The morphology-performance-fitness paradigm is usually explored by determining whether natural or “phenotypically engineered” variation among individuals in morphology (physiology) or performance covaries with an index of fitness such as survival. Here we study between-line covariation between performance and fitness for 44 lines of flies that had undergone mutation accumulation (in the absence of natural selection) on the second chromosome for 62 generations, plus 13 control lines. These mutation accumulation (MA) lines were known to have reduced competitive fitness and life history scores, and to have positive between-line covariances among life history traits. We measured several performance traits of larvae and adults (and a life history trait), examined covariances among those trait means, and also examined covariances of traits with competitive fitness. MA lines had significantly lower performances than did control lines in most traits. However, because control lines had been unknowingly contaminated, a conclusion that MA reduces performance must be tentative. Correlations among performance traits were highly variable in sign, suggesting that MA does not negatively affect all traits equivalently. Even so, correlation matrices for MA and for control lines were very similar. In bivariate comparisons, only one performance trait (a “get-a-grip index,” which measures the ability of a falling fly to catch itself on baffles) was positively correlated with competitive fitness. Multivariate analyses again suggested the importance primarily of get-a-grip. Two main patterns emerge from this study. First, MA negatively affects diverse aspects of physiological performance, but does so differentially across traits. Second, except for GAG, MA-induced variation in performance is at best weakly correlated with competitive fitness.
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Vol. 43 • No. 3