VARIABILITY IN A PREDOMINANTLY SELF-FERTILIZING ANNUAL WITH FRAGMENTED DISTRIBUTION, MICROSERIS-DOUGLASII (ASTERACEAE, LACTUCEAE)

Five offspring each Of 41 strains derived from single plants in 19 pop ulations of M. douglasii have been raised under common greenhouse cond itions. Six identical sublines of one strain have been included to mon itor residual environmental variance. 32 phenotypic characters have be en scored or measured including developmental timing, shape and size o f the plant and details of the capitulum structure including meristic characters (numbers of parts). Using the replicate sublines, we found a non-genetic component of variance from 0 % to 61 % of the total vari ance among the strains. This reflects mainly the plasticity of the cha racters and is strongly dependent on the precise definition of the cha racter including the time when it is scored. The character states in g eneral are not normally distributed within the species. This is due to the uneven representation of various phenotypes in various population s and to the structure of some characters, e.g. those in which quantit ative variation only modifies qualitative alternatives and those that are numerically canalized. Some characters are correlated via the basi c variables of flowering time or plant size, otherwise there is very l ittle correlation among characters either due to pleiotropy or to asso ciation in populations (founder effects or selection). Many of the cha racters are genetically polymorphic in one or more of the populations. As a consequence, the overall phenetic relationships among the strain s show little structure except for similarities of strains isolated fr om the same population and a strong similarity of two neighboring popu lations. On the basis of all pairwise comparisons, phenetic distance i s significantly but weakly (R2 = 0.16) correlated with geographical di stance. Only one of the 32 individual characters, color intensity of t he violet stripe on the outer ligules, had a significant non-random ge ographical distribution. The variance of some characters could be dete rmined in the natural field situation. The genetic component of varian ce for achenes per capitulum is completely swamped by environmental va riation in the field, while heritability for pappus part number and es pecially for the proportion of hairy peripheral achenes was high under field conditions.