pesticide (pirimicarb) and pharmaceutical chemical (diazepam) were investigated. The larvae (<48-h-old) in each generation were exposed to both chemicals for 48 h and then the surviving chironomids were cultured until the fifth generation (F0-F4) without chemical addition. The 48-h 50% effective concentration (EC₅₀) value of chironomids was determined for each generation. In the pirimicarb treatment group, the EC₅₀ values significantly increased in F3 and F4, and those in the diazepam treatment group slightly increased. Catalase, Cytochrome P450 and hemoglobin (Hb) mRNA levels were monitored to see whether these were related to the trans-generational sensitivity. Although the generalized linear model results showed that the sensitivity to diazepam was slightly increased in the diazepam treatment, we could not find any mRNA levels related to sensitivity alteration. In contrast, the model approach showed that the chironomids exposed to pirimicarb trans-generationally became tolerant with increasing Hb mRNA levels. Therefore, they might decrease their chemical stress by modifying Hb gene transcription.