Hybridization between two polyploid Cardamine (Brassicaceae) species in North-western Spain: discordance between morphological and genetic variation patterns.

Abstract

Hybridization is an important evolutionary phenomenon, and therefore a detailed understanding of the dynamics of interspecific gene flow and resulting morphological and genetic patterns is of widespread interest. Here hybridization between the polyploids Cardamine pratensis and C. raphanifolia at four localities is explored. Using different types of data, the aim is to provide simultaneous and direct comparisons between genotype and phenotype variation patterns in the studied hybrid populations. Evidence of hybridization has been gathered from morphology, molecular markers (amplified fragment length polymorphism and chloroplast DNA sequences), pollen viability, karyology and nuclear DNA content. All data support extensive gene flow occurring in the hybrid populations. A wide range of morphological and genetic variation is observed, which includes both parental and intermediate types. Unbalanced pollen fertility and several ploidy levels are recorded. Incongruence reported between genotype and phenotype suggests that parental phenotypes are affected by introgression, and intermediate hybrid phenotypes can be genetically closer to one of the parents. Thus, it is evident that morphology, when used alone, can be misleading for interpreting hybridization, and critical evaluation of other data is needed.