THE EVOLUTION OF ENDOTHERMY: TESTING THE AEROBIC CAPACITY MODEL

Area of Science:

• Evolutionary Biology
• Physiology
• Metabolic Research

Background:

• Endothermy, the ability to maintain a body temperature above the environment using metabolic heat, is a key vertebrate evolutionary event.
• The aerobic capacity model proposes that selection for higher maximal aerobic capacity drove the evolution of endothermy, with elevated resting metabolic rate as a correlated response.

Purpose of the Study:

• To critically evaluate the evolutionary and genetic assumptions underpinning the aerobic capacity model.
• To assess the utility of phenotypic and genetic correlations in testing the aerobic capacity model.
• To identify new avenues for research into the selective factors driving the evolution of high metabolic rates and endothermy.

Main Methods:

• Evaluation of existing evolutionary and genetic assumptions of the aerobic capacity model.
• Assessment of phenotypic and genetic correlations using intraspecific and interspecific data from terrestrial vertebrates.
• Analysis of limitations in using correlation data to distinguish between models.

Main Results:

• Intraspecific data generally support a positive phenotypic correlation between resting and maximal oxygen consumption rates.
• Interspecific analyses provide inconclusive support for this correlation.
• Current correlation assessments may not sufficiently differentiate the aerobic capacity model from alternative hypotheses, such as direct selection on thermoregulation.

Conclusions:

• Phenotypic and genetic correlations, while informative, have limitations in definitively testing the aerobic capacity model.
• Further research combining mechanistic physiology and quantitative genetics is needed.
• Determining if a positive genetic correlation between resting and maximal oxygen consumption is inherent to vertebrate physiology is crucial for understanding endothermy's evolution.