Abstract
BackgroundAluminum is the third most prevalent element in the earth’s crust. In most conditions, it is tightly bound to form inaccessible compounds, however in low soil pH, the ionized form of aluminum can be taken up by plant roots and distributed throughout the plant tissue. Following this uptake, nectar and pollen concentrations in low soil pH regions can reach nearly 300 mg/kg. Inhibition of acetylcholinesterase (AChE) has been demonstrated following aluminum exposure in mammal and aquatic invertebrate species. In honey bees, behaviors consistent with AChE inhibition have been previously recorded; however, the physiological mechanism has not been tested, nor has aversive conditioning.ResultsThis article presents results of ingested aqueous aluminum chloride exposure on AChE as well as acute exposure effects on aversive conditioning in an Apis mellifera ligustica hive. Contrary to previous findings, AChE activity significantly increased as compared to controls following exposure to 300 mg/L Al3+. In aversive conditioning studies, using an automated shuttlebox, there were time and dose-dependent effects on learning and reduced movement following 75 and 300 mg/L exposures.ConclusionsThese findings, in comparison to previous studies, suggest that aluminum toxicity in honey bees may depend on exposure period, subspecies, and study metrics. Further studies are encouraged at the moderate-high exposure concentrations as there may be multiple variables that affect toxicity which should be teased apart further.
Highlights
IntroductionIt is tightly bound to form inaccessible compounds, in low soil pH, the ionized form of aluminum can be taken up by plant roots and distributed throughout the plant tissue
Aluminum is the third most prevalent element in the earth’s crust
Acetylcholinesterase enzyme activity Analyses of variance were run within subspecies followed by Tukey post-hoc tests to compare each concentration mean (ANOVA: F(4,203) =20.34, p < 0.0001, Table 1)
Summary
It is tightly bound to form inaccessible compounds, in low soil pH, the ionized form of aluminum can be taken up by plant roots and distributed throughout the plant tissue. There has yet to be confirmation that the same mechanism of neurodisruption observed in mammals, acetylcholinesterase activity inhibition, occurs in terrestrial insects in response to aluminum exposure nor is there definitive aversive conditioning data [13, 14, 28, 30, 48]. The cholinergic system relies on the enzyme acetylcholinesterase (AChE), to degrade acetylcholine through hydrolysis for successful synaptic reuptake This system is well studied in mammals, invertebrates, birds, and fish [34]. Determining if AChE disruption is occurring in insects would provide a mechanistic explanation of previously recorded behavioral data [13, 14]
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