POLLINATOR-MEDIATED SELECTION ON FLORAL TRAITS IN A SYNTHETIC POPULATION OF SENECIO-INTEGRIFOLIUS (ASTERACEAE)

We measured pollinator-mediated selection on quantitative floral traits through female reproductive success in a phenotypically variable population of Senecio integrifolius, consisting of plants derived from two natural populations, including genotypes with extreme trait values (head width) and plants on which all rays had been removed. In addition to significant heritabilities for all traits, we also documented genetic variation in phenotypic plasticity for head width. A phenotypic selection analysis demonstrated (1) a strong positive relationship between the percentage seed-set and the overall cross-fertility determined in a previous greenhouse study, (2) non-linear selection on plant height with an optimum above the population mean, and (3) a negative correlation between seed-set and the number of heads on the plant. No selection on head width could be detected and there was a relatively small decline in seed-set following the removal of all rays (15%). Multiple regression using paternal family means largely confirmed the patterns of selection seen at the phenotypic level.