THE IMPACT OF A FLOWER‐COLOR POLYMORPHISM ON MATING PATTERNS IN EXPERIMENTAL POPULATIONS OF WILD RADISH ( RAPHANUS RAPHANISTRUM L.)

Abstract

We conducted field experiments to determine how a naturally occurring petal-color polymorphism influences mating patterns in wild radish (Raphanus raphanistrum). The polymorphism is controlled at a single genetic locus, with white petal color being completely dominant to yellow. In experimental populations with equal numbers of yellow- and white-flowered homozygous individuals, insect visitors strongly discriminated against white flowers. Pieris rapae, the most frequent pollinator, was almost 50% more likely to visit yellow than white flowers. Maternal fecundity did not differ between the morphs and was not significantly influenced by a plant's compatibility with potential donors, suggesting that seed production was not limited by receipt of compatible pollen. In contrast, the yellow-flowered morph sired approximately 75% of all seeds produced during the study. This paternity proportion was consistently greater than that expected on the basis of postpollination compatibility measures and was indistinguishable from that expected on the basis of pollinator-visitation frequency. We conclude that the male-fitness advantage of the yellow morph resulted from enhanced pollen export due to the greater attractiveness of its flowers to insect pollinators. With color morphs evenly distributed in experimental arrays, insects did not move assortatively on the basis of petal color, and we found no evidence for assortative pollen flow due to the floral polymorphism. Once postpollination compatibility relationships within populations were taken into account, paternal success of yellow donors did not differ between yellow- and white-flowered maternal plants.

Evidence of pollen transfer efficiency as the natural selection factor favoring a large corolla of Campanula punctata pollinated by Bombus diversus

“…This relationship, however, is in contrast to the results of a number of studies (e.g., Bell 1985;Galen and Newport 1987;Galen 1989;Stanton et al 1989;Johnson et al 1995). If the theoretical work by Charnov (1976) on optimal diet is applied to nectar-foraging pollinators, then such non-preferential foraging strategies will be selected under conditions where there are small values of (1) visitation duration per¯ower, (2) density of large, higher-reward¯owers, and (3) the ratio of the reward amount in large¯owers to that in small¯owers.…”

“…When considering that male RS is achieved solely by pollen grains removed from donor¯owers, it becomes apparent that a larger corolla width serves a reproductive function of enhancing the ratio of male RS/pollen removal, termed hereafter as pollen transfer eciency. This ®nding is signi®cant in that it provides the ®rst evidence that ā oral trait aects male RS by altering pollen transfer eciency, although¯oral traits are known to aect male RS through visitation frequency (Stanton et al 1989) and pollen removal per visitation (Campbell et al 1996). In other words, the natural selection factor leading to a larger corolla width is pollen transfer eciency.…”

“…In fact, numerous studies have found that larger¯owers or those of a particular color receive more frequent visitations by pollinators than¯owers that are smaller or of other colors such that they achieve either higher male reproductive success (RS) (seed sired: Stanton et al 1986Stanton et al , 1989 or female RS (seed production: Galen and Newport 1987;Galen 1989;Johnson et al 1995). Moreover, the lengths of spurs or oral tubes in various groups of plants show good correlation with the lengths of the mouth parts of their pollinators (Grant and Grant 1965;Miller 1981;Inoue 1983;Suzuki 1992), with long spurs being particularly advantageous in improving the eciency of pollen transfer between¯owers and pollinators (Inoue 1986;Nilsson 1988).…”

Anti-bacterial function in the sexually dimorphic pollinator rewards of Clusia grandiflora (Clusiaceae)

“…These include such diverse features as petal color, corolla shape, pollen presentation, and pollinator reward (e.g., Stanton et al 1989;Campbell et al 1991; Thomson and Thomson 1992;Mitchell 1993). In the case of the resin rewards presented by Clusia species, apid-bee pollinators may have provided a selective force that has shaped resin chemistries associated with particular resin functions, both mechanical and antimicrobial.…”

The potential for selection on pollen colour dimorphisms in Nigella degenii: morph-specific differences in pollinator visitation, fertilisation success and siring ability

“…Numerous authors have documented associations between flower colour and pollinator visitation, fecundity or outcrossing rate (e.g. Mogford, 1974;Price, 1981, 1983;Stanton, 1987;Stanton et al, 1989;Rausher and Fry, 1993;Jones, 1996;Jones and Reithel, 2001; for exceptions, see e.g. Stone, 2000).…”