CONSEQUENCES OF FLORAL VARIATION FOR MALE AND FEMALE REPRODUCTION IN EXPERIMENTAL POPULATIONS OF WILD RADISH, RAPHANUS SATIVUS L

Abstract

We documented effects of floral variation on seed paternity and maternal fecundity in a series of small experimental populations of wild radish, R. sativus. Each population was composed of two competing pollen donor groups with contrasting floral morphologies and several designated maternal plants. Progeny testing with electrophoretic markers allowed us to measure paternal success. Realized fecundity by each maternal plant and the fraction of those seeds attributable to each pollen donor group were used as outcome variables in path analysis to explore relationships between floral characters (petal size, pollen grain number per flower, and modal pollen grain size), pollinator visitation patterns, and reproductive success. A wide range of pollinator taxa visited the experimental populations, and patterns of discrimination appeared to vary among them. The impact of visitation on male and female reproduction also varied among taxa; visits of small native bees significantly increased paternal success, while those of honey bees reduced male fitness. Only visits by large native bees had discernible effects on recipient fecundity, and, overall, fecundity was not limited by visitation. Maternal plants bearing large-petalled flowers produced fewer flowers during the experiment, reducing their total seed production. In these small populations, postpollination processes (at least in part, compatibility) significantly influenced male and female reproductive success. Variation in pollinator pools occurring on both spatial and temporal scales may act to preserve genetic variation for floral traits in this species.

Reproductive biology of Davilla kunthii A. St-Hil. (Dilleniaceae) in Central Amazonia

“…In our study, pollinators have no morphological characters substantially diff erent to mediate any modifi cation in the fl oral traits. Th erefore the plant has no possibility of establishing a hierarchy of pollinators according to the diff erential importance of them (Schemske & Horvitz 1984;Stanton et al 1991;Galen 1999;Zamora 2000). In such a process fl owers would be adapted to be pollinated by the "most effective group of pollinators" rather than the "most eff ective pollinator" species (Stebbins 1970).…”

Temporal and spatial variation in heritability and genetic correlations among floral traits in Raphanus sativus, wild radish

“…Total pollen export increases with pollen production; more pollen is removed per visit and, in some cases, a higher proportion of pollen is exported from flowers with large pollen production (Young & Stanton, 1990). In small experimental populations, increased pollen production has a positive effect on seed paternity (Stanton et at., 1991). Pollen grain size might be expected to influence pollen performance (Kumar & Sarkar, 1980;Cruzan, 1990) and/or flower attractiveness.…”

“…Pollen production per flower is known to affect both pollinator visitation and components of male reproduction. Pollen production is a strong predictor of visitation by small native bees (other than Agapostemma; Stanton et at., 1991) and although honey-bees appear insensitive to small differences in pollen production, they avoid flowers from which all pollen has been removed (Young & Stanton, 1990). Total pollen export increases with pollen production; more pollen is removed per visit and, in some cases, a higher proportion of pollen is exported from flowers with large pollen production (Young & Stanton, 1990).…”

“…Pollen grain size might be expected to influence pollen performance (Kumar & Sarkar, 1980;Cruzan, 1990) and/or flower attractiveness. Most pollinators show no direct response to pollen size but honey-bees significantly overvisited flowers with large pollen grains (Stanton et at., 1991). Preliminary analyses show no evidence of a direct effect of pollen size on postpollination fertilization success in R. sativus (Stanton et al, 1991).…”

“…Because the evolutionary ecology of this wild species has been studied extensively in California (Ellstrand, 1984;Marshall & Ellstrand, 1986;Stanton, 1987;Stanton & Preston, 1986, 1988Young & Stanton, 1990;Stanton et at., 1991), its reproductive ecology is unusually well understood. A high degree of phenotypic variation has been documented for petal colour (Panetsos & Baker, 1964;Stanton, 1987), ovule number (Stanton & Preston, 1988), and petal size, pollen production per flower, and pollen size (Stanton & Preston, 1986, 1988Young & Stanton, 1990).…”