Neural coding underlying the cue preference for celestial orientation
112 (36):
11395--11400 (2015)Abstract
Diurnal and nocturnal African dung beetles use celestial cues, such<br/><br>
as the sun, the moon, and the polarization pattern, to roll dung<br/><br>
balls along straight paths across the savanna. Although nocturnal<br/><br>
beetles move in the same manner through the same environment<br/><br>
as their diurnal relatives, they do so when light conditions are at<br/><br>
least 1 million-fold dimmer. Here, we show, for the first time to<br/><br>
our knowledge, that the celestial cue preference differs between<br/><br>
nocturnal and diurnal beetles in a manner that reflects their<br/><br>
contrasting visual ecologies. We also demonstrate how these cue<br/><br>
preferences are reflected in the activity of compass neurons in the<br/><br>
brain. At night, polarized skylight is the dominant orientation cue<br/><br>
for nocturnal beetles. However, if we coerce them to roll during<br/><br>
the day, they instead use a celestial body (the sun) as their primary<br/><br>
orientation cue. Diurnal beetles, however, persist in using a<br/><br>
celestial body for their compass, day or night. Compass neurons<br/><br>
in the central complex of diurnal beetles are tuned only to the<br/><br>
sun, whereas the same neurons in the nocturnal species switch<br/><br>
exclusively to polarized light at lunar light intensities. Thus, these<br/><br>
neurons encode the preferences for particular celestial cues and alter<br/><br>
their weighting according to ambient light conditions. This flexible<br/><br>
encoding of celestial cue preferences relative to the prevailing visual<br/><br>
scenery provides a simple, yet effective, mechanism for enabling<br/><br>
visual orientation at any light intensity.