Phylogenetics and diversification of morning glories (tribe Ipomoeeae, Convolvulaceae) based on whole plastome sequences.

PREMISE OF THE STUDY

Morning glories are an emerging model system, and resolving phylogenetic relationships is critical for understanding their evolution. Phylogenetic studies demonstrated that the largest morning glory genus, Ipomoea, is not monophyletic, and nine other genera are derived from within Ipomoea. Therefore, systematic research is focused on the monophyletic tribe Ipomoeeae (ca. 650-900 species). We used whole plastomes to infer relationships across Ipomoeeae.

METHODS

Whole plastomes were sequenced for 29 morning glory species, representing major lineages. Phylogenies were estimated using alignments of 82 plastid genes and whole plastomes. Divergence times were estimated using three fossil calibration points. Finally, evolution of root architecture, flower color, and ergot alkaloid presence was examined.

KEY RESULTS

Phylogenies estimated from both data sets had nearly identical topologies. Phylogenetic results are generally consistent with prior phylogenetic hypotheses. Higher-level relationships with weak support in previous studies were recovered here with strong support. Molecular dating analysis suggests a late Eocene divergence time for the Ipomoeeae. The two clades within the tribe, Argyreiinae and Astripomoeinae, diversified at similar times. Reconstructed most recent common ancestor of the Ipomoeeae had blue flowers, an association with ergot-producing fungi, and either tuberous or fibrous roots.

CONCLUSIONS

Phylogenetic results provide confidence in relationships among Ipomoeeae lineages. Divergence time estimation results provide a temporal context for diversification of morning glories. Ancestral character reconstructions support previous findings that morning glory morphology is evolutionarily labile. Taken together, our study provides strong resolution of the morning glory phylogeny, which is broadly applicable to the evolution and ecology of these fascinating species.