Pollinator-Mediated Selection on Flower Color, Flower Scent and Flower Morphology of Hemerocallis: Evidence from Genotyping Individual Pollen Grains On the Stigma

Abstract

To trace the fate of individual pollen grains through pollination processes, we determined genotypes of single pollen grains deposited on Hemerocallis stigmas in an experimental mixed-species array. Hemerocallis fulva, pollinated by butterflies, has diurnal, reddish and unscented flowers, and H. citrina, pollinated by hawkmoths, has nocturnal, yellowish and sweet scent flowers. We observed pollinator visits to an experimental array of 24 H. fulva and 12 F2 hybrids between the two species (H. fulva and H. citrina) and collected stigmas after every trip bout of swallowtail butterflies or hawkmoths. We then measured selection by swallowtail butterflies or hawkmoths through male and female components of pollination success as determined by single pollen genotyping. As expected, swallowtail butterflies imposed selection on reddish color and weak scent: the number of outcross pollen grains acquired is a quadratic function of flower color with the maximum at reddish color, and the combined pollination success was maximal at weak scent (almost unrecognizable for human). This explains why H. fulva, with reddish flowers and no recognizable scent, is mainly pollinated by swallowtail butterflies. However, we found no evidence of hawkmoths-mediated selection on flower color or scent. Our findings do not support a hypothesis that yellow flower color and strong scent intensity, the distinctive floral characteristics of H. citrina, having evolved in adaptations to hawkmoths. We suggest that the key trait that triggers the evolution of nocturnal flowers is flowering time rather than flower color and scent.

Direct genotyping of single pollen grains of a self-compatible mutant of Japanese pear (Pyrus pyrifolia) revealed inheritance of a duplicated chromosomal segment containing a second S-haplotype

“…Single-pollen genotyping and sequencing have so far been utilized only in molecular taxonomy and ecological genetics (Zhou et al 2007;Ito et al 2008;Hirota et al 2013). However, we think that singlepollen analysis has the potential for important applications in breeding science, and we expect further utilization of this method.…”

UV bullseye contrast of Hemerocallis flowers attracts hawkmoths but not swallowtail butterflies

“…Papilio helenus) and crepuscular hawkmoths (Theretra japonica, Theretra oldenlandiae, and Theretra silhetensis) are effective pollinators of H. fulva and H. citrina, respectively (Hirota et al, 2012(Hirota et al, , 2013. Because of the tetrachromatic vision of P. xuthus (Koshitaka et al, 2008), we employed a tetrachromatic model for swallowtail butterflies.…”

“…Scent intensity was measured immediately after flower opening by a handheld odour meter (OMX-SR; Shinyei, Japan) (Hirota et al, 2012(Hirota et al, , 2013. Two morphological traits significantly affecting pollination success (e.g., pollinator preference, Hirota et al, 2013) were measured before observations commenced: corolla orientation (the angle between a flower's main axis (from the floral base to the tip of pistil) and the horizontal) and stem height (from the ground to the top of an inflorescence). Two morphological traits significantly affecting pollination success (e.g., pollinator preference, Hirota et al, 2013) were measured before observations commenced: corolla orientation (the angle between a flower's main axis (from the floral base to the tip of pistil) and the horizontal) and stem height (from the ground to the top of an inflorescence).…”

“…Thus, flower color may be a more reliable foraging cue for butterflies than for hawkmoths. In the wild, swallowtail butterflies showed a significant preference for human reddish flowers over human yellowish ones while they also preferred weaker scent and taller stems (Hirota et al, 2012(Hirota et al, , 2013. In the wild, swallowtail butterflies showed a significant preference for human reddish flowers over human yellowish ones while they also preferred weaker scent and taller stems (Hirota et al, 2012(Hirota et al, , 2013.…”

“…Artificial F2 hybrids show highly variable floral traits, ranging from the floral traits of H. fulva to those of H. citrina (Hirota et al, 2012(Hirota et al, , 2013Nitta, Yasumoto, & Yahara, 2010 (Hirota et al, 2012). Artificial F2 hybrids show highly variable floral traits, ranging from the floral traits of H. fulva to those of H. citrina (Hirota et al, 2012(Hirota et al, , 2013Nitta, Yasumoto, & Yahara, 2010 (Hirota et al, 2012).…”