Chromosomal polymorphism in isolated populations of Elymus (Agropyron) in the Aegean:

A striking chromosomal polymorphism predominates in Elymus striatulus (2n = 14), E. rechingeri (2n = 28) and E. diae (2n = 56) which grow in small isolated populations largely on the Aegean islands. The polymorphism was expressed mainly in the existence of several variant types of the satellite chromosomes. Satellite chromosomes might be more susceptible to structural alterations due to the presence of secondary constrictions, nucleolar organizers, heterochromatic blocks and repetitive DNA which are known to be labile sites. Chromosomal polymorphism was more pronounced in the two polyploid species which might be attributed to the compensatory effect of the high number of homologous, homoeologous or related genomes in the polyploids. Chromosomal polymorphism was also favored by the rhizomatous or tufted patterns of vegetative growth of these species. The evolutionary aspects of the chromosomal, genetical and morphological differences between populations might be related to (1) inbreeding of crossfertilizers and selection for chromosomal heterogeneity and/or (2) drift or a founder effect which is also supported by the paleogeographical records. The species in the Aegean area are apparently in an active phase of evolutionary change.