Are sulfate effects in the mayfly Neocloeon triangulifer driven by the cost of ion regulation?

Elevated major ion concentrations in streams are commonly observed as a consequence of resource extraction, de-icing and other anthropogenic activities. Ecologists report biodiversity losses associated with increasing salinity, with mayflies typically being highly responsive to increases of different major ions. In this study, we evaluated the performance of the mayfly Neocloeon triangulifer reared for its entire larval phase in a gradient of sulfate concentrations. Two natural waters were amended with SO4 as a blend of CaSO4 and MgSO4 and exposures ranged from 5 to 1500 mg SO4, Survival (per cent successful emergence to the subimago stage) was significantly reduced at the highest SO4 concentration in both waters, while development was significantly delayed at 667 mg l(-1) SO4. Final sub-adult body weights were consistent across treatments, except at the highest treatment concentration. Despite evidence for sulfate uptake rates increasing with exposure concentrations and not being saturated at even extremely high SO4 concentrations, total body sulfur changed little in subimagos. Together, these results suggest that elevated SO4 imposes an energetic demand associated with maintaining homeostasis that is manifested primarily as reduced growth rates and associated developmental delays. We identified two genes related to sulfate transport in N. triangulifer. This article is part of the theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.