Mechanisms for Crests--Guo, American Journal of Botany

1. 1. Jinyan Guo ²

1. 1. Department of Biology, Brigham Young University, Provo, Utah 84602 USA

2. Received for publication 25 November 2014.

3. Accepted for publication 11 May 2015.

   Abstract

   • Premise of the study: Crested sepals, which have evolved at least five times in Iris, are adaxially elaborated with a sinuous and/or uneven median structure (crest) along the proximal–distal axis and sometimes with various lateral structures (ridges, crests, and linear protuberances) flanking the median crest. These structural elaborations are complex yet diverse in form, providing a good opportunity to investigate developmental mechanisms for the diversification of reproductive lateral organs.

   • Methods: Morphologies of the median and lateral structures at different developmental stages from selected crested sepals representing the major types of structural elaborations were recorded using scanning electron microscopy and light microscopy. Developmental (morphogenetic) events that contribute to changes in shape (e.g., sinuousness, unevenness) between consecutive stages were recorded. Developmental sequences—trajectories that consist of a series of developmental events—were compared in a phylogenetic context.

   • Key results: Three developmental events (development of outgrowths, greater expansion of the upper zone, and greater expansion of the lower zone), are shared across lineages, occur in the same developmental sequences, and are responsible for the changes in shape during the development of diverse structural elaborations. In addition, two novel developmental events and the development of trichomes on elaborate structures were observed within the core-crested clade.

   • Conclusions: Developmental sequences are conserved across independently evolved crested lineages. Heterochronic and heterotopic shifts of developmental events play the major role in the diversification of elaborations of crested sepals in Iris. The evolution of novel developmental events and the development of trichomes also contribute to the diversity.

   Key words:

developmental events

developmental sequences

evolutionary development

heterochrony

heterotopy

Iridaceae

Iris

lateral organ

perianth elaboration

trichomes

1. The study is part of the author’s doctoral dissertation research at Rancho Santa Ana Botanic Garden and Claremont Graduate University. The author thanks her academic advisor, Carol A. Wilson, for helping to obtain funding and extramural research facilities for this research; her dissertation committee, Carol A. Wilson, J. Travis Columbus, and J. Mark Porter, for comments on her dissertation chapter related to this manuscript; the Department of Physics and Astronomy of Pomona College for providing SEM facilities and the Department of Biological Sciences of California State Polytechnic University, Pomona, for providing equipment for light microscopy; and Jinzheng Zhang and Guofeng Sun (Beijing Botanical Garden of the Chinese Academy of Sciences), Cuifen Wu and Qianyu Zuo (Caojian Forest Institute of Yunlong County), Weibang Sun (Kunming Institute of Botany), Yuee Xiao (ShangHai Botanical Garden), Mingshui Zhao (TianMu Mountain Institute), personnel from the Shaw Nature Preserve, and Erin Riggs and Lisa Karst for providing plant materials and/or assisting with field trips. The author thanks Tom Kloster for providing photos of Iris tenuis, Clyde Calvin for light microscopy training, Sarah De Groot and Beth E. Hazen for checking the English of the manuscript, and the Associate Editor and two anonymous reviewers for comments on the manuscript. Funding was provided by the Graduate Student Research Awards Program at Rancho Santa Ana Botanic Garden, the American Iris Society Foundation, and the National Science Foundation (DEB-1011731).

2. ↵2 Author for correspondence (e-mail: j.yanguo@gmail.com)

3. © 2015 Botanical Society of America, Inc.

4. Published online before print 29 May 2015, doi: 10.3732/ajb.1400519 Am. J. Bot. June 2015