Sj. Beaupre et D. Duvall, VARIATION IN OXYGEN-CONSUMPTION OF THE WESTERN DIAMONDBACK RATTLESNAKE (CROTALUS-ATROX) - IMPLICATIONS FOR SEXUAL SIZE DIMORPHISM, Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology, 168(7), 1998, pp. 497-506
Variation in metabolism affects energy budgets of individuals and may
serve as a mechanism that influences variation at whole organism or po
pulation 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 rattlesnak
es (Crotalus atrox) from a sexually dimorphic population and tested th
e effects of body mass, body temperature and time of day, in three gro
ups of snakes: males, non-reproductive females, and vitellogenic femal
es. Metabolic rates of male and non-reproductive female C. atrox were
similar to rates reported for other rattlesnakes (mass exponents rangi
ng from 0.645-0.670), Oxygen consumption was affected by body mass, bo
dy temperature and time of day, and was approximately 1.4 times greate
r in vitellogenic females than in non-reproductive females. No differe
nces were found between males and non-reproductive females. Accordingl
y, differences in metabolic rate apparently do not contribute directly
to sexual dimorphism in this population. Nevertheless, estimates of s
ize-dependent maintenance expenditure lead us to hypothesize that adul
t female body size may represent a compromise between selection for in
creased litter size (accomplished by increasing body size), and select
ion for increased reproductive frequency (accomplished by decreasing b
ody size, and, therefore inactive maintenance expenditure); this is a
mechanistic scenario suggested previously for some endotherms.