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First published online September 9, 2003
Morphological and enzymatic correlates of aerobic and burst performance in different populations of Trinidadian guppies Poecilia reticulata
1 Department of Biology, University of California, Riverside, CA 92521,
USA
2 Department of Biological Science, California State University, Fullerton,
CA 92834, USA
Author for correspondence (e-mail:
Mark.Chappell{at}ucr.edu)
Accepted 15 July 2003
We examined the mechanistic basis for two whole-animal performance traits,
aerobic capacity and burst speed, in six laboratory-reared Trinidadian guppy
populations from different native drainages with contrasting levels of
predation. Using within- and between-population variation, we tested whether
variation in organs and organ systems (heart, gill and swimming motor mass)
and the activities of several enzymes that support locomotion (citrate
synthetase, lactate dehydrogenase and myofibrillar ATPase) are correlated with
aerobic performance (maximum rates of oxygen consumption,
O2max) or burst
performance (maximum swim speed during escape responses). We also tested for
associations between physiological traits and habitat type (different
drainages and predation levels).
Organ size and enzyme activities showed substantial size-independent
variation, and both performance measures were strongly correlated to body
size. After accounting for size effects, neither burst nor aerobic performance
was strongly correlated to any organ size or enzymatic variable, or to each
other. Two principal components (PCI, PC2) in both males and females accounted
for most of the variance in the organ size and enzymatic variables. In both
sexes, heart and gill mass tended to covary and were negatively associated
with citrate synthetase and lactate dehydrogenase activity. In males (but not
females), variation in aerobic performance was weakly but significantly
correlated to variation in PC1, suggesting that heart and gill mass scale
positively with
O2max. Neither
of the component variables and no single morphological or enzymatic trait was
correlated to burst speed in either sex.
Evolutionary changes in important life history traits occur rapidly in guppy populations subjected to different predation intensities (high mortality in downstream sites inhabited by large predatory fish; low mortality in upstream sites lacking large predators). We found significant differences between stream drainages in all morphological variables and most enzymatic variables, but only the mass of the swimming motor and LDH activity were significantly affected by predation regime. Overall, our data show that microevolution has occurred in the physiological foundations of locomotor performance in guppies, but evolutionary changes in physiology do not closely correspond to the predation-induced changes in life history parameters.
Key words: locomotion, swimming, predation, life history, burst speed, aerobic capacity, guppy, Poecilia reticulata, trade-off, lactate dehydrogenase, myofibrillar ATPase, citrate synthetase
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