SMALL AND UGLY? PHYLOGENETIC ANALYSES OF THE “SELFING SYNDROME” REVEAL COMPLEX EVOLUTIONARY FATES OF MONOMORPHIC PRIMROSE FLOWERS

Authors

  • Jurriaan M. de Vos,

    1. Institute of Systematic Botany, University of Zürich, 8008 Zürich, Switzerland
    2. Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island
    Search for more papers by this author
  • Rafael O. Wüest,

    1. Institute of Systematic Botany, University of Zürich, 8008 Zürich, Switzerland
    2. Landscape Dynamics, Swiss Federal Research Institute WSL, 8903 Birmensdorf, Switzerland
    Current affiliation:
    1. Laboratoire d'Ecologie Alpine, UMR CNRS 5553, Université J. Fourier, 38041 Grenoble Cedex 9, France
    Search for more papers by this author
  • Elena Conti

    1. Institute of Systematic Botany, University of Zürich, 8008 Zürich, Switzerland
    Search for more papers by this author

Abstract

One of the most common trends in plant evolution, loss of self-incompatibility and ensuing increases in selfing, is generally assumed to be associated with a suite of phenotypic changes, notably a reduction of floral size, termed the selfing syndrome. We investigate whether floral morphological traits indeed decrease in a deterministic fashion after losses of self-incompatibility, as traditionally expected, using a phylogeny of 124 primrose species containing nine independent transitions from heterostyly (heteromorphic incompatibility) to homostyly (monomorphic self-compatibility), a classic system for evolution of selfing. We find similar overall variability of homostylous and heterostylous species, except for diminished herkogamy in homostyles. Bayesian mixed models demonstrate differences between homostylous and heterostylous species in all traits, but net effects across species are small (except herkogamy) and directionality differs among traits. Strongly drift-like evolutionary trajectories of corolla tube length and corolla diameter inferred by Ornstein–Uhlenbeck models contrast with expected deterministic trajectories toward small floral size. Lineage-specific population genetic effects associated with evolution of selfing may explain that reductions of floral size represent one of several possible outcomes of floral evolution after loss of heterostyly in primroses. Contrary to the traditional paradigm, selfing syndromes may, but do not necessarily evolve in response to increased selfing.

Ancillary