Vergeer could have chalked it all up to harmful rare genes. But then she thought more about the environmental conditions. Drought and poor nutrition are known to cause so-called epigenetic changes to DNA, the addition or removal of small chemical tags known as methyl groups that effectively turn genes on or off. Could such modifications be causing inbreeding depression?
To find out, Vergeer and colleagues counted the methyl groups in the genomes of inbred and outbred S. columbaria. The inbred plants showed a variety of health problems, including difficulty photosynthesizing and slow maturation. They also had 10% more methyl groups in their genomes than did outbred plants, indicating significant epigenetic changes.