Rocío Mussali-Galante’s scientific contributions

Hybrid zones provide interesting systems to study genetic and ecological interaction between different species. The correct identi-fication of hybrids is necessary to understand the evolutionary process involved in hybridization. An oak species complex occurring in Mexico formed by two parental species, Quercus crassifolia H. & B. and Q. crassipes H. & B., and their putative hybrid species, Q. dysophylla, was analyzed with molecular markers (random amplified polymorphic DNA [RAPDs]) and morphological tools in seven hybrid zones (10 trees per taxa in each hybrid zone) and two pure sites for each parental species (20 trees per site). We tested whether geographic proximity of hybrid plants to the allopatric site of a parental species increases its morphological and genetic similarity with its parent. Seventeen morphological traits were measured in 8700 leaves from 290 trees. Total DNA of 250 individuals was analyzed with six diagnostic RAPD primers. Quercus crassifolia differed significantly from Q. crassipes in all the examined characters. Molecular markers and morphological characters were highly coincident and support the hypothesis of hybridization in this complex, although both species remain distinct in mixed stands. Clusters and a hybrid index (for molecular and morphological data) showed that individuals from the same parental species were more similar among themselves than to putative hybrids, indicating occasional hybridization with segregation in hybrid types or backcrossing to parents. Evidence does not indicate a unidirectional pattern of gene flow. Hybridization is a natural phenomenon that occurs frequent-ly in plants and animals (Harrison, 1993). This process pro-duces new genetic combinations by the introduction of semi-compatible genes into another genotype, upon which interac-tion of environment and genetic variation can isolate a novel taxon from parental types. Hybrids may be defined as species, subspecies, variants, or races, depending on the degree of di-vergence (Futuyma, 1998). Interspecific gene transfer is an important evolutionary force, because the genetic material in-troduced by introgression exceeds that which is produced di-rectly by mutation (Anderson, 1949). The genus Quercus (Fagaceae) is one of the most diversified groups of temperate trees with more than 500 species distrib-uted worldwide (Nixon, 1993). Hybridization and hybrid zones are common among oaks (Trelease, Ishida et al., 2003). However, despite the perception that hybrid zones are well documented among oaks, few comparative analyses of oak hybrid zones have used both morphological characters and genetic markers (Howard et al., 1997). Hybridization in oaks was initially detected based on mor-phological characters (Stebbins et al.