Gila monsters in the desert – 20+ years disproving the maladaptation dogma

DeNardo, Dale F.

denardo@asu.edu

School of Life Sciences

Arizona State University

Tempe, Arizona USA

Gila monsters, Heloderma suspectum, have been widely popularized for more than a century and are seen as an icon of the American Southwest. Despite this attention and interest, surprisingly little was truly known about the species. In fact, it was previously suggested that Gila monsters are poorly adapted to living in the desert. However, this is not sensible since Gila monsters have resided in the Sonoran Desert for as long as the desert has existed in its current state. The misconception likely reflects the fact that Gila monsters do not use survival strategies that are typical of desert lizards. Instead, they use a suite of behavioral and physiological adaptations that are rarely seen in other desert lizards yet are convergently represented in a scattering of other desert vertebrates. These include large home range size, seasonal shifts in foraging activity, relatively low preferred body temperature, specialized cooling mechanisms, parenteral water storage, and the production of venom. Together, this unique assemblage of traits enables Gila monsters to have an otherwise unachievable specialized diet – the contents of vertebrate nest. Surviving on such a seasonally limited and widely dispersed resource clearly demonstrates that Gila monsters are extremely well adapted to their environment and the niche that they fill.