Document Type

Thesis

Date of Degree Completion

Spring 2017

Degree Name

Master of Science (MS)

Department

Biology

Committee Chair

Daniel D. Beck

Second Committee Member

Alison G. Scoville

Third Committee Member

Alan Ross Kiester

Abstract

Previous investigations in the field of biological thermoregulation have primarily focused on small organisms that inhabit ecosystems that are not as strongly seasonal as the tropical dry forests found along the Pacific Coast of Jalisco, Mexico. Small organisms have little or no appreciable thermal inertia, and thus, reach thermal equilibrium with their immediate surroundings relatively rapidly. In this investigation, we describe the behavioral and thermal ecology of the Mexican beaded lizard (Heloderma horridum), which commonly weighs more than 1kg. This large body size means that this species has significant thermal inertia, which, depending on the characteristics of the immediate thermal gradient, can cause its core-body temperature (Tb¬) to lag behind surrounding operative temperatures (Te) by as much as 20 minutes. A lag of this length negates shuttling as a thermoregulatory strategy because it would be too time intensive to be ecologically feasible. Beaded lizards are also resource limited by the strongly seasonal dry forests that they inhabit, and must carefully budge energy and water reserves to survive. Tb and Te were recorded every 15 minutes from a group of six beaded lizards and two copper Te models, respectively, using iButton dataloggers. Tb and Te records were used to explore body temperature time series and to estimate the timing of refuge emergence and refuge emergence-immergence intervals. These data support the hypothesis that beaded lizards have a relatively cool active Tb range, which is maintained by precisely timing refuge emergence and by modulating the length of refuge emergence-immergence intervals. Strategic maintenance of a cool active Tb range when Te models demonstrate that warmer ranges are available directly contradicts the “hotter is better” hypothesis, which posits that warmer adapted phenotypes will exhibit increased Darwinian Fitness relative to cooler adapted phenotypes.

Language

English

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