Capitulum characters in a seed heteromorphic plant, Crepis sancta (Asteraceae): variance partitioning and inference for the evolution of dispersal rate

In Crepis sancta (Asteraceae), achenes produced in the periphery of the flo wer head have reduced dispersal ability and are larger than achenes produce d in the centre of the head, which disperse farther. The proportion of cent ral achenes produced by a single individual represents the potential disper sal rate of its progeny. Seed variation in dispersal ability may be importa nt where there is: spatio-temporal variability of habitats, but its evoluti onary significance mainly depends on the heritability of the relative propo rtions of each achene morph. However, the number of peripheral achenes in a capitulum, and that of involucral bracts are suggested to depend on the nu mber of parastichies, a canalized character. From a diallel cross design, p henotypic variance for several capitulum traits was partitioned among six v ariance components, including the additive variance. The phenotypic values of some head traits reflected the expected frequency due to ontogeny, in pa rticular the number of involucral bracts. Yet, this character also had a si gnificant heritability, suggesting that variation around the mode of the di stribution was not only due to developmental noise. The additive variance f or number of peripheral and central achenes was not significantly different from zero. In contrast, their respective proportion had a narrow sense her itability greater than 0.20. The present results suggest that the percentag e of central achenes per individual, and thus the potential dispersal rate in Crepis sancta, is under quantitative genetic control, and could undergo microevolutionary changes in natural populations.