The acclimatory response of the mayfly Neocloeon triangulifer to dilute conditions is linked to the plasticity of sodium transport

Relative to a growing body of knowledge about the negative consequences of freshwater salinization, little is known about how aquatic insects respond to progressively ion poor conditions. Here, we examined life-history and physiological acclimation in N. triangulifer by rearing larvae from 1 day post egg hatch to adulthood across a gradient of decreasing salinities (15, 8, 4, 2 and 1 mg L-1 Na). We found no significant changes in survival, growth, development time and whole-body Na content across these treatments. Radiotracer data revealed that larvae acclimated to their dilute exposures by increasing their rates of Na uptake and were able to maintain a relatively narrow range of uptake rates (± SEM) of 38.5 ± 4.2 µg Na g-1 hr-1 across all treatments. In contrast, the Na uptake rates observed in naïve larvae were much more concentration dependent. This acclimatory response is partially explained by differences in ionocyte counts on the gills of larvae reared under different salinities. ...