Research

Research Foci of the DeNardo Lab

Research in our lab examines physiological processes from an integrative perspective. Studies examine how physiological processes shape the ecology of a species, influence indiviudal behavior, and provide driving forces for evolution. We are also interestesed in the counter relationship of how the ecology and behavior of an animal influence physiological processes. Most of our research projects incorporate both laboratory experiments that allow for close assessment of subjects under controlled conditions and intensive field studies which allow for more complex ecologically relevant assessments. While challenging, simultaneously undertaking both laboratory and field studies provides a powerful means to thoroughly address our research questions. Field research includes both observational studies and manipulative experiments (e.g., hormone manipulation, food or water supplementation). Our work addresses broad physiological questions and typically uses squmate reptiles (lizards and snakes) as models for these studies. Each project incorporates at least one but usually more of the following broad areas:

Physiological capabilities

A key focus of our lab is exploring the physiological potential of our study species. By understanding the capabilities of an organism, we are able to appreciate the physiological constraints that may limit an animal's distribution, habitat use, and reproductive activity. Some of the physiological measures we assess include metabolic rate, evaporative water loss, growth, body condition, and digestion.

Physiological regulation

In addition to recognizing the physiological potential of an organism, we are also interested in how these processes are regulated. Therefore, we often examine hormonal profiles of our study organisms and conduct manipulative experiments that alter circulating hormone levels.

Physiological trade-offs

Of key interests in our lab is not only how animals physiologically cope with environmental challenge, but also how adjustments to meet one challenge affect other physiological processes. Of particular interest is the relationship among water balance, thermoregulation, and energy balance. For example, evaporative water loss aids thermoregulation, but comes at a potential cost to water balance. We are interested in how the current state of the animal influences the behavioral and physiological response to environmental challenge.

Environmental use

We are very interested in how organisms use their environment to meet physiological needs and how they avoid physiologically challenging situations. Similar to our interests in physiology of homeostatic trade-offs, we are interested in how homeostatic trade-offs affect activity patterns. For example, underground burrows provide critical refuge from the hot arid surface conditions of the desert, but most animals must surface in order to forage and maintain energy balance. The timing of activity bouts and the physiological implications of such bouts are areas of interest to our lab.

Proximal mechanisms for evolution

Some studies in the lab examine proximal mechanisms that may explain traits that are often considered "adaptive". While we cannot determine what selective pressures led to the evoultion of particular traits, we conduct studeis that assess proximate mechansims and their potential as driving forces for evolution. For example, we have examined proximate mechanisms for the sexual size dimorphism in rattlesnakes and the potential for the regulation of the developmental environment to serve as a driving force for the evoution of endothermy.

Recent and current projects

Some of the recent and current projects being conducted in the lab are briefly outlined here. More details for each of these projects can be found in the research focus statement of each lab member (by clicking on their photo within the Team DeNardo directory). The lead particants of each project are provided in parenthesis.

What are the proximal mechanisms for sexual size dimorphism in western diamond-backed rattlesnakes, Crotalus atrox? (Emily Taylor) This project, examined the basis for sexual size dimrphism (SSD) in rattlesnakes. This dissertation project used a combination of studies including monitoring of a free-ranging population, laboratory growth studies, supplemental feeding in the field, and hormone manipulation and monitoring. Results demonstrated that the SSD was not a fixed trait, but rather a result of environmental constraints acting on sexual differences in energy expenditure.

How do environmental constraints affect physiological trade-offs in a desert ectotherm, the Gila monster (Heloderma suspectum)? (Jon Davis) This project examines how Gila monsters maintain thermal, water, and energy balances despite the challenging environmental conditions of the Sonoran Desert. The study explores how environmental and physiological conditions impact trade-offs among these critical parameters and also investigates how specialized phyisological processes such as cloacal water loss and reabsorption of bladder water aid Gila monsters in coping with extreme environmental conditions.

Does facultative endothermy during brooding improve the developmental environment of python offspring? (Dale DeNardo) This study has two primary objectives. First, it evaluates the endothermic capability of various python species. Second, the study utilizes controllable snake models to determine whether stepwise increases in endothermic capability provide progressively enhanced control of the developmental environment and whether such enviornmental control enhances offspring quality. This study provides an empiracal test of Farmer's reproductive model for the evolution of endothermy.

How do brooding pythons regulate the thermal, hydric, and gas exchange needs of their developing offspring? (Zach Stahlschmidt) While not all pythons are endothermic, all species brood their eggs suggesting benefits to brooding beyond those derived from endothermy. While tight coiling around the eggs may benefit thermal conditions and hydric balance, gas exchange may be compromised. Interestingly, females periodically adjust their brooding posture, allowing exposure of at least some part of the clutch to the nest environment for short periods of time. This studies examines how postural changes during brooding impact thermoregulation, water balance, and gas exchange of the developing embryos. This study provides a rare examination of discontinuous gas exchange in a vertebrate and assesses its value to egg water balance.