Novel experimental apparatus for laboratory measurements of phototaxis: A comparison between amphipod species

Intricate adaptations to visual systems have allowed amphipods to thrive in extreme habitats like caves. In addition to rearranging ocular dioptric elements, adaptations have also been made to photobehaviors to accommodate the environmental conditions of their habitats. Given the prevalence or absence of discernible eyes or photoreceptors across species, phototaxis is a commonly used behavior to assess light sensing mechanisms. Amphipod photobehaviors have increasingly been utilized within neuroethological and ecotoxicological studies but the quality of light used during laboratory experiments is often overlooked. We describe a novel experimental chamber that allows for accurate and efficient measurement of phototaxis under precisely controlled light conditions. We used this experimental chamber to test phototaxis in two related amphipod species, one subterranean (Stygobromus tenuis potomacus) and one surface dwelling (Crangonyx shoemakeri). Our results confirm that the behaviors of these species are indicative of natural photopreferences and that in certain populations, these preferences vary with light quality. This low cost and efficient method could easily be applied to a variety of animal models and light conditions, allowing for a reproducible and high throughput method to measure phototaxis in laboratory trials.