mRNA Transcript Analysis of Hypothesis-driven Pathways as Known Responders to Organophosphate Exposure: Rhinella Arenarum Larvae Transcriptome Study

Transcriptional analysis of the network of transcription regulators and target pathways in exposed organisms may be a hard task when their genome remains unknown. We used a whole transcriptome study on Rhinella arenarum larvae exposed to the organophosphorus pesticides azinphos-methyl and chlorpyrifos to evaluate transcriptional effects on a priori selected groups of genes. This approach allowed us to evaluate the effects on hypothesis-selected pathways such as target esterases, detoxifying enzymes, polyamine metabolism and signaling and regulatory pathways modulating them. We could then compare the responses at the transcriptional level with previously described effects at the enzymatic or metabolic levels to obtain global insight into toxicity-response mechanisms. The effects of both pesticides on the transcript levels of these pathways could be considered moderate, while the responses elicited by chlorpyrifos were more potent and earlier than those elicited by azinphos-methyl. Finally, we infer a prevailing downregulation effect of pesticides on signaling pathways and transcription factor transcripts encoding products that modulate/control the polyamine and antioxidant response pathways. We additionally tested and selected potential housekeeping genes based on those reported for other species. These results allow us to go through future confirmatory studies on pesticide gene expression modulation in toad larvae.

The Effect of Glyphosate And Ciprofloxacin Eexposure On The Gut Bacterial Microbiota Diversity of Rhinella Arenarum (Anura: Bufonidae) Tadpoles

The high load of agrochemicals and antibiotics coexisting in aquatic environments within agroecosystems represents a risk for wildlife. As the gut microbiota plays a key role on its host’s functioning and is sensitive to a wide variety of pollutants, its study allows evaluating organisms’ health and therefore, the ecosystem. We studied toxic effects of commercial formulations of a glyphosate-based herbicide (GBH) and the antibiotic ciprofloxacin (CIP) on gut bacterial microbiota diversity of the common toad (Rhinella arenarum) tadpoles, considered a sentinel species. The study was carried out by classic microbiological analysis and matrix-assisted laser desorption ionization-time of flight mass spectrometry. The microbiota from GBH treatment had greater taxa diversity and richness, including some genera, such as Proteus spp. and Yersinia spp. that were absent in control. In contrast, microbiota from CIP treatment registered a decrease of diversity indexes, dominance of Aeromonas spp. and presence of Leclercia spp. The GBH-CIP treatment showed changes in taxa composition, including decrease of Klebsiella spp. and Pseudomonas spp. and trends of individual pollutant treatments. For all cases, changes in the composition of bacterial community (dysbiosis) were linked to a significant decrease in tadpoles’ weight. To the best of our knowledge, this is the first report on the disruption of gut bacterial microbiota of tadpoles by a mixture of two contaminants of emerging concern worldwide. These findings contribute to understanding how the presence of two co-occurring pollutants in freshwaters results in deleterious effects on the amphibian community and potentially affect the microbiota of those environments.

Evidence of the peptide identity of the epidermal alarm cue in tadpoles of the toad Rhinella arenarum

Chemical cues associated with predation attempts allow prey to trigger defensive behaviours. Accordingly, tadpoles of several species of anurans display strong behavioural responses to chemical cues of injured conspecifics. As part of the antipredator response, tadpoles show rapid and sustained inhibition of activity when exposed to chemical cues of predation. Although the ability to respond to cues of conspecifics has been confirmed in a wide variety of anuran species, studies about the tissue source and the chemical aspects of the molecules involved are scarce and contradictory. In the present work, we analysed the chemical characteristics, tissue source and release mechanism of the chemical alarm cue in Rhinella arenarum tadpoles. Our results support the hypothesis that a peptide of epidermal origin in mediates amphibian tadpole communication.