Abstract Detail

Ecological Section

Berry, Eapsa [1], Geeta, R. [2].

Is there a positive correlation between floral monosymmetry and the presence of nectar guides in Rhododendron?

Symmetry and pigmentation enhance the attractiveness of flowers to pollinators. Variation in structure, position and orientation of floral organs contributes to whether a flower is polysymmetric (symmetric around multiple lines through the centre) or monosymmetric (symmetric around a specific line through the centre). In general, symmetry of pigmentation patterns or nectar guides is related to the symmetry of flowers.
Rhododendron (Ericaceae), a large temperate genus of ~1000 species, has large attractive, flowers in which the corolla varies from poly- to mono-symmetric. Variation in the position and orientation of the androecium and gynoecium also contributes to variation in symmetry. Nectar guides, i.e., spots or blotches, mostly occur on bilaterally symmetric flowers. Markings may occur on radially symmetric corollas, but there the style, stamens, or both, are monosymmetric. Thus, unlike many other taxa, symmetry features of all floral whorls may play a role in the occurrence of markings. Here, we conduct a phylogenetic test of the evolutionary hypotheses (Leppik 1974) that, in Rhododendron, floral monosymmetry is a derived feature and nectar guides co-occur with this feature.
Variation in corolla, androecium and gynoecium characteristics of Rhododendron were analyzed based on personal observations as well as published and online sources. The characters scored were corolla symmetry (monosymmetric; polysymmetric), flexion of androecium (flexed; slightly curved/straight), flexion of gynoecium (flexed; slightly curved/straight), arrangement of stamens (bundled; not bundled) and corolla markings (present; absent). Phylogenetic analyses used RNA Polymerase II subunit (RPB2-I) gene sequences (TreeBASE: M2277, 89 sequences and 12 new sequences of species from the Sikkim Himalaya). Phylogenetic trees were obtained by maximum likelihood analyses (RAxML). The evolution of the complex trait of floral symmetry was analyzed using ancestral states reconstructions. A phylogenetic test of correlation was done using Pagel’s (1994) method (Mesquite).
Phylogenetic patterns in corolla, androecium and gynoecium showed evolutionary transitions from monosymmetry to polysymmetry; nectar guides went from being present to absent. There was a strong, significant positive correlation between monosymmetry of corolla, flexion of stamens, flexion of pistils and presence of nectar guides (p<< 0.01); stamen arrangement and markings were only weakly correlated (p = 0.07). Apparently there were multiple evolutionary transitions from the ancestral, monosymmetric flower with nectar guides toward derived, polysymmetric flowers with no nectar guides. This trend is the reverse of what has been assumed for Rhododendron, and suggests a shift in pollination mechanism.

Broader Impacts:

1 - University of Delhi, Botany, Chhatra Marg, Delhi, 110007, India
2 - University of Delhi, Department of Botany, Chhatra Marg, Delhi, 110007, India

Keywords:
Rhododendron
floral symmetry
nectar guides
Evolution
Phylogenetic analysis.

Presentation Type: Poster:Posters for Sections
Session: P
Location: Grand Salon A - D/Riverside Hilton
Date: Monday, July 29th, 2013
Time: 5:45 PM
Number: PEC030
Abstract ID:904
Candidate for Awards:Ecological Section Best Graduate Student Paper