Evolution of floral traits and impact of reproductive mode on diversification in the phlox family (Polemoniaceae)

Abstract

Pollinator-mediated selection is a major driver of evolution in flowering plants, contributing to the vast diversity of floral features. Despite long-standing interest in floral variation and the evolution of pollination syndromes in Polemoniaceae, the evolution of floral traits and known pollinators has not been investigated in an explicit phylogenetic context. Here we explore macroevolutionary patterns of both pollinator specificity and three floral traits long considered important determinants of pollinator attraction across the most comprehensive species-level phylogenetic tree yet produced for the family. The presence of floral chlorophyll is reconstructed as the ancestral character state of the family, even though the presence of floral anthocyanins is the most prevalent floral pigment in extant taxa. Mean corolla length and width of the opening of the floral tube are correlated, and both appear to vary with pollinator type. The evolution of pollination systems appears labile, with multiple gains and losses of selfing and conflicting implications for patterns of diversification. Explicit testing of diversification models rejects the hypothesis that selfing is an evolutionary dead-end. This study begins to disentangle the individual components that comprise pollination syndromes and lays the foundation for future work on the genetic mechanisms that control each trait.

Keywords: Comparative methods; Diversification; Flower color; MuSSE; Phylogeny; Pollinator-mediated selection; Stochastic mapping.