Exploring phenotypic floral integration in Iris pumila L.: A common-garden experiment

Abstract

The angiosperm flower is a complex integrated phenotype, but within this structure there are partly independent units or modules. The interconnections among floral organ traits are hypothesized to be mostly generated by pollinatormediated selection. In this study, we explore whether floral dry mass per area (DMA) in an insect-pollinated herb, Iris pumila, exhibits a modular correlation pattern as has been reported for some size-related traits. We found that the overall pattern of floral organ integration with regard to DMA was uneven in the offspring of Iris pumila derived from a sunexposed and a shaded natural population. Since principal component analysis (PCA) showed that most of the eigenvalue variance was explained by the first two principal components (PCs), these PCs were considered as two floral modules. The greatest factor loadings on the first PC axis was that of the perianth and style arm DMA (PSDMA) and perianth tube DMA (PTDMA),while on the second PC axis, the greatest factor loading was that of stamen DMA (STDMA). The results indicate that the function of the first module would be to attract a pollinating vector, while the second one would reflect male functions. Selection analyses revealed that the targets of phenotypic selection were both intra-floral integration and individual floral traits. Both PSDMA and PC1DMA were under strong linear selection, while PTDMA experienced direct stabilization selection. The level of integration in floral organ DMA expressed in the term of relative eigenvalue variance appeared to be rather low, as was documented for other angiosperm taxa.