Phylogeny-based comparative methods question the adaptive nature of sporophytic specializations in mosses

PLoS One. 2012;7(10):e48268. doi: 10.1371/journal.pone.0048268. Epub 2012 Oct 30.

Abstract

Adaptive evolution has often been proposed to explain correlations between habitats and certain phenotypes. In mosses, a high frequency of species with specialized sporophytic traits in exposed or epiphytic habitats was, already 100 years ago, suggested as due to adaptation. We tested this hypothesis by contrasting phylogenetic and morphological data from two moss families, Neckeraceae and Lembophyllaceae, both of which show parallel shifts to a specialized morphology and to exposed epiphytic or epilithic habitats. Phylogeny-based tests for correlated evolution revealed that evolution of four sporophytic traits is correlated with a habitat shift. For three of them, evolutionary rates of dual character-state changes suggest that habitat shifts appear prior to changes in morphology. This suggests that they could have evolved as adaptations to new habitats. Regarding the fourth correlated trait the specialized morphology had already evolved before the habitat shift. In addition, several other specialized "epiphytic" traits show no correlation with a habitat shift. Besides adaptive diversification, other processes thus also affect the match between phenotype and environment. Several potential factors such as complex genetic and developmental pathways yielding the same phenotypes, differences in strength of selection, or constraints in phenotypic evolution may lead to an inability of phylogeny-based comparative methods to detect potential adaptations.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological / genetics*
  • Bryophyta / anatomy & histology
  • Bryophyta / genetics*
  • Bryophyta / physiology*
  • Diploidy*
  • Ecosystem
  • Evolution, Molecular
  • Phylogeny*

Grants and funding

This research was supported by a Marie Curie Intra-European Fellowship (MEIF-CT-2005–009452; years 2005–2008 to SH); a Marie Curie Reintegration Grant (PERG03-GA-2008–230953; years 2008–2011 to SH) within the 6th European Community Framework Program; a post doctoral researcher grant from the Academy of Finland (project no. 121373; years 2008–2011 to SH); researcher exchange grants by the Academy of Finland/German Academy Exchange Service (DAAD) to JE, DQ, VB, SO and DAAD/The Swedish Foundation for International Cooperation in Research and Higher education (STINT) to VB, LH, SH, SO, DQ; the Swedish Research Council (Vetenskapsrådet project no. 621 2003 3338; to LH); the Deutsche Forschungsgemeinschaft (DFG QU 153/3–1, 153/3–2 to DQ); and SYNTHESYS grants financed by the European Community Research Infrastructure Action under the FP6 ‘Structuring the European Research Area’ Programme (http://www.synthesys.info) to VB, JE, SO). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.