Native range variation in Capsella bursa-pastoris (Brassicaceae) along a 2500 km latitudinal transect

Abstract

Capsella bursa-pastoris (L.) Medik. is a self compatible tetraploid annual species which has successfully spread to most continents and is mostly confined to man-made habitats. The colonising success may be associated with fine-scaled ecotypic differentiation, and regional adaptation. Seeds of 377 individuals from 40 provenances were collected over a distance of more than 2500 km from the Kola Peninsula in the north to the Caspian Sea in the south in Russia and from northern to southern Scandinavia. 3558 progenies were investigated in common garden field experiments in order to distinguish between phenotypic variability and genetic variation of quantitative life-history traits (onset of flowering, rosette diameter, leaf type, plant height, and branching and fruit characters). Genetic diversity and population structure was examined with isozyme analysis. Along both transects, Capsella showed clinal differentiation in phenotypic traits: e.g., the most northern and most southern provenances flowered earlier than the provenances from in between. A highly significant quadratic correlation exists between morphological traits and the degree of latitude. Distribution of leaf types showed no geographical pattern, unlike that observed for other regions. Allozyme variation follows a pattern of isolation by distance.