Morphology of the feeding system in agamid lizards: Ecological correlates

The interaction of organismal design with ecology, and its evolutionary dev elopment are the subject of many functional and ecomorphological studies. M any studies have shown that the morphology and mechanics of the masticatory apparatus in mammals are adapted to diet. To investigate the relations bet ween diet and the morphological and physiological properties of the lizard jaw system, a detailed analysis of the structure of the jaw apparatus was u ndertaken in the insectivorous lizard Plocederma stellio and in closely rel ated herbivorous lizards of the genus Uromastix. The morphological and phys iological properties of the jaw system in P. stellio and U. aegyptius were studied by means of dissections, light microscopy, histochemical characteri sations, and in vivo stimulation experiments. The skull of Uromastix seems to be built; for forceful biting (high, short snout). Additionally, the pte rygoid muscle is modified in P. stellio, resulting in an additional force c omponent: during static biting. Stimulation experiments indicate that jaw m uscles in both species are fast, which is supported by histochemical staini ngs. However, the oxidative capacity of the jaw muscles is larger in Uromas tix. Contraction characteristics and performance of the feeding system (for ce output) are clearly thermally dependent. We conclude that several charac teristics of the jaw system (presence of extra portion of the pterygoid mus cle, large oxidative capacity of jaw muscles) in Uromastix may be attribute d to its herbivorous diet. Jaw muscles, however, are still faster than expe cted. This is presumably the result of trade-offs between the thermal chara cteristics of the jaw adductors and the herbivorous lifestyle of these anim als. Anat Rec 254:496-507, 1999. (C) 1999 Wiley-Liss, Inc.