Relative influence of biological versus historical factors on isozyme variation of the genus Androcymbium (Colchicaceae) in Africa

Abstract.

 We carried out isozyme electrophoresis in the South African taxa of Androcymbium to compare their levels of genetic variation with those reported for their North African congeners and to evaluate the influence of reproductive traits, phylogenetic relationships and environmental histories on the evolutionary dynamics of this disjunction between arid zones of North and South Africa. One possible factor to explain the higher number of alleles detected in South Africa is that diversification in this area started within the early Oligocene, whereas the ancestor of the North African species is more recent and corresponds to the late Miocene. Strong environmental selection and habitat specialization in South Africa probably fostered genetic differentiation between species further in this area. In South African taxa, isozymic variation levels were significantly correlated to breeding systems but not to lineage circumscription (i.e. phylogenetic closeness). The assessment of the relative influence of diverse biotic and abiotic factors on isozyme variation shows that, on a short geological time scale, breeding system is the most reliable predictor of levels of genetic variation. On a longer time frame, represented by the splitting that gave rise to the south–north disjunction of the genus in the late Miocene, the influence of environmental histories of North and South Africa on genetic variation overrides that of breeding systems.