Influence of Ambient Illumination on the Use of Olfactory and Visual Signals by a Nocturnal Hawkmoth During Close-Range Foraging.

As a goal-directed behavior, foraging for nectar functions on the basis of a sequence of innate stereotyped movements mainly regulated by sensory input. The operation of this inherited program is shaped by selective pressures acting on its efficiency, which is largely dependent upon the way the system handles sensory information. Flowers offer a wealth of signals, from odors acting as distant attractants, to colors eliciting approximation and feeding responses, to textures guiding feeding responses toward a reservoir of nectar. Thus, animals use different signals in the regulation of particular motor outputs. Nevertheless, the use of these sensory signals can be user-specific (e.g. species, motivation, experience, learning) as well as context-dependent (e.g. spatiotemporal patterns of stimulation, availability of signals, multimodal integration). The crepuscular/nocturnal hawkmoths Manduca sexta experience a wide range of illuminations during their foraging activity, which raises the question of how these environmental changes might affect the use of two important floral signals, odor and visual display. In a flight cage, we explored the use of these signals under different illuminances. Under conditions of starlight and crescent moonlight, moths showed very low levels of responsiveness to unscented feeders (artificial flowers). However, responsiveness was recovered either by increasing illumination, or by offering olfactory signals. Additionally, we recorded a bias toward white over blue feeders under dim conditions, which disappeared with increasing illumination. We discuss how this kind of experimental manipulation may provide insights to the study of how innate behavioral programs, and their underlying neural substrates, overcome selective forces imposed by the uncertainty of natural, ever-changing environments.