Evolution of the process underlying floral zygomorphy development in pentapetalous angiosperms

Abstract

PREMISE OF THE STUDY:Observations of fl oral ontogeny indicated that fl oral organ initiation in pentapetalous fl owers most commonly results in a medianabaxial (MAB) petal during early development, a median-adaxial (MAD) petal being less common. Such diff erent patterns of fl oral organ initiation might be linked with diff erent morphologies of fl oral zygomorphy that have evolved in Asteridae. Here, we provide the fi rst study of zygomorphy in pentapetalous angiosperms placed in a phylogenetic framework, the goal being to fi nd if the diff erent patterns of fl oral organ initiation are connected with particular patterns of zygomorphy. METHODS:We analyzed patterns of fl oral organ initiation and displays of zygomorphy, extracted from fl oral diagrams representing 405 taxa in 330 genera, covering 83% of orders (30 out of 36) and 37% of families (116 out of 313) in core eudicots in the context of a phylogeny using ancestral state reconstructions. KEY RESULTS:The MAB petal initiation is the ancestral state of the pattern of fl oral organ initiation in pentapetalous angiosperms. Taxa with MAD petal initiation represent ~30 independent origins from the ancestral MAB initiation. There are distinct developmental processes that give rise to zygomorphy in diff erent lineages of pentapetalous angiosperms, closely related lineages being likely to share similar developmental processes. CONCLUSIONS:We have demonstrated that development indeed constrains the processes that give rise to fl oral zygomorphy, while phylogenetic distance allows relaxation of these constraints, which provides novel insights on the role that development plays in the evolution of fl oral zygomorphy. Crepet, 1996 ; Friis et al., 2011 ;Sauquet et al., 2017 ). Th e subsequent repeated shift s of fl oral symmetry are believed to refl ect responses to selection by insect and later by vertebrate pollinators and result in specialized plant-pollinator interactions ( Giurfa et al., 1999 ;Endress, 2001 ). Some of these shift s in fl oral symmetry seem related to shift s in species diversifi cation rates ( Cubas, 2004 ;Sargent, 2004 ;Armbruster and Muchhala, 2009 ;Vamosi and Vamosi, 2010 ;O'Meara et al., 2016 ). Recent work in developmental genetics has begun to reveal the molecular mechanisms underlying the development of the diverse zygomorphic fl owers in angiosperms ( Citerne et al., 2010 ;Busch et al., 2014 ;Hileman, 2014b ;Madrigal et al., 2017 ). While these researches have advanced our knowledge on the evolution of fl oral symmetry, how the particularities of development in individual clades infl uence the course of morphological evolution of zygomorphy in those clades has rarely been investigated. Th e infl uence of development on the evolution of fl oral symmetry has, however, been noted in Asteridae ( Donoghue et al., 1998 ). In this clade, zygomorphic-fl owered species possess three major types of fl oral zygomorphy, 2:3, 4:1, and 0:5, the numbers referring to the number of petals located on the dorsal and ventral sides respectively of the fl ower...

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