Influence of a climatic gradient on genetic exchange between two oak species

Premise of the study. In plant groups with limited intrinsic barriers to gene flow, it is thought that environmental conditions can modulate interspecific genetic exchange. Oaks are known for limited barriers to gene flow among closely related species. Here, we use Quercus as a living laboratory in which to pursue a fundamental question in plant evolution: do environmental gradients restrict or promote genetic exchange between species? Methods. We focused on two North American oaks, the rare Q. dumosa and the widespread Q. berberidifolia. We sampled intensively along a contact zone in California. We sequenced restriction site associated DNA markers and measured vegetative phenotype. We tested for genetic exchange, the association with climate, and the effect on phenotype. Key results. There is evidence for genetic exchange between the species. Admixed plants are found in areas of intermediate climate, while less admixed plants are found at the extremes of the climatic gradient. Genetic ...