Diversity, diversification processes and conservation of high mountains and arctic biota

November 12,2005, Oxana, Mexico
Chairs: Irène Till-Bottraud (U Joseph Fourier, Grenoble, France) and Mary T Kalin Arroyo (U Chile, Chile)

Programme

Mary T. Kalin Arroyo (Millennium Centre for Advanced Studies in Ecology and Biodiversity Research, Universidad de Chile, Chile, southern@abello.dic.uchile.cl)
Diversity and diversification processes in high elevation habitats - using the South American Andes as a model to set the stage

High elevation habitats provide a global resource for understanding patterns of biodiversity and evolutionary processes involved in diversification. Located above treeline on all continents of the world, and found from tropical to high latitudes, the biota of high elevation habitats has evolved from ancestors found in a diverse sample of lowland ecosystems, with subsequent enrichment through long-distance dispersal and migration along mountain corridors. A conceptual framework for thinking about diversity and diversification processes in high elevation habitats, using the vascular flora of the South American Andes as a model is developed. I will critically examine how unique the entire high elevation flora of the South America Andes, whether species diversity decreases with latitude, and compare diversification patterns in the pa_ramo, puna and southern temperate alpine zone. I examine the role of certain reproductive biology parameters as drivers of alpine diversity. Although the South American high elevation flora is of a similar age throughout the entire length of the Andes, species diversity, significantly, is higher at tropical latitudes. The latter trend is strongly influenced by major radiations in some key genera. Limited evidence suggests that a number of monotypic high elevation genera are closely phylogenetically related to larger genera, suggesting rapid morphological differentiation, while other are relictual. A trend for higher species richness in genera exhibiting obligate outcrossing systems may exist. A full understanding of diversity in high elevation ecosystems requires an integrated approach. The Andes are a useful model for understanding diversity patterns in high elevation habitats, and for testing hypotheses on latitudinal gradients in species richness.

Lohengrin Cavieres and Ragan Callaway (The University of Chicago, USA, j-coyne@uchicago.edu)
Facilitation and its consequences on local species-richness in the alpine: examples from the Andes of Southern-South America

Taking the Cameroon Volcanic Line, an archipelago of oceanic and continental rainforest 'islands' extending 2000km from Guinea Gulf Islands to Cameroon high volcanoes as an example and Drosophila as a model we focus on the mechanisms triggering biodiversity in tropical montane biota. Analysing altitudinal hybrid zones allows to understand how much gene flow between sympatric entities can occur while they still remain distinct. Sympatric clusters may differ at only a few loci while showing substantial introgression throughout the rest of the genome, or sister species may exchange genes freely for only few traits while selection maintains distinctness for the majority of genes. D. yakuba occurs in open lowland habitats on Sao Tome_, while the endemic D. santomea is restricted to misty forests at higher elevations up to 2024m. At mid elevations they form a hybrid zone where sterile male and fertile female hybrids have been found. We studied polymorphism and divergence patterns in 29 different regions throughout the genome, including mtDNA and 3 genes on the Y chromosome, to determine the extent of gene flow between these species. This multilocus approach allowed us to distinguish between forces that should affect some genes (such as introgression) and forces that should act on all genes (such as common ancestry). Our results show that D. yakuba mtDNA has replaced that of D. santomea, and there is detectable introgression for only two nuclear genes, yellow and Salr. The majority of genes, however, have remained distinct. These two species therefore do not conform a « hybrid swarm » in which disruptive selection maintains distinctness for only few traits while the rest of the genome shows substantial introgression. Our data suggest that specific regions of the genome introgress more readily than others and regions linked to genes causing speciesspecific adaptations -like coping to montane conditions- might be limited in their ability to move between species.

Steven Schmidt, Liz Costello, Al Meyer (University of Colorado, USA, steve.schmidt@colorado.edu)
Seasonal dynamics of alpine soil organisms: implications for understanding the functioning of alpine systems

We will review our recent efforts to construct a complete library of rRNA sequences for all below-ground life in alpine tundra meadows in Colorado, USA and Peru. To our knowledge this is the most intensive effort to date to catalogue all soil organisms in one site using molecular techniques. In order not to bias our work towards any one group, we used separate primer sets for the three domains of life: Bacteria, Archaea and Eucarya. In addition we sampled during the three most dynamic periods for microbial activity in alpine systems (under snow, snow melt and summer). Our results demonstrate a staggering diversity of microbial life in these soils. Many of our sequences represent deeply-divergent microbial lineages that have not been previously described. For example, we found 3 new fungal groups that are divergent at the subphylum or class level. We also found that the diversity of microbes changed dramatically on a seasonal basis. Most surprising was our discovery of a large and deeply-divergent group of Ascomycetes that is only detected under the snow or during snow melt. The implications of these seasonal shifts in diversity will be discussed

Jürg Stöcklin (University of Basel, Switzerland, juerg.stoecklin@unibas.ch)
Intraspecific differentiation, adaptation and gene flow at the landscape level in alpine plants

Background and goals: Steep environmental gradients and patchy habitats characterize alpine environments. Life conditions change dramatically with altitude, exposition, snow cover or succession. As a consequence, shifts in selection pressure may lead to local adaptations. Spatial isolation and limited gene flow are the rule for alpine plants, and differentiation may also result from small population size and genetic drift. Furthermore, most alpine areas include cultural landscapes and agricultural land use has considerably added to the natural diversity of alpine habitats. The characteristics of alpine environments are well known but consequences for evolutionary processes are still poorly understood. Material and methods: Molecular studies and common garden experiments with plant species from natural and man-made alpine habitats will be summarized. Particularly, I present effects of altitude and succession on genetic diversity, growth and reproductive traits in species with different life histories, seed dispersal and longevity. Furthermore, adaptations and genetic diversity due to land use in an alpine fodder plant are described. Population differentiation is discussed in relation to gene flow from seed and pollen dispersal. Results and discussion: There is evidence for considerable gene flow among populations of alpine plants. Genetic diversity was found to be generally high, genetic differentiation was not particularly pronounced, but mostly increasing with distance. Results suggest considerable genetic drift among populations of alpine plants. Adaptive trait differentiation was observed due to altitude and as a consequence of different land use. However, selection pressure in contrasting habitats is not always strong enough for pronounced differentiation. Conclusion: Genetic variation in growth and reproduction are common among isolated populations of alpine plants and is shaped by adaptive as well as random evolutionary processes.

Irène Till-Bottraud, Mary Arroyo, Cristian Torres (Université Joseph Fourier, France, irene.till@ujf-grenoble.fr)
Genetic variation in the alpine; linking genetic diversity, breeding system and population dynamics

Do alpine species exhibit different genetic variability patterns than lowland species, and if yes, to what extent? What are the driving forces behind genetic variation in alpine species? The breeding system of species partly determines the level and distribution of genetic diversity by mixing genes through pollen transport and fecundation. However, in plants, the breeding system is in turn conditioned by environmental conditions such as pollinator availability (very low pollinator activity selects for either higher selfing or increased flower attractivity) or flight distance but also by plant longevity: annuals tend to be selfed, while perennials are mostly outcrossed. As elevation increases, pollinator availability decreases, but longevity increases, leading to conflicting hypothesesabout selfing rates and thus genetic diversity. We review literature data addressing these questions and present current research on estimation of genetic variability and outcrossing rates using molecular markers, population dynamics analysis to estimate life history parameters, measure of pollinator activity and floral attractivity. Literature data show that obligate outbreeding systems increase in frequency with elevation on some mountains, but the reverse trend has also been found. Similarly, very few annual species are found in the alpine belt of some mountains, but annuals are much more frequent in others. Additionally, perennial plants can exhibit very different longevities and the pattern is complicated because the level of selfing itself determines some of the life history parameters. The general pattern of level and structure of genetic diversity is thus very complex and varies from massif to massif depending on historical (at the level of flora installation) or climatic factors. Research financed by: ECOS, FONDECYT 1020956, 7020956, ICM P02-051

Richard Winkworth (Yale University, USA, richard.winkworth@yale.edu)
The evolution of alpine plant diversity

In general alpine life zones contain considerable biological diversity; indeed, many biodiversity hotspots are associated with mountainous regions. The evolution of plant diversity in alpine habitats has fascinated botanists for many years and various hypotheses have been suggested to explain contemporary alpine plant diversity. In conjunction with palynological and distributional data, molecular phylogenetic and phylogeographic approaches permit hypotheses about the origins, diversification, and distribution of alpine plant lineages to be tested. Here I review recent studies, using these to explore patterns and processes of evolution in the alpine zone. The floras of different mountain systems appear to have evolved in comparative isolation, with relative diversity reflecting specific differences in the physical and biotic environment. However, taken together molecular, palynological, and distributional data indicate that contemporary patterns of diversity and distribution have arisen recently. Specifically such studies indicate the importance of: (i) migration and/or dispersal during the late Tertiary and Quaternary, and (ii) recent morphological and ecological diversification, perhaps reflecting alpine habitat diversity and/or environmental instability during the Pliocene and Pleistocene. Further, polyploidy and hybridization appear to have been important for alpine plant diversification. Recent studies provide new insights into the evolution of alpine plants; most often suggesting that contemporary patterns have originated recently. Despite advances we are still far from a detailed understanding of evolutionary patterns and processes, however many of the remaining questions also have wider implications.