Abstract
ABSTRACTWithin anurans (frogs and toads), cane toads (Bufo marinus) perform particularly controlled landings in which the forelimbs are exclusively used to decelerate and stabilize the body after impact. Here we explore how toads achieve dynamic stability across a wide range of landing conditions. Specifically, we suggest that torques during landing could be reduced by aligning forelimbs with the body's instantaneous velocity vector at impact (impact angle). To test whether toad forelimb orientation varies with landing conditions, we used high-speed video to collect forelimb and body kinematic data from six animals hopping off platforms of different heights (0, 5 and 9 cm). We found that toads do align forelimbs with the impact angle. Further, toads align forelimbs with the instantaneous velocity vector well before landing and then track its changes until touchdown. This suggests that toads may be prepared to land well before they hit the ground rather than preparing for impact at a specific moment, and that they may use a motor control strategy that allows them to perform controlled landings without the need to predict impact time.
Highlights
Toads have recently been used as a model system for understanding the biomechanics and control of landing in anurans (Gillis et al, 2014)
Our results are consistent with Nauwelaert’s model of landing in Rana esculenta (Nauwelaerts and Aerts, 2006), in which peak ground reaction forces were minimized by positioning forelimbs more vertically during hops of greater height
These results align with the requirements for dynamic stability during landing put forth by Patton et al (1999), which suggested hops with higher horizontal velocities could be stabilized at impact by positioning the landing limbs further forward of the center of mass (COM)
Summary
Toads have recently been used as a model system for understanding the biomechanics and control of landing in anurans (frogs and toads) (Gillis et al, 2014). Cane toads (Bufo marinus), a group well known for jumping, perform controlled landings in which they can absorb impact energy exclusively with their forelimbs (Fig. 1) before lowering their hind limbs relatively slowly to the ground (Essner et al, 2010; Gillis et al, 2010; Akella and Gillis, 2011; Reilly et al, 2016). The dynamic stability (sensu Hof et al, 2005) cane toads achieve during landing requires both that the underlying musculature is prepared and sufficient to absorb the hop’s energy, and that the impact forces are orientated appropriately with respect to the forelimbs.
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