Genetic variation and differentiation of populations within the Quercus affinis Quercus laurina (Fagaceae) complex analyzed with RAPD markers
The population genetics of two hybridizing Mexican red oaks, Quercus affinis Schweid. and Quercus laurina Humb. & Bonpl., was investigated with 54 randomly amplified polymorphic DNA (RAPD) markers scored in 415 individuals from 16 populations representing the distribution area of the two species and a probable secondary hybrid zone. Genetic relationships among populations, depicted in a unweighted pair group method with arithmetic averaging (UPGMA) dendrogram, were largely incongruent with the morphological classification of populations as Q. affinis-like or Q. laurina-like that was obtained in previous studies. In contrast, the two main population clusters in the UPGMA dendrogram corresponded to the location of populations in two distinct geographical areas: southwestern and northeastern. A Mantel test confirmed a significant association between geographic and genetic distances among populations. Analyses of molecular variance (AMOVA) indicated that most genetic variation is contained within populations (84%), while 10.5% (P < 0.0001) is among populations, and 5.1% (P = 0.007) is between the two morphological groups. Differentiation between the southwestern and northeastern geographical groups (as recognized by the UPGMA), was 7.8% (P < 0.0001). The incongruence between genetic and phenotypic patterns suggests that introgression of neutral markers has been considerable between the two species in the hybrid zone, while morphological differentiation has remained comparatively stable.Key words: hybridization, population genetics, Quercus, RAPD markers.