Tropical Heterothermy: Does the Exception Prove the Rule or Force a Re-Definition?

Canale, Cindy I.; Levesque, Danielle L.; Lovegrove, Barry G.

doi:10.1007/978-3-642-28678-0_3

Cited by 42 publications

(51 citation statements)

References 49 publications

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“…Basoendotherms (sensu [36]) such as tenrecs (Fig. 1d) and echidnas show the highest level of variability with rest-phase T b closely following T a during most times of the year [52][53][54][55][56].…”

Section: Daily Variability In Mammalian T Bmentioning

confidence: 99%

Modelling mammalian energetics: the heterothermy problem

Levesque

Nowack

Stawski

2016

Clim Chang Responses

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Global climate change is expected to have strong effects on the world's flora and fauna. As a result, there has been a recent increase in the number of meta-analyses and mechanistic models that attempt to predict potential responses of mammals to changing climates. Many models that seek to explain the effects of environmental temperatures on mammalian energetics and survival assume a constant body temperature. However, despite generally being regarded as strict homeotherms, mammals demonstrate a large degree of daily variability in body temperature, as well as the ability to reduce metabolic costs either by entering torpor, or by increasing body temperatures at high ambient temperatures. Often, changes in body temperature variability are unpredictable, and happen in response to immediate changes in resource abundance or temperature. In this review we provide an overview of variability and unpredictability found in body temperatures of extant mammals, identify potential blind spots in the current literature, and discuss options for incorporating variability into predictive mechanistic models.

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Section: Daily Variability In Mammalian T Bmentioning

confidence: 99%

Modelling mammalian energetics: the heterothermy problem

Levesque

Nowack

Stawski

2016

Clim Chang Responses

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“…As has been reported in previous studies on tenrecs (Lovegrove and Génin, 2008;Poppitt et al, 1994), there is no threshold normothermic T b under which all animals can be considered to be torpid. However, a coarse definition of torpor using the difference between T b and T a (∆T) (Arlettaz et al, 2000;Canale et al, 2012) was supported somewhat by the V · O 2 data. As an approximation, an animal with a ∆T of less than 5°C could be considered torpid, but only reliably at T a less than 25°C, and only if other methods for diagnosis (such as activity, metabolic rate or heart rate) are unavailable.…”

Section: Research Articlementioning

confidence: 99%

“…Although torpor and normothermy are difficult to distinguish in species with a high degree of thermolability (Canale et al, 2012;Stephenson and Racey, 1993b), it was necessary to consider 'torpid' animals separately from those that thermoregulated. Individuals were therefore classed as torpid if the ∆T (T b -T a ) was less than 5°C, and thermoregulating if ∆T was greater than 5°C (Hosken and Withers, 1999).…”

Section: List Of Symbols and Abbreviationsmentioning

confidence: 99%

“…Activity at low T b has similarly been observed in monotremes (Kuchel, 2003), marsupials (Rojas et al, 2012;Turner et al, 2012), placental mammals (Wooden and Walsberg, 2004) and birds (Merola-Zwartjes and Ligon, 2000). As a consequence, differentiating torpor from normothermy in these species using T b alone is complicated (Brice et al, 2002;Canale et al, 2012). Without a discernible pattern in the thermal profiles of the reproductive females, we would be reluctant to accept the inflection point found at 24.9°C in the non-reproductive individuals as a valid T lc as prescribed by the Scholander-Irving model.…”

Section: Research Articlementioning

confidence: 99%

“…Termed 'protoendotherms' by Grigg, Beard and Augee (Grigg et al, 2004), and 'basoendotherms' by Lovegrove (Lovegrove, 2012a), extant basal eutherians, often found on lowlatitude islands with little paleoclimatic history of Cenozoic cooling, are highly heterothermic, with variable T b and frequent use of torpor. The large amplitudes in the circadian rhythm of T b in these animals can lead to difficulties in differentiating between torpor and normothermy using T b alone (Brice et al, 2002;Canale et al, 2012;Kuchel, 2003;Lovegrove and Génin, 2008;Poppitt et al, 1994). Also, the determination of a distinct thermoneutral zone (TNZ), a range of T a over which MR remains minimal and constant, is highly problematic if T b is not maintained at a constant level (Brice, 2008;Scholander et al, 1950).…”

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Increased homeothermy during reproduction in a basal placental mammal

Levesque

Lovegrove

2014

Journal of Experimental Biology

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Homeothermic endothermy, the maintenance of a high and stable body temperature (T b ) using heat produced by elevated metabolism, is energetically expensive. There is increasing evidence that the earliest endotherms were heterotherms that, rather than maintaining strict homeothermy, allowed T b to fluctuate with large variations between active and rest-phase T b . The high level of homeothermy observed in modern mammals is therefore likely to have evolved from an ancestral heterothermic state. One of the hypotheses for the evolution of endothermy is that homeothermy allows for greater energetic output during reproduction (parental care model). We tested this hypothesis by measuring metabolic rates over a range of ambient temperatures in both reproductive and non-reproductive greater hedgehog tenrecs (Setifer setosus), a physiologically primitive mammal from Madagascar. Tenrecs have some of the lowest metabolic rates and highest levels of T b variability of any mammal and are therefore good models of the ancestral eutherian state. During pregnancy and lactation, there was an increase in metabolism and T b below the thermoneutral zone, accompanied by a decrease in T b variability. The lower critical limit of the thermoneutral zone was estimated at ~25°C. However, whereas increases in resting metabolism were substantial below 20°C (up to 150% higher during reproduction), daytime rest-phase ambient temperatures at the study site rarely reached equivalent low levels. Thus, S. setosus provide an example for how relatively low-cost increases in homeothermy could have led to substantial increases in fitness by allowing for the faster production of young. The mechanisms necessary for increases in thermogenesis during reproduction would have further benefited the development of homeothermy in mammals.

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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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Tropical Heterothermy: Does the Exception Prove the Rule or Force a Re-Definition?

Cited by 42 publications

References 49 publications

Modelling mammalian energetics: the heterothermy problem

Modelling mammalian energetics: the heterothermy problem

Increased homeothermy during reproduction in a basal placental mammal

Metabolic Flexibility: Hibernation, Torpor, and Estivation

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