Heteranthery, the presence of two or more anther types in the same flower, is taxonomically widespread among bee-pollinated angiosperms, yet has puzzled botanists since Darwin. We test two competing hypotheses for its evolution: the longstanding “division of labour” hypothesis, which posits that some anthers are specialized as food rewards for bees whereas other are specialized for surreptitious pollination, and our new hypothesis that heteranthery is a way to gradually release pollen that maximizes pollen delivery. We examine the evolution of heteranthery and associated traits across the genus Clarkia (Onagraceae) and study plant-pollinator interactions in two heterantherous Clarkia species. Across species, heteranthery is associated with bee pollination, delayed dehiscence and colour crypsis of one anther whorl, and movement of that anther whorl upon dehiscence. Our mechanistic studies in heterantherous species show that bees notice, forage on, and export pollen from each anther whorl when it is dehiscing, and that heteranthery promotes pollen export. We find no support for division of labour, but multifarious evidence that heteranthery is a mechanism for gradual pollen presentation that likely evolved through indirect male-male competition for siring success.

File name

BombusTrials2018.R contains the scripts to analyze pollen export data from dosing v. no dosing C. unguiculata flowers exposed to Bombus impatiens in the greenhouse. 

ClarkiaPhyloHeteranthery.R contains the analysis scripts for comparative phylogenetic analyses of heteranthery in Clarkia, including ancestral reconstructions of characters, correlated evolution of heteranthery and pollination, correlated evolution of heteranthery and anther movement, differences in anther timing separation between heterantherous and non-heterantherous species, and comparisons of colors of flower parts

Color.R contains the scripts that take raw reflectance data from flower parts and interpret it in bee vision models.

cylindrica.R contains the analysis script for analyzing pollen fates from inner v outer anthers in Clarkia cylindrica.

FieldManipulationsCung.R contains the scripts for analyzing visitation data to Clarkia unguiculata flowers with phenotypic manipulations.

BombusColorPosition.csv contains a summary of the visitation data for captive bumblebees exposed to manipulated C. unguiculata flowers. R = filaments painted red, Y = filaments painted yellow, I = anthers drawn together in an erect position, O = anthers left reflexed

BombusColorPosition1stVisit.csv contains the visitation data for captive bumblebees exposed to manipulated C. unguiculata flowers. R = filaments painted red, Y = filaments painted yellow, I = anthers drawn together in an erect position, O = anthers left reflexed, N = nectaring behavior, P = pollen-collecting behavior

BombusTrials2018.csv is the data of pollen exported to stigmas and collected by bees from dosing v. no dosing C. unguiculata flowers exposed to Bombus impatiens in the greenhouse. It is the input file for BombusTrials2018.R.

CLABIL.csv is the reflectance data from various flower parts of Clarkia biloba. It is reported as percent reflectance by wavelength.

CLACYL.csv is the reflectance data from various flower parts of Clarkia cylindrica. It is reported as percent reflectance by wavelength.

CLADUD.csv is the reflectance data from various flower parts of Clarkia dudleyana. It is reported as percent reflectance by wavelength.

CLALIN.csv is the reflectance data from various flower parts of Clarkia lingulata. It is reported as percent reflectance by wavelength.

Clarkia_Phenotype_Heteranthery.csv contains phenotype data for phylogenetic comparative analyses and is called by ClarkiaPhyloHeteranthery.R.

ClarkiaITS.nex is the tree file (posterior distribution) from the Clarkia phylogenetic analysis published in supplement of Briscoe Runquist R, Grossenbacher D, Porter S, Kay K, Smith J. 2016. Pollinator-mediated assemblage processes in California wildflowers. Journal of Evolutionary Biology 29(5):1045-58. doi: 10.1111/jeb.12845

CLAUNG.csv is the reflectance data from various flower parts of Clarkia unguiculata. It is reported as percent reflectance by wavelength.

CLAXAN.csv is the reflectance data from various flower parts of Clarkia xantiana. It is reported as percent reflectance by wavelength.

CungManipulative.csv is the input file for FieldManipulationsCung.R and contains the visitation data for C. unguiculata flowers.

CungSeeds.csv contains the seed set data (viable seeds) and proportion of ovules fertilized (viable seeds out of the total ovules observed) for the Clarkia unguiculata flowers included in the field flower manipulations.

D65_Poppy_paper.txt is illuminance data from van der Kooi CJ, Elzenga JTM, Staal M, Stavenga DG. 2016. How to colour a flower: on the optical principles of flower coloration. Proceedings of the Royal Society B: Biological Sciences 283: 20160429.

Green Contrasts_All.csv is the output file from the pavo color analyses of flower parts and is used as input for comparisons in ClarkiaPhyloHeteranthery.R

leaf_average_8spp.csv is background reflectance data from van der Kooi CJ, Elzenga JTM, Staal M, Stavenga DG. 2016. How to colour a flower: on the optical principles of flower coloration. Proceedings of the Royal Society B: Biological Sciences 283: 20160429.

name_change.csv is a translation file for taxon names in Clarkia_Phenotype_Heteranthery.csv to match the tip names in the phylogeny

pollen_available.csv presents measurers (mm) of exposed pollen on dosing v. no dosing C. unguiculata flowers exposed to Bombus impatiens in the greenhouse. It is an input file for BombusTrials2018.R.

pollen_data.csv is the input file for cylindrica.R and contains counts of pollen from inner v outer anthers for bee scopae and plant stigmas.

sensitivity-normalised.txt is is bee photoreceptor data from Peitsch D, Fietz A, Hertel H, de Souza J, Ventura DF, Menzel R. 1992 The spectral input systems of hymenopteran insects and their receptor-based colour vision. J Comp Physiol A 170, 23–40.

time_lapse_data.csv contains the data on anther dehiscence timing for species grown in the greenhouse. It was used to plot Fig 3.