The morphology-performance-behavior-fitness paradigm provides an integrative framework within which to examine the functional and adaptive relevance of traits at different levels of biological organization. Variation in morphological or other subordinate traits result in differences in organismal performance abilities. In turn, performance capacities constrain behavioral options, thus influencing the success of an individual during tasks that impact Darwinian fitness. These connections are frequently investigated in the context of locomotion, as locomotor abilities and behaviors are frequent determining factors in survival and/or reproductive success.

Chapter One examines the relationship between endurance capacity and home range size in free-living adult male desert iguanas over two seasons. Individual endurance capacity positively predicted the home range size of adult male desert iguanas.

Chapter Two describes the results of corticosterone manipulation via hormone implants with adult male desert iguanas in a laboratory setting. Neither circulating corticosterone levels nor treadmill endurance differed significantly between treatment groups.

Chapter Three examines the home range of free-living desert iguanas in relation to endurance capacity, circulating corticosterone levels, and body mass, as well as ecological variables quantified for each home range. Corticosterone, endurance capacity, and home range size were not significantly related. Home range size was significantly negatively related to shade plant density.

Chapter Four describes the results of corticosterone manipulation via hormone implants (modified from those used in Chapter 2) with free-living adult male desert iguanas and relationships with endurance capacity and home range size. Desert iguanas that received corticosterone implants had significantly larger home ranges, but not higher endurance, compared with those that received saline implants. Home range size was again significantly negatively related to shade plant density. No relations between corticosterone, endurance capacity, or home range size were significant.

Chapter Five presents an estimate of Darwinian fitness using number of offspring sired by free-living adult male desert iguanas studied in two different years. Offspring number was calculated using DNA microsatellite analysis of paternity. In one year, home range size was a significant negative predictor of number of offspring when included in a multiple regression with corticosterone and endurance capacity. This study was limited due to small sample sizes.