Adult fitness components may strongly depend on variation in locomotory performance such as flight; this variation can be sex specific. Fast take-off to intercept females and competing males is an essential behavioral component of the territorial perching behavior in male speckled wood butterflies (Pararge aegeria L.). Females on the other hand avoid frequent take-offs particularly under suboptimal temperatures, typically showing fewer but longer flights than males. We estimated the heritability of take-off acceleration performance under suboptimal body temperatures by a restricted maximum-likelihood model. We calculated genetic correlations between this performance and a selection of morphological traits: size (body mass), flight muscle investment (relative thorax mass), and wing shape (forewing aspect ratio). Our results show significant additive genetic variation for mean acceleration performance and a similar but nonsignificant trend (P = 0.08) for maximal acceleration performance during take-off in males (h2 = 0.15). In females, heritability was not significantly different from zero for either of the acceleration performance measures. Morphological traits and take-off performance were genetically linked in a sex-specific way. In males, relative thorax mass and forewing aspect ratio were positively genetically correlated with acceleration performance. In females, there was a negative genetic correlation between acceleration performance and abdomen mass, but not with residual abdomen mass (i.e., regressed on total body mass). To fully understand the evolution of sexual differences in flight performances and morphology, several other flight performances will have to be included. This multifunctional nature of flight and its consequences for the evolutionary study of flight has not yet been fully appreciated in the literature.
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Vol. 62 • No. 10