Heterozygosity–fitness correlations in pedunculate oak

Increased homozygosity caused by population fragmentation can directly affect individual plant fitness through the expression of deleterious alleles, and drought stress induced by climate change may exacerbate these effects. Vranckx et al. investigate various transpiration and growth traits of seedlings of pedunculate oak, Quercus robur, correlate them with their multilocus heterozygosity (MLH), and then study the effects of drought stress on these relationships. They find significant heterozygosity–fitness correlations for most fitness traits, and high atmospheric stress increases the strength of these correlations for the transpiration variables. They conclude that that ongoing climate change may strengthen the negative fitness responses to low MLH, highlighting the need to maximize individual multilocus heterozygosity in forest tree breeding programs.