It is generally believed that Bacillus thuringiensis var. israelensis (Bti) biopesticides are harmless to non-target organisms; however, new research shows controversial results. We exposed acutely and chronicallyLithobates sylvaticusandAnaxyrus americanus tadpoles until metamorphic climax to VectoBac 200G (granules) and VectoBac 1200L (aqueous suspension) at 300–20,000 ITU/L covering field-relevant concentrations and higher. The data show that the exposure parameters tested did not affect significantly the survival, total length, total weight, hepatosomatic index, gonadosomatic index, the expression of genes of interest (i.e., related to xenobiotic exposure, oxidative stress, and metamorphosis), and the intestine tissue layer detachment ofL. sylvaticusandA. americanus in a concentration–response pattern. In contrast, VectoBac 200G significantly increased the median time to metamorphosis ofL. sylvaticus tadpoles by up to 3.5 days and decreased the median by up to 1 day inA. americanus. VectoBac 1200L significantly increased the median time to metamorphosis ofL. sylvaticusandA. americanustadpoles by up to 4.5 days. Also, the exposure to VectoBac 200G and 1200L altered the intestine bacterial community composition inA. americanus at application rates recommended by the manufacturer, which led to an increase in the relative abundance of Verrucomicrobia, Firmicutes, Bacteroidetes, and Actinobacteria. Changes in the intestine microbiota might impact the fitness of individuals, including the susceptibility to parasitic infections. Our results indicate that the effect of Bti commercial products is limited; however, we recommend that Bti-spraying activities in amphibian-rich ecosystems should be kept minimal until there is more conclusive research to assess if the changes in the time to metamorphosis and microbiota can lead to negative outcomes in amphibian populations and, eventually, the functioning of ecosystems.
21An international sampling program investigating the causes of the decline of American 22 eels (Anguilla rostrata) and European eels (Anguilla anguilla) in the St. Lawrence (Canada) and 23Gironde (France) rivers systems provided the opportunity to compare early growth of eels of each 24 species among habitats using back-calculated size-at-age from 1 to 5 years old. Our study 25 supports previous studies showing that the early back-calculated lengths of A. anguilla were 26 higher in downstream and more saline Gironde system habitats than in the upstream fluvial 27 section, and provides a new indication that length at 1-year-old is twice higher than that reported 28 10 years earlier. However, our data contradict the current paradigm for A. rostrata by providing 29 evidence that early size-at-age of eels from the upstream St. Lawrence system, most distant from 30 the spawning area, exceeds those of eels sampled downstream, at less distant sites in the estuarine 31 section. Overall these observations are consistent with the hypothesis that the observed spatial 32 variations in early growth rate of yellow eels sampled in the St. Lawrence and Gironde systems 33 are the consequence of processes occurring in the first year of age such as genetic selection 34 and/or genetically-dependent habitat choice. 35 36
Since the early 1980s, populations of American (Anguilla rostrata) and European eels (Anguilla anguilla) have suffered a sharp decline. The causes of their decline are likely multifactorial and include chemical pollution. A field study was conducted in eight sites varying in organic and metal contamination along the St. Lawrence (Eastern Canada) and Gironde (France) systems to investigate the relationships among contaminants, biological characteristics and biotransformation, antioxidant and histopathological biomarkers in eels from both species. For A. rostrata, no major influences of persistent organic contaminants on biomarkers were identified. For A. anguilla, eels from the most contaminated site expressed higher surface of MelanoMacrophage Centers (MMCs) and eels from another contaminated site expressed higher amount of spleen lipofuscin pigment. These two histopathological biomarkers were also associated with aging. Compared to eels from the cleanest French site, higher hepatic catalase activity and density of MMC in eels from contaminated sites was related to higher concentration of organic (DDT and metabolites, sum of PCBs, sum of PBDEs) and inorganic (Hg and Cd) contaminants. In both species, a higher deposition of spleen hemosiderin pigment was measured in eels from the most brackish sites compared to eels living in freshwater environments. Our results suggest an association between higher hemosiderin pigment and metal contamination (As for A. anguilla and Pb for A. rostrata). Parasitism by A. crassus was observed in European eels from freshwater sites but not in eels from brackish habitats. Overall, contamination may pose a greater risk for the health of European compared to American eels.
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