Warren P. Porter

Physiological and ecological consequences of sleeping-site selection by the Galapagos land iguana (Conolophus pallidus)

Field observations and biophysical models were combined to analyze sleeping-site selection by Galapagos land iguanas (Conolophus pallidus). Iguanas slept in different kinds of sleeping sites during different seasons. In the coolest season (garua), adult land iguanas were found in sleeping sites that were warmer than the coolest sites available. This may be because the garua season (cool, overcast, and foggy) is a time when environmental conditions mitigate against rapid warm-up in the mornings, so lizards may regulate nighttime body temperatures so that it is easier to warm up to preferred daytime body temperatures. In the warmest season, adult iguanas were found in the coolest sleeping sites available. This observation is consistent with hypotheses of voluntary hypothermia, which can be advantageous in energy conservation and in avoiding detrimental effects associated with maintenance of constant body temperatures throughout the day and night. Juvenile iguanas were found sleeping in rock crevices regardless of the ambient thermal environments. Such sites are likely to be important as refugia for this life stage, which, unlike the adult stage, is vulnerable to predation. It was concluded that selection of sleeping sites is a process that may help in avoidance of predation, optimization of body temperature at the morexa0» end of the sleeping period, and reduction of metabolic costs during sleeping. The importance of some of these factors may change with the thermal milieu (e.g., season). «xa0less

THEORETICAL AND EXPERIMENTAL STUDIES OF ENERGY EXCHANGE FROM JACKRABBIT EARS AND CYLINDRICALLY SHAPED APPENDAGES

Convection properties of jackrabbit ears were examined in a wind tunnel and in the field in an attempt to study the possible thermal role of the large ears. This work was part of a study on energy exchange of appendages. Cylindrical copper models of various shapes, aluminum castings of domestic and jackrabbit ears, and an amputated jackrabbit ear were studied in a wind tunnel (a) to define the range for convective heat loss for appendages of various shapes, and (b) to study the effect on convection of model shape and orientation to the wind. Shape, i.e. length and closure, proved important. Orientation to the wind produced no consistent or significant variation in the convection coefficient. The convection coefficients from the ear castings fell within the range generated from the cylindrical models. The convection coefficients for the amputated rabbit ear fell partially within the range. Net thermal radiation loss at midday from the jackrabbit ears was found to be small. Convection from the ears, however, could account for the loss of over 100% of the animals metabolic heat at an air temperature of 30 degrees C. If air temperature exceeds body temperature, the animal must either store heat or resort to the evaporation of water.

Metabolic Evidence of Diminished Lipid Oxidation in Women With Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS), a common female endocrinopathy, is a complex metabolic syndrome of enhanced weight gain. The goal of this pilot study was to evaluate metabolic differences between normal (n=10) and PCOS (n=10) women via breath carbon isotope ratio, urinary nitrogen and nuclear magnetic resonance (NMR)-determined serum metabolites. Breath carbon stable isotopes measured by cavity ring down spectroscopy (CRDS) indicated diminished (p<0.030) lipid use as a metabolic substrate during overnight fasting in PCOS compared to normal women. Accompanying urinary analyses showed a trending correlation (p<0.057) between overnight total nitrogen and circulating testosterone in PCOS women, alone. Serum analyzed by NMR spectroscopy following overnight, fast and at 2 h following an oral glucose tolerance test showed that a transient elevation in blood glucose levels decreased circulating levels of lipid, glucose and amino acid metabolic intermediates (acetone, 2-oxocaporate, 2-aminobutyrate, pyruvate, formate, and sarcosine) in PCOS women, whereas the 2 h glucose challenge led to increases in the same intermediates in normal women. These pilot data suggest that PCOS-related inflexibility in fasting-related switching between lipid and carbohydrate/protein utilization for carbon metabolism may contribute to enhanced weight gain.

Environmental Constraints on Some Predator—Prey Interactions

The study of environmental relationships of living organisms has a long history. Environmental effects on animals were reported by Davenport and Castle (1896). Early work on reptiles was done by Atsatt (1939) and by Cowles and Bogert (1944). Quantitative engineering approaches to the energy balance of humans first began appearing with the work of Hardy and DuBois (1938). The extension of energy-balance modeling to outdoor situations and nonhuman animals was firmly established with the publication of papers by Bartlett and Cates (1967) and Norris (1967). Porter and Gates (1969) made some initial efforts to generalize energy-balance calculations for a variety of animals. Their development of a climate-space niche was useful in expressing physiological limits of animals as they related to various combinations of environmental parameters. But the concept is limited because, first, it is a steady-state model; second, animals rarely live at their physiological limits; and third, microhabitats available in time and space are not specified. Although a climate-space diagram represents a useful concept, ecological and behavioral limits needed to be defined. Transient energy-balance models were needed and had to include more biology along with physics and engineering. Microhabitat specification was needed. Tests needed to be done on live animals in both controlled environmental facilities and out of doors. Recently, these things have been done for a relatively simple desert environment and a desert lizard, Dipsosaurus dorsalis (Porter et al., 1973). This paper outlines the usefulness of energy-balance concepts to examine predator—prey relationships. It is the basis for the extension of our investigations to other predator—prey systems, one of which we describe here. We shall attempt only a semiquantitative description here since the equations and experiments testing them have been published elsewhere.

Breath carbon stable isotope ratios identify changes in energy balance and substrate utilization in humans

Rapid detection of shifts in substrate utilization and energy balance would provide a compelling biofeedback tool for individuals attempting weight loss. As a proof of concept, we tested whether the natural abundance of exhaled carbon stable isotope ratios (breath δ13C) reflects shifts between negative and positive energy balance. Volunteers (n=5) consumed a 40% energy-restricted diet for 6 days followed by 50% excess on day 7. Breath was sampled immediately before and 1u2009h and 2u2009h after breakfast, lunch and dinner. Exhaled breath δ13C values were measured by cavity ring-down spectroscopy. Using repeated measures analysis of variance (ANOVA) followed by Dunnett’s contrasts, pre-breakfast breath values on days 2–6 were compared with day 1, and postprandial day 7 time points were compared with pre-breakfast day 7. Energy restriction diminished pre-breakfast breath δ13C by day 3 (P<0.05). On day 7, increased energy intake was first detected immediately before dinner (−23.8±0.6 vs −21.9±0.7‰, P=0.002 (means±s.d.)), and breath δ13C remained elevated at least 2u2009h post dinner. In conclusion, when shifting between negative and positive energy balance, breath δ13C showed anticipated isotopic changes. Although additional research is needed to determine specificity and repeatability, this method may provide a biomarker for marked increases in caloric intake.