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Lessons from Hopeful Monsters: Emerging Insights from the Field of “Helodermatology”

Gienger, Christopher M. Department of Biology Austin Peay State University Clarksville, Tennessee USA

DeNardo, Dale F. Davis, Jon School of Life Sciences Arizona State University Tempe, Arizona USA

Goode, Matt School of Natural Resources and the Environment University of Arizona Tucson, Arizona USA

Jones, Jason Nevada Department of Wildlife Las Vegas, Nevada USA

Emblidge, Patrick G. Department of Fisheries and Wildlife Oregon State University

Corvallis, Oregon USA

Holcomb, Kerry U.S. Fish and Wildlife Service Las Vegas, Nevada USA

Beck, Daniel D. Department of Biology Central Washington University Ellensburg, Washington USA

Helodermatid lizards have become icons of our desert southwest, flagships of the tropical dry forest, and models for the value of biological diversity. Heloderma first appeared in seasonal tropical environments over 23 mya, and later colonized the warm Sonoran, Mojave, and Chihuahuan deserts. Extant helodermatid lizards span over 22 degrees latitude and 2000 miles from their northern limit in the Mojave Desert to the southern extent of their distribution in the tropical dry forests of eastern Guatemala. In this presentation, I will summarize how recent discoveries about the ecology, physiology, and evolution of helodermatid lizards inform other realms of biology, medicine, and conservation. Also, I will present results of a latitudinal analysis of thermal biology and energy use of Heloderma from temperate to tropical habitats. We analyzed body and environmental temperatures along a 1500-mile latitudinal gradient, from Mojave populations in Utah and Nevada, Sonoran and Chihuahuan desert populations in Arizona and New Mexico, to a H. horridum population in tropical dry forest of coastal Jalisco, Mexico. Average resting body temperatures varied from approximately 18C in Utah, 22C in Nevada and New Mexico, 23C in Arizona to 25C in Jalisco, Mexico. Average activity temperatures, on the other hand, were fairly consistent throughout this gradient, hovering around 30C for all populations; Heloderma seldom tolerates body temperatures above 37C. Annual energy expenditures align with these patterns of body temperature variation. Beaded Lizards in tropical dry forests have considerable higher annual energy demands than Gila Monsters in more northerly desert habitats. Energy and water considerations will likely determine how Heloderma respond to climate change. As our planet continues to warm, Heloderma might tolerate changes in temperature better than changes in precipitation. Habitat loss and habitat fragmentation, however, remain significant threats to their survival, especially along the margins of their geographic distribution.

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