Data from: Range expansion compromises adaptive evolution in an outcrossing plant

Neutral genetic diversity gradients have long been used to infer the
colonization history of species, but range expansion may also influence
the efficacy of natural selection and patterns of non-synonymous
polymorphism in different parts of a species’ range. Recent theory
predicts both an accumulation of deleterious mutations and a reduction in
the efficacy of positive selection as a result of range expansion. These
signatures have been sought in a number of studies of the human range
expansion out of Africa, but with contradictory results. We analyzed the
polymorphism patterns of 578,125 SNPs (17,648 genes) in the European
diploid plant Mercurialis annua, which expanded its range from an eastern
Mediterranean refugium into western habitats with contrasted climates. Our
results confirmed strong signatures of bottlenecks and revealed the
accumulation of mildly to strongly deleterious mutations in range-front
populations. A significantly higher number of these mutations were
homozygous in individuals in range-front populations, pointing to
increased genetic load and reduced fitness under a model of recessive
deleterious effects. We also inferred a reduction in the number of
selective sweeps in range-front versus core populations. These signatures
have persisted even in a dioecious herb subject to substantial
interpopulation gene flow. Our results extend support from humans to
plants for theory on the dynamics of mutations under selection during
range expansion, showing that colonization bottlenecks can compromise
adaptive potential.