Molecular Ecology and Evolution
Johnson , Matthew G , Shaw, Jonathan , Granath, Gustaf , Rydin, Hakan , Stenøien, Hans , Rochefort, Line , Tahvanainen, Teemu .
Evolution of microhabitat preference in Sphagnum.
The phylogenetic comparative method predicts that the continuous traits, such as niche preferences, evolve under a Brownian motion process, where trait values and branch lengths are correlated. Often, the data used to test for Phylogenetic Niche Conservatism (PNC) is climatic, and may not be the most relevant data for many groups. The Sphagnum peatmosses are an ideal candidate to test for PNC at a microhabitat scale. A long history of peatland ecologists have found as many as 30 species co-occuring in a single peatland, and find these species differentiated into narrow microhabitat niches along two primary gradients: an abiotic, ionic gradient (pH, Conductivity, cations) and a biotic gradient (height above water table, shade preference, hummock vs. hollow). We measured eight traits in these gradients in 39 Sphagnum species at four sites in North America and Scandinavia. To test for phylogenetic signal, we built an 18-gene phylogeny and tested the trait data against eight models of trait evolution. These models included violations of the pure Brownian motion process, such as Pagel's lambda, multiple rates on the tree, and stabilizing selection (OU model). Our tests allowed for within-species measurement error as suggested by Ives et al (2007), and accounted for phylogenetic uncertainty by using AICc scores across 1000 trees taken from a Bayesian inference. We found that the best model fitting the ionic the traits was White Noise (no phylogenetic signal). This was surprising, given the consistent observation of ionic niche differentiation by peatland ecologists, but ionic habitat preference in Sphagnum may be driven by plasticity or interspecies competition, rather than by phylogeny. By contrast, height above water table and shade percentage had strong evidence of phylogenetic signal. These traits load strongly upon the second principal component, which we found to have evidence for two regimes of stabilizing selection-- one for "hummock" species and another for "hollow." Taken together, these results show that species currently occupy hummock/hollow niches that reflect their phylogenetic history, but differentiate independent of phylogeny along ionic gradients.
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1 - Duke University, Biology, 130 Science Drive, Box 90338, Durham, NC, 27705, USA
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3 - Uppsala University, Plant Ecology and Evolution, Norbyvägen 18 D, Uppsala, SE-752 36, Sweden
4 - Norwegian University of Science and Technology, Section of Natural History, Schøninghuset*B335, Erling Skakkes gate 47, NTNU, Trondheim, Norway
5 - Universite Laval, Plant Sciences, Paul-Comtois Building , 2425 rue de l'Agriculture, Quebec, G1V 0A6, Canada
6 - University of Eastern Finland, Science and Forestry, Yliopistokatu 7, PO Box 111, FIN-80101, Joensuu, Finland
phylogenetic niche conservatism
Presentation Type: Poster:Posters for Topics
Location: Battelle South/Convention Center
Date: Monday, July 9th, 2012
Time: 5:30 PM