Local Adaptation in European Firs Assessed Through Extensive Sampling Across Altitudinal Gradients in Southern Europe

PLoS One. 2016 Jul 8;11(7):e0158216. doi: 10.1371/journal.pone.0158216. eCollection 2016.

Abstract

Background: Local adaptation is a key driver of phenotypic and genetic divergence at loci responsible for adaptive traits variations in forest tree populations. Its experimental assessment requires rigorous sampling strategies such as those involving population pairs replicated across broad spatial scales.

Methods: A hierarchical Bayesian model of selection (HBM) that explicitly considers both the replication of the environmental contrast and the hierarchical genetic structure among replicated study sites is introduced. Its power was assessed through simulations and compared to classical 'within-site' approaches (FDIST, BAYESCAN) and a simplified, within-site, version of the model introduced here (SBM).

Results: HBM demonstrates that hierarchical approaches are very powerful to detect replicated patterns of adaptive divergence with low false-discovery (FDR) and false-non-discovery (FNR) rates compared to the analysis of different sites separately through within-site approaches. The hypothesis of local adaptation to altitude was further addressed by analyzing replicated Abies alba population pairs (low and high elevations) across the species' southern distribution range, where the effects of climatic selection are expected to be the strongest. For comparison, a single population pair from the closely related species A. cephalonica was also analyzed. The hierarchical model did not detect any pattern of adaptive divergence to altitude replicated in the different study sites. Instead, idiosyncratic patterns of local adaptation among sites were detected by within-site approaches.

Conclusion: Hierarchical approaches may miss idiosyncratic patterns of adaptation among sites, and we strongly recommend the use of both hierarchical (multi-site) and classical (within-site) approaches when addressing the question of adaptation across broad spatial scales.

MeSH terms

  • Abies / genetics*
  • Adaptation, Physiological / genetics*
  • Altitude*
  • Bayes Theorem
  • Climate
  • Computer Simulation
  • DNA, Plant / genetics
  • Expressed Sequence Tags
  • Gene Frequency
  • Genetic Variation*
  • Genotype
  • Geography
  • Phenotype
  • Polymorphism, Single Nucleotide*
  • Trees / genetics

Substances

  • DNA, Plant

Grant support

Funding was provided by the ERAnet BiodivERsA project ‘LinkTree’ (ANR-08-Biodiversa-006-06), the ERAnet BiodivERsA project 'TipTree' (ANR-12-EBID-0003) and COST Action FP 1202. GGV was also supported by a grant by the Italian MIUR project ‘Biodiversitalia’ (RBAP10A2T4). LB was funded by a ‘Young Scientist Contract’ (INRA, CJS).