Time Budgets, Thermoregulation, and Maximal Locomotor Performance: Are Reptiles Olympians or Boy Scouts?

SYNOPSIS. DO ectothermal vertebrates routinely make full useof their locomotor capacities in nature? We address this questionby asking whether reptiles ever sprint at maximum burst speedsand whether they often move at speeds near maximum aerobicallysustainable levels. Relevant data are largely anecdotal butsuggest that lizards (and perhaps other vertebrate ectotherms)do not routinely perform at maximal capacities. They appearto do so only in situations that have a critical impact on fitness.Nevertheless, active lizards do thermoregulate carefully suchthat they usually maintain the potential for performing at maximalcapacity. We consider alternative, but not exclusive, explanationsfor why reptiles might maintain apparently "excessive" capacitiesand conclude with suggestions for new field and laboratory studiesthat would more rigorously address these issues.     

Metabolic Correlates of Anuran Behavior

Frogs exhibit extensive diversity in their repertoires of social,reproductive, defensive, and predatory behavior, and in themetabolic processes that support these activities. Three aspectsof anuran biology (foraging mode, post-metamorphic ontogeneticchanges in ecology, and reproductive behavior) are analyzedfor their correlations with metabolic capacities. Anurans thatforage widely for prey have greater capacities for aerobic ATPproduction than do sedentary foragers. This relationship appearsto extend to intraspecific analyses; significant differencesin aerobic capacity among populations of a species of dart-poisonfrog are associated with differences in feeding ecology. Ontogenetic change in metabolic capacity is directly coupledwith ontogeny of behavior. The magnitude of post-metamorphicchanges in physiology, behavior, and ecology appears to be relatedto differences in life history. A relatively short larval stageand small body size at metamorphosis, such as that found inAmerican toads, are associated with extensive post-metamorphicchanges in oxygen carrying capacity of the blood, cardiac musclemass, and aerobic capacity of predispersal juveniles. In contrast,predispersal juveniles of species with long larval periods andlarge body size at metamorphosis possess adult physiologicaland behavioral features. Anuran reproductive activities, especially calling to attractmates, are energetically demanding, suggesting that the behaviorof male frogs at a breeding pond may be limited by their metaboliccapacities. However, the only study that has attempted to relateindividual variation in reproductive behavior to individualvariation in aerobic capacity found no correlation between thosecharacteristics. The complexity of anuran biology ensures that physiologicalcharacteristics of anurans reflect many aspects of ecologyandbehavior, some of which act independently, others in concert.Carefully designed experiments that incorporate both field andlaboratory data are required to assess these interlocking features.     

Lipid Requirements and Lipid Uptake by Giardia lamblia Trophozoites in Culture

To better understand the lipid requirements of Giardia lamblia trophozoites and the mechanisms of lipid uptake, we supplemented serum-free TYI-S-33 medium with lipids incorporated into different lipid carriers. We found that serum lipoproteins, β-cyclodextrins, and bile salts are able to supply cholesterol and phospholipids to Giardia and to support the multiplication of the parasite in vitro. The growth rates obtained with different lipoproteins or bile salts and lipid mixtures were similar to that in standard culture medium containing serum. Pulse labelling experiments using fluorescent lipid analogs demonstrated that Giardia can take up lipids from lipoproteins, β-cyclodextrins, or bile salt micelles, but with different kinetics, and that bile salts greatly facilitated lipid transfer from lipoproteins and cyclodextrins to the parasite surface. The binding of different radioiodinated lipoprotein classes to the trophozoite surface, inhibition of lipoprotein interiorization at 4°C or by cytochalasin D, and incorporation studies using fluorescent LDL suggested that a small component of lipid uptake by trophozoites was likely due to endocytosis of lipoproteins.     

The Mechanism of Onset of the Stationary Phase in Euglena gracilis Grown with 10 mM Succinate: Intracellular pH Values*

SYNOPSIS. When Euglena gracilis were grown with 10mM succinate at pH 3.5 the extracellular pH averaged 3.62 and the cultures had produced 6 × 10⁵ cells/ml when the stationary phase began. Oxygen consumption values reached a maximum of 30 μliters/10⁶ cells/hr. Total protein and dry weights per cell remained constant during the logarithmic phase and began to decline when the late logarithmic phase was reached. Added succinate caused the cultures in stationary phase to commence logarithmic growth once more. Onset of the stationary phase in cultures grown at pH 3.5 was due to depletion of succinate. When cultures were grown at pH 6.9 the extracellular pH averaged 7.62 and the cultures produced 3 × 10⁵ cells/ml when the stationary phase began. Oxygen consumption values reached a maximum of 20 μliters/10⁶ cells/hr during the logarithmic phase. The decline in total protein and dry weights per cell began at the beginning of the logarithmic phase and continued into the stationary phase of growth. Cultures grown at pH 3.5 should produce a larger number of cells/ml than cultures grown at pH 6.9 if the cells are responding to the unionized moiety of succinate and not the ionized moiety. At pH 3.5 83% of the succinate is unionized, whereas at pH 6.9 0.20% of the succinate is unionized. The onset of the stationary phase in cultures grown at pH 3.5 and pH 6.9 is due to lack of an adequate amount of extracellular unionized succinate. Intracellular pH values were determined in cultures grown at pH 6.9 using the weak acid DMO (5.5-dimethyl-2,4-oxazolidinedione). As the extracellular pH increased from 6.90 to 7.62, the intracellular pH increased from 5.89 to 6.89. As the extracellular pH increased from 7.62 to 8.44, the intracellular pH increased from 6.89 to 7.50.     

Life Cycle and Epizootiology of Amblyospora sp. (Microspora: Amblyosporidae) in the Mosquito,Aedes cantator1

In Aedes cantator, Amblyospora sp. is transovarially transmitted and has two developmental sequences. The life cycle is initiated in the adult female with the release of sporoplasms from binucleated spores not bounded by membranes, lying free within host oenocytes. Sporoplasms infect the developing oocytes and are transmitted to the filial generation when the eggs are laid. In some of the female progeny that hatch from infected eggs, diplokaryotic cells infect host oenocytes and divide by binary fission during merogony. Sporulation and spore formation do not occur until a blood meal is taken by the host and they coincide with the development and maturation of the oocytes to complete the cycle. In other female and all male progeny, pathogen development occurs within fat body tissue of the host where diplokaryotic cells divide by multiple fission during merogony to spread the infection. Sporulation in this developmental sequence is characterized by the secretion of an accessory membrane and the meiotic division of diplokaryotic sporonts, which result in the formation of octonucleated plasmodia that undergo cytokinesis to form eight haploid spores which are not perorally infectious to other mosquito larvae. There is no increase in the prevalence of either type of infection in field populations during juvenile development, indicating that there is no direct horizontal transmission of the pathogen within any one generation. Data obtained from laboratory rearings of infected progeny, however, show that infections cannot persist relying solely upon maternal-mediated transmission and that some other mode of transmission must be operative for continued maintenance of this microsporidium in A. cantator.     

Adenosine Triphosphate Acceleration of the Nephridial Apparatus of Paramecium multimicronucleatum*

SYNOPSIS. Paramecium multimicronucleatum was exposed to various external concentrations of adenosine triphosphate (Na₂ATP) to determine the effects thereof on the cycling rate of the nephridial apparatus. Normal rate was found to vary from 3.46 to 4.28 cycles/min with a mean rate of 3.85 cycles/min at 20 C. Concentrations of ATP of less than 5 × 10⁻⁴ M caused only slight, very temporary acceleration of the cycling rate. At 5 × 10⁻⁴ M the cycling rate was accelerated less than 15%. At 3 × 10⁻³ M cycling rate was accelerated, varying from 5.35 to 7.24 cycles/min, with a mean accelerated rate of 6.25 cycles/min, a mean aoceleration of 88.3%. Changes in rate after addition of 5 × 10⁻³ M ATP ranged from a decrease of 6.2% to an increase of 1.8%, with the nephridial apparatus ultimately stopping. At higher concentrations, stoppage was almost immediate. Paramecium is rapidly dehydrated by the ATP-accelerated cycling of its nephridial apparatuses, with a net loss of 27% of its volume in 6 minutes in the 3 × 10⁻³ M ATP.     

Effect of food type on the acute and chronic toxicity of copper to Daphnia magna

SUMMARY. Daphnia magna was maintained on two diets and exposed to acute and chronic copper stresses. Animals fed vitamin-enriched algae were less sensitive to a chronic copper stress than animals fed a trout-granule diet. This conclusion is based on the responses of cohorts as measured by survival, mean brood size and r , the instantaneous rate of population growth. Application factors were also significantly different for animals reared on the two foods (0.47 for algal-fed animals, 0.12 for animals reared on trout-granules). In contrast to chronic toxicity, 72 h LC₅₀ values were not significantly different for animals maintained on the two foods. This suggests that the mechanism of toxic action is different for acute and chronic toxicity and that, if so, the ratio between chronic and acute toxicity would not be a constant under different environmental conditions.