Exploring floral evolution in Pelargonium (Geraniaceae) : linking shapes and macro-evolution

For flowering plants, there are multiple drivers of shape change that effect the process of speciation. In the background, species are constrained by their phylogenetic history, i.e. evolutionary changes that were advantageous to their ancestors, might turn out to no longer be beneficial. At the same time, speciation brought about by pollinator pressure is highly dynamic and can happen quickly. In my research, I aimed to bring together multiple layers of influence on floral shape in Pelargonium (Geraniaceae) in order to paint a comprehensive picture of the evolution of floral diversity in this clade. By building upon the extensive knowledge on speciation processes in the South African Greater Cape Floristic Region, we find that speciation in this clade may not be as clear-cut as expected and place Pelargonium in a broader, evolutionary perspective.</p

Pelargonium geometric morphometric data

Photographs and TPS file including landmark placement for Pelargonium species included in the SPUR and PETAL dataset. Outcome of the virtual3D reconstruction analysis

Capturing variation in floral shape; a virtual3D based morphospace for Pelargonium

Background: Variation in floral shapes has long fascinated biologists and its modelling enables testing of evolutionary hypotheses. Recent comparative studies that explore floral shape have largely ignored 3D floral shape. We propose quantifying floral shape by using geometric morphometrics on a virtual3D model reconstructed from 2D photographical data and demonstrate its performance in capturing shape variation.Methods: This approach offers unique benefits to complement established imaging techniques (i) by enabling adequate coverage of the potential morphospace of large and diverse flowering-plant clades; (ii) by circumventing asynchronicity in anthesis of different floral parts; and (iii) by incorporating variation in copy number of floral organs within structures. We demonstrate our approach by analysing 90 florally-diverse species of the Southern African genus Pelargonium (Geraniaceae). We quantify Pelargonium floral shapes using 117 landmarks and show similarities in reconstructed morphospaces for nectar tube, corolla (2D datasets), and a combined virtual3D dataset.Results: Our results indicate that Pelargonium species differ in floral shape, which can also vary extensively within a species. PCA results of the reconstructed virtual3D floral models are highly congruent with the separate 2D morphospaces, indicating it is an accurate, virtual, representation of floral shape. Through our approach, we find that adding the third dimension to the data is crucial to accurately interpret the manner of, as well as levels of, shape variation in flowers

Plastome based phylogenetics and younger crown node age in Pelargonium

The predominantly South-African plant genus Pelargonium L'Hér. (Geraniaceae) displays remarkable morphological diversity, several basic chromosome numbers as well as high levels of organelle genomic rearrangements, and represents the 7th largest Cape Floristic Region clade. In this study, we reconstructed a phylogenetic tree based on 74 plastome exons and nuclear rDNA ITS regions for 120 species, which represents 43% taxon coverage for Pelargonium. We also performed a dating analysis to examine the timing of the major radiations in the genus. Phylogenetic analyses of nucleotide, amino acid, and ITS alignments confirmed the previously-documented subgeneric split into five main clades ((C1,C2),(B(A1,A2))) although clade only A1 received low bootstrap support. Using calibration evidence from a range of sources the Pelargonium crown age was estimated to be 9.7 My old, much younger than previous estimates for the genus but similar to recent studies of other Cape Floristic lineages that are part of both Fynbos and Succulent Karoo biomes.</p