Rolf Holderegger

Effects of litter removal on the germination of Anemone nemorosa L.

Summary In a recent article, Eriksson (1995) showed high germination rates in Anemone nemorosa. To check whether ERIKSSONS results are also valid in Central Europe, a litter removal experiment was carried out in Northeastern Switzerland. In both experimental series, litter removal plots and control plots, high germination of A. nemorosa occured. Nevertheless, litter removal greatly enhanced germination of A. nemorosa. A significant correlation between seedling number and ramet density within the plots pointed to a dominance of very local dispersal. These facts lead to the hypothesis that reproduction by seeds in A. nemorosa as well as vegetative reproduction by clonal growth are of great importance for the maintenance of populations of this species. Surprisingly, no successful germination of A. nemorosa was detected in seed bank investigations.

Estimation of the relative importance of sexual and vegetative reproduction in the clonal woodland herb Anemone nemorosa

Anemone nemorosa is a perennial rhizomatous plant of European woodlands. The “probability of clonal identity” method estimated the relative proportion of sexual to vegetative reproduction in this species to be 4.4% from allozyme genotype distributions. This result is congruent with investigations on the germination, short-term demography, population genetics, and breeding system of this species, and supports the hypothesis that even low levels of seedling recruitment can maintain considerable intrapopulational genetic diversity.

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.

Understanding population history for conservation purposes: population genetics of Saxifraga aizoides (Saxifragaceae) in the lowlands and lower mountains north of the Alps.

Several alpine species have outlying populations in the lowlands and lower mountains north of the Alps. These small, isolated populations are usually described as either (1) glacial relics, (2) descendants from populations living on forelands and moraines during the ice ages, or (3) populations founded by long-distance dispersal after glaciation. A floristic survey of the historic and present distributions and an allozyme investigation were performed on one of these relic species, Saxifraga aizoides. The species was historically more abundant and had more stations in more regions of northeastern Switzerland. The former population structures within regions, nowadays destroyed, were still reflected in distinct and high regional genetic diversity and variation. There was weak evidence of increased inbreeding in outlying populations, but populations did not deviate from Hardy-Weinberg equilibrium. No geographic pattern of genetic variation above the regional scale (>10 km) was found. Based on the spatial and genetic structures found, it was not possible to discriminate between the abovementioned hypotheses. Nevertheless, the study shows how a thorough evaluation of distribution and abundance data aids the interpretation of genetic data with respect to population history, biogeography, and conservation biology.

Variation in breeding system among populations of the common woodland herbAnemone nemorosa (Ranunculaceae)

Recent studies of germination in natural habitats, of genetic variation within populations and of the relative proportion of vegetative and sexual reproduction in the clonal plant speciesAnemone nemorosa suggest that sexual recruitment by seeds from outcrossed flowers is important for the maintenance of this species populations. Because published reports on its breeding system are controversial, pollination experiments were performed in five natural populations ofA. nemorosa. Differences in ovule number per flower were recorded among populations, but they were not related to obvious habitat differences. Seed/ovule-ratios were significantly higher after open pollination and artificial crossing than after either artificial or spontaneous selfing. Populations had no effect on seed/ovuleratios. Different breeding indices indicated thatA. nemorosa is mainly self-incompatible. Nevertheless, some seed set also occurred after selfing, and both artificial and spontaneous selfing exhibited higher variation in seed/ovule-ratios than open pollination and artificial crossing. Continuous variation in seed/ovule-ratios after selfing suggested that the expression and effectiveness of the self-incompatibility system ofA. nemorosa is influenced by both genetic variation and phenotypic plasticity.

Intrapopulational size structure of the monocarpic species Saxifraga mutata and its relationship to succession

Summary The monocarpic Saxifraga mutata, a locally endangered species in Central Europe, grows at sites which are strongly influenced by erosion. Three populations of S. mutata were investigated in Northeastern Switzerland. Each of the localities is characterized by a succession series from almost bare slopes to sparse Pinus-woods (Molinio-Pinetum). Rosette diameters of vegetative and generative individuals showed L-shaped distributions in two populations. A normal-shaped distribution, indicating low rejuvenation, was found in the third population. Rosette diameters were significantly correlated with other fitness-related traits such as number of flowers, number of leaves, and flowering stem length. A reproductive threshold size of c. 4 cm in rosette diameter was recorded. Investigations of size structures in plots of 1 m2 demonstrated that rosette size, rosette density, recruitment, and frequency of flowering individuals were closely related to successional stages as well as intensity and frequency of erosion. Maintenance of local populations of S. mutata depends on the balance between erosion and succession. Landscape dynamics must be warranted in order to conserve this species.

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-

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.

Localized hybridization betweenSaxifraga aizoides andS. mutata (Saxifragaceae): Reproductive ecology ofS. ×hausmannii and implications for conservation

The roles of hybridization and of introgression as potential threats to small native populations are current topics of interest both for evolutionary and conservation biologists. Two factors are mainly involved in the threat to natural populations through hybridization: demographic swamping and genetic assimilation. At prealpine locations, twoSaxifraga species with very different growth habits,S. aizoides andS. mutata, form a hybrid,S. ×hausmannii. Investigation of meiosis and crossing experiments revealed regular pairing of the 26 chromosomes and development of viable seeds in the hybrid. Analysis of hybrid indices, GPI allozymes, germination experiments and seed sizes showed an intermediate position ofS. ×hausmannii between its parental species.Saxifraga aizoides andS. mutata were separated by only weak hybridization barriers. Introgression occurred mostly in direction ofS. aizoides, although to a small amount. There is no actual threat to small, prealpine populations ofS. aizoides andS. mutata through interspecific gene flow because hybridization is localized, resulting from different flowering phenologies of the parental species and from the narrow habitat requirements ofS. ×hausmannii, which are similar to those ofS. aizoides. The major threat to local, prealpine populations ofS. aizoides andS. mutata is the loss of landscape dynamics. Both species need open erosion slopes for successful recruitment.

Erhaltung und Wiederansiedlung des Kleinen Rohrkolbens (Typha minima) - Vegetationsaufnahmen, Monitoring und genetische Herkunftsanalysen

Abstract.Galeuchet D. J. and Holderegger R. 2005. Conservation and re-introduction of Dwarf Bulrush (Typha minima) – vegetation surveys, monitoring and genetic analysis of origin. Bot. Helv. 115: 15–32.Typha minima was formerly widespread along fast flowing alpine rivers but is now red-listed as critically endangered. To assess its conservation perspectives, we surveyed the few remaining natural populations along the alpine part of the River Rhine from 1997 to 2002 and determined their genetic diversity using isozyme electrophoresis. Six of the populations became extinct or extremely small, probably due to shading by taller plants and trampling, while six other populations remained stable or increased, partly due to habitat restoration measures. The largest populations, with areas of more than 10’000 m2, are found in secondary habitats which are regularly disturbed due to water regime management. Of the 19 investigated isozyme loci, only six were polymorphic. Allelic diversity (1.4–1.8) was low in all populations, and the number of multilocus genotpyes (1–18) was low for 11 of 13 investigated populations. Genetic diversity was also studied for ex-situ cultivations of T. minima in Swiss botanical gardens and reintroduced stands.These artificial populations (each with 1–3 multilocus genotypes) were genetically similar to natural populations (average genetic distance 0.094). For two ex-situ cultivations with unknown origin, the likely origin could genetically be defined. Hybridisation between two ex-situ cultivations of different origin (i.e. a potential risk of genetic introgression) was detected in one botanical garden. It is concluded that the long-term conservation of T. minima requires both the restoration of regularly disturbed, sparsely vegetated river margins and the re-introduction of plants from ex-situ cultivations with appropriate origin.