THEOBALD, J. C.; University of Washington, Seattle, Washington: Night vision strategies of sphingid moths match feeding behavior

A nocturnal eye must make the most of scarce photons. Reliable vision in dim light is difficult because light is absorbed discretely and randomly. This ‘photon noise’ is an inescapable problem for nocturnal animals; they must use both optical and neural strategies to extract a useful signal from available light. Nocturnal sphingid moths perform agile, visually demanding behaviors in the dark. While they possess extraordinary optics for collecting light, this by itself is insufficient, very dim conditions require neural strategies as well. Two major neural strategies for improving signal to noise ratios in a dim environment are spatial and temporal pooling. These filters improve reliability, but sacrifice high frequency information. This is a necessary cost, but how much spatial or temporal information to give up depends on behavior and ecology. I compared the wide-field motion-sensitive neurons of two species of nocturnal sphingids: elephant (Deilephila) and death’s head (Acherontia) hawkmoths. The pooling strategies they use to filter motion signals are matched to their feeding behaviors in nature. The elephant hawkmoth, which hovers to feed, utilizes primarily temporal pooling along its motion pathway. This is preserves the low velocity motion information required for hovering. The death’s head hawkmoth utilizes spatial pooling to a much greater degree. This gives it faster responses to the onset of motion and a higher optimal velocity, consistent with faster flight.