The effect of step size on straight-line orientation

Abstract

Moving along a straight path is a surprisingly difficult task. This is because, with each ensuing step, noise is generated in the motor and sensory systems, causing the animal to deviate from its intended route. When relying solely on internal sensory information to correct for this noise, the directional error generated with each stride accumulates, ultimately leading to a curved path. In contrast, external compass cues effectively allow the animal to correct for errors in its bearing. Here, we studied straight-line orientation in two different sized dung beetles. This allowed us to characterize and model the size of the directional error generated with each step, in the absence of external visual compass cues ( motor error ) as well as in the presence of these cues ( compass and motor errors ). In addition, we model how dung beetles balance the influence of internal and external orientation cues as they orient along straight paths under the open sky. We conclude that the directional error that unavoidably accumulates as the beetle travels is inversely proportional to the step size of the insect, and that both beetle species weigh the two sources of directional information in a similar fashion.

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

“…when the apparent position of the sun is changed by 180° with the aid of a mirror, while simultaneously blocking the real sun from view under a natural sky, K. lamarcki will turn in response to the mirrored sun (Dacke et al, 2014;Khaldy et al, 2019a;Khaldy et al, 2019b).…”

“…For the dung beetle Kheper lamarcki , the sun is naturally the most prominent directional compass cue in its heading direction network ( Dacke et al, 2013a ; 2014 ; el Jundi et al, 2015 ; Khaldy et al, 2019a ; 2019b ; Smolka et al, 2016 ) . If the position of the sun is experimentally set in conflict with other celestial cues (with the aid of a mirror), K. lamarcki changes its bearing by 180 deg in response to this positional change ( Dacke et al, 2014 ).…”

Cold-induced anesthesia impairs path integration memory in dung beetles

“…Interestingly, beetles trained over a longer distance (2.55 m) initiated their search behaviors after covering only 40% and 30% of their home vectors (i.e., 1.01 ± 0.56 m [n = 13] and 0.74 ± 0.36 m [mean ± SD, n = 11]) after 10 and 60 min immobilization, respectively (Figures 2Ai, 2Aiii, and 2C; Table 1). An increase in accumulated errors with increasing path length 8 or number of steps as recently shown in ants and ball-rolling dung beetles 17,18 could possibly increase the positional uncertainty, resulting in the observed transition to a systematic search proportionally earlier when trained over longer distances.…”

Operationalizing Goal Directedness: An Empirical Route to Advancing a Philosophical Discussion

“…And Turchin (1998) introduced a way to evaluate directional bias of caterpillars, which compares probabilities of making turns toward or away from an attractor as a function of distance from the attractor. Thus, detecting and quantifying directional bias in organismal movement has been a long-standing project in the biological literature (e.g., Marsh and Jones 1988;Bailey et al 2018;Bearon and Durham 2019;Peleg and Mahadevan 2016;McClintock et al 2012;Bailey and Thompson 2006;Fortin et al 2005;Papastamatiou et al 2011;Khaldy et al 2019).…”