- Email: [email protected]
22.5. Survival of subzero temperatures as a metabolic strategy: A test of the metabolic control hypothesis
S100
Abstracts / Comparative Biochemistry and Physiology, Part A 148 (2007) S99–S102
laboratory. The factors responsible for this confinement of the technique in the past have included the high-power consumption and fragility of the required equipment, and limitations on the portability of data acquisition systems. In this talk, I describe a number of investigations in which respirometry was successfully deployed in the field to measure metabolic parameters of unrestrained animals in ecologically meaningful contexts, ranging in size from cetaceans to ants. I describe how various technical issues can be addressed, how sources of error are identified and accounted for, the correct equations to use for different system configurations, and statistically defensible methods for selecting representative, ecologically meaningful data. doi:10.1016/j.cbpa.2007.06.258
22.4. Phenotypic plasticity in avian metabolic traits: Implications for comparative analyses McKechnie, A. University of the Witwatersrand, South Africa [email protected] The metabolic rates of many birds exhibit considerable phenotypic plasticity, such as the up- or down-regulation of basal metabolic rate (BMR) during thermal acclimation. Phenotypic plasticity has far-reaching implications for comparative analyses, many of which have assumed metabolic traits, and BMR in particular, to be static within species or populations. One broad-scale source of variation that needs to be accounted for is the difference in metabolic scaling exponents between captive-raised (0.670) and wild-caught birds (0.744). Within individuals, seasonal adjustments and/or acclimation typically causes BMR to vary by 20–50%, although larger changes have been reported. This variation potentially affects comparative analyses in two ways: (a) the parameters of statistical procedures that correct for phylogenetic non-independence, and (b) the results of comparisons (e.g., ANCOVA) among groups of taxa. The fact that phenotypic flexibility appears to be a general feature of avian metabolic systems raises several key questions. First, does the magnitude and/or rate of phenotypic adjustments scale with body mass? Second, what are the relative roles of genotypic adaptation and phenotypic plasticity in matching metabolic rates to physical and/or biotic variables? A comparison of data from wild-caught and captiveraised birds raises the possibility that the low BMR of desert birds primarily reflects phenotypic adjustments. A particularly intriguing possibility, that is beginning to be addressed, is that more unpredictable environments drive the evolution of greater phenotypic flexibility. doi:10.1016/j.cbpa.2007.06.259
22.5. Survival of subzero temperatures as a metabolic strategy: A test of the metabolic control hypothesis Marais, E., Irlich, U., and Chown, S.L. Stellenbosch University, South Africa [email protected] It has been hypothesized that freezing tolerance and freeze intolerance, the two major responses to subzero temperatures shown by animals, represent two more general alternatives for surviving stress, i.e. abandoned metabolic control or minimum metabolic control, respectively. In the case of abandoned metabolic control, the organism maximally protects its cellular structures against degradation and then switches off most other metabolic processes. No matter how low, the rate of spontaneous degradation of structures is never zero and repair is not possible during this state. Therefore, once a critical threshold has passed, the animal dies. In the case of minimum metabolic control, the organism survives by continually sustaining order at a minimum metabolic level, which is independent of both body mass and temperature. The period of survival depends on energy stored by the organism. The energy losses tolerated in the regime of abandoned metabolic control are much lower than those tolerated under minimum metabolic control. Here, using a freeze-tolerant insect species and a freeze-intolerant one, we test these hypotheses. The evidence suggests that at present, the hypothesis cannot be rejected, but may need further modification to account for time effects of repair processes. doi:10.1016/j.cbpa.2007.06.260
22.6. Integrative physiology of seasonal acclimatized plateau pikas and root voles from the Qinghai–Tibet Plateau Wang, D.-H., Wang, J.-M., and Zhang, Y.-M. Institute of Zoology, Chinese Academy of Sciences, Beijing, China [email protected] Survival of small mammals in winter requires proper adjustments in physiology, behavior and morphology. Changes in photoperiod, ambient temperature and food availability trigger the seasonal adaptations of many animals. Qinghai–Tibet Plateau characterized with extreme cold and hypoxia. Small mammals living here are facing extreme harsh environment, especially for non-hibernating species which do not store food for winter. We conducted an integrated study of the physiological responses to cold from molecular to organismal levels in plateau pikas (Ochtona curzoniae) and root voles (Microtus oeconomus), two non-hibernating herbivorous species which do not store food, from the Qinghai–Tibet Plateau. Plateau pikas maintained a constant body mass throughout the year and showed no seasonal change in body fat mass and circulating levels of serum leptin. However, non-shivering thermogenesis
Abstracts / Comparative Biochemistry and Physiology, Part A 148 (2007) S99–S102
laboratory. The factors responsible for this confinement of the technique in the past have included the high-power consumption and fragility of the required equipment, and limitations on the portability of data acquisition systems. In this talk, I describe a number of investigations in which respirometry was successfully deployed in the field to measure metabolic parameters of unrestrained animals in ecologically meaningful contexts, ranging in size from cetaceans to ants. I describe how various technical issues can be addressed, how sources of error are identified and accounted for, the correct equations to use for different system configurations, and statistically defensible methods for selecting representative, ecologically meaningful data. doi:10.1016/j.cbpa.2007.06.258
22.4. Phenotypic plasticity in avian metabolic traits: Implications for comparative analyses McKechnie, A. University of the Witwatersrand, South Africa [email protected] The metabolic rates of many birds exhibit considerable phenotypic plasticity, such as the up- or down-regulation of basal metabolic rate (BMR) during thermal acclimation. Phenotypic plasticity has far-reaching implications for comparative analyses, many of which have assumed metabolic traits, and BMR in particular, to be static within species or populations. One broad-scale source of variation that needs to be accounted for is the difference in metabolic scaling exponents between captive-raised (0.670) and wild-caught birds (0.744). Within individuals, seasonal adjustments and/or acclimation typically causes BMR to vary by 20–50%, although larger changes have been reported. This variation potentially affects comparative analyses in two ways: (a) the parameters of statistical procedures that correct for phylogenetic non-independence, and (b) the results of comparisons (e.g., ANCOVA) among groups of taxa. The fact that phenotypic flexibility appears to be a general feature of avian metabolic systems raises several key questions. First, does the magnitude and/or rate of phenotypic adjustments scale with body mass? Second, what are the relative roles of genotypic adaptation and phenotypic plasticity in matching metabolic rates to physical and/or biotic variables? A comparison of data from wild-caught and captiveraised birds raises the possibility that the low BMR of desert birds primarily reflects phenotypic adjustments. A particularly intriguing possibility, that is beginning to be addressed, is that more unpredictable environments drive the evolution of greater phenotypic flexibility. doi:10.1016/j.cbpa.2007.06.259
22.5. Survival of subzero temperatures as a metabolic strategy: A test of the metabolic control hypothesis Marais, E., Irlich, U., and Chown, S.L. Stellenbosch University, South Africa [email protected] It has been hypothesized that freezing tolerance and freeze intolerance, the two major responses to subzero temperatures shown by animals, represent two more general alternatives for surviving stress, i.e. abandoned metabolic control or minimum metabolic control, respectively. In the case of abandoned metabolic control, the organism maximally protects its cellular structures against degradation and then switches off most other metabolic processes. No matter how low, the rate of spontaneous degradation of structures is never zero and repair is not possible during this state. Therefore, once a critical threshold has passed, the animal dies. In the case of minimum metabolic control, the organism survives by continually sustaining order at a minimum metabolic level, which is independent of both body mass and temperature. The period of survival depends on energy stored by the organism. The energy losses tolerated in the regime of abandoned metabolic control are much lower than those tolerated under minimum metabolic control. Here, using a freeze-tolerant insect species and a freeze-intolerant one, we test these hypotheses. The evidence suggests that at present, the hypothesis cannot be rejected, but may need further modification to account for time effects of repair processes. doi:10.1016/j.cbpa.2007.06.260
22.6. Integrative physiology of seasonal acclimatized plateau pikas and root voles from the Qinghai–Tibet Plateau Wang, D.-H., Wang, J.-M., and Zhang, Y.-M. Institute of Zoology, Chinese Academy of Sciences, Beijing, China [email protected] Survival of small mammals in winter requires proper adjustments in physiology, behavior and morphology. Changes in photoperiod, ambient temperature and food availability trigger the seasonal adaptations of many animals. Qinghai–Tibet Plateau characterized with extreme cold and hypoxia. Small mammals living here are facing extreme harsh environment, especially for non-hibernating species which do not store food for winter. We conducted an integrated study of the physiological responses to cold from molecular to organismal levels in plateau pikas (Ochtona curzoniae) and root voles (Microtus oeconomus), two non-hibernating herbivorous species which do not store food, from the Qinghai–Tibet Plateau. Plateau pikas maintained a constant body mass throughout the year and showed no seasonal change in body fat mass and circulating levels of serum leptin. However, non-shivering thermogenesis