Does domestication mimic speciation? 1. A population-genetic analysis of Hordeum spontaneum and Hordeum vulgare based on AFLP and evolutionary considerations

To answer the question whether Hordeum spontaneum K. Koch. and Hordeum vulgare L. are conspecific taxonomic entities or not", we carried out an investigation with amplified restriction fragment length polymorphism (AFLP™) using H. vulgare cultivars, H. spontaneum from the Fertile Crescent, and material from China, primarily Xizang (Tibet), containing landraces and accessions identified morphologically as Hordeum agriocrithon Åberg. and H. spontaneum. Population genetic analyses and discriminant analyses were based on three groupings, H. vulgare, H. spontaneum, and H. agriocrithon, determined from morphology. To independently find groups, cluster analyses were carried out followed by population-genetic analyses and discriminant analyses of the clusters. The results of population-genetic analyses of morphologically based groups were not very different from those of comparable analyses of groups inferred from clustering. Based on 795 AFLP bands scored on 506 individuals, genetic diversity was 30% higher within H. spontaneum than within H. agriocrithon or H. vulgare. The variation among the three entities was 27.3% (F_CT = 0.27) and among populations within the three was 40.4% (F_SC = 0.56) leaving 32.3% (F_ST = 0.68) within populations/accessions. Three entities were clearly defined by clustering and supported by discriminant analyses, and then nomenclaturally formulated, two as species and one as an interspecific hybrid. The first, H. spontaneum, comprises populations in the Near East, the second, H. vulgare, comprises the cultivars, and the third, H. xagriocrithon, comprises all barley landraces and hybrids from China as well as hybrids from the Near East. We discuss evolutionary perspectives of speciation and conclude that barley cultivars form a species distinct from the wild progenitor, H. spontaneum. This analysis may highlight the dilemma regarding other cultivated plants and domesticated animals, a still unresolved evolutionary-taxonomic problem.