Phylogenetic relationships and the repeated loss of traits associated with sicklebill pollination in Centropogon subgenus Centropogon (Campanulaceae)

Premise

Centropogon subgenus Centropogon comprises 55 species found primarily in midelevation Andean forests featuring some of the most curved flowers among angiosperms. Floral curvature is linked to coevolution with the sicklebill hummingbird, which pollinates most species. Despite charismatic flowers, there is limited knowledge about the phylogenetic relationships and floral evolution.

Methods

We conducted the first densely sampled phylogenomic analysis of the clade using methods that account for incomplete lineage sorting on a sequence capture dataset generated with a lineage-specific probe set. Using phylogenetic comparative methods, we test for correlated evolution of two traits central to sicklebill pollination.

Results

We improve understanding of species relationships by more than doubling past taxon sampling. We confirm the monophyly of the subgenus and two sections, and the non-monophyly of remaining sections. The subgenus is characterized by high gene tree discordance. Three widespread species display contrasting phylogenetic dynamics, with C. cornutus forming a clade and C. granulosus and C. solanifolius forming non-monophyletic, biogeographically clustered lineages. Correlated evolution of floral curvature and inflorescence structure has led to multiple putative losses of sicklebill pollination.

Conclusions

Centropogon subgenus Centropogon adds to a growing body of literature of Andean plant clades with high gene tree discordance. This phylogeny serves as a foundational framework for further macroevolutionary investigations into the environmental and biogeographic factors shaping the evolution of pollination-related traits.