EVOLUTIONARY HISTORY OF THE OLD WORLD LUPINES

Abstract

SummaryAbout twelve species of Lupinus are centered in the Mediterranean and North African parts of the Old World. They show limited morphologocal polymorphism, but they are diverse in other ways. The group as a whole features three unique characteristics of evolutionary significance: (a) a special geographical distribution, disjunct from the main center in America, with allopatric rough‐seeded and partially sympatric smooth‐seeded species; (b) karyotype polymorphism, with at least seven different chromosome numbers, none of which has been encountered in the New World; (c) systematic disassociation, by which most species are taxonomically unrelated and genetically isolated.This cyto‐geographical complex pattern and systematic divergence are best understood on the assumption that a few lupines of various origins migrated by means of long‐range dispersal from their primary center in North America during the Neogene. The migrations were repeated quite haphazardly.Rough‐seeded migrules were established in NW Africa, while smooth‐seeded ones arrived at the Mediterranean, probably later on.During the Miocene lupine populations spread and diverged along the Mediterranean and in Africa north of the equator, succeeding the Tethyan flora.Their present eco‐geographical distribution is the outcome of both climatic and edaphic changes during the Quaternary, combined with the impact of human activities from the Pleistocene on. Whereas the evolution of Lupinus in the New World has been enhanced by processes such as ecological differentiation and intensive hybridization, that of the Old World lupines has been inhibited owing to rapidly increasing aridity and civilization. The main changes in the gene pool of wild populations could be caused by disruptive differentiation, i.e., occasional hybridization and subsequent intergradations with escaped or neglected, sporadically domesticated strains.