THE EVOLUTION OF CHEMORECEPTION IN SQUAMATE REPTILES - A PHYLOGENETICAPPROACH

Recent advances in the field of squamate reptile chemoreception have b een paralleled by the growth and preeminence of cladistics in the fiel d of systematics, but for the most part, workers in the former have fa iled to incorporate the conceptual and informational advances of the l atter. In this paper, I attempt a preliminary rapprochement by combini ng the methods of phylogenetic systematics and current hypotheses of s quamate relationships with an overview of squamate chemosensory biolog y. This purely phylogenetic approach leads to a number of falsifiable generalizations about the evolution of chemoreception in squamates: 1) Evolution of this system is conservative rather than plastic, reflect ing to a large extent suprafamilial attributes rather than adaptation to local conditions; 2) Anguimorphs are highly chemosensory and teiids show convergence with this group; 3) Tongue-flicking, a bifurcated to ngue tip, a vomeronasal (VNO) mushroom body, and a complete circular m uscle system in the tongue are a correlated character complex associat ed with the attainment, in squamates, of a direct VNO-oral connection and the loss of a VNO-nasal connection; 4) There is little support for a visual-chemosensory dichotomy within Squamata; 5) Gekkotans are all ied with Autarchoglossa, both phylogenetically and in terms of chemose nsory biology; 6) Iguania are highly variable in chemosensory developm ent; iguanids represent the primitive iguanian condition, while agamid s and chamaeleonids have secondarily reduced or lost their chemosensor y abilities; 7) Apparent contradictions in chemosensory behavior among iguanids probably represent intrafamilial divergence; 8) Ecological c orrelates within Iguanidae and other taxa might be spurious, resulting from historical factors unrelated to the adaptations in question; 9) The mechanical demands of lingual food prehension have constrained che mosensory evolution in Iguania; chemosensory evolution within Sclerogl ossa was permitted by the liberation of the tongue from this ancestral role.