AN ASSESSMENT OF THE EVAPORATIVE RELEASE OF HEAT FROM THE
BUCCOPHARYNGEAL, CUTANEOUS, AND CLOACAL EPITHELIA OF BIRDS
AND REPTILES
by
Ty C.M. Hoffman


A Dissertation Presented in Partial Fulfillment
of the Requirements for the Degree
Doctor of Philosophy
ARIZONA STATE UNIVERSITY

May 2007 C.E.


ABSTRACT

    Buccopharyngeal evaporation occurs from the mouth and pharynx, and it is only one component of an animal's total evaporation. For tetrapods other than mammals, non-buccopharyngeal evaporation (the remainder of total evaporation) occurs despite an incapacity for sweating. High rates of non-buccopharyngeal evaporation have been measured in many bird species, and rates of non-buccopharyngeal evaporation have been shown to change gradually during acclimation to changes in temperature or aridity. This dissertation demonstrates that mourning doves (Zenaida macroura Linnaeus) are able to effect rapid, endogenous adjustment to the rate of non-buccopharyngeal evaporation when faced with a suppression of buccopharyngeal evaporation. This implies that non-buccopharyngeal evaporation can serve as a transient mechanism for thermoregulation. However, the adjustment of non-buccopharyngeal evaporation shown in mourning doves prompts the question of how that non-buccopharyngeal evaporation is apportioned among the non-buccopharyngeal epithelia.
    Historically, researchers have assumed that all non-buccopharyngeal evaporation occurs from the skin (cutaneous evaporation). This research demonstrates that the cloaca can be the site of  much of an animal's total evaporation and that cloacal evaporation sheds enough heat to be important for thermoregulation. Both Gila monsters (Heloderma suspectum Cope) and Inca doves (Columbina inca Lesson) underwent a transition from negligible to significant rates of cloacal evaporation as ambient temperature increased beyond a critical point. Cloacal evaporation accounted for 82% of Gila monsters' total evaporation at 40°C and for 21% of Inca doves' total evaporation at 42°C. The heat dissipation that cloacal evaporation affords these two species could allow them to inhabit hotter microclimates for longer time periods, potentially increasing time allocated to foraging and reproductive behaviors.
    Evidence that cloacal evaporation is not a universal feature of all animals possessing a cloaca is provided by results from Eurasian quail (Coturnix coturnix Linnaeus) and ball pythons (Python regius Shaw), both of which exhibited negligible cloacal evaporation even when heat-stressed. The negative results from these species, especially from the ball python, a tropical snake unlikely to require cloacal evaporative cooling, serve as preliminary evidence that cloacal evaporation is an adaptive mechanism for thermoregulation.


Full Dissertation





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