Date of Award

Fall 12-1-2003

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Life Sciences

First Advisor

George S. Bakken

Second Advisor

Charles J. Amlaner

Third Advisor

Diana K. Hews

Abstract

Pitvipers (Viperidae: Crotalinae) possess unique sensory organs, the facial pits, capable of sensing subtle fluctuations in thermal radiation. Prey acquisition has long been regarded as the sole function of the facial pits. However, the ability to sense thermal radiation could also direct thermoregulatory behavior by remotely sensing nearby surface temperatures. Using a series ofbehavioral arenas of varying spatial complexity and ecological relevance, I surveyed the ability of western diamondback rattlesnakes (Crotalus atrox) to direct successful thermoregulatory movements with either functional or disabled facial pits. I found that western diamondback rattlesnakes could base thermoregulatory decisions on thermal radiation cues when their pits were functional, but not when blocked. To further investigate possible ecological and phylogenetic correlates of facial pit mediated thermoregulation, I examined 12 pitvipers that represented both key nodes in the evolution of pitvipers and a broad range of thermal environments. I also investigated a single species of true viper, a closely related subfamily of snakes which lacks facial pits but possess supranasal sacs, organs that have been reported to be putative thermal radiation detectors. All pitviper species tested were able to direct thermoregulatory movements with functional pits and failed to do so when their pits were disabled. The single true viper species in the study was unable to use radiative cues to mediate thermoregulation. The results of these studies indicate that facial pits are part of a generalized sense and that thermoregulation cued by thermal radiation appears to be an ancestral trait among the pitvipers. Further, these findings suggest thermoregulation as an alternative hypothesis to prey acquisition for the adaptive force which drove the evolution of facial pits.

Download

Share

COinS