01996nas a2200169   4500008004100000245012500041210006900166260000900235300001200244490000700256520145500263100000501718700001601723700001701739700001401756856005601770       2004                        eng d00aMorphological and RAPD analysis of hybridization between Quercus affinis and Q. laurina (fagaceae), two Mexican red oaks0 aMorphological and RAPD analysis of hybridization between Quercus  c2004  a401-4090 v913 aQuercus affinis and Q. laurina are two closely related Mexican red oaks with partially overlapping distributions. Within the area of overlap, there are localities where morphological intergradation occurs. A previous hypothesis explained this pattern as a result of secondary contact between the two species, followed by hybridization and introgression. This possibility was analyzed here by examining foliar and genetic variation in 16 localities situated along a macrogeographic gradient, which included morphologically representative populations of both species and populations from within the area of overlap. Maximum-likelihood hybrid index scores calculated from nine semi-diagnostic RAPD markers indicated a shift in the genetic composition of populations from one species to the other along the macrogeographic gradient, with genetically intermediate populations situated in the area of overlap. Foliar variation followed a partially congruent pattern, but Q. laurina-like morphology predominated in some of the genetically intermediate populations. There were several instances of correlated frequency changeovers of single RAPD markers and morphological characters along the macrogeographic gradient and a few cases of markedly parallel patterns between markers. The results were interpreted as consistent with a hypothesis of secondary contact between the two oak species that has resulted in some differential introgression among markers.1 a1 aArias, D.M.1 aValencia, S.1 aOyama, K.  uhttp://www.amjbot.org/cgi/content/abstract/91/3/401