Quantitative genetic variation in a population of Crepis tectorum subsp. pumila (Asteraceae)

Quantitative genetic variation was assessed in a population of Crepis tectorum subsp. pumila , a winter annual confined to calcareous grassland on the Baltic island of öland (SE Sweden). Plants from 40 maternal sibships were grown in a greenhouse and scored for a large number of traits representing all stages of the life cycle. The study included several characters that have been subject to ecotypic differentiation as well as traits known to be under current selection. Highly significant family differences were found for all but one character, suggesting that past selection was too weak to eliminate the genetic variability of characters presumed to be adaptive and there is a potential for further adaptive change in most traits. Two additional traits treated as qualitative were also found to differ significantly among families. A parallel cultivation experiment showed that the extent of population divergence in a quantitative trait was positively correlated with the amount of inter- family variation, implying stability of the relative variability for substantial periods of time, a possible reflection of phenotypic constraints being expressed both within and between populations. Additional data indicated that genetic trade-offs among traits under simultaneous selection, year-to- year variation in selection in combination with a long-lived seed bank, and genotype × environment interactions, could prevent the erosion of genetic variability in some characters connected with fitness.