Johann Jakob Schneller

Biosystematic investigations on the lady fern(Athyrium filix-femina)

In EuropeAthyrium filix-femina has a constant chromosome number (2n = 80) and is sexual. The normal type of reproduction is intergametophytic crossing. In the gametophyte phase there is a hormone system which induces dark germination of spores and antheridium formation. Sporophytes originating from single prothalli show that a genetic load is present in all population examined. It appears not to be a simple allelic load but a complicated balanced system. Morphological variability can be interpreted as the expression of the genetic heterogeneity of populations. There are no crossing barriers, not even between insular populations hundreds of kilometers apart.

Genetic variation in small, isolated fern populations

. Differences in genetic variability of several small, isolated populations of four fern species in a restricted area in the Swiss lowlands reflect differences in breeding system, population size, the degree of population fragmentation, and ecological requirements. The investigated populations of Asplenium septentrionale show only little genetic variability (isozyme variation) without gene flow among populations (based on the banding pattern of multi-locus phenotypes), and they persist for long periods despite the small population sizes. In Asplenium ruta-muraria, genetic variability is correlated with age. Young populations show no genetic variation, while old populations show some. All individuals of Polypodium vulgare investigated, either epiphytic or epilithic, share exactly the same enzyme phenotype. The results for these three species can be related to predominance of inbreeding, lack of inbreeding depression, polyploidy, long-distance dispersal, production of large amounts of diaspores, single-spore colonization, and perennial life cycles. Genetic variability in these three species does not seem to be absolutely necessary for the maintenance of their populations. Ecological and demographic factors are considered to be more important. An isolated, glacial relict population of diploid Asplenium viride shows high variability in two out of eight enzyme systems, which may be due to prevailing outbreeding. We discuss aspects of the importance of genetics and life history for conservation biology.

Phenotypic and isozyme variation in Cystopteris fragilis (Pteridophyta) along an altitudinal gradient in Switzerland

Summary Plants of Cystopteris fragilis from 9 different populations along an altitudinal gradient and from two additional populations were investigated. In three populations at 1410 m, 1630 m and 1830 m a.s.l., respectively, climatic conditions were recorded. The phenology of the plants, the sizes and dimensions of leaves and fitness parameters such as leaves per plant and fertility were studied. Leaf sizes and leaf number per plant were negatively correlated with altitude. However, the duration of development from snow melt and onset of the leaves till ripening was similar at different altitudes. Additionally, isozyme investigations and chromosome counts of a set of randomly sampled plants were performed. The genetic differentiation between populations suggests a relatively low gene flow. A significant positive correlation between number of enzyme phenotypes and altitude was recorded. Two different cytotypes were distinguished, a hexaploid and a pentaploid one.

Aspects of Spore Dispersal in Selaginella

The evolution of heterospory changed the conditions for spore dispersal. Assuming wind as the dispersal agent, microspores will be dispersed to greater distances than megaspores. We investigated aspects of spore size and sculpture as well as spore dispersal under calm con- ditions and under the effect of artificial wind of some Selaginella species. We found that differ- ences between the species existed that were correlated with active or passive release of micro- and megaspores. The dispersal efficacy changed drastically under the effect of wind, showing differences between the species. There was no support for the hypothesis of synaptospory between micro- and megaspores during active dispersal. Evidence suggests that active spore dispersal and wind may enhance outbreeding. More detailed investigations may reveal species specific corre- lations between life history traits, breeding systems, and spore dispersal. Heterospory and dioecy of gametophytes evolved independently in different clades of the pteridophytes. The separation of female megaspores and male microspores changed the conditions of spore dispersal. In homosporous, wind dispersed ferns the probability of being transported a certain distance is much the same for each spore. Assuming that in heterosporous pteridophytes wind dispersal is still dominant, the smaller and lighter microspores are likely to be dispersed to longer distances than the larger and heavier megaspores (Tryon and Lugardon, 1991). The dispersal distances of male and female gameto- phytes thus differ. Heterospory also affects the production of spores. Because of higher energetic investments, the number of megaspores per individual plant is reduced in comparison to the number of microspores (Tryon and Tryon, 1982). As a consequence, the dispersal ecology of heterosporous pte- ridophytes is likely to differ from that of homosporous ferns (Cousens, 1988). The heterosporous genus Selaginella P. Beauv. is widespread and contains numerous species (Jermy, 1990). The efficacy of their active spore dispersal mechanisms was first investigated by Goebel (1901). He showed that the mega- sporangium ejects the megaspores in a manner quite different from the micro-

Evidence for intergeneric incompatibility in ferns

The archegonial mucilage ofAthyrium filix-femina andA. distentifolium paralyses spermatozoids ofDryopteris filix-mas (and in one caseD. inaequalis) before they penetrate the archegonial venter. The archegonial mucilage ofDryopteris filix-mas has a weak positive chemotactic influence on the spermatozoids of the twoAthyrium species. The spermatozoids ofDryopteris were never observed in the archegonia ofAthyrium. Incompatibility was not observed within and between the twoAthyrium species, withinDryopteris filix-mas or betweenAthyrium filix-femina and twoAsplenium species.

How selfing and intra- and interspecific crossing influence seed set, morphology and ploidy level in Euphrasia: An experimental study of species occurring in the Alps of Switzerland

Annual alpine species rely on selfing rather than on cross-pollination for successful reproduction. However, insect visits may occasionally cause cross-pollination not only within but also between closely related species. The aim of this study was to investigate four species of Euphrasia for their efficiency in spontaneous selfing and their success in intra- and interspecific crossing. We used the seed sets that followed spontaneous selfing and artificial cross- and selfpollination to measure the breeding success. We compared the morphological characters of species and hybrids and determined their ploidy level using flow cytometry. We verified the hybridogenous origin of plants resulting from interspecific crosses using RAPD banding patterns. While spontaneous seed set was high in the two small-flowered species, seed set in the large-flowered species was small and affected by external circumstances. We obtained F1 and F2 hybrids from interspecific crosses of two diploid species and detected polyploid individuals in both generations.

Besiedelungsstrategie und Populationsentwicklung am Beispiel des Farns Asplenium Ruta-Muraria

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.

Vigor and Survival of Inbred and Outbred Progeny of Athyrium filix-femina

Morphology and mortality of sporophytes resulting from intergametophytic and intragametophytic mating were studied in the fern Athyrium filix-femina. In a long-term experiment, we determined the relevance of heterosis and/or genetic load in this homosporous fern species. Progeny from intergametophytic crossing, probably consisting of heterozygous individuals, exhibited most vigorous growth, small morphological variation, and low mortality. Progeny resulting from intergametophytic selfing, likely to include individuals with various levels of homozygosity, showed larger morphological variation, higher mortality, and smaller mean leaf length. Progeny from intragametophytic selfing (completely homozygous) had the smallest mean leaf length, highest mortality, and considerable morphological variation. These results for a homosporous fern species agree with theoretical and empirical studies on heterosis and genetic load in flowering plants.

Remarks on reproductive biology of homosporous ferns

Some results obtained in breeding experiments of homosporous ferns cannot be explained by genetic load alone. Simple models of epistasis or heterogenic unilateral incompatibility are discussed which may help to explain the exceptional observations. The need for further experiments is emphasized.