1 Title: Parallelism in flower evolution and development 2 3 Authors: Carolyn A. Wessinger1 and Lena C. Hileman2 4 5 Affiliations: 6 1Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, 7
[email protected], https://orcid.org/0000-0003-3687-2559 8 2Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence KS 66045, 9
[email protected], https://orcid.org/0000-0001-6116-666X 10 11 12 13 Corresponding author: Lena C. Hileman, Department of Ecology and Evolutionary Biology, 14 University of Kansas, Lawrence KS 66045,
[email protected] 15 16 17 18 19 Key words: petal fusion, flower symmetry, nectar spur, heterostyly, flower development, 20 evolution 21 22 1 23 ABSTRACT 24 Flower evolution is characterized by widespread repetition, with adaptations to pollinator 25 environment evolving in parallel. Recent studies have expanded our understanding of the 26 developmental basis for adaptive floral novelties—petal fusion, bilateral symmetry, heterostyly, 27 and floral dimensions. Here we highlight patterns of trait evolution and review developmental 28 genetic mechanisms underlying floral novelties. We discuss the diversity of mechanisms for 29 parallel adaptation, the evidence for constraints on these mechanisms, and how constraints 30 help explain observed macroevolutionary patterns. We describe parallel evolution resulting from 31 similarities at multiple hierarchical levels—genetic, developmental, morphological, functional— 32 which indicate general principles in floral evolution, including the central role of hormone 33 signaling. An emerging pattern is mutational bias that may contribute to rapid patterns of parallel 34 evolution, especially if the derived trait can result from simple degenerative mutations. We argue 35 that such mutational bias may less likely govern the evolution of novelties patterned by complex 36 developmental pathways.