EVOLUTIONARY SORTING OF CHARACTERS IN A HYBRID SWARM. I: DIRECTION OF SLOPE

Quercus Douglasii and Quercus turbinella subsp. californica intergrade in California in a belt about 250 miles long. In the area of each parental taxon and near Lebec, in the middle of the zone where hybrids are common and where the gene pool is about evenly divided as to origin, the phenotypes were scored on a six-point scale to establish hybrid indices. At Lebec populations on slopes facing at intervals of one-eighth the distance around the compass were scored. The composition of each population was heterogeneous but restricted markedly according to exposure to the sun. Plants on northeast-facing slopes approached but did not equal the high score of Quercus Douglasii in Madera County; those on southwest-facing slopes approached but did not equal the extreme low score of subsp. californica near Victorville. Evolutionary sorting must be very rapid, for it is correlated with slopes of the same hills, and the hybrid swarm must be very sensitive to the environment.