Evolution of Climatic Adaptation in Homeotherms

Scholander, P. F.

doi:10.1111/j.1558-5646.1955.tb01510.x

Cited by 285 publications

(214 citation statements)

References 29 publications

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“…Contrary to prediction and similar to mammals, however, the largest bird species (30-111 kg) occur only in environments with temperatures ranging from moderate to the hottest (5-45°C). These patterns support previous studies suggesting that adaptive shifts in body size are not a major avenue of climatic adaptation in birds and mammals, except perhaps at the within-species level (12,13).…”

Section: Significancesupporting

confidence: 79%

Metabolic heat production and thermal conductance are mass-independent adaptations to thermal environment in birds and mammals

Fristoe

Burger

Balk

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

123

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The extent to which different kinds of organisms have adapted to environmental temperature regimes is central to understanding how they respond to climate change. The Scholander-Irving (S-I) model of heat transfer lays the foundation for explaining how endothermic birds and mammals maintain their high, relatively constant body temperatures in the face of wide variation in environmental temperature. The S-I model shows how body temperature is regulated by balancing the rates of heat production and heat loss. Both rates scale with body size, suggesting that larger animals should be better adapted to cold environments than smaller animals, and vice versa. However, the global distributions of ∼9,000 species of terrestrial birds and mammals show that the entire range of body sizes occurs in nearly all climatic regimes. Using physiological and environmental temperature data for 211 bird and 178 mammal species, we test for mass-independent adaptive changes in two key parameters of the S-I model: basal metabolic rate (BMR) and thermal conductance. We derive an axis of thermal adaptation that is independent of body size, extends the S-I model, and highlights interactions among physiological and morphological traits that allow endotherms to persist in a wide range of temperatures. Our macrophysiological and macroecological analyses support our predictions that shifts in BMR and thermal conductance confer important adaptations to environmental temperature in both birds and mammals.macrophysiology | Bergmann's rule | body size | metabolic rate | thermal conductance A fundamental problem in ecology and biogeography is to elucidate the physiological processes that determine the environmental tolerances and influence the distributions of species. Across their nearly worldwide distributions, endothermic birds and mammals maintain near-constant body temperatures in the face of extreme and fluctuating environmental temperatures. Elucidating the morphological and physiological adaptations that allow species to inhabit such a wide spectrum of thermal environments is important for understanding the distribution of biodiversity and for predicting responses of species to climate change (1, 2).In a seminal paper, Scholander et al. (3) showed how endotherms balance rates of heat production and heat loss so as to maintain a constant body temperature in the face of varying environmental temperatures. The essence of the Scholander-Irving (S-I) model is the equation:where T b is body temperature, T a is ambient temperature, B is the rate of metabolic heat production, and C is the rate of heat loss or thermal conductance (4). For a resting animal, which has minimized heat loss by maximizing insulation and optimizing body posture, C = minimum thermal conductance (C MIN ); B = basal metabolic rate (BMR); and T a = T lc , where T lc is the lower critical temperature or the lower limit of the thermal neutral zone (TNZ).The TNZ is ecologically important because it is the range of environmental temperatures where energy expenditure is minimal; out...

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Section: Significancesupporting

confidence: 79%

Metabolic heat production and thermal conductance are mass-independent adaptations to thermal environment in birds and mammals

Fristoe

Burger

Balk

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

123

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“…From the considerations above it is clear that animals of the same volume but of different shape should reach their TNZ at different metabolic chamber temperatures (16). Although a number of studies have considered the influence of shape on metabolic rate (e.g., refs.…”

Section: Resultsmentioning

confidence: 99%

“…A major explanation for Bergmann's clines in body size is based on energetic and hydric considerations (35,36). Yet body size is the end result of a tug of war of a great many selective forces, and there are numerous alternative explanations and expectations for body size clines that are not mutually exclusive (16,35). Efforts to distinguish among explanations for Bergmann's clines often involve comparisons of the relative strength of correlations between size and distal environmental variables such as latitude and mean annual temperature (34,37).…”

Section: Resultsmentioning

confidence: 99%

Size, shape, and the thermal niche of endotherms

Porter

Kearney

2009

Proc. Natl. Acad. Sci. U.S.A.

227

250

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A key challenge in ecology is to define species' niches on the basis of functional traits. Size and shape are important determinants of a species' niche but their causal role is often difficult to interpret. For endotherms, size and shape define the thermal niche through their interaction with core temperature, insulation, and environmental conditions, determining the thermoneutral zone (TNZ) where energy and water costs are minimized. Laboratory measures of metabolic rate used to describe TNZs cannot be generalized to infer the capacity for terrestrial animals to find their TNZ in complex natural environments. Here, we derive an analytical model of the thermal niche of an ellipsoid furred endotherm that accurately predicts field and laboratory data. We use the model to illustrate the relative importance of size and shape on the location of the TNZ under different environmental conditions. The interaction between body shape and posture strongly influences the location of the TNZ and the expected scaling of metabolic rate with size at constant temperature. We demonstrate that the latter relationship has a slope of approximately 1 ⁄2 rather than the commonly expected surface area/volume scaling of 2 ⁄3. We show how such functional traits models can be integrated with spatial environmental datasets to calculate null expectations for body size clines from a thermal perspective, aiding mechanistic interpretation of empirical clines such as Bergmann's Rule. The combination of spatially explicit data with biophysical models of heat exchange provides a powerful means for studying the thermal niches of endotherms across climatic gradients.biophysical ecology ͉ functional traits ͉ lower critical temperature ͉ metabolic scaling ͉ thermoneutral zone T he ecological niche reflects the interaction between an organism and its environment and how that interaction affects its fitness (1, 2). An understanding of a species' niche requires knowledge of its traits (morphology, physiology, and behavior) and how that species interacts with its habitat to construct environments (2). This two-way interaction between organism and environment is also key to understanding how a species' traits, and hence its niche, evolves (3, 4). A species' energy and water balance are key determinants of its niche, reflecting both its requirements for life (Grinnellian niche) and its impact on the other species with which it interacts (Eltonian niche). Here, we illustrate how biophysical principles can be used to link variation in the size, shape, and other functional traits of organisms with environmental data to predict the thermal niches of endotherms. Such a model can be conceived as a mechanistic depiction of the Hutchinsonian niche, a hypervolume describing conditions suitable for survival, growth, and reproduction along trait and environmental axes. Biophysical models provide a way to calculate spatially explicit null models of selective pressures on functional traits from the perspectives of energy and water conservation (5).Basal metabolic rate ...

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“…The near-ubiquity of clines in traits along gradients, such as latitude, has been used to identify major biogeographical trends, such as Bergmann's rule (Blackburn et al, 1999) and Allen's rule (Scholander, 1955). Classic studies of clinal variation in plants have played a particularly noteworthy role in our understanding of local adaptation (Clausen et al, 1948;Antonovics & Bradshaw, 1970), with plant populations frequently showing covariance between environmental gradients and phenology, morphology, physiology and life history (for example, Drezner, 2003;Stinchcombe et al, 2004;Ingvarsson et al, 2006;Savolainen et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Adaptation and colonization history affect the evolution of clines in two introduced species

et al. 2009

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Summary• Phenotypic and genetic clines have long been synonymous with adaptive evolution. However, other processes (for example, migration, range expansion, invasion) may generate clines in traits or loci across geographical and environmental gradients. It is therefore important to distinguish between clines that represent adaptive evolution and those that result from selectively neutral demographic or genetic processes.• We tested for the differentiation of phenotypic traits along environmental gradients using two species in the genus Silene, whilst statistically controlling for colonization history and founder effects. We sampled seed families from across the native and introduced ranges, genotyped individuals and estimated phenotypic differentiation in replicated common gardens.• The results suggest that post-glacial expansion of S. vulgaris and S. latifolia involved both neutral and adaptive genetic differentiation (clines) of life history traits along major axes of environmental variation in Europe and North America. Phenotypic clines generally persisted when tested against the neutral expectation, although some clines disappeared (and one cline emerged) when the effects of genetic ancestry were statistically removed.• Colonization history, estimated using genetic markers, is a useful null model for tests of adaptive trait divergence, especially during range expansion and invasion when selection and gene flow may not have reached equilibrium.

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Evolution of Climatic Adaptation in Homeotherms

Cited by 285 publications

References 29 publications

Metabolic heat production and thermal conductance are mass-independent adaptations to thermal environment in birds and mammals

Metabolic heat production and thermal conductance are mass-independent adaptations to thermal environment in birds and mammals

Size, shape, and the thermal niche of endotherms

Adaptation and colonization history affect the evolution of clines in two introduced species

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