Comparative functional analysis of the hyolingual anatomy in lacertid lizards

Abstract

The tongue is often considered a key innovation in the evolution of a terrestrial lifestyle as it allows animals to transport food items through the oral cavity in air, a medium with low density and viscosity. The tongue has been secondarily coopted for a wide diversity of functions, including prey capture, drinking, breathing, and defensive behaviors. Within basal lizard groups, the tongue is used primarily for the purpose of prey capture and transport. In more derived groups, however, the tongue appears specialized for chemoreceptive purposes. Here we examine the tongue structure and morphology in lacertid lizards, a group of lizards where the tongue is critical to both food transport and chemoreception. Because of the different mechanical demands imposed by these different functions, regional morphological specializations of the tongue are expected. All species of lacertid lizards examined here have relatively light tongue muscles, but a well developed hyobranchial musculature that may assist during food transport. The intrinsic musculature, including verticalis, transversalis, and longitudinalis groups, is well developed and may cause the tongue elongation and retraction observed during chemoreception and drinking. The papillary morphology is complex and shows clear differences between the tongue tips and anterior fore-tongue, and the more posterior parts of the tongue. Our data show a subdivision between the fore- and hind-tongue in both papillary structure and muscular anatomy likely allowing these animals to use their tongues effectively during both chemoreception and prey transport. Moreover, our data suggest the importance of hyobranchium movements during prey transport in lacertid lizards.