Energetic consequences of metabolic depression in tropical and temperate-zone lizards

Christian, Keith A.; Bedford, Gavin S.; Schultz, Tim

doi:10.1071/zo98061

Cited by 44 publications

(52 citation statements)

References 22 publications

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“…Since then reports of actively regulated suppression of standard metabolism in response to water and food deprivation are rare and varied (reviewed in ref. 62). In fact, though Australian freshwater crocodiles (Crocodylus johnstoni) can survive for several months without access to water they "do not appear to have any specific adaptations for estivation" (61).…”

Section: Estivating Ectothermsmentioning

confidence: 93%

Metabolic Flexibility: Hibernation, Torpor, and Estivation

Staples

2016

Comprehensive Physiology

136

116

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Many environmental conditions can constrain the ability of animals to obtain sufficient food energy, or transform that food energy into useful chemical forms. To survive extended periods under such conditions animals must suppress metabolic rate to conserve energy, water, or oxygen. Amongst small endotherms, this metabolic suppression is accompanied by and, in some cases, facilitated by a decrease in core body temperature-hibernation or daily torpor-though significant metabolic suppression can be achieved even with only modest cooling. Within some ectotherms, winter metabolic suppression exceeds the passive effects of cooling. During dry seasons, estivating ectotherms can reduce metabolism without changes in body temperature, conserving energy reserves, and reducing gas exchange and its inevitable loss of water vapor. This overview explores the similarities and differences of metabolic suppression among these states within adult animals (excluding developmental diapause), and integrates levels of organization from the whole animal to the genome, where possible. Several similarities among these states are highlighted, including patterns and regulation of metabolic balance, fuel use, and mitochondrial metabolism. Differences among models are also apparent, particularly in whether the metabolic suppression is intrinsic to the tissue or depends on the whole-animal response. While in these hypometabolic states, tissues from many animals are tolerant of hypoxia/anoxia, ischemia/reperfusion, and disuse. These natural models may, therefore, serve as valuable and instructive models for biomedical research.

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Section: Estivating Ectothermsmentioning

confidence: 93%

Metabolic Flexibility: Hibernation, Torpor, and Estivation

Staples

2016

Comprehensive Physiology

136

116

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“…The lack of moisture in the dry season limits plant growth, and insect numbers are greatly reduced compared to the wet season (Churchill 1994;Griffiths and Christian 1996). The dry season is thus a season of limiting resources for many animals (Christian et al , 1999aGriffiths and Christian 1996). Most species of reptiles are much less conspicuous in the dry season, and some enter a period of aestivation (Christian et al 1996a(Christian et al , 1996b(Christian et al , 1996c(Christian et al , 1996dKennett and Christian 1994).…”

Section: Introductionmentioning

confidence: 99%

“…Others are active to some extent, but nevertheless expend less energy in the dry season compared to the wet. This reduction in field metabolic rate (FMR) can be accomplished by physiological mechanisms such as metabolic depression (Christian et al 1996b(Christian et al , 1996c(Christian et al , 1999a(Christian et al , 1999b, and behavioural strategies such as thermoregulation at lower body temperatures (T b ) (Christian and Bedford 1995, Christian et al 1996c, 1999b and reduced activity (Christian et al 1996b(Christian et al , 1996c(Christian et al , 1999b. Determining which strategies are employed by a species is critical to our understanding of the annual or life-time energy budgets of the animals.…”

Section: Introductionmentioning

confidence: 99%

Energetics of bluetongue lizards ( Tiliqua scincoides ) in a seasonal tropical environment

2003

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We studied the physiological ecology of bluetongue lizards (Tiliqua scincoides) on the Adelaide River floodplain in tropical Australia to determine the seasonal patterns of energy expenditure and to determine the mechanisms by which seasonal differences were achieved. Field metabolic rates (FMR) were significantly lower in the dry season (37.6 kJ kg(-1) day(-1); n=9) than in the wet (127.3 kJ kg(-1) day(-1); n=7). Water flux was also lower in the dry season (6.8 ml kg(-1) day(-1); n=9) than in the wet (39.4 ml kg(-1) day(-1); n=7). Measurements of body temperatures (T(b)) and movements of free-ranging animals, and standard metabolic rate (SMR) of recently caught animals, allowed a detailed analysis of energy budgets for wet and dry seasons. In the dry, bluetongue lizards expended 90 kJ kg(-1) day(-1) less energy than in the wet season. Unlike some other lizards of the wet-dry tropics, SMR did not differ between seasons. About 5% of the seasonal difference in FMR was due to lower night time T(b) during the dry season, and about 7% was due to lower diurnal T(b). The remaining 88% of the decrease in energy expended in the dry season was due to a substantial decrease in other costs that may include reproduction, growth, digestion and activity. If we assume the animals fed daily and the costs of digestion are taken into account, the estimates are: 14% of the savings result from lower T(b) at night, 20% from lower T(b) in the day, and 66% result from decreased activity. It is therefore apparent that, unlike some agamid and varanid lizards that use a combination of behavioural and physiological mechanisms to conserve energy when food and water are limited, bluetongue lizards primarily use behavioural mechanisms to achieve a dramatic reduction in energy expenditure in the dry season.

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“…The cues that initiate entrance into dormancy or other states of metabolic suppression in reptiles remain enigmatic (for reviews, see Gregory 1982;Christian et al 1999). The mechanisms that underlie seasonal metabolic suppression also remain elusive.…”

Section: Is This Metabolic Suppression?mentioning

confidence: 99%

“…In a recent review, these reductions have been reported to range from 25% to 69% for 11 species of temperate and ) and Andrade and Abe (1999; open circle; mass range 525-n p 12 2,140 g; ) for winter animals only are also included for comn p 6 parison. Note: for comparison, in all cases, the values of oxygen consumption rate have been converted to milliliters O 2 per hour normalized to 1 kg body mass using the scaling equations from Toledo et al (2008). tropical lizards (Christian et al 1999), and our 50%-90% reductions fall within or exceed this range.…”

Section: Is This Metabolic Suppression?mentioning

confidence: 99%

Seasonal Changes in Daily Metabolic Patterns of Tegu Lizards (Tupinambis merianae) Placed in the Cold (17°C) and Dark

Milsom

Andrade²,

Brito³

et al. 2008

Physiological and Biochemical Zoology

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. ABSTRACTOxygen consumption rate was measured continuously in young tegu lizards Tupinambis merianae exposed to 4 d at 25ЊC followed by 7-10 d at 17ЊC in constant dark at five different times of the year. Under these conditions, circadian rhythms in the rate of oxygen consumption persisted for anywhere from 1 d to the entire 2 wk in different individuals in all seasons except the winter. We also saw a progressive decline in standard oxygen consumption rate (at highly variable rates in different individuals) to a very low rate that was seasonally independent (ranging from to mL kg Ϫ1 h Ϫ1 across seasons). 19.1 ‫ע‬ 6.2 27.7 ‫ע‬ 0.2 Although this degree of reduction appeared to take longer to invoke when starting from higher metabolic rates, tegu lizards reduced their metabolism to the low rates seen in winter dormancy at all times of the year when given sufficient time in the cold and dark. In the spring and summer, tegus reduced their standard metabolic rate (SMR) by 80%-90% over the experimental run, but only roughly 20%-30% of the total fall was due to the reduction in temperature; 70%-80% of the total fall occurred at constant temperature. By autumn, when the starting SMR on the first night at 25ЊC was already reduced by 59%-81% (early and late autumn, respectively) from peak summer values, virtually all of the fall (63%-83%) in metabolism was due to the reduction in temperature. This suggests that the temperature-independent reduction of metabolism was already in place by autumn before the tegus had entered winter dormancy.

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Energetic consequences of metabolic depression in tropical and temperate-zone lizards

Cited by 44 publications

References 22 publications

Metabolic Flexibility: Hibernation, Torpor, and Estivation

Metabolic Flexibility: Hibernation, Torpor, and Estivation

Energetics of bluetongue lizards ( Tiliqua scincoides ) in a seasonal tropical environment

Seasonal Changes in Daily Metabolic Patterns of Tegu Lizards (Tupinambis merianae) Placed in the Cold (17°C) and Dark

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