Sources of phenotypic variation in floral traits in wild radish, Raphanus raphanistrum (Brassicaceae)

Pollinator-mediated natural selection has been shown to act on phenotypic variation in floral morphology, and this variation has often been demonstrated to be heritable, but few details are available concerning the sources of floral variation. We examined phenotypic variation in seven floral traits in wild radish (Raphanus raphanistrum) at six levels: between two populations grown in a common garden, among plants within populations, among flowers measured on different weeks, between flowers on two flowering stalks measured on the same day, between adjacent flowers on a flowering stalk, and within individual flowers. There were no significant differences between plants derived from the two source populations, which were similar to 800 km apart. Most of the variance was within individual plants; repeatabilities were all <0.35. There were highly significant differences between flowers measured in different weeks and also highly significant plant by week interactions, indicating that the among-plant variation was not consistent over time. There was substantial variance among adjacent flowers on the same stalk, particularly in the gynoecium. This high within-plant variance is partly responsible for the low heritability of floral traits in the field and the weak selection on floral traits found in previous studies of wild radish.