Fiddler crabs accurately measure two-dimensional distance over three-dimensional terrain

Abstract

SUMMARYForaging fiddler crabs (Uca spp.) monitor the location of, and are able to return to, their burrows by employing path integration. This requires them to accurately measure both the directions and distances of their locomotory movements. Even though most fiddler crabs inhabit relatively flat terrain, they must cope with vertical features of their environment, such as sloping beaches, mounds and shells, which may represent significant obstacles. To determine whether fiddler crabs can successfully perform path integration among such three-dimensional obstacles, we tested their ability to measure distance while we imposed a vertical detour. By inserting a large hill in the homeward path of foraging crabs we show that fiddler crabs can cope with vertical detours: they accurately travel the correct horizontal distance, despite the fact that the shape of the hill forces them to change their gait from what would be used on flat ground. Our results demonstrate a flexible path integrator capable of measuring, and either integrating or discarding, the vertical dimension.

Comparative Homing Behaviors in Two Species of Crayfish, Fallicambarus Fodiens and Orconectes Rusticus

“…In cases of imposed displacements, crabs were found to miscalculate the distance and/or the direction to the shelters (Layne et al. ; Walls & Layne ). The miscalculation of distance or direction corresponded to the experimental displacements.…”

“…This odometer may receive input from the walking legs that is used to update the home vector after each movement. In cases of imposed displacements, crabs were found to miscalculate the distance and/or the direction to the shelters (Layne et al 2003a;Walls & Layne 2009). The miscalculation of distance or direction corresponded to the experimental displacements.…”

Neuronal processing of translational optic flow in the visual system of the shore crabCarcinus maenas

“…Merkle and Wehner, 2010), use stride integration (summing of individual stride lengths) to estimate distance covered (Wittlinger et al, 2006;Wittlinger et al, 2007). Turning to crustaceans, fiddler crabs certainly use optomotor responses (generated by rotational optic flow) to compensate for deviations from their intended path (Layne et al, 1999) but, like ants, judge distance travelled by flexible stride integration (Layne et al, 2003a;Layne et al, 2003b;Walls and Layne, 2009a;Walls and Layne, 2009b). Homing, however, requires that the individual knows direction as well as distance, and recent evidence suggests that maintenance of the angle between the eye and the burrow (even when the actual burrow is no longer visible to the crab) is crucial to this (Layne, 2008) (J. E. Layne, W.J.P.B.…”

The role of abiotic and biotic cues in burrow habitat selection by juvenile crayfish

“…Additionally, there is evidence that navigating in groups ("many-wrongs principle") is more advantageous than individual navigation due to suppression of individual error by group cohesion (Simons 2004, Codling et al 2007. Crustaceans use a particularly diverse set of environmental cues to aid in navigation, migration, and orientation, largely due to a wide range in patterns and scales of mobility across species (Zeil andHemmi 2006, Walls andLayne 2009). Several groups of crustaceans, including amphipods, isopods, and spiny lobsters can orient to the Earth's geomagnetic field (Lohmann and Ernst 2014).…”