THE EVOLUTION OF BODY ARMOR IN MAMMALS: PLANTIGRADE CONSTRAINTS OF LARGE BODY SIZE

Predictions associated with opposing selection generating minimum variance in basal metabolic rate (BMR) in mammals at a constrained body mass (CBM; 358 g) were tested. The CBM is presumed to be associated with energetic constraints linked to predation and variable resources at intermediate sizes on...

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Bibliographic Details
Published in:Evolution 2001-07, Vol.55 (7), p.1464-1473
Main Author: Lovegrove, Barry Gordon
Format: Article
Language:English
Subjects:
Anatomy & physiology
Animal physiology
Animals
Basal metabolic rate
Basal Metabolism
Biological Evolution
Biological taxonomies
body armor
Body Constitution - physiology
Body size
Cope's rule
Evolution
Mammalia
Mammals
Mammals - anatomy & histology
Mammals - physiology
Metabolism
Oxygen Consumption
Phylogeny
Predation
Protective vests
Regression Analysis
REGULAR ARTICLES
Running
Running speed
running speeds
Species Specificity
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Summary:Predictions associated with opposing selection generating minimum variance in basal metabolic rate (BMR) in mammals at a constrained body mass (CBM; 358 g) were tested. The CBM is presumed to be associated with energetic constraints linked to predation and variable resources at intermediate sizes on a logarithmic mass scale. Opposing selection is thought to occur in response to energetic constraints associated with predation and unpredictable resources. As body size approaches and exceeds the CBM, mammals face increasing risks of predation and daily energy requirements. Fast running speeds may require high BMRs, but unpredictable and low resources may select for low BMRs, which also reduce foraging time and distances and thus predation risks. If these two selection forces oppose each other persistently, minimum BMR variance may result. However, extreme BMR outliers at and close to the CBM should be indicative of unbalanced selection and predator avoidance alternatives (escapers vs. defenders), and may therefore provide indirect support for opposing selection. It was confirmed that body armor in defenders evolves at and above the CBM, and armored mammals had significantly lower BMRs than their nonarmored counterparts. However, analyses comparing the BMR of escapers—the fastest nonarmored runners (Lagomorpha)—with similar-sized counterparts were inconclusive and were confounded by limb morphology associated with speed optimization. These analyses suggest that the risks and costs of predation and the speed limitations of the plantigrade foot may constrain the evolution of large body sizes in plantigrade mammals. Corresponding Editor: T. Garland Jr.
ISSN:0014-3820
1558-5646
DOI:10.1554/0014-3820(2001)055[1464:TEOBAI]2.0.CO;2