Changes in heart rate are important for thermoregulation in the varanid lizard Varanus varius

Laboratory studies and a single field study have shown that heart rate in some reptiles is faster during heating than during cooling at any given body temperature. This phenomenon, which has been shown to reflect changes in peripheral blood flow, is shown here to occur in the lizard Varanus varius (lace monitor) in the wild. On a typical clear day, lizards emerged from their shelters in the morning to warm in the sun. Following this, animals were active, moving until they again entered a shelter in the evening. During their period of activity, body temperature was 34-36 degrees C in all six study animals (4.0-5.6 kg), but the animals rarely shuttled between sun and shade exposure. Heart rate during the morning heating period was significantly faster than during the evening cooling period. However, the ratio of heating to cooling heart rate decreased with increasing body temperature, being close to 2 at body temperatures of 22-24 degrees C and decreasing to 1.2-1.3 at body temperatures of 34-36 degrees C. There was a significant decrease in thermal time constants with increasing heart rate during heating and cooling confirming that changes in heart rate are linked to rates of heat exchange

Immune-challenged fish up-regulate their metabolic scope to support locomotion

ArticleEnergy-based trade-offs occur when investment in one fitness-related trait diverts energy away from other traits. The extent to which such trade-offs are shaped by limits on the rate of conversion of energy ingested in food (e.g. carbohydrates) into chemical energy (ATP) by oxidative metabolism rather than by the amount of food ingested in the first place is, however, unclear. Here we tested whether the ATP required for mounting an immune response will lead to a trade-off with ATP available for physical activity in mosquitofish (Gambusia holbrooki). To this end, we challenged fish either with lipopolysaccharide (LPS) from E. coli or with Sheep Red Blood Cells (SRBC), and measured oxygen consumption at rest and during swimming at maximum speed 24h, 48h and 7 days post-challenge in order to estimate metabolic rates. Relative to saline-injected controls, only LPS-injected fish showed a significantly greater resting metabolic rate two days post-challenge and significantly higher maximal metabolic rates two and seven days post-challenge. This resulted in a significantly greater metabolic scope two days post-challenge, with LPS-fish transiently overcompensating by increasing maximal ATP production more than would be required for swimming in the absence of an immune challenge. LPS-challenged fish therefore increased their production of ATP to compensate physiologically for the energetic requirements of immune functioning. This response would avoid ATP shortages and allow fish to engage in an aerobically-challenging activity (swimming) even when simultaneously mounting an immune response. Nevertheless, relative to controls, both LPS- and SRBC-fish displayed reduced body mass gain one week post-injection, and LPS-fish actually lost mass. The concomitant increase in metabolic scope and reduced body mass gain of LPS-challenged fish indicates that immune-associated trade-offs are not likely to be shaped by limited oxidative metabolic capacities, but may instead result from limitations in the acquisition, assimilation or efficient use of resources.We are very grateful to Noah Ashley for helpful comments on the manuscript, to all the participants of the Disease Group meeting of the University of Exeter (Cornwall) for useful discussion. All procedures were approved by a prefectorial order from Ariège, France (Agréments de l'établissement pour l’élevage et l'expérimentation no. 0108 and no. SA-013-PB-092; certificats d'autorisation d’élevage et d'expérimentation sur poissons vivants to Oliver Guillaume, no. 09-273 and no. A09-3) and by the University of Sydney Animal Ethics Committee (approval no. L04/10-2010/3/5411). This research was supported by a Marie Curie Reintegration Grant to C.B. (FP7-PEOPLE-IRG-2008 #239257) and an Australian Research Council grant to F.S

Physiology can predict animal activity, exploration, and dispersal

Physiology can underlie movement, including short-term activity, exploration of unfamiliar environments, and larger scale dispersal, and thereby influence species distributions in an environmentally sensitive manner. We conducted meta-analyses of the literature to establish, firstly, whether physiological traits underlie activity, exploration, and dispersal by individuals (88 studies), and secondly whether physiological characteristics differed between range core and edges of distributions (43 studies). We show that locomotor performance and metabolism influenced individual movement with varying levels of confidence. Range edges differed from cores in traits that may be associated with dispersal success, including metabolism, locomotor performance, corticosterone levels, and immunity, and differences increased with increasing time since separation. Physiological effects were particularly pronounced in birds and amphibians, but taxon-specific differences may reflect biased sampling in the literature, which also focussed primarily on North America, Europe, and Australia. Hence, physiology can influence movement, but undersampling and bias currently limits general conclusions

Diving behaviour of a reptile (Crocodylus johnstoni) in the wild: Interactions with heart rate and body temperature

The differences in physical properties of air and water pose unique behavioural and physiological demands on semiaquatic animals. The aim of this study was to describe the diving behaviour of the freshwater crocodile Crocodylus johnstoni in the wild and to assess the relationships between diving, body temperature, and heart rate. Time-depth recorders, temperature-sensitive radio transmitters, and heart rate transmitters were deployed on each of six C. johnstoni (4.0-26.5 kg), and data were obtained from five animals. Crocodiles showed the greatest diving activity in the morning (0600-1200 hours) and were least active at night, remaining at the water surface. Surprisingly, activity pattern was asynchronous with thermoregulation, and activity was correlated to light rather than to body temperature. Nonetheless, crocodiles thermoregulated and showed a typical heart rate hysteresis pattern (heart rate during heating greater than heart rate during cooling) in response to heating and cooling. Additionally, dive length decreased with increasing body temperature. Maximum diving length was 119.6 min, but the greatest proportion of diving time was spent on relatively short

Crocodiles as dinosaurs: Behavioural thermoregulation in very large ectotherms leads to high and stable body temperatures

Empirical field data describing daily and seasonal cycles in body temperature (Tb) of free-ranging Crocodylus porosus (32-1010 kg) can be predicted by a mathematical analysis. The analysis provides a mechanistic explanation for the decreased amplitude of daily cycles in Tb and the increase in 'average' Tb with increasing mass. Assessments of 'average' daily Tb were made by dividing the integral of the difference between measured values of Tb and minimum operative temperature by the period of integration, to yield a thermal index expressing relative 'warmth' of crocodiles. The average daily Tb of a 1010 kg crocodile was 3.7 degrees C warmer than that of a 42 kg individual in summer and 1.9 degreesC warmer than that of a 32 kg individual in winter. The success of this mathematical approach confirms that crocodiles are simple ectotherms and that there is unlikely to be a significant contribution to their thermal biology from physiological mechanisms. Behaviour, however, is very important even in large individuals. Crocodiles in the field typically move daily between land and water in cycles that vary seasonally. We predicted Tb for the reverse of these behavioural cycles, which more than doubled seasonal fluctuations in Tb compared with the observed fluctuations. We were also able to predict the Tb of very large, dinosaur-sized crocodiles in a similar climate to that at our study site. A 10 000 kg 'crocodile', for example, would be expected to have a Tb of 31 degreesC in winter, varying by less than 0.1 degrees C during a day when operative temperatures varied by nearly 20 degrees C, from 20 to 38 degrees C. The study confirms that, in low latitudes at least, large dinosaurs must have had an essentially high and stable value of Tb, without any need for endothermy. Also, access to shade or water must have been crucial for the survival of large dinosaurs at low latitudes. Furthermore, the finding of increasing 'average' Tb as ectotherms grow larger may have implications for the metabolic rates of very large reptiles, because the Q10 effect could counteract the downscaling of metabolic rate with mass, an effect that seems not to have been recognised previously

Control of heart rate during thermoregulation in the heliothermic lizard Pogona barbata: importance of cholinergic and adrenergic mechanisms

During thermo regulation in the bearded dragon Pogona barbata, heart rate when heating is significantly faster than when cooling at any given body temperature (heart rate hysteresis), resulting in faster rates of heating than cooling. However, the mechanisms that control heart rate during heating and cooling are unknown. The aim of this study was to test the hypothesis that changes in cholinergic and adrenergic tone on the heart are responsible for the heart rate hysteresis during heating and cooling in P. barbata. Heating and cooling trials were conducted before and after the administration of atropine, a muscarinic antagonist, and sotalol, a beta-adrenergic antagonist. Cholinergic and beta-adrenergic blockade did not abolish the heart rate hysteresis, as the heart rate during heating was significantly faster than during cooling in all cases. Adrenergic tone was extremely high (92.3%) at the commencement of heating, and decreased to 30.7% at the end of the cooling period. Moreover, in four lizards there was an instantaneous drop in heart rate (up to 15 beats min(-1)) as the heat source was switched off, and this drop in heart rate coincided with either a drop in beta-adrenergic tone or an increase in cholinergic tone. Rates of heating were significantly faster during the cholinergic blockade, and least with a combined cholinergic and beta-adrenergic blockade. The results showed that cholinergic and beta-adrenergic systems are not the only control mechanisms acting on the heart during heating and cooling, but they do have a significant effect on heart rate and on rates of heating and cooling

Dishonest signals of strength in male slender crayfish (Cherax dispar) during agonistic encounters

Many animals resolve disputes without combat by displaying signals of potential strength during threatening displays. Presumably, competitors use each other's displays to assess their relative strengths, and current theory predicts that these signals of strength should generally be honest. We tested this prediction by investigating the relationships among morphology, performance, and social dom inance in males of the slender crayfish Cherax dispar. Crayfish routinely use their enlarged front claws (chelae) for both intimidation and fighting, making this species ideal for studying the honesty of weapon size. We evaluated five competing models relating morphological and physiological traits to dominance during paired competitive bouts. Based on the best model, larger chelae clearly resulted in greater dominance; however, chela strength had no bearing on dominance. Thus, displays of chela size were dishonest signals of strength, and the enlarged chelae of males seemingly function more for intimidation than for fighting. In addition, an analysis of the performance of isolated chela muscle showed that muscle from male crayfish produced only half the force that muscle from female crayfish produced (236.6 +/- 26.4 vs. 459.5 +/- 71.6 kN m(-2)), suggesting that males invest more in developing larger chelae than they do in producing high-quality chela muscle. From our studies of crayfish, we believe dishonest signaling could play a greater role in territorial disputes than previously imagined

Synthesis and antiprotozoal activity of azabicyclo-nonane pyrimidine hybrids

2,4-Diaminopyrimidines and (dialkylamino)azabicyclo-nonanes possess activity against protozoan parasites. A series of fused hybrids were synthesized and tested in vitro against pathogens of malaria tropica and sleeping sickness. The activities and selectivities of compounds strongly depended on the substitution pattern of both ring systems as well as on the position of the nitrogen atom in the bicycles. The most promising hybrids of 3-azabicyclo-nonane with 2-aminopyrimidine showed activity against P. falciparum NF54 in submicromolar concentration and high selectivity. A hybrid with pyrrolidino substitution of the 2-azabicyclo-nonane as well as of the pyrimidine moiety exhibited promising activity against the multiresistant K1 strain of P. falciparum. A couple of hybrids of 2-azabicyclo-nonanes with 2-(dialkylamino)pyrimidines possessed high activity against Trypanosoma brucei rhodesiense STIB900 and good selectivity

Antarctic fish can compensate for rising temperatures: Thermal acclimation of cardiac performance in Pagothenia borchgrevinki

Antarctic fish Pagothenia borchgrevinki in McMurdo Sound, Antarctica, inhabit one of the coldest and most thermally stable of all environments. Sea temperatures under the sea ice in this region remain a fairly constant -1.86 degrees C year round. This study examined the thermal plasticity of cardiac function in P. borchgrevinki to determine whether specialisation to stable low temperatures has led to the loss of the ability to acclimate physiological function. Fish were acclimated to - 1 degrees C and 4 degrees C for 4 - 5 weeks and cardiac output was measured at rest and after exhaustive exercise in fish acutely transferred from their acclimation temperature to - 1, 2, 4, 6 and 8 degrees C. In the - 1 degrees C acclimated fish, the factorial scope for cardiac output was greatest at - 1 degrees C and decreased with increasing temperature. Increases in cardiac output with exercise in the - 1 degrees C acclimated fish was achieved by increases in both heart rate and stroke volume. With acclimation to 4 degrees C, resting cardiac output was thermally independent across the test temperatures; furthermore, factorial scope for cardiac output was maintained at 4, 6 and 8 degrees C, demonstrating thermal compensation of cardiac function at the higher temperatures. This was at the expense of cardiac function at - 1 degrees C, where there was a significant decrease in factorial scope for cardiac output in the 4 degrees C acclimated fish. Increases in cardiac output with exercise in the 4 degrees C acclimated fish at the higher temperatures was achieved by changes in heart rate alone, with stroke volume not varying between rest and exercise. The thermal compensation of cardiac function in P. borchgrevinki at higher temperatures was the result of a change in pumping strategy from a mixed inotropic/chronotropic modulated heart in - 1 degrees C acclimated fish at low temperatures to a purely chronotropic modulated heart in the 4 degrees C acclimated fish at higher temperatures. In spite of living in a highly stenothermal cold environment, P. borchgrevinki demonstrated the capacity to thermally acclimate cardiac function to elevated temperatures, thereby allowing the maintenance of factorial scope and the support of aerobic swimming at higher temperatures

Antiprotozoal activity of azabicyclo-nonanes linked to tetrazole or sulfonamide cores

N-(Aminoalkyl)azabicyclo[3.2.2]nonanes possess antiplasmodial and antitrypanosomal activity. A series with terminal tetrazole or sulfonamido partial structure was prepared. The structures of all new compounds were confirmed by NMR and IR spectroscopy and by mass spectral data. A single crystal structure analysis enabled the distinction between isomers. The antiprotozoal activities were examined in vitro against strains of Plasmodium falciparum and Trypanosoma brucei rhodesiense (STIB 900). The most active sulfonamide and tetrazole derivates showed activities in the submicromolar range