Molecular genetic analyses of glacier foreland populations

The alpine region is one of the few relatively undisturbed biomes. Thus, alpine ecosystems offer excellent possibilities to investigate the structure of natural populations. The retreats of the glaciers during the last centuries lead to an increase of land area available for plant colonization. Since these glacier forelands represent a temporal sequence, they are impressively reflecting the development of a new ecosystem. The study of the multiple biotic and abiotic mechanisms determining primary succession on glacier forelands has been part of scientific surveys for many decades. However, there is a lack of information on the populational dynamics of the early settling species and their various specific traits (e.g. pollination, sexual and asexual reproduction). The potential invasion routes of pioneers and their colonizing pattern on habitats of different age of substrate exposure are still not clarified. In general, older populations are regarded genetically less diverse than younger ones, and genetic diversity is expected to be highest at the beginning of colonization. The main objective of the project is to test these hypotheses exemplary for glacier forelands, by means of two species, characteristic for early successional stages. For this purpose, the patterns of the intra- and interpopulational genetic variation of Saxifraga. aizoides and Trifolium pallescens will be studied in three parallel valleys above the timberline in the Central Alps (Ötztal, Tyrol). The patterns obtained will elucidate the genetic variation of the populations established on soils of different age of exposure. In addition the colonizing history and the potential route(s) of invasion should be clarified. Molecular genetics of Saxifraga aizoides and Trifolium pallescens will be analysed by AFLP (amplified fragment length polymorphism) fingerprinting of total DNA. Additionally, the breeding system of the species will be investigated.

A molecular genetic approach was used to study the variability within populations of two early colonizing plant species (Saxifraga aizoides, Trifolium pallescens) on three parallel glacier forelands (Central Alps, Austria). The potential origins of the plants occurring directly in front of the glacier should be identified. The retreats of the alpine glaciers during the last centuries lead to an increase of land area available for plant colonization. Since these glacier forelands represent a temporal sequence, they are impressively reflecting the development of a new ecosystem. So they are of high scientific interest in many concerns. Despite the numerous studies carried out on glacier forelands, there still is a lack of information on the population dynamics of the early settling species. In general, it is assumed that genetic variability is highest on newly colonized areas since the seeds presumably derive from numerous different sites in the extended surrounding. On the older stages diversity might decrease due to competition as vegetation closes up. This hypothesis has never been tested for glacier forelands so far. Populations were sampled in early-, mid- and late successional stages on three glacier forelands of the Central Alps (Ötztal, Tyrol, Austria), as well as on the slopes of these glacier valleys and on one site below those valleys. Plant material was subsequently analysed in a molecular laboratory. Contrary to general expectations, genetic variation within the populations did not correspond with the extent of time being released from the permanent ice. The constant level of genetic diversity observed may be ascribed to a presently continuous high immigration of plants, not only on the youngest sites. Our results identified several potential sources for the populations on the earliest stages, such as the rest of the same glacier foreland, the adjacent valley slopes as well as another parallel glacier valley. Additionally, plants presumably also come from sites far apart. The potential routes of invasion turned out to be determined by the topography and the vegetation structure of the glacier valley, the character of the enclosing mountain ridges, and species specific characteristics (e.g. seed size). We conclude that repeated immigration and seedling establishment during primary succession might be more frequent than commonly suggested and thus plays a prominent role in embossing the vegetation structure on glacier forelands in the Alps.