title: The effect of drought stress on heterozygosity-fitness correlations in pedunculate oak (Quercus robur).
abstract: OBJECTIVE
  The interaction between forest fragmentation and predicted climate change may pose a serious threat to tree populations. In small and spatially isolated forest fragments, increased homozygosity may directly affect individual tree fitness through the expression of deleterious alleles. Climate change-induced drought stress may exacerbate these detrimental genetic consequences of forest fragmentation, as the fitness response to low levels of individual heterozygosity is generally thought to be stronger under environmental stress than under optimal conditions.
  
  
  METHODS
  To test this hypothesis, a greenhouse experiment was performed in which various transpiration and growth traits of 6-month-old seedlings of Quercus robur differing in multilocus heterozygosity (MLH) were recorded for 3 months under a well-watered and a drought stress treatment. Heterozygosity-fitness correlations (HFC) were examined by correlating the recorded traits of individual seedlings to their MLH and by studying their response to drought stress.
  
  
  RESULTS
  Weak, but significant, effects of MLH on several fitness traits were obtained, which were stronger for transpiration variables than for the recorded growth traits. High atmospheric stress (measured as vapour pressure deficit) influenced the strength of the HFCs of the transpiration variables, whereas only a limited effect of the irrigation treatment on the HFCs was observed.
  
  
  CONCLUSIONS
  Under ongoing climate change, increased atmospheric stress in the future may strengthen the negative fitness responses of trees to low MLH. This indicates the necessity to maximize individual multilocus heterozygosity in forest tree breeding programmes.
authors.affiliation: Plant Conservation and Population Biology, Biology Department, University of Leuven, Kasteelpark Arenberg 31, Box 2435, 3001 Leuven, Belgium.
authors.forename: Guy
authors.initials: G
authors.lastname: Vranckx
authors.forename: Hans
authors.initials: H
authors.lastname: Jacquemyn
authors.forename: Joachim
authors.initials: J
authors.lastname: Mergeay
authors.forename: Karen
authors.initials: K
authors.lastname: Cox
authors.forename: Pieter
authors.initials: P
authors.lastname: Janssens
authors.forename: Bie An Sofie
authors.initials: BA
authors.lastname: Gielen
authors.forename: Bart
authors.initials: B
authors.lastname: Muys
authors.forename: Olivier
authors.initials: O
authors.lastname: Honnay
mesh_terms: D018533:Biomass; D055864:Droughts; D017343:Genes, Plant; D006579:Heterozygote; D018895:Microsatellite Repeats / Q000235:genetics; D029963:Quercus / Q000235:genetics* / Q000254:growth & development / Q000502:physiology*
keywords: Climate change; Quercus robur; drought stress; forest fragmentation; greenhouse experiment; growth traits; heterozygosity–fitness correlations; pedunculate oak; transpiration