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Manganese (Mn2+ as MnSO 4 &/or MnCl 2) is a common and essential element for maintaining life in plants and animals and is found in soil, fresh waters and marine waters; however, over exposure is toxic to organisms. MnSO 4 is added to soil for agricultural purposes and people are exposed to Mn2+ in the mining industry. Hypermanganesemia in mammals is associated with neurological issues mimicking Parkinson's disease (PD) and appears to target dopaminergic neural circuits. However, it also seems that hypermanganesemia can affect many aspects of health besides dopaminergic synapses. We examined the effect on development, behavior, survival, cardiac function, and glutamatergic synaptic transmission in the Drosophila melanogaster. In addition, we examined the effect of Mn2+ on a sensory proprioceptive organ and nerve conduction in a marine crustacean and synaptic transmission at glutamatergic neuromuscular junctions of freshwater crayfish. A dose-response effect of higher Mn2+ retards development, survival and cardiac function in larval Drosophila and survival in larvae and adults. MnSO 4 as well as MnCl 2 blocks stretch activated responses in primary proprioceptive neurons in a dose-response manner. Mn2+ blocks glutamatergic synaptic transmission in Drosophila as well as crayfish via presynaptic action. This study is relevant in demonstrating the effects of Mn2+ on various physiological functions in order to learn more about acute and long-term consequences Mn2+ exposure. [Display omitted] • Exposure to Mn2+ slows development and decreases survival of Drosophila larvae. • Mn2+ depresses cardiac function in larval Drosophila. • Synaptic transmission at neuromuscular junctions in Drosophila and crayfish is depressed by Mn2+. • Proprioceptive function in crab limbs is compromised by Mn2+ in a dose-dependent manner. [ABSTRACT FROM AUTHOR]