Robert E Espinoza

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Herbivory has evolved in many groups of vertebrates, but it is rare among both extinct and extant nonavian reptiles. Among squamate reptiles, (lizards, snakes, and their relatives), <2% of the >7,800 species are considered to be herbivorous, and herbivory is restricted to lizards. Here, we show that within a group of South American lizards (Liolaemidae,(More)
We tested for the occurrence of Bergmann's rule, the pattern of increasing body size with latitude, and Rapoport's rule, the positive relationship between geographical range size and latitude, in 34 lineages of Liolaemus lizards that occupy arid regions of the Andean foothills. We tested the climatic-variability hypothesis (CVH) by examining the(More)
Many of the threats to the persistence of populations of sensitive species have physiological or pathological mechanisms, and those mechanisms are best understood through the inherently integrative discipline of physiological ecology. The desert tortoise was listed under the Endangered Species Act largely due to a newly recognized upper respiratory disease(More)
Diet quality can influence many aspects of digestion, but the links between diet quality and resting metabolism are poorly understood. In nature, it might be beneficial to reduce energy expenditure when only poor quality diets are available. Alternatively, animals might increase the processing capacity of the gut to more thoroughly extract energy. If(More)
Our experiments were designed to test the hypotheses that dietary lipids can affect whole-animal physiological processes in a manner concordant with changes in the fluidity of cell membranes. We measured (1) the lipid composition of five tissues, (2) body temperatures selected in a thermal gradient (T(sel)), (3) the body temperature at which the righting(More)
The Liolaemus elongatus group currently includes eight species (including the species described herein) of mid-sized, long-tailed, primarily saxicolous lizards. Members of this lineage are distributed in northwestern Argentina along the Andean Cordillera south to the Patagonian Steppe (27–448 S) and over a wide range of elevations (350–3900 m). Here we(More)
Animals that are unable to meet their metabolic needs should adopt compensatory behaviors to mitigate their energetic deficits. Voluntary hypothermia is one such energy-saving strategy. Physiological constraints associated with the digestion of plant tissues, however, may limit the thermoregulatory options of herbivorous ectotherms. In this laboratory(More)
Aggregating has been widely studied in a variety of animals and found to have important benefits in terms of sociality, courtship, predator avoidance and physiology. Several species of nocturnal geckos form diurnal aggregations; however, little is known about the benefits of these groupings. We conducted a series of experiments to determine the benefit of(More)
The spermatozoa of Crotaphytus bicinctores and Gambelia wislizenii (Crotaphytidae), and Anolis carolinensis (Polychrotidae) exhibit the squamate autapomorphies of a single perforatorium extending anteriorly from the apical tip of the paracrystalline subacrosomal cone, the presence of an epinuclear electron-lucent region, and extension of the fibrous sheath(More)
227 in Western Province, the 2000 wet season lasted well into July. Nevertheless, humidity levels were moderate (50–60%), and the environment was generally dry and warm (29–31°C). Though we have no direct evidence of the diet of this python in PNG, there were numerous geckos (Hemidactylus frenatus) between the same metal sheets. The live specimen was left(More)
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