The mitochondrial basal proton leak (MBPL) significantly contributes to high body temperatures (T_b) and basal metabolic rates (BMR) in endotherms. In endotherms at a given body mass (M), liver MBPL is higher than in ectotherms, supporting the notion that MBPL may partly explain the evolutionary increase in metabolic rate (MR), fostering endothermy. Here, we re-addressed this assumption by performing a phylogenetic analysis comparing all available liver MBPL data for ecto- and endotherms. While MBPL within endotherms negatively scales with M and BMR as shown previously, MBPL of ectotherms does not scale allometrically with M. Phylogenetic analysis reveals that this result is confounded by a positive scaling coefficient for MBPL with M for reptiles. Strikingly, the reptilian MBPL reaches endothermic levels above a body mass of 6.6 kg. Thus, phylogenetic scaling of MBPL supports previous claims of endotherm-like physiological characteristics in large reptiles. It appears that diversification of ancestral ectothermic tetrapods to a body mass of at least 6 kg may have been required to reach a MBPL that is beneficial for sustained high body temperatures. Novel MBPL data for the lesser hedgehog tenrec, a protoendothermic eutherian that displays reptile-like thermoregulatory patterns, fall within the endo- and ectothermic allometric regressions. Finally, we add additional evidence that within endotherms, phylogenetic differences in MR do not correlate with MBPL. Collectively, these data suggest that MBPL does not universally scale with metabolic rate in ecto- or endotherms and that an increasing MBPL with M may have played an important physiological role in the evolutionary history of reptilian thermoregulation.

Item Type:	Refereed Article
Keywords:	mitochondrial proton leak, metabolic rate, allometry, phylogeny, scaling
Research Division:	Biological Sciences
Research Group:	Evolutionary biology
Research Field:	Phylogeny and comparative analysis
Objective Division:	Environmental Management
Objective Group:	Other environmental management
Objective Field:	Other environmental management not elsewhere classified
UTAS Author:	Polymeropoulos, ET (Dr Elias Polymeropoulos)
ID Code:	114483
Year Published:	2017
Web of Science® Times Cited:	5
Deposited By:	Menzies Institute for Medical Research
Deposited On:	2017-02-16
Last Modified:	2018-05-29
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