Climatic influences on basal metabolic rates among circumpolar populations

Abstract

This article examines evidence for elevations in basal metabolic rate (BMR) among indigenous Northern (circumpolar) populations and considers potential mechanisms and the adaptive basis for such elevations. Data on BMR among indigenous (n = 109 males; 122 females) and nonindigenous (n = 15 males; 22 females) circumpolar groups of North America and Siberia are compiled and compared to predicted BMRs based on three different references: body surface area (Consolazio et al., 1963), body mass (Schofield, 1985), and fat-free mass (Poehlman and Toth, 1995). Regardless of which reference is used, indigenous circumpolar groups show systematic and statistically significant elevations in BMR ranging from +7% to +19% above predicted values for indigenous men and from +3 to +17% for indigenous women. Nonindigenous males also show elevations in BMR, although not to the same extent as in indigenous men (deviations = +3 to +14%), whereas nonindigenous females show no clear evidence of elevated BMRs (deviations = -7 to +5%). This pattern of variation between indigenous and nonindigenous groups suggests that both functional and genetic factors play a role in metabolic adaptation to northern climes. Recent studies on the ecology and genetics of thyroid function offer insights into the mechanisms through which indigenous circumpolar populations may regulate metabolic rates. Studies of seasonal variation in thyroid hormone levels suggest that indigenous circumpolar populations may have a greater capacity to elevate BMR during severe cold than nonindigenous groups. Recent twin studies indicate a significant genetic component of thyroid responses to environmental stressors. Further research exploring the genetics of seasonal variation in thyroid function and BMR among circumpolar groups would advance understanding of the role that selection may have played in shaping metabolic variation.

Natural selection shaped regional mtDNA variation in humans

“…Partial uncoupling of the mitochondria would increase the basal metabolic rate of the individual and hence would require a higher caloric intake, such as that provided by a high-fat diet. Thus, mtDNA ATP6 variants that reduce coupling might partially account for the increased basal metabolic rate that has been observed in indigenous, circumpolar, human populations (29).…”

Climatic Adaptation and the Evolution of Basal and Maximum Rates of Metabolism in Rodents

“…Clades differences in the elevations of allometric relations (i.e., grade shifts) have been identified by conventional analysis of covariance (ANCOVA), and clade-specific allometric equations have been developed (e.g., MacMillen and Nelson 1969;Dawson and Hulbert 1970;Hayssen and Lacy 1985;McNab 1988McNab , 2002MacMillen and Garland 1989;Koteja and Weiner 1993). However, to our knowledge the clade differences have not been demonstrated with phylogenetically based statistical analyses (e.g., see Cruz-Neto et al 2001; with respect to avian metabolic rates, see Garland and Ives 2000;Rezende et al 2002).Aside from possible clade differences, several studies have attempted to explain the residual variation in BMR (i.e., after correlations with body size have been controlled statistically) by associations with various biotic or abiotic factors (for reviews, see Leonard et al 2002;McNab 2002). Interspecific comparisons of mammalian BMR have reported a significant association with diet using conventional statistics (McNab 1992(McNab , 2002(McNab , 2003, but not with phylogenetically based methods (Degen et al 1998;Speakman 2000;Cruz-Neto et al 2001;Genoud 2002).…”

Ecological Genetics of Thyroid Hormone Physiology in Humans and Wild Animals

“…Serum free T4 levels are higher in indigenous Evenki women than in nonindigenous Russian women living in the same communities in central Siberia [27]. The variation in free T4 levels was correlated with the variation in basal metabolic rate both in Evenki and Russian men and women [27].…”

“…The variation in free T4 levels was correlated with the variation in basal metabolic rate both in Evenki and Russian men and women [27]. Similar cases were also found for indigenous Nenets and nonindigenous Russians: both showed significant increases in total T4 levels during winter, but the magnitude of the increase was significantly greater in the Nenets than in the Russians [27]. Because thyroid hormones play important roles in regulating metabolic rate and adaptation to cold environments [28,29], human populations inhabiting colder environments may acquire genetic basis for more efficient thyroid hormone-induced thermogenesis and may therefore be genetically adapted to cold environments [30].…”

“…Serum free T4 levels are higher in indigenous Evenki women than in nonindigenous Russian women living in the same communities in central Siberia [27]. The variation in free T4 levels was correlated with the variation in basal metabolic rate both in Evenki and Russian men and women [27]. Similar cases were also found for indigenous Nenets and nonindigenous Russians: both showed significant increases in total T4 levels during winter, but the magnitude of the increase was significantly greater in the Nenets than in the Russians [27].…”