Abstract Detail

Evolutionary Developmental Biology (Evo-Devo)

Bukhari, Ghadeer [1], Zhang, Jingbo [1], Stevens, Peter [2], Zhang, Wenheng [1].

Floral symmetry and the evolution of floral characters in angiosperms.

We have to understand the origin and evolution of the morphology of the flower if we are to understand the evolutionary success of the angiosperms. The developmental patterns in flowers of the two largest angiosperm clades, i.e., monocots usually having trimerous flowers and eudicots usually having pentamerous flowers, were thought to be distinct. For example, the monocots typically have a single adaxial or lateral bracteole, while the eudicots commonly have two lateral ones. The presence and position of the bracteole(s) were considered to play a critical role in floral organ orientation in monocots but not so much in pentamerous eudicots. Here, we investigate the evolution of floral characteristics in angiosperms, focusing on exploring whether the presence of bract or bracteoles influences floral symmetry using a phylogenetic approach. We extracted the character state information from floral diagrams representing phylogenetically diverse angiosperms with diverse flower morphologies from 1031 species representing 60 orders (95%), 223 families (52%). We analyzed these floral traits using six phylogenies based on published mega trees representing three different hypotheses of angiosperm evolution. The ancestral state reconstruction with a maximum-likelihood approach was used to analyze the evolutionary transition of 31 floral characteristics, such as floral merism, phyllotaxy, and the number of organs in each floral whorl. Our preliminary analyses suggest that a single abaxial bract is present in the most recent common ancestor (MRCA) of angiosperms (98% - 99%) and lost many times independently across angiosperms. Paired lateral bracteoles evolved 20 times independently during angiosperm evolution with a major shift that occurred in the MRCA of core eudicots (75% - 87%). Importantly, the correlation tests based on the two largest trees with 969 and 816 species indicated the presence of floral zygomorphy is strongly correlated with the presence of a single abaxial bract (p = 0.000 and p = 0.000), and two lateral bracteoles (p = 0.005 and p = 0.003). However, no significant correlation between floral zygomorphy and the presence of bracteole(s). These results suggest that the bract and its location is likely key in promoting the origin and maintenance of floral zygomorphy. We also demonstrate that for comparative studies, including both pentamerous and trimerous angiosperms, is critical in revealing general patterns of floral development and evolution.

1 - Virginia Commonwealth University, Department Of Biology, 1000 W Cary Street, Richmond, VA, 23284, United States
2 - University of Missouri-St. Louis, Department of Biology, One University Boulevard, Saint Louis, MO, 63121, United States

Keywords:
Bract
Bracteole
Floral Zygomorphy
flower symmetry
phylogeny
ancestral state reconstruction
floral morphology
angiosperms.

Presentation Type: Oral Paper
Session: EVDV1, Evolutionary Developmental Biology (Evo-Devo)
Location: Virtual/Virtual
Date: Thursday, July 30th, 2020
Time: 1:00 PM
Number: EVDV1012
Abstract ID:763
Candidate for Awards:Katherine Esau Award