Microhabitat selection by the lotic amphipod Gammarus pseudolimnaeus Bousfield: mechanisms for evaluating local substrate and current suitability

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Abstract
This study examined key environmental cues used by Gammarus pseudolimnaeus during microhabitat selection, and cues and mechanisms used to evaluate and react to changing current conditions. Thigmotactic cues for complexity and texture were used independently during microhabitat selection. Neither the external leg sensilla nor the antennae appeared to detect these cues. Neither hydromechanical cues detected by either the antennae or type II microtrich sensilla nor visual cues appear to play a key role. The amphipods showed no ability to compensate when deprived of individual cues. These results suggest that internal proprioceptors were involved, that current is not a major proximal factor, and that the presence of substrate interstices is the critical factor considered during microhabitat selection, not substrate size. Animals displayed a mechanical capability to turn into the flow, probably owing to differential inertial forces resulting from the centre of gravity being located forward and above the physical midpoint. During a field experiment, animals displayed no preference for maintaining their position after disturbance, or for moving upstream or downstream. However, they were less able to move upstream when their microtrich sensilla were masked. Excessively displaced animals did not show a preferred mechanism for returning to the substrate.

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