Direct Evidence for Distance Measurement via Flexible Stride Integration in the Fiddler Crab

Abstract

While on foraging excursions, fiddler crabs track their burrow location despite having no visual contact with it . They do this by path integration, a common navigational process in which motion vectors (the direction and distance of animals' movements) are summed to form a single "home vector" linking the current location with the point of origin. Here, we identify the mechanism by which the integrator measures distance, by decoupling motor output from both inertial and visual feedback. Fiddler crabs were passively translated to a position such that the home vector lay across an acetate sheet on the ground. After being frightened, crabs tried to escape but slipped as they did so. Detailed high-speed video analysis reveals that crabs measure distance by integrating strides, rather than linear acceleration or optic flow: the number of steps they took depended on both the length of the home vector and how large their steps were, whether they slipped and fell short or not. This is the most direct evidence to date of a stride integrator that is flexible enough to account for significant variation in stride length and frequency.

Human odometer is gait-symmetry specific

“…It might, however, measure in units of stride length (it might be a stride length integrator; Wittlinger et al 2006Wittlinger et al , 2007Walls & Layne 2009). One would expect that for any distance measure made in units definable at the level of the single limb, gait should not be a factor, as figure 2a would seem to affirm.…”

“…Seguinot et al 1998), arachnids (e.g. Seyfarth & Barth 1972, arthropods (Walls & Layne 2009) and insects (e.g. Wohlgemuth et al 2001).…”

Odometry and insect navigation

“…In animals walking on the earth's surface, such as desert ants, which have been studied in some detail in this regard (Wittlinger et al, 2006;Wittlinger et al, 2007a), but also in fiddler crabs (Walls and Layne, 2009), another mechanism would appear suitable for odometry, namely, stride integration. In any animal walking without aerial phases, i.e.…”

“…In fiddler crabs (Walls and Layne, 2009), an experimentally introduced slick surface can cause homing animals to slip, which induces accordant errors in distance assessment. The stride integrator of the fiddler crab thus apparently sums up the strides taken regardless of whether the ground contact is slippery or with good grip.…”

Symmetry and order parameter dynamics of the human odometer

“…In Gibson's (1966) classification of perceptual systems, the substrate variant of idiothetic information is detected by the haptic perceptual system and the inertial variant is detected by the basic orienting system (statocyst, vestibular organ). The substrate variant seems to be the more general basis for a non-visual ability to measure traveled distance (Etienne et al 1998), an ability common to humans (Isenhower et al 2012;Klatzky et al 1990;Mittelstaedt and Mittelstaedt 2001;Schwartz 1999;Turvey et al 2009), dogs (Séguinot et al 1998), fiddler crabs (Walls and Layne 2009), spiders (Barth 2004;Seyfarth and Barth 1972), and desert ants (Wittlinger et al 2006(Wittlinger et al , 2007Wohlgemuth et al 2001).…”