Comparative analysis of corolla shape transitions in the sister genera Gesneria and Rhytidophyllum (Gesneriaceae)

Convergence, the independent acquisition of similar phenotypes, is an important aspect of diversity that can provide valuable insights about the nature of evolutionary change. In plants, pollination syndromes - combinations of floral traits adapted to their pollinators - make good examples of convergence occurring on flowers. We used a comprehensive approach that includes cell morphology and transcriptomics to analyze the floral shape convergence of two pollination syndromes found in the sister genera Gesneria and Rhytidophyllum (Gesneriaceae), an Antillean group that contains approximately 81 species with different morphologies and pollination strategies varying in their degree of ecological specialization. Flower shape has already been found to play an important role in the evolution of this group, which shows many transitions between pollination strategies. We tested convergence in the corolla cell shapes and in gene expression for the pollination syndromes using (1) cell measurement statistical analysis (Phylogenetic Mixed Model) of mature petals and (2) a comparative transcriptomic approach that combined differential gene expression (DESEq2) and co-expression analysis (WGCNA) in genes expressed in specific regions of the petals. All analyses took the phylogenetic relationships of the species into account. We found convergent cellular anisotropy occurring in the distal regions of the petals within species of the same syndrome (form). We also found greater similarity in gene expression patterns occurring among species of the same syndromes than between more closely related species and produced a list of 203 genes potentially associated with convergent flower forms. The floral morphological convergence observed in the pollination syndromes of the investigated species is paralleled both at the cellular and expression levels. The results shown here amplify the background information of the Gesneriaceae family for future studies of convergence and floral form in the group.