Straight-line orientation in the woodland-living beetle Sisyphus fasciculatus

Abstract

To transport their balls of dung along a constant bearing, diurnal savannah-living dung beetles rely primarily on the sun for compass information. However, in more cluttered environments, such as woodlands, this solitary compass cue is frequently hidden from view by surrounding vegetation. In these types of habitats, insects can, instead, rely on surrounding landmarks, the canopy pattern, or wide-field celestial cues, such as polarised skylight, for directional information. Here, we investigate the compass orientation strategy behind straight-line orientation in the diurnal woodland-living beetle Sisyphus fasciculatus. We found that, when manipulating the direction of polarised skylight, Si. fasciculatus responded to this change with a similar change in bearing. However, when the apparent position of the sun was moved, the woodland-living beetle did not change its direction of travel. In contrast, the savannah-living beetle Scarabaeus lamarcki responded to the manipulation of the solar position with a corresponding change in bearing. These results suggest that the dominant compass cue used for straight-line orientation in dung beetles may be determined by the celestial cue that is most prominent in their preferred habitat.

The effect of step size on straight-line orientation

“…The large change in roll bearing recorded for Scarabaeus ambiguus and S. lamarcki in response to a 180°displacement of the sun (figure 2) demonstrates the common use of a sun compass in these species during straight-line orientation. These results are well in line with previous studies of the celestial compass system of S. lamarcki [6,[27][28][29][30].…”

“…To understand the effect of step size on straight-line orientation [34,35], and to model how much weight is given to external sky compass cues over internal proprioceptive cues for straight-line orientation in dung beetles, we chose to connect a vector-weighted biased correlated random walk model for directed movement, where external cues are balanced with internal ones [34,35]. The model assumes that the beetle intends to move in a straight line, which is what we have observed in this and many earlier studies of dung beetle orientation (figure 5b) [6,12,[26][27][28][29][30][31][32].…”

“…In order to obtain a sufficient amount of food, beetles gather and shape dung into balls and roll them away. To ensure the most efficient escape from the competitors at the pat, the beetles exit in all directions along paths as straight as the terrain allows [6,[26][27][28][29]. In this way, with every step taken, they maximize the distance between themselves and their competitors.…”

“…This is because most theoretical models assume a straight-line optimal trajectory [33], while the actual trajectories travelled by these animals may be more tortuous. In contrast, ballrolling dung beetles strive to move along straight paths from the start to the end of their journeys [6,12,[27][28][29][30]. Here, we characterize the size of the directional error generated with each step in the presence or absence of external compass cues in two closely related species of dung beetle, that differ greatly in size.…”

Rules for the Leg Coordination of Dung Beetle Ball Rolling Behaviour

“…Dung beetles perform complex versatile behaviours including flying, walking, manipulating or creating a large dung ball, and dynamically pushing or transporting it 18 . Typically, dung beetles walk with a tripod gait but at least one species occasionally gallops 19 .…”