POLLINATOR BEHAVIOR AND POSTPOLLINATION REPRODUCTIVE SUCCESS IN ALTERNATIVE FLORAL PHENOTYPES OF CLARKIA-GRACILIS (ONAGRACEAE)

Clarkia gracilis ssp. sonomensis has a floral polymorphism (presence v s. absence of petal spots) that is determined by a single gene. Most p opulations are monomorphic, indicating that frequency-dependent select ion may limit the spread of the rare allele within a population. Also, the vast majority of populations are composed of the dominant (spotte d) phenotype. To determine whether fertility selection mechanisms migh t favor one phenotype over the other and/or act in a frequency-depende nt manner, I examined pollinator behavior and postpollination success in these plants. Differential pollinator visitation among floral spot phenotypes was tested using experimental arrays placed into natural po pulations composed of different frequencies of the two phenotypes. Sli ght pollinator preference for spotted plants was detected in some arra ys; in no array was there significant preference for unspotted plants, even when the background population was 100% unspotted plants. There was no evidence of frequency-dependent visitation behavior by pollinat ors. A hand-pollination experiment explored the relative abilities of the two floral morphs to sire and mature seeds when given ample pollin ation, both in single- and mixed-donor pollen loads. Pollen from spott ed plants shed 10% more seeds than pollen from unspotted plants in the single-donor treatments, although phenotypic frequencies of offspring from mixed-donor loads did not differ from random expectation. Matern al seed maturation rates did not differ between morphs. These results support a previous finding of a consistent male fitness advantage for spotted plants over the whole range of phenotypic frequencies found in natural populations.