THE QUANTITATIVE GENETICS OF FLORAL CHARACTERS IN MIMULUS-GUTTATUS

We examined the quantitative genetics of 20 floral traits in Mimulus guttatus including flowering time, autofertility, flower size, the spatial arrangement of flower parts, pollen and ovule production and seed number and size. A six by six diallel crossing design including selfs was performed in the glasshouse between plants derived from one population of M. guttatus from California. All characters with the exception of pollen number showed significant amounts of additive genetic variance indicating a potential to respond to selection. A principal components analysis revealed that some variation in many characters could be explained by general flower size. However, most characters still displayed heritable variation after the flower size effect was removed by analysis of covariance. Families showed considerable variation in the ability to self in glasshouse conditions. Only a weak relationship between autofertility and herkogamy was detected, suggesting that an unidentified mechanism was responsible for differences in selfing ability. Pollen quality and ovule production were also strongly heritable, suggesting the potential for gender specialization of plants but no trade-off between male and female function could be detected. Inbreeding depression was evident in flower size and pollen and ovule production. It is postulated that the heritable variation observed is maintained in this population through disruptive selection on autofertility in response to seasonal variation in the onset of spring drought and pollinator availability.