Two Kinds of Gene Centers in Bothriochloininae

Abstract

An endemic center is located in the Western Ghats of India and includes some 9 species. Microcenters are located along the junction of the Panjabi plains and the foothills of the mountains of northern West Pakistan. Characteristics of the two kinds of gene centers are Endemic Center: species narrowly endemic; species narrowly restricted ecologically; habitats old and stable; mostly basic diploids; populations rather uniform; plants mostly sexual? (not all tested yet); evident introgression. Microcenters: species cosmopolitan; species generally ruderal; habitats new and disturbed; segmental alloploids, 4n, 5n, 6n; populations extremely polymorphic; plants mostly apomictic, but with low frequency of sexual reproduction; introgression conspicuous. In the case of the endemic center, we have a group of old, relict, basic diploid species that have become highly adapted to a few special stable environments. The species have endured for geologic time because the habitats have endured for geologic time. In the case of the microcenters, we have extreme polymorphism due to active hybridization of cosmopolitan, ruderal species under the influence of relatively recent human disturbance. The two kinds of centers are easily distinguished in the field and may provide models for the study of variation patterns in cultivated plants.