Lack of Isozyme Variation in the Agamosporous Fern Dryopteris remota (A. Braun) Druce

Abstract

When we study apomictic taxa two basic questions are of special relevance. The first is the question of their phylogenetic and/or geographic origin, the second is that of their genetic composition (variability or uniformity). There exists a variety of allozyme studies in apomictic angiosperms (Asker & Jerling, 1992; Battjes et al., 1992) which allows insights into the genetic patterns of apomicts and their evolution. In apomictic plants various genetic structures are observed. For example, the populations of apomictic species are sometimes multiclonal and the genetic differences between populations may often be relatively high (Ellstrand & Roose, 1987). According to Walker (1984) about 10% of all ferns are agamosporous. In the last decade a few investigations on apomictic (agamosporous) ferns using isozyme methods were published. In contrast to the earlier opinion, that agamosporous species are exclusively of hybrid origin (Walker, 1984), it was shown that in some examples, for instance Pellaea andromedifolia (Gastony & Gottieb, 1985), the Pellaea glabella complex (Gastony, 1988), and in Dryopteris sparsa (Darnaedi et al., 1990b), autopolyploidy may play an important role in the formation of apomicts. The apomictic species Pellaea atropurpurea (Gastony & Windham, 1989), Asplenium unilaterale (Watano & Iwatsuki, 1988), Pteris cretica (Suzuki & Iwatsuki, 1990), and Dryopteris yakusilvicola (Darnaedi et al., 1990a), on the other hand seem to have originated through hybridization events between different species. Agamospory in D. remota was first described by Fischer (1909). It was Dopp (1932) who worked out the detailed cytological background of the agamospory in this fern. Dopp's findings are valid for most of the agamosporous fern species (Walker, 1979). Dryopteris remota is triploid and appears to be strictly agamosporous (Fraser-Jenkins & Reichstein, 1984). This European species is distributed from the eastern Pyrenees to the Caucasus but is everywhere rare. Dryopteris remota usually grows as single individuals or forms small stands of a few to sometimes about 50 individuals. The populations are isolated from each other, sometimes by large distances. The largest population known so far was described by Benl & Eschelmiller (1973). About 130 individuals were found in one site (2000 x 300 m2) in Bavaria. In terms of morphological characteristics, D. remota seems to be quite uniform (except for characters most likely due to phenotypic plasticity) (Fraser-Jenkins & Reichstein, 1984). In our investigation the following questions were of interest: Are there different enzyme genotypes, either within populations or between populations from different parts of the distribution area? Do enzyme data point to a unique, or a multiple origin of the species? MATERIALS AND METHODS