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The mechanistic bases of natural and sexual selection on physiological and behavioral traits were examined in male morphs of three colors of the side-blotched lizard, Uta stansburiana. Orange-throated males are aggressive and defend large territories with many females. Blue-throated males defend smaller territories with fewer females; however, blue-throated(More)
We report seasonal variation in steroid hormone levels in blood samples from free-ranging Western Diamond-backed Rattlesnakes (Crotalus atrox), and the relationship between these hormones and events in the reproductive cycle. At a field site in the Sonoran Desert of south-central Arizona, we collected monthly blood samples over the course of two active(More)
A major challenge in biology is understanding how organisms partition limited resources among physiological processes. For example, offspring production and self-maintenance are important for fitness and survival, yet these critical processes often compete for resources. While physiological trade-offs between reproduction and immune function have been(More)
Steroid hormones play a major role in influencing the physiology and behavior of all animals, including reptiles. Oftentimes, it is an interaction between two or more hormones that is ultimately responsible for the observed response or behavior. We designed a pair of field studies on adjacent communities of side-blotched lizards (Uta stansburiana) to(More)
The phylogeography of the California mountain kingsnake, Lampropeltis zonata, was studied using mitochondrial DNA sequences from specimens belonging to the seven recognized subspecies and collected throughout the range of the species. Maximum parsimony and maximum likelihood methods identified a basal split within L. zonata that corresponds to southern and(More)
Recent field studies on the reproductive ecology of western diamond-backed rattlesnakes (Crotalus atrox) from populations in southern Arizona showed significant differences in the concentration of plasma sex steroids (testosterone, T; 5alpha-dihydrotestosterone, DHT; and 17beta-estradiol, E2) throughout the active season (March-October), and peak levels(More)
In desert species, seasonal peaks in animal activity often correspond with times of higher rainfall. However, the underlying reason for such seasonality can be hard to discern because the rainy season is often associated with shifts in temperature as well as water and food availability. We used a combination of the natural climate pattern of the Sonoran(More)
During 1991 through 1994, natural selection on reproductive effort in side-blotched lizards was indexed by measuring total clutch mass produced on the first clutch of the reproductive season and assessing how such effort in current reproduction affects subsequent survival and clutch production. In addition, selection was also experimentally assessed in(More)
Nocturnal geckos are active at body temperatures 10-35°C below the thermal optima for maximum rate of aerobic metabolism (V.O2max) of diurnal lizards. Therefore, given ancestral (diurnal) lizard physiology, nocturnality causes a substantial thermal handicap in locomotor performance. In prior studies, we hypothesized that a low minimum cost of locomotion(More)
Examination of the selective forces behind the transition from oviparity to viviparity in vertebrates must include an understanding of the relative energy costs of the two reproductive modes. However, interspecific comparisons of reproductive mode are confounded by numerous other inherent differences among the species. Therefore, we compared oxygen(More)