Sexual Dimorphism of Staminate- and Pistillate-Phase Flowers of Saponaria officinalis (Bouncing Bet) Affects Pollinator Behavior and Seed Set

The sequential separation of male and female function in flowers of dichogamous species allows for the evolution of differing morphologies that maximize fitness through seed siring and seed set. We examined staminate- and pistillate-phase flowers of protandrous Saponaria officinalis for dimorphism in floral traits and their effects on pollinator attraction and seed set. Pistillate-phase flowers have larger petals, greater mass, and are pinker in color, but due to a shape change, pistillate-phase flowers have smaller corolla diameters than staminate-phase flowers. There was no difference in nectar volume or sugar content one day after anthesis, and minimal evidence for UV nectar guide patterns in staminate- and pistillate-phase flowers. When presented with choice arrays, pollinators discriminated against pistillate-phase flowers based on their pink color. Finally, in an experimental garden, in 2012 there was a negative correlation between seed set of an open-pollinated, emasculated flower and pinkness (as measured by reflectance spectrometry) of a pistillate-phase flower on the same plant in plots covered with shade cloth. In 2013, clones of genotypes chosen from the 2012 plants that produced pinker flowers had lower seed set than those from genotypes with paler flowers. Lower seed set of pink genotypes was found in open-pollinated and hand-pollinated flowers, indicating the lower seed set might be due to other differences between pink and pale genotypes in addition to pollinator discrimination against pink flowers. In conclusion, staminate- and pistillate-phase flowers of S. officinalis are dimorphic in shape and color. Pollinators discriminate among flowers based on these differences, and individuals whose pistillate-phase flowers are most different in color from their staminate-phase flowers make fewer seeds. We suggest morphological studies of the two sex phases in dichogamous, hermaphroditic species can contribute to understanding the evolution of sexual dimorphism in plants without the confounding effects of genetic differences between separate male and female individuals

Bacterial Communities of Diverse Drosophila Species: Ecological Context of a Host–Microbe Model System

Drosophila melanogaster is emerging as an important model of non-pathogenic host–microbe interactions. The genetic and experimental tractability of Drosophila has led to significant gains in our understanding of animal–microbial symbiosis. However, the full implications of these results cannot be appreciated without the knowledge of the microbial communities associated with natural Drosophila populations. In particular, it is not clear whether laboratory cultures can serve as an accurate model of host–microbe interactions that occur in the wild, or those that have occurred over evolutionary time. To fill this gap, we characterized natural bacterial communities associated with 14 species of Drosophila and related genera collected from distant geographic locations. To represent the ecological diversity of Drosophilids, examined species included fruit-, flower-, mushroom-, and cactus-feeders. In parallel, wild host populations were compared to laboratory strains, and controlled experiments were performed to assess the importance of host species and diet in shaping bacterial microbiome composition. We find that Drosophilid flies have taxonomically restricted bacterial communities, with 85% of the natural bacterial microbiome composed of only four bacterial families. The dominant bacterial taxa are widespread and found in many different host species despite the taxonomic, ecological, and geographic diversity of their hosts. Both natural surveys and laboratory experiments indicate that host diet plays a major role in shaping the Drosophila bacterial microbiome. Despite this, the internal bacterial microbiome represents only a highly reduced subset of the external bacterial communities, suggesting that the host exercises some level of control over the bacteria that inhabit its digestive tract. Finally, we show that laboratory strains provide only a limited model of natural host–microbe interactions. Bacterial taxa used in experimental studies are rare or absent in wild Drosophila populations, while the most abundant associates of natural Drosophila populations are rare in the lab

Sexual dimorphism of staminate- and pistillate-phase flowers of Saponaria officinalis (bouncing bet) affects pollinator behavior and seed set.

The sequential separation of male and female function in flowers of dichogamous species allows for the evolution of differing morphologies that maximize fitness through seed siring and seed set. We examined staminate- and pistillate-phase flowers of protandrous Saponaria officinalis for dimorphism in floral traits and their effects on pollinator attraction and seed set. Pistillate-phase flowers have larger petals, greater mass, and are pinker in color, but due to a shape change, pistillate-phase flowers have smaller corolla diameters than staminate-phase flowers. There was no difference in nectar volume or sugar content one day after anthesis, and minimal evidence for UV nectar guide patterns in staminate- and pistillate-phase flowers. When presented with choice arrays, pollinators discriminated against pistillate-phase flowers based on their pink color. Finally, in an experimental garden, in 2012 there was a negative correlation between seed set of an open-pollinated, emasculated flower and pinkness (as measured by reflectance spectrometry) of a pistillate-phase flower on the same plant in plots covered with shade cloth. In 2013, clones of genotypes chosen from the 2012 plants that produced pinker flowers had lower seed set than those from genotypes with paler flowers. Lower seed set of pink genotypes was found in open-pollinated and hand-pollinated flowers, indicating the lower seed set might be due to other differences between pink and pale genotypes in addition to pollinator discrimination against pink flowers. In conclusion, staminate- and pistillate-phase flowers of S. officinalis are dimorphic in shape and color. Pollinators discriminate among flowers based on these differences, and individuals whose pistillate-phase flowers are most different in color from their staminate-phase flowers make fewer seeds. We suggest morphological studies of the two sex phases in dichogamous, hermaphroditic species can contribute to understanding the evolution of sexual dimorphism in plants without the confounding effects of genetic differences between separate male and female individuals

Pollen limitation.

<p>Seeds produced by emasculated open-pollinated and hand-pollinated flowers and intact hand-pollinated flowers of <i>S. officinalis</i> growing in shaded and sun exposed plots in 2012. Different letters above the bars indicate statistically significant differences (α = 0.05).</p

Pollen limitation.

<p>Seeds produced by emasculated open-pollinated and hand-pollinated flowers and intact hand-pollinated flowers of <i>S. officinalis</i> growing in shaded and sun exposed plots in 2012. Different letters above the bars indicate statistically significant differences (α = 0.05).</p

Seed production in pale vs. pink genotypes.

<p>The number of seeds produced in open-pollinated (A) and hand pollinated (B) flowers by genotypes producing whiter flowers (“Pale”) and genotypes producing pinker flowers (“Pink”) under shade and sun treatments.</p

Staminate-phase (left) and pistillate-phase (right) flowers of <i>Saponaria officinalis</i>.

<p>Staminate-phase (left) and pistillate-phase (right) flowers of <i>Saponaria officinalis</i>.</p

Nested ANOVA results examining the effects of treatment (shade vs. sun) and genotype (nested within pale vs pink sets) on anthocyanin concentration and seed set in open-pollinated and hand-pollinated flowers of <i>S. officinalis</i>.

<p>Values in the table are the Wald Chi-square statistic (df) and the probability value for each effect in the test for model effects.</p

Artificial decoupling of shape and color in <i>S. officinalis</i>.

<p>Inflorescence arrays were constructed of either pale staminate flowers (A), pale pistillate flowers from plants that had been shaded (B), or pink pistillate flowers from plants growing in the sun (C).</p

Likelihood of initial visits.

<p>The percentage of insects that initially visited artificial inflorescences of staminate-, pink pistillate-, or pale pistillate-phase flowers in pollinator observation trials in 2012 (A) and 2013 (B). Each trial type was tested against a hypothesis of each flower type receiving 50% of the first visits of an insect visitor. An asterisk (*) indicates a ratio significantly different from 50∶50 (α = 0.05).</p