Multiple innovations underpinned branching form diversification in mosses.

Yoan Coudert,Claude Edelin,C Jill Harrison,Neil E Bell

doi:10.1111/nph.14553

Abstract

Summary Broad‐scale evolutionary comparisons have shown that branching forms arose by convergence in vascular plants and bryophytes, but the trajectory of branching form diversification in bryophytes is unclear. Mosses are the most species‐rich bryophyte lineage and two sub‐groups are circumscribed by alternative reproductive organ placements. In one, reproductive organs form apically, terminating growth of the primary shoot (gametophore) axis. In the other, reproductive organs develop on very short lateral branches. A switch from apical to lateral reproductive organ development is proposed to have primed branching form diversification.Moss gametophores have modular development and each module develops from a single apical cell. Here we define the architectures of 175 mosses by the number of module classes, branching patterns and the pattern in which similar modules repeat. Using ancestral character state reconstruction we identify two stages of architectural diversification.During a first stage there were sequential changes in the module repetition pattern, reproductive organ position, branching pattern and the number of module classes. During a second stage, vegetative changes occurred independently of reproductive fate.The results pinpoint the nature of developmental change priming branching form diversification in mosses and provide a framework for mechanistic studies of architectural diversification.

Highlights

Morphological convergence is of major interest to evolutionary biologists, yet the mechanisms underlying convergence are poorly understood (Christin et al, 2010)
Whilst this initial stage of branching form diversification occurred during a 60 Myr period from 420 to 360 Myr ago (Ma) (Niklas, 2004; Edwards et al, 2014), laterally branching forms with leaves arranged around a main stem arose later in monilophytes and seed plants (Harrison, 2016) and lateral branching is thought to optimize photosynthetic efficiency during indeterminate growth (Niklas & Kerchner, 1984)
Thirteen architectural morphotypes capture most of the variation in branching form In order to analyse branching forms in mosses and test the hypothesis introduced above, we rehydrated, photographed and drew by hand herbarium specimens of 175 species from 15 orders and 60 families of Bryopsida, the largest class of mosses (Table S1)

Summary

Introduction

Morphological convergence is of major interest to evolutionary biologists, yet the mechanisms underlying convergence are poorly understood (Christin et al, 2010). More complex bifurcating architectures arose in vascular plants in response to selection for multiple traits including mechanical stability, photosynthetic efficiency, reproductive success and water-use efficiency (Niklas, 1997, 2004) Whilst this initial stage of branching form diversification occurred during a 60 Myr period from 420 to 360 Myr ago (Ma) (Niklas, 2004; Edwards et al, 2014), laterally branching forms with leaves arranged around a main stem arose later in monilophytes and seed plants (Harrison, 2016) and lateral branching is thought to optimize photosynthetic efficiency during indeterminate growth (Niklas & Kerchner, 1984).

Methods

Results

Discussion

Conclusion