Running blind: Static antennae as locomotory guides in a diurnal, keen-eyed predator
Daniel B. Zurek and Cole Gilbert
Poorly sighted or nocturnal animals typically acquire spatial information through expanded mechanosensory abilities mediated by longer, more mobile antennae or vibrissae. High visual acuity allows parallel processing of environmental features at greater distances than are reached by “feelers”. Diurnal tiger beetles (Carabidae: Cicindelinae) have high visual acuity for insects and visually pursue prey in open, flat habitats. Their high speed, however, causes motion blur that degrades visual contrast and forces stop-and-go pursuit. Here we demonstrate that motion blur during running also impairs visual obstacle negotiation. However, the antennae of diurnal, but not nocturnal, tiger beetles have compensatory morphological and behavioral adaptations. Nocturnal Omus dejeanii waves its antennae in a pattern typical of poorly sighted insects, but diurnal Cicindela hirticollis holds its antennae rigidly forward close to the ground. Sensory modification of C. hirticollis crossing different obstacles revealed that antennal touch is necessary and sufficient to successfully negotiate obstacles. Sighted beetles lacking antennae often crashed into high contrast obstacles. Moreover, antennal contact with obstacles increases subsequent body pitch that facilitates surmounting obstacles with minimal slowdown. These results demonstrate mechanosensory augmentation of blurred visual information during fast locomotion, and indicate that future studies may reveal non-visual sensory compensation in other fast-moving animals.