The colonizing history of Capsella in Patagonia (South America) - Molecular and adaptive significance

Abstract

Twenty-two provenances of Capsella bursa-pastoris (Brassicaceae) from Patagonia and Tierra del Fuego and 13 provenances from the middle part of South America have been investigated for phenotypic traits (flowering, growth form parameters, fruit characters), isozymes (AAT, GDH, LAP), and RAPDs. Capsella is native to Europe and was introduced into South America in the 16th century. In Patagonia, we detected 23 different multilocus associations, but only five occurred in a frequency of more than 5%. By comparison with the geographic distribution patterns of multilocus genotypes in Europe, we inferred the ancestral European gene pools and the possible introduction routes. A particular multilocus genotype (MMG) was most frequent in the investigated area, and is native to the Iberian Peninsula. This genotype was with all probability introduced by Spaniards into central and northern South America, and it could have reached Patagonia from the north step by step. Other genotypes probably used a direct route from Europe, most likely via British sheep farmers in the second half of the 19th century. Rare genotypes in Patagonia may have been introduced recently by chance, or might be due to multilocus rearrangements in connection with rare outcrossing events. RAPD markers helped to trace colonial gene pools outside Europe and ancestral European gene pools and support the isozyme studies. Correlations between the life history traits and allozyme markers give evidence of the role adaptation may play in the colonizing process.