Humidity behaviour and reception in the sphaeromatid isopod Gnorimosphaeroma oregonensis (Dana)

Abstract

This study examined the humidity behaviour of the sphaeromatid isopod Gnorimosphaeroma oregonensis and tested the hypothesis of an osmotic or ionic mechanism of humidity reception. This intertidal isopod often inhabits air-exposed microhabitats having high relative humidities, and movements away from these microhabitats are prevented by orientation mechanisms. Gnorimosphaeroma oregonensis orients behaviourally in experimental humidity gradients. In a gradient of 76–100% relative humidity at 20 °C, the animals aggregated in high-humidity areas by a 'reversal turn' reaction occurring in lower humidity areas and possibly by a negative hygroorthokinesis. Klinokinetic orientation was not demonstrated.In testing the hypothesis of an internal osmotic or ionic mechanism of humidity reception, it was found that animals acclimated to 100% seawater had higher response intensities and lower activity rates than 25% seawater acclimated animals. These results suggest that humidity information may be received by receptor cells or neurons that are sensitive to osmotic or ionic concentrations of the body fluids.