IBN-9601173 Schwenk Squamate reptiles (lizards and snakes) have figured prominently in the growth of biological thought over the last fifty years. In particular, they have served as model organisms in studies that have shaped the field of vertebrate ecology, strongly influencing the development of modern ecological theory. It is now universally acknowledged that much of the behavioral ecology of lizards and snakes is directed by the chemical senses, especially the vomeronasal system (VNS). Therefore, elucidation of VNS function is a desirable goal within this broader context. The VNS is mediated by paired sensory receptors called the vomeronasal (or Jacobson's) organs (VNO) which lie in the snout just above the palate. In squamates the VNO are separated from the nasal cavities but open directly to the oral cavity through two tiny holes in the palate. They are stimulated by a unique behavior called tongue-flicking (TF) during which the tongue is protruded and oscillated to varying degrees. The tongue tip samples environmental chemicals extra-orally, either from the air or from the ground, and delivers these chemicals to the openings in the palate where they make their way to the VNO. The study will elucidate the anatomical and functional bases of VNS function in a representative species, the Gila monster (Heloderma suspectum). Gila monsters are an ideal study species for VNS function because they retain an intermediate morphology of the chemosensory apparatus that can serve as a functional baseline for future comparative studies. By embodying both primitive and derived features, their morphology and behavior provides information that can be generalized up and down the squamate evolutionary tree. The study will use dissection, histology and electron microscopy to examine the gross and microscopic anatomy of the tongue- vomeronasal system. The morphological mode l generated from these data will be combined with functional data derived from high speed cinegraphic (slow motion movie) and cineradiographic (x-ray movie) analyses to create a functional-morphological model of (1) tongue protrusion and oscillation; (2) environmental chemical sampling; (3) chemical delivery to the VNO. This model of VNS function will be supplemented with a theoretical/mathematical model of how chemical molecules diffuse into the fluid coating the tongue surface so that chemicals can be concentrated on the tongue during a tongue-flick. By clarifying the mechanism of the most fundamental sensory system in squamate reptiles, an important model group, this study should contribute substantively to our further understanding of how this and other animal groups diversify through time.
