Besiedelungsstrategie und Populationsentwicklung am Beispiel des Farns Asplenium Ruta-Muraria

Abstract

Colonization strategy and genetic variation in Asplenium ruta-muraria. — The Wall-rue (Asplenium ruta-muraria) is a widely distributed fern in Europe. It mainly grows in crevices in limestone rocks, and particularly in man-made walls. Because of the nature of this habitat the populations are scattered. The question that arises is: can new populations be founded from a single spore developing into a single gametophyte? If this happens, identical gametes will unite to form a completely homozygous sporophyte. The offspring of this sporophyte will show no genetic variation. The present investigation is based on studies of the breeding system and the enzyme polymorphisms of Wall-rue populations. The results support the hypothesis of a possible single genotype colonization of new habitats. Inspite of the possibility to establish new populations through this ‘extreme bottleneck’, it is shown that a considerable amount of genetic variation among populations exists. The individual plants are perennial and may live for a long time. The probability of the arrival of more than one genotype in a population increases with time: the populations on old walls and natural rocks showed more than one enzyme-pheno-type (genotype), whereas young wall populations showed no genetic variation. Old, established populations therefore make recombination and segregation possible and are sources for genetic variation.