Significant Differences In Metabolic Rates Research Articles

Metabolic rates of Neomysis americana (Smith, 1873) (Mysida: Mysidae) from a temperate estuary vary in response to summer temperature and salinity conditions

AbstractThe mysid Neomysis americana (Smith, 1873) is native to shallow shelf waters and estuaries of the western Atlantic coast of North America. Despite the important role mysids such as N. americana play in estuarine ecosystems as both consumers and as prey for higher trophic levels, there is limited information on how metabolism influences their spatial ecology and habitat requirements. In tributaries of Chesapeake Bay, MD, USA, previous research has shown that summer water temperatures can approach the lethal upper tolerance limit for N. americana. We measured the per capita metabolic rate (µgO2 min–1) of N. americana from the upper Patuxent River near Benedict, MD, a tributary of Chesapeake Bay in the laboratory to evaluate the metabolic response to salinity and temperature conditions that mysids experience in natural habitats. Sex-specific and diel patterns in metabolic rate were quantified. Metabolic rates did not differ between night and day and there was no significant difference in metabolic rate between males and females, exclusive of gravid females. Metabolic rates were lowest in salinity treatments of 2 and 8 at 29 °C, and highest in the salinity 2 treatment at 22 °C. Only temperature had a statistically significant, albeit unexpected, effect. This study shows that the metabolic response of N. americana to temperature and salinity conditions is complex and plastic, and that metabolic rates can vary 3–4 fold within realistic summer temperature and salinity conditions. As environmental conditions continue to change, understanding metabolic response of mysids to realistic salinity and temperature conditions is necessary for understanding their distributions in temperate estuaries.

Metabolic rates, climate and macroevolution: a case study using Neogene molluscs

Basal metabolic rate (BMR) is posited to be a fundamental control on the structure and dynamics of ecological networks, influencing organism resource use and rates of senescence. Differences in the maintenance energy requirements of individual species therefore potentially predict extinction likelihood. If validated, this would comprise an important link between organismic ecology and macroevolutionary dynamics. To test this hypothesis, the BMRs of organisms within fossil species were determined using body size and temperature data, and considered in the light of species' survival and extinction through time. Our analysis focused on the high-resolution record of Pliocene to recent molluscs (bivalves and gastropods) from the Western Atlantic. Species-specific BMRs were calculated by measuring the size range of specimens from museum collections, determining ocean temperature using the HadCM3 global climate model, and deriving values based on relevant equations. Intriguingly, a statistically significant difference in metabolic rate exists between those bivalve and gastropod taxa that went extinct and those that survived throughout the course of the Neogene. This indicates that there is a scaling up from organismic properties to species survival for these communities. Metabolic rate could therefore represent an important metric for predicting future extinction patterns, with changes in global climate potentially affecting the lifespan of individuals, ultimately leading to the extinction of the species they are contained within. We also find that, at the assemblage level, there are no significant differences in metabolic rates for different time intervals throughout the entire study period. This may suggest that Neogene mollusc communities have remained energetically stable, despite many extinctions.

Thermoregulation Deficiencies in Mice with a Deletion in the Muscle Protein Titin

The muscular dystrophy with myositis (mdm) mouse carries a deletion in the muscle protein titin. A previous study found that mdm mice shiver at a lower than expected frequency for their body size, are mostly heterothermic with a narrow thermoneutral zone beginning at 34C, and have reduced active muscle stiffness in vivo compared to their wildtype siblings. Impairment in heat production (shivering thermogenesis) could be due to the N2A deletion in the titin protein leading to a more compliant muscle and a lower shivering frequency. The ability of mdm mice to use nonshivering thermogenesis via Uncoupling Protein 1 in brown adipose tissue to generate heat during cold stress may also be impaired and contributing to their heterothermy. The purpose of this study was to evaluate mechanisms for the inability of mdm mice to maintain homeothermy during cold stress and to further understand their metabolic properties. We hypothesized the inability of mdm mice to maintain homeothermy is due to an impairment in heat production (e.g. shivering thermogenesis and nonshivering thermogenesis) and that metabolic rate will reach a maximum at a higher ambient temperature than in wildtype mice. In a temperature experiment, mice were placed in a mouse cage that used indirect calorimetry to measure metabolic rate at four different temperatures (34C, 29C, 24C, 19C). Nonshivering thermogenesis was stimulated by administering 1.2 mg kg−1 of norepinephrine subcutaneously. In the temperature experiment, there was a significant interaction between genotype and temperature, with significant differences in metabolic rates at the lowest temperatures of 19C and 24C (Two‐Way ANOVA and Tukey HSD, p<0.05. Mdm mice had significantly lower body temperatures than wildtype mice at 29C, 24C, and 19C, and reached their maximum metabolic rate at 24C, suggesting that a temperature between 19–24C is the minimum at which mdm mice are able to sustain thermogenesis. Area under the curve (AUC) using the trapezoidal rule was used to calculate total thermogenic capacity following norepinephrine injection. Mdm mice had a lower overall AUC (Welch's T‐Test, p=0.03) as well as a lower overall time that they increased metabolic rate after norepinephrine injection (Welch's T‐Test, p=0.02). Our results suggest that in addition to a deficiency in shivering frequency, mdm mice also have a reduced capacity for nonshivering thermogenesis. The deficiency in shivering thermogenesis and nonshivering thermogenesis combined likely lead to inability to maintain euthermic body temperatures below 34C.Support or Funding InformationNSF IOS‐0742483, NSF IOS‐1025806, and NSF IOS‐1456868, the W. M. Keck Foundation, and the Technology Research Initiative Fund of Northern Arizona University.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Improving rational thermal comfort prediction by using subpopulation characteristics: A case study at Hermitage Amsterdam

ABSTRACTThis study aims to improve the prediction accuracy of the rational standard thermal comfort model, known as the Predicted Mean Vote (PMV) model, by (1) calibrating one of its input variables “metabolic rate,” and (2) extending it by explicitly incorporating the variable running mean outdoor temperature (RMOT) that relates to adaptive thermal comfort. The analysis was performed with survey data (n = 1121) and climate measurements of the indoor and outdoor environment from a one year-long case study undertaken at Hermitage Amsterdam museum in the Netherlands. The PMVs were calculated for 35 survey days using (1) an a priori assumed metabolic rate, (2) a calibrated metabolic rate found by fitting the PMVs to the thermal sensation votes (TSVs) of each respondent using an optimization routine, and (3) extending the PMV model by including the RMOT. The results show that the calibrated metabolic rate is estimated to be 1.5 Met for this case study that was predominantly visited by elderly females. However, significant differences in metabolic rates have been revealed between adults and elderly showing the importance of differentiating between subpopulations. Hence, the standard tabular values, which only differentiate between various activities, may be oversimplified for many cases. Moreover, extending the PMV model with the RMOT substantially improves the thermal sensation prediction, but thermal sensation toward extreme cool and warm sensations remains partly underestimated.

Metabolic rate, evaporative water loss and thermoregulatory state in four species of bats in the Negev desert

Life in deserts is challenging for bats because of their relatively high energy and water requirements; nevertheless bats thrive in desert environments. We postulated that bats from desert environments have lower metabolic rates (MR) and total evaporative water loss (TEWL) than their mesic counterparts. To test this idea, we measured MR and TEWL of four species of bats, which inhabit the Negev desert in Israel, one species mainly restricted to hyper-arid deserts (Otonycteris hemprichii), two species from semi-desert areas (Eptesicus bottae and Plecotus christii), and one widespread species (Pipistrellus kuhlii). We also measured separately, in the same individuals, the two components of TEWL, respiratory water loss (RWL) and cutaneous evaporative water loss (CEWL), using a mask. In all the species, MR and TEWL were significantly reduced during torpor, the latter being a consequence of reductions in both RWL and CEWL. Then, we evaluated whether MR and TEWL in bats differ according to their geographic distributions, and whether those rates change with Ta and the use of torpor. We did not find significant differences in MR among species, but we found that TEWL was lowest in the species restricted to desert habitats, intermediate in the semi-desert dwelling species, and highest in the widespread species, perhaps a consequence of adaptation to life in deserts. Our results were supported by a subsequent analysis of data collected from the literature on rates of TEWL for 35 bat species from desert and mesic habitats.

Effectiveness of eugenol sedation to reduce the metabolic rates of cool and warm water fish at high loading densities

Effects of eugenol (AQUI-S®20E, 10% active eugenol) sedation on cool water, yellow perch Perca flavescens (Mitchill), and warm water, Nile tilapia Oreochromis niloticus L. fish metabolic rates were assessed. Both species were exposed to 0, 10, 20 and 30 mg L−1 eugenol using static respirometry. In 17°C water and loading densities of 60, 120 and 240 g L−1, yellow perch controls (0 mg L−1 eugenol) had metabolic rates of 329.6–400.0 mg O2 kg−1 h−1, while yellow perch exposed to 20 and 30 mg L−1 eugenol had significantly reduced metabolic rates of 258.4–325.6 and 189.1–271.0 mg O2 kg−1 h−1 respectively. Nile tilapia exposed to 30 mg L−1 eugenol had a significantly reduced metabolic rate (424.5 ± 42.3 mg O2 kg−1 h−1) relative to the 0 mg L−1 eugenol control (546.6 ± 53.5 mg O2 kg−1 h−1) at a loading density of 120 g L−1 in 22°C water. No significant differences in metabolic rates for Nile tilapia were found at 240 or 360 g L−1 loading densities when exposed to eugenol. Results suggest that eugenol sedation may benefit yellow perch welfare at high densities (e.g. live transport) due to a reduction in metabolic rates, while further research is needed to assess the benefits of eugenol sedation on Nile tilapia at high loading densities.

In vitro metabolism of anti-tumor compound E7 in different species of liver microsomes

To investigate the metabolic stability of E7 in liver microsomes of human, Beagle dog, Cynomolgus monkey and SD rats, and compare the metabolic differences between different species. Selective chemical inhibitors were used to determine the effects of different inhibitors on E7 metabolic rate, and predict the main enzymes involved in E7 metabolism in rat liver microsomes. The experimental results showed that the in vitro half-lives (T1/2) of E7 in liver microsomes of human, dog, monkey and rats were 57.75, 69.30, 16.90,30.13 min respectively. Their intrinsic clearance rate was 0.004 8, 0.004 0, 0.016 4 and 0.009 2 mL•min⁻¹•mg⁻¹ respectively. Hence, it could be speculated that the metabolic rate of E7 was similarly slow in human and dog liver microsomes; while it was similarly fast in monkey and rat liver microsomes. There was significant difference in metabolic rate of E7 between different species. The results showed that CYP2E1, CYP2A6, CYP1A2 and CYP2D6 might participate in metabolism of E7, while the contribution of polymorphic CYP3A4 was small.

Inbreeding effects on standard metabolic rate investigated at cold, benign and hot temperatures in Drosophila melanogaster

Inbreeding increases homozygosity, which is known to affect the mean and variance of fitness components such as growth, fecundity and mortality rate. Across inbred lines inbreeding depression is typically observed and the variance between lines is increased in inbred compared to outbred lines. It has been suggested that damage incurred from increased homozygosity entails energetic cost associated with cellular repair. However, little is known about the effects of inbreeding on standard metabolic rate. Using stop-flow respirometry we performed repeated measurements of metabolic rate in replicated lines of inbred and outbred Drosophila melanogaster at stressful low, benign and stressful high temperatures. The lowest measurements of metabolic rate in our study are always associated with the low activity period of the diurnal cycle and these measurements therefore serve as good estimates of standard metabolic rate. Due to the potentially added costs of genetic stress in inbred lines we hypothesized that inbred individuals have increased metabolic rate compared to outbred controls and that this is more pronounced at stressful temperatures due to synergistic inbreeding by environment interactions. Contrary to our hypothesis we found no significant difference in metabolic rate between inbred and outbred lines and no interaction between inbreeding and temperature. Inbreeding however effected the variance; the variance in metabolic rate was higher between the inbred lines compared to the outbred control lines with some inbred lines having very high or low standard metabolic rate. Thus genetic drift and not inbreeding per se seem to explain variation in metabolic rate in populations of different size.

Variation in metabolic rate ofAnopheles gambiaeandA. arabiensisin a Sahelian village

In the Sahel, the Anopheles gambiae complex consists of Anopheles arabiensis and the M and S molecular forms of A. gambiae sensu stricto. However, the composition of these malaria vectors varies spatially and temporally throughout the region and is thought to be linked to environmental factors such as rainfall, larval site characteristics and duration of the dry season. To examine possible physiological divergence between these taxa, we measured metabolic rates of mosquitoes during the wet season in a Sahelian village in Mali. To our knowledge, this study provides the first measurements of metabolic rates of A. gambiae and A. arabiensis in the field. The mean metabolic rate of A. arabiensis was higher than that of M-form A. gambiae when accounting for the effects of female gonotrophic status, temperature and flight activity. However, after accounting for their difference in body size, no significant difference in metabolic rate was found between these two species (whilst all other factors were found to be significant). Thus, body size may be a key character that has diverged in response to ecological differences between these two species. Alternatively, these species may display additional differences in metabolic rate only during the dry season. Overall, our results indicate that changes in behavior and feeding activity provide an effective mechanism for mosquitoes to reduce their metabolic rate, and provide insight into the possible strategies employed by aestivating individuals during the dry season. We hypothesize that female mosquitoes switch to sugar feeding while in dormancy because of elevated metabolism associated with blood digestion.

Energetics in Liolaemini lizards: implications of a small body size and ecological conservatism

Liolaemini lizards occur in southern South America in a variety of dietary habits across a broad latitudinal and altitudinal distribution. We studied standard metabolic rates of 19 Liolaemini species and analyzed these data using both conventional and phylogenetically informed statistics. Oxygen consumption showed a significant and positive relationship with body mass (SMR=0.109×body mass(0.876±0.023)), with a higher slope than that expected on the basis of the three-quarter power law model. After phylogenetically informed and conventional analyses, no significant differences in metabolic rates were found to be related to diet or elevation. We hypothesize that small body size, ecological conservatism and physiological compensation may explain the lack of differences in metabolic rates observed among these lizards.

Determination of metabolic stability of positron emission tomography tracers by LC–MS/MS: An example in WAY-100635 and two analogues

A method is presented for determination of microsomal metabolic stability of potential positron emission tomography (PET) tracers by LC–MS/MS in the lower nm range. The PET tracers used for the study were the serotonin receptor antagonist WAY-100635 and two potential tracer analogues. The sensitivity permitted the substrates to be directly collected from PET radiolabelling batches, containing very low amounts of substance (0.3–7 μg), for subsequent metabolic stability incubations. Sample preparation was minimal, with addition of internal standard, acetonitrile and a fast centrifugation step, as a result of the low protein concentration of the microsome solutions. Linearity ( R 2 ≥ 0.99), precision (inter-assay R.S.D. < 7%) and accuracy (bias ≤8%) for the tested concentration range 0.5–5 nM proved to be well within accepted limits. No significant differences in metabolic rates were detected using substrates from cold (non-labelling) chemistry syntheses and PET labelling batches, indicating the validity of using substrates from the latter source. A para-methoxy-benzamide analogue (MeO-WAY) displayed a significantly lower rate of metabolism compared to WAY-100635, whereas a para-iodo-benzamide analogue was more susceptible to metabolic transformation. LC–MS/MS Analysis of formed metabolites from WAY-100635 and MeO-WAY suggested similar metabolic pathways, with hydroxylation, demethylation and dearylation reactions. The main metabolic route in humans, amide hydrolysis, was not observed with the rat liver microsome assay.

Effect of Polymorphisms in the Cytochrome P450 CYP2C9 Gene on Warfarin Anticoagulation

Abstract Context.—Warfarin is a widely used anticoagulant with efficacy in treatment and prevention of thrombosis. Patient management, however, is difficult because of interindividual variation in response to standard doses due to significant differences in metabolic rates. Warfarin metabolism is under genetic control, involving primarily the CYP2C9 gene encoding the enzyme that catalyzes the conversion of warfarin to inactive metabolites. Objective.—Several polymorphisms of CYP2C9 have been reported; the variant alleles *2 and *3 have decreased enzymatic activity. The objective of this case study is to investigate the relationship between CYP2C9 genotype and warfarin anticoagulation. Design.—A case of deep vein thrombosis treated with the standard warfarin dose is investigated for intensity of anticoagulation and CYP2C9 genotype; the case illustrates the relationship between CYP2C9 variant and overanticoagulation with subsequent bleeding complication. Results.—The patient's genotype, CYP2C9*1*3, correlat...

Effect of Polymorphisms in the Cytochrome P450 CYP2C9 Gene on Warfarin Anticoagulation

Warfarin is a widely used anticoagulant with efficacy in treatment and prevention of thrombosis. Patient management, however, is difficult because of interindividual variation in response to standard doses due to significant differences in metabolic rates. Warfarin metabolism is under genetic control, involving primarily the CYP2C9 gene encoding the enzyme that catalyzes the conversion of warfarin to inactive metabolites. Several polymorphisms of CYP2C9 have been reported; the variant alleles *2 and *3 have decreased enzymatic activity. The objective of this case study is to investigate the relationship between CYP2C9 genotype and warfarin anticoagulation. A case of deep vein thrombosis treated with the standard warfarin dose is investigated for intensity of anticoagulation and CYP2C9 genotype; the case illustrates the relationship between CYP2C9 variant and overanticoagulation with subsequent bleeding complication. The patient's genotype, CYP2C9*1*3, correlated with an exaggerated anticoagulant response during the initiation of warfarin therapy at standard dose, and a bleeding episode ensued. Based on heterozygosity for the *3 variant allele, it was recommended that the patient be maintained on a low-dose warfarin regimen. The practical implications of identifying genetic risk factors that lead to overanticoagulation are multiple. Genotype knowledge of the CYP2C9 variant alleles may help the clinician to individualize warfarin therapy with the ultimate goals of shortening the initial period of induction therapy, reaching a stable maintenance dose earlier, and minimizing bleeding complications in patients who are high responders and need lower warfarin doses.

Effects of Temperature and Time of Day on the Resting Metabolic Rates of Paedomorphic and Metamorphic Mole Salamanders,Ambystoma talpoideum

Abstract Mole salamanders, Ambystoma talpoideum, are one of several species that exhibit facultative paedomorphosis. Many characteristics of paedomorphs and metamorphs have been compared in an effort to understand the ecological and evolutionary significance of facultative paedomorphosis, but few physiological comparisons have been made. We measured resting metabolic rates (oxygen consumption) of paedomorphic and metamorphic mole salamanders, under aquatic (both morphs) and terrestrial (metamorphs) conditions in an effort to compare maintenance energy expenditures of these phenotypes. There were no statistically significant differences in metabolic rates between morphs during aquatic trials. Under aquatic conditions, size adjusted oxygen consumption rates ranged from a low of 0.085 ml/h to 0.194 ml/h. There was a trend for oxygen consumption to increase with temperature, and at night compared to day, but significant interactions among time of day, temperature, and phenotype revealed complex responses. Mos...

Metabolic ecology of cockatoos in the south-west of Western Australia

This study examined the metabolic ecology of six cockatoo taxa endemic to the south-west of Western Australia. As the availability of food is one factor that may influence the abundance and distribution of these cockatoos, we document here their baseline energy requirements and feeding patterns. Evaporative waterloss was also measured as this may correlate with the aridity of the species’ environment. Basal metabolic rate was significantly lower at 0.62 ± 0.13 mL O2 g–1 h–1 for the inland red-tailed black cockatoo than 1.11 ± 0.16 mL O2 g–1 h–1 for the forest red-tailed black cockatoo, but there was no significant difference in metabolic rate between the two white-tailed black cockatoos (0.86 ± 0.18 for Carnaby’s and 0.81 ± 0.11 mL O2 g–1 h–1 for Baudin’s) or the two corellas (0.95 ± 0.12 for Butler’s and 0.70 ± 0.04 mL O2 g–1 h–1 for Muir’s). There were no significant differences between the two white-tailed black cockatoos, and between the two corellas, with respect to evaporative water loss. The inland red-tailed black cockatoo had a significantly lower rate of evaporative water loss (0.44 ± 0.07 mg g–1 h–1) than the forest red-tailed black cockatoo (0.70 ± 0.06 mg g–1 h–1), which is presumably an adaptation to its more arid habitat. The total energy content of assorted native and introduced food items that form significant proportions of the diets for these cockatoos varied from only 0.17 kJ for a 9-mg Emex australis seed to 63.9 kJ for a 3-g Banksia attenuata nut. The energy content of each food item and the estimated daily energy requirements of the cockatoos enabled the calculation of the numbers of nuts/cones/seeds required by each species for a day, which ranged from 11 B. attenuata nuts for a Carnaby’s cockatoo to 3592 Persoonia longifolia seeds for a forest red-tailed black cockatoo.

Behavioural and metabolic effects of chronic exposure to sublethal aluminum in acidic soft water in juvenile rainbow trout (Oncorhynchus mykiss)

Triplicate groups of 15 softwater-acclimated juvenile rainbow trout (Oncorhynchus mykiss) were randomly allocated to one of three treatments: pH 6.5 with no aluminum, pH 5.2 with no aluminum, and pH 5.2 with 30 µg labile aluminum·L-1. The aluminum dose was sublethal and continued for 34 days. Treatment effects on swimming behaviour, metabolism, feeding, food conversion efficiency, and blood parameters were determined. Fish exposed to aluminum displayed hypoactivity that was statistically distinct from both control groups from day 1 onwards. Exposure to acid alone elicited no behavioural effects. There were no significant differences in metabolic rates between the treatment groups. Feeding rates of the fish exposed to aluminum became depressed, reaching a minimum on day 15, and gradually recovered thereafter, but never to the preexposure levels. Swimming behaviour was a more sensitive index of exposure to aluminum than feeding. Fish exposed to aluminum had significantly fewer red blood cells and lower haematocrit than the controls, indicating haemodilution. Aluminum is known to act as a respiratory toxicant, restricting aerobic scope. In addition, these data suggest that fish respond to aluminum exposure by reducing metabolically costly activities such as routine swimming behaviour to allow for the increased maintenance costs associated with acclimation and damage repair.

Metabolic rate of embryonic little skate,Raja erinacea (Chondrichthyes: Batoidea): The cost of active pumping

Near-hatching embryonic little skates, Raja erinacea, are highly active within their egg capsules, displaying a characteristic tail beating, which pumps water through the cap- sule. We measured the metabolic rate of late-stage embryos to determine whether oxygen suffi- cient for the embryo's needs will diffuse through the egg capsule, and to assess the energetic cost of tail beating. Metabolic rate was inferred from oxygen consumption rates while embryos were in the capsules, unencapsulated, and anesthetized and unencapsulated. Anesthesia inhibited volun- tary movements, including tail wagging, allowing an estimate of the standard metabolic rate (SMR). Averaged over five embryos, the SMR was 0.032 ± 0.004 ml O2 g -1 hr -1 . There was no significant difference in metabolic rate between encapsulated (0.058 ± 0.009 ml O2 g -1 hr -1 ) and unencapsu- lated (0.049 ± 0.009 ml O2 g -1 hr -1 ) skates. Tail beating was found to be energetically expensive, requiring a 53%-81% increase over the SMR. From literature values for the oxygen permeability of the egg capsule we conclude that tail beating is required to supply sufficient oxygen to the embryonic skate. This observation is consistent with the proposal that actively pumping water through the capsule, by tail beating, has played an evolutionary role in the shape of the capsule. J. Exp. Zool. 283:13n18, 1999. © 1999 Wiley-Liss, Inc.

Malate Dehydrogenase Phenotype, Temperature and Colony Effects on Flight Metabolic Rate in the Honey-Bee, Apis mellifera

1. The 'fast' and 'medium' alleles of malate dehydrogenase (MDH-1) exhibit clines on three continents in Honey-bees (Nielsen, Page & Crosland 1994), suggesting that MDH-1 phenotype may have functional consequences. 2. To test the effect of MDH-1 phenotype on a relatively constant genetic and environmental background in Honey-bees, we compared slow-fast (SF) and slow-medium (SM) workers within two colonies containing medium-fast (MF) queens singly inseminated with semen from an (S) drone. Within each colony, all genes not tightly linked to MDH-1 should be randomly distributed among SM and SF workers. 3. SF bees had higher flight metabolic rates (MR) than SM bees at ambient temperatures of 21 °C and 38 °C, and higher wing-beat frequencies (WBF) at 21 °C. 4. There were also highly significant differences in MR of foragers from adjacent, similarly sized, related colonies, suggesting that there are other strong unexplained effects on flight MR. Flight MR and WBF decreased while thorax temperatures (T th ) increased as ambient temperature increased. 5. The data suggest that during high-intensity flight, Honey-bees reduce motor behaviour, either as a behavioural mechanism to prevent overheating or owing to direct inhibition of flight muscle metabolism by high T th . 6. Our data and a previous study (Coelho & Mitton 1988) indicate a link between MDH-1 allozymes and flight metabolism in Honey-bees, supporting the contention that MDH-1 phenotype has functional metabolic consequences which may be subject to selection.

Resting metabolism of helodermatid lizards: allometric and ecological relationships

We measured metabolic rates at 15 and 25°C in 42 helodermatid lizards ranging in mass from 26 to 1616 g. No consistent repeatable daily rhythms of metabolism were detected. There were no significant differences in metabolic rates between the two species of Heloderma. The temperature coefficient for metabolism (Q10) was 3.0 between 15 and 25°C. The mass exponent for helodermatids (0.69) differed significantly from the among-species mass exponent of 0.80 for all squamates combined. However, adult Heloderma had a mass exponent of 0.80. Rates of metabolism of adult helodermatids were lower than those of other squamate reptiles, and at 15°C periods of apnea contributed to a further reduction in metabolic rate. Our finding that helodermatids have low SMRs supports the hypothesis that ecology is important in influencing metabolic rate, and that “reclusive” squamates have lower rates of metabolism than do nonreclusive species.

Preparatory adaptations for winter survival in the cold hardy beetles,Dendroides canadensis andDendroides concolor

Thermal hysteresis (indicative of macromolecular antifreeze levels) was measured in hemolymph samples from the beetle,Dendroides canadensis, after acclimation to a short (8 h) photoperiod at 20 °C, or long (16 h) photoperiod at temperatures of 10 and 20 °C. Both the short photoperiod and low temperature (10 °C) treatment caused a significant elevation of thermal hysteresis, thereby implicating increased antifreeze protein production. Oxygen consumption rates of animals in each acclimation treatment were measured and no significant differences in metabolic rates were noted between treatments when measured at a high (20 °C) temperature. Thus, conditions which initiate antifreeze protein production fail to induce a diapause condition, characterized by a drop in metabolic rates. Likewise, natural populations sampled in mid-winter possess elevated levels of thermal hysteresis, and accumulated glycerol and sorbitol, but do not show a depressed metabolic rate. Therefore,D. canadensis do not enter a diapause during the winter, but are fully capable of achieving a high level of cold hardiness through the accumulation of antifreeze proteins and polyhydroxy alcohols.