Variation in oxygen consumption of the western diamondback rattlesnake (Crotalus atrox): implications for sexual size dimorphism |
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Authors: | S J Beaupre D Duvall |
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Institution: | (1) Department of Life Sciences, Arizona State University West, Phoenix, AZ 85069-7100, USA, US |
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Abstract: | Variation in metabolism affects energy budgets of individuals and may serve as a mechanism that influences variation at whole
organism or population levels. For example, sex differences in metabolic expenditure may contribute to bioenergetic sources
of sexual size dimorphism. We measured oxygen consumption rates of 48 western diamondback rattlesnakes (Crotalus atrox) from a sexually dimorphic population and tested the effects of body mass, body temperature and time of day, in three groups
of snakes: males, non-reproductive females, and vitellogenic females. Metabolic rates of male and non-reproductive female
C. atrox were similar to rates reported for other rattlesnakes (mass exponents ranging from 0.645–0.670). Oxygen consumption was affected
by body mass, body temperature and time of day, and was approximately 1.4 times greater in vitellogenic females than in non-reproductive
females. No differences were found between males and non-reproductive females. Accordingly, differences in metabolic rate
apparently do not contribute directly to sexual dimorphism in this population. Nevertheless, estimates of size-dependent maintenance
expenditure lead us to hypothesize that adult female body size may represent a compromise between selection for increased
litter size (accomplished by increasing body size), and selection for increased reproductive frequency (accomplished by decreasing
body size, and, therefore inactive maintenance expenditure); this is a mechanistic scenario suggested previously for some
endotherms.
Accepted: 20 May 1998 |
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Keywords: | Metabolism Gender Bioenergetics Sexual selection |
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