Genetic variation and hybridization among red oaks of California: A case study of Quercus parvula, Quercus wislizeni and Quercus kelloggii

Quercus wislizenii and Q. parvula are evergreen oaks of California. The latter was recognized as a species distinct from Q. wislizenii only recently, but has not received full acceptance. In an attempt to study differentiation between these two taxa and the genetic architecture of their populations, a molecular genetic analysis was carried out using Amplified Fragment Length Polymorphism (AFLP) markers. This study examined patterns of genetic variation among Q. wislizenii and Q. parvula and other red oaks (Q. agrifolia and Q. wislizenii) in California as well as molecular evidence of hybridization.; Although species specific markers were observed between Q. kelloggii and other members of the red oak group in California, fixed genetic differences were not apparent among Q. agrifolia, Q. parvula and Q. wislizenii. Genetic differentiation between Q. wislizenii and Q. parvula was low (phi ct = 0.013, P = 0.09) and neither UPGMA cluster analysis nor principal coordinates analysis revealed any clear separation of the taxa.; Genetic variability within populations of Q. parvula and Q. wislizenii was high with mean percent polymorphic loci of 56. Most of the genetic variability was within populations (81%, P < 0.001) compared to 18% and 1.23% among populations within each species and between species respectively.; Low genetic differentiation betweenQ. parvula and Q. wislizenii could be due in part to the relatively short time since divergence and rapid radiation of these species. In addition, repeated hybridization between Q. parvula and Q. wislizenii and between these species and other red oaks of California could have caused convergence of the characters.; Species-specific AFLP markers clearly showed intermediacy of field identified hybrids between Q. wislizenii and Q. kelloggii. Their hybrid status was further supported by intermediacy in principal coordinates analysis. The data suggest differential interspecific gene flow in the direction of Q. kelloggii to Q. wislizenii.