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The symmetry spectrum in a hybridising, tropical group of rhododendrons


Soza, Valerie L. et al. (2022), The symmetry spectrum in a hybridising, tropical group of rhododendrons, Dryad, Dataset,


Many diverse plant clades possess bilaterally symmetrical flowers and specialized pollination syndromes suggesting these traits may promote diversification. We examine the evolution of diverse floral morphologies and the association with diversification history in a species-rich tropical radiation of Rhododendron. We used restriction-site associated DNA sequencing on 114 taxa from Rhododendron sect. Schistanthe to reconstruct phylogenetic relationships, infer colonization of Southeast Asia and examine hybridization. We then captured and quantified floral variation using geometric morphometric analyses which we interpret in a phylogenetic context. We uncovered phylogenetic complexity caused by introgression within and between clades. Morphometric analyses revealed flower symmetry to be a morphological continuum without a clear transition from radial to bilateral symmetry. The largest radiation of tropical Rhododendron species is associated with an expansion into novel floral morphological space as species diversified in New Guinea about 6 million years ago. Our results showed that the recent radiation of tropical Rhododendron is a consequence of hybridization, genetic isolation caused by mountain building, and the evolution of floral novelty. Floral variation evolved via changes to multiple components of the corolla that are only recognized in geometric morphometrics with both front and side views of flowers.


Consensus sequences representing loci within taxa were assembled and aligned in ipyrad v.0.7.17. Four different datasets were generated that allowed different amounts of sample coverage across loci: requiring a minimum of 4, 37, 74 and 111 samples per locus. We refer to these datasets subsequently as minsamples4, minsamples37, minsamples74 and minsamples111 or min4, min37, min74 and min111, respectively, in filenames for alignments and phylogenetic trees deposited in Dryad. Resulting sequence alignments were analyzed by Maximum Likelihood in RAxML v.8.2.11 and the multispecies coalescent model in SVDQuartets for phylogenetic tree reconstructions. The RAxML min4 analysis was used to generate a chronogram in treePL. Introgression analyses were also performed using resulting alignments and trees with the D-statistic in Dsuite v.0.3r21. Use “Vireya_RADsamples_treenames_sed” file below for defining taxon codes in all alignment and tree files for full species names and accession details for Rhododendron sect. Schistanthe and outgroup samples used in analyses. See Soza et al 2022 for more detailed methods.

For morphometric analyses, we used images of the front and side views of flowers from sampled taxa above to quantify flower symmetry using elliptical Fourier analysis (eFa) in the R library Momocs. See Soza et al 2022 for more detailed methods:

Soza, Valerie L., Ricardo Kriebel, Elizabeth Ramage, Benjamin D. Hall, and Alex D. Twyford. “The Symmetry Spectrum in a Hybridising, Tropical Group of Rhododendrons.” New Phytologist 243 (2022): 1491–1506.


Natural Environment Research Council, Award: NE/L011336/1