Determinants of intra-specific variation in basal metabolic rate

Abstract

Basal metabolic rate (BMR) provides a widely accepted benchmark of metabolic expenditure for endotherms under laboratory and natural conditions. While most studies examining BMR have concentrated on inter-specific variation, relatively less attention has been paid to the determinants of within-species variation. Even fewer studies have analysed the determinants of within-species BMR variation corrected for the strong influence of body mass by appropriate means (e.g. ANCOVA). Here, we review recent advancements in studies on the quantitative genetics of BMR and organ mass variation, along with their molecular genetics. Next, we decompose BMR variation at the organ, tissue and molecular level. We conclude that within-species variation in BMR and its components have a clear genetic signature, and are functionally linked to key metabolic process at all levels of biological organization. We highlight the need to integrate molecular genetics with conventional metabolic field studies to reveal the adaptive significance of metabolic variation. Since comparing gene expressions inter-specifically is problematic, within-species studies are more likely to inform us about the genetic underpinnings of BMR. We also urge for better integration of animal and medical research on BMR; the latter is quickly advancing thanks to the application of imaging technologies and ‘omics’ studies. We also suggest that much insight on the biochemical and molecular underpinnings of BMR variation can be gained from integrating studies on the mammalian target of rapamycin (mTOR), which appears to be the major regulatory pathway influencing the key molecular components of BMR.

Variation in Metabolic Rate among Individuals Is Related to Tissue-Specific Differences in Mitochondrial Leak Respiration

“…However, while a positive correlation between minimum and maximum metabolic rates at the intraspecific level has indeed been found in some contexts Biro and Stamps 2010;Careau et al 2014aCareau et al , 2014b, this is not the case in others (Chappell et al 2004(Chappell et al , 2007Gomes et al 2004;Careau et al 2014b). The mechanisms underlying this purported link are also equivocal, with some studies reporting a positive relationship between metabolic rates and underlying traits such as organ size (Konarzewski and Ksiazek 2013) or mitochondrial density (Norin and Malte 2012), whereas others find no relationship (Selman et al 2001;Chappell et al 2007;Larsen et al 2011;Norin and Malte 2012;Boldsen et al 2013). This makes it impossible to explain mechanisms behind variation in AS, since it could be a consequence of variation in minimum and maximum metabolic rates that is either concomitant and connected or independent and separated.…”

A strong response to selection on mass-independent maximal metabolic rate without a correlated response in basal metabolic rate

“…Its central importance is reflected in the thousands of studies published on energy metabolism (Houston et al, 1993;Hayes and O'Connor, 1999;Speakman, 2008; Burton et al, 2011, Konarzewski andKsiążek, 2013;White and Kearney, 2013). Despite these studies, many questions about metabolic rates and energy metabolism remain unanswered.…”

Basal metabolic rate can evolve independently of morphological and behavioural traits

“…Energy metabolism is a burgeoning area of research in evolutionary ecology, with major contemporary interest in understanding the causes and consequences of interindividual variation (Speakman et al, 2004;Burton et al, 2011;Konarzewski and Książek, 2013). One of the most commonly studied measures of energy metabolism is basal metabolic rate or BMR (White and Kearney, 2013), which is defined as the minimum energy requirement of an endothermic animal that is at rest, postabsorptive (that is, not digesting food) and thermoneutral during its normal period of inactivity (McNab, 1997).…”

“…Such between-individual differences in the amount of energy required for basic self-maintenance may have important consequences for how much energy individuals have to allocate to other energetically demanding tasks, such as growth and reproduction (Burton et al, 2011). Consequently, the presence of large differences in metabolic rates among individuals from the same population is intriguing, and there is growing interest in understanding the adaptive significance of such variation (Speakman et al, 2004;Burton et al, 2011;Konarzewski and Książek, 2013).…”