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The short-term evolvability of a character is closely related to its level of additive genetic variation. However, a large component of the variation in any one character may be pleiotropically linked to other characters under the influence of different selective factors. Therefore, the organization of the organism into quasi-independent modules may be an important prerequisite for evolvability. In this paper we propose to study character evolvability in terms of conditional genetic variation. By estimating the amount of genetic variation in a character, y, that is independent of other characters, x, we can assess the evolvability of y when there is stabilizing selection on x. We suggest that systematic use of conditioning may help build a picture of modular organization and quasi-independent evolvability. As an illustration, we use this approach to assess the evolvability of floral characters in Dalechampia scandens (Euphorbiaceae). Although our study population had relatively low levels of genetic variation at the outset, we find evidence that conditioning may lead to substantial further reduction in the genetic variation available for independent adaptation. This provides additional evidence that the D. scandens blossom is constrained in its short-term evolvability. J. Exp. Zool. (Mol. Dev. Evol.) 296B:23–39, 2003. © 2003 Wiley-Liss, Inc.

Abstract: Fluctuating asymmetry (FA) refers to small random differences that occur between the right and the left sides of bilateral characters. Under the hypothesis that the degree of FA in secondary sex traits reflects the ability of males to cope with environmental stress, and consequently reflects individual quality, a negative relationship is expected between FA and the trait size. Additionally, selective mortality acting preferentially on individuals in poor condition, presumably more asymmetric, should lead to a decrease in FA with age. We tested these hypotheses on roe deer (Capreolus capreolus) antlers, analysing the FA pattern in antler size from individuals culled over 18 years in a single population. Absolute asymmetry significantly decreased with age, and tended to decrease with antler size, at constant carcass mass, within age classes. Moreover, increase in the population density negatively affected carcass mass and antler size, and resulted in a significant increase in the degree of asymmetry in antlers. These results suggest that antler development in roe deer represents a reliable signalling of individual quality. Moreover, due to the deciduous nature of antlers, asymmetry in antler size appears to be a valuable indicator of the current environmental conditions encountered by populations.

Young fallow deer (Dama dama) held in captivity were weighed at birth and at the onset of winter to test if weight at birth predicted body weight in winter. A positive relationship was obtained between these two measurements. In previous studies, existence of compensatory growth, which accounts for the absence of relationship between these two measurements, was associated with good conditions encountered by populations. In this population, the absence of resource limitation suggested that level of polygyny might be a better predictor of the absence of compensatory growth during the first summer of life.