The interplay of directional information provided by unpolarised and polarised light in the heading direction network of the diurnal dung beetle Kheper lamarcki

Abstract

The sun is the most prominent source of directional information in the heading direction network of the diurnal, ball-rolling dung beetle Kheper lamarcki. If this celestial body is occluded from the beetle's field of view, the distribution of the relative weight between the directional cues that remain shifts in favour of the celestial pattern of polarised light. In this study, we continue to explore the interplay of the sun and polarisation pattern as directional cues in the heading direction network of K. lamarcki. By systematically altering the intensity and degree of the two cues presented, we effectively change the relative reliability of these directional cues as they appear to the dung beetle. The response of the ball-rolling beetle to these modifications allows us to closely examine how the weighting relationship of these two sources of directional information is influenced and altered in the heading direction network of the beetle. We conclude that the process in which K. lamarcki relies on directional information is very likely done based on Bayesian reasoning, where directional information conveying the highest certainty at a particular moment is afforded the greatest weight.

Varieties of visual navigation in insects

“…In a recent study, Khaldy et al ( 2022 ) demonstrated Bayesian integration of celestial cues in dung beetle orientation. They tested Scarabaeus (Kheper) lamarcki in a controlled indoor arena and showed that the beetles could maintain directional orientation in their dung rolling behaviour with either a green light source that served as an artificial ersatz sun or with an artificial polarised light source.…”

Mechanisms of spectral orientation in a diurnal dung beetle

“…Unfortunately, our current data do not allow us to answer this question, but it is possible that with the 365 + 530 nm combination, the excitation ratio fed into the colour opponent system was just right to facilitate antagonistic neural processing [11] and, as a consequence, the beetles relied more heavily on spectral directional information for orientation than in the other experimental conditions. Such flexible use of compass cue preferences relative to the prevailing visual scenery is well documented within the heading compass network of the beetles [40,41]. However, as soon as the intensity of the light presented in isolation was decreased by 1 log unit, the beetles could no longer orient to it (figure 4 b ), again demonstrating that intensity still plays a role when orienting with spectral information.…”

Vector navigation in walking bumblebees

“…However, the influence of the polarizer became stronger with increased amounts of UV light transmitted. Celestial cue preferences in honeybees thus depend on the relative strengths of the two cues, 51 a finding that is also true in ants 36 and dung beetles 37 and is likely to be true for orientation cue preferences in bumblebees as well.…”

“…When orientation responses are examined in a natural environment or in a laboratory setting, some cues are weighted more heavily than others and therefore dominate in experimentally generated cue-conflict situations. 5,10,12,18,36,37 Since we demonstrated that B. terrestris will orient to overhead polarization patterns and a point source when both cues were in isolation, we next were interested in which of the two cues the bumblebees preferred to orient with when both were available in concert.…”