The Evolution of Chemoreception in Squamate Reptiles: A Phylogenetic Approach

Abstract

Recent advances in the field of squamate reptile chemoreception have been paralleled by the growth and preeminence of cladistics in the field of systematics, but for the most part, workers in the former have failed to incorporate the conceptual and informational advances of the latter. In this paper, I attempt a preliminary rapprochement by combining the methods of phylogenetic systematics and current hypotheses of squamate relationships with an overview of squamate chemosensory biology. 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, reflecting to a large extent suprafamilial attributes rather than adaptation to local conditions; Anguimorphs are highly chemosensory and teiids show convergence with this group; 3) Tongue-flicking, a bifurcated tongue tip, a vomeronasal (VNO) mushroom body, and a complete circular muscle system in the tongue are a correlated character complex associated 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 allied with Autarchoglossa, both phylogenetically and in terms of chemosensory biology; 6) Iguania are highly variable in chemosensory development; iguanids represent the primitive iguanian condition, while agamids and chamaeleonids have secondarily reduced or lost their chemosensory abilities; 7) Apparent contradictions in chemosensory behavior among iguanids probably represent intrafamilial divergence; 8) Ecological correlates 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 chemosensory evolution in Iguania; chemosensory evolution within Scleroglossa was permitted by the liberation of the tongue from this ancestral role.

Extensive Jaw Mobility in Suckermouth Armored Catfishes (Loricariidae): A Morphological and Kinematic Analysis of Substrate Scraping Mode of Feeding

“…Because most phenotypic traits are part of complex integrated functional systems, changing the morphology of one part of such an integrated system is likely to have a profound impact on the functional performance of that system as a whole and on all its functions (Herrel et al 2001;Russell and Bauer 2005). Specialization of the tongue for chemoreceptive purposes in snakes, for example, prevents its use in prey transport and could explain the coevolution of an alternative prey-transport mechanism: the pterygoid walk (Schwenk 1993(Schwenk , 1994Cundall and Greene 2000). Even though the polarity of cause and effect between structural modifications and functional implications is difficult to unravel, a proper design of comparative and experimental work may provide some insights into the close match between structure and function (Russel and Bauer 2005).…”

The correlated evolution of biomechanics, gait and foraging mode in lizards

“…Movement patterns have been used to categorize lizards as sit-and-wait or wide foraging (Perry, 2007;Pianka, 1966) and numerous physiological, morphological, behavioral, life history, dietary and other ecological traits have been shown to covary with foraging mode (Cooper, 1994;Schwenk, 1993). For example, sit-and-wait foragers (SW) rely primarily on vision to ambush prey (and accordingly have poorly developed chemosensory abilities), and use large sticky tongues coupled with short broad skulls to capture and process prey.…”

Nervi Olfactorius, Opticus and Octavus of Malpolon Moilensis.

“…In Squamata such organs are relatively poorly understood (Rehorek et al, 2000). Most studies, however, have far concentrated on the behavioural and functional aspects (Schwenk, 1993) as well as developmental studies (Kaczmarek et al, 2017); with little attention being given to the innervation of this system (Kratzing, 1975;Wang and Halpern, 1980). In contrast to Ophidia, the cranial nerves of lizards have been studied in more detail and by many investigators Dakrory, 1994).…”