Hyolingual feeding systems of the Plethodontidae: Comparative kinematics of prey capture by salamanders with free and attached tongues

Abstract

AbstractHigh‐speed cinematography (500 fps) was used to analyze quantitatively the kinematics of terrestrial prey capture in Bolitoglossa occidentalis, B. mexicana, Ensatina esch‐scholtzii, Plethodon glutinosus, Desmognathus quadramaculatus, Hynobius kimurae, and H. nebulosus. The gape cycle of these salamanders is highly stereotyped. In B. occidentalis the mouth is opened by a combination of cranial elevation and mandibular depression. The gape increases dramatically during tongue retraction, thus allowing the prey to be delivered to the rear of the oral cavity without being impeded by the marginal teeth. The absence of a feeding function for these teeth apparently has resulted in their reduction and/or morphological alteration in some bolitoglos‐sines. Observed differences in jaw rotation between successful and unsuccessful prey capture attempts appear to be biomechanical phenomena and not adjustments by the salamander in response to neural feedback.Tongue projection is most rapid and highly accurate in the two bolitoglossines and Ensatina. The distance to which the tongue can be protracted from the mouth is 7% snout‐vent length in D. quadramaculatus, P. glutinosus, H. kimurae, and H. nebulosus (attached protrusible tongue); 15% in E. eschscholtzii (attached projectile tongue); and 30% in B. occidentalis (free projectile tongue). Even though tongue protraction is significantly faster in salamanders with projectile tongues than those with protrusible tongues, the range of times for the entire gape cycle is generally similar for all salamanders (ca. 100 ms). However, less derived salamanders spend a shorter period preparing the tongue for firing and more time in its projection than E. eschscholtzii and B. occidentalis. One obvious advantage for increasing the speed of tongue protraction is that it decreases the prey's available escape time. In the supergenus Bolitoglossa prey are limited to small, active invertebrates by a combination of stereotyped feeding behavior, a small tongue pad, and a lightweight hyolingual apparatus that is projected extremely fast.While all terrestrial salamanders possess the same basic feeding system, the bolitoglossines have evolved an impressive array of unique specializations for capturing small, rapidly moving prey. This suite of characters has enabled the tribe to radiate rapidly into a vast variety of microhabitats.