Odell JP, Chappell MA, Dickson KA (2003) Morphological and enzymatic correlates of aerobic and burst performance in different populations of Trinidadian guppies, Poecilia reticulata. Journal of Experimental Biology 206: 3707-3718.
ABSTRACT --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; VO2max) 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 VO2max. Neither of the component variables and no single morphological or enzymatic trait was correlated to burst speed in either sex.
Well-known work by Reznick and his colleagues has demonstrated rapid
evolutionary change in important life history traits 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.