Meeting Abstract
Burrowing is crucial for many terrestrial anurans as it provides protection from predators, high temperatures, or desiccation, as well as access to otherwise inaccessible food resources. In particular, the spade foot toad (Scaphiopus hurterii) is well known for its burrowing capabilities. These toads use relatively short hind limbs with a spade-like keratinous tubercle on the foot to excavate burrows. However, the kinematics of this movement remains unclear and the significance of this specialized morphology is unknown. Given the importance of ankle extension in other anuran locomotor behaviors, we hypothesized that this motion would also be critical for burrowing. We examined burrowing behavior in 5 toads using 3D high-speed video. The toads used one limb to dig, the working side, and the other for support, the bracing side. The motion of the working limb was cyclical with two phases, pushing and re-positioning, with an average cycle duration of 256 ± 74 ms. The motion of the joints was tracked by digitizing anatomical landmarks on the toads’ limbs. The pushing phase included flexion of the hip (average of -9.0 ± 1.1°) and dorsiflexion of the ankle (average of -29.6 ± 4.3°), indicating that ankle muscles are not contributing significant mechanical work. On the other hand, the knee extended up to 15.8 ± 4.9° during pushing, suggesting that this motion provides much of the work for digging. This finding is reflected in the lower proportion of hind limb muscle mass associated with ankle extensors (11%) compared to other non-burrowing species (19%). Future experiments will identify the morphological or physiological specializations of the knee extensors that may relate to their crucial role in this behavior.
