CONTENS - International Organization of Plant Biosystematists

ECOLOGICAL FACTORS IN PLANT EVOLUTION
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Population differentiaton, local adaptation and gene flow in the
alpine landscape
Jürg Stöcklin
Botanical Institute, University of Basel, Schönbeinstrasse 6, CH-4056 Basel,
Switzerland. E-mail: juerg.stoecklin@unibas.ch
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 are to be expected.
Spatial isolation and limited gene flow are the rule for alpine plants, and
differentiation might also result from small population size and genetic drift.
Furthermore, most alpine areas include cultural landscapes; 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. Here I present case studies of alpine plant species to
answer the following general questions. Does genetic diversity decrease with
altitude? How is genetic diversity distributed within and among populations and by
what factors is it affected? How important is population differentiation in important
liefe history traits? Is selection pressure strong enough for pronounced adaptation
along ecological gradients? Genetic diversity was found to be generally high, and
genetic differentiation was not particularly pronounced, but increasing with
geographic distance in all studied cases. Results suggest considerable genetic drift
among populations of alpine plants, but it is not high enough to mask genetic imprints
of glacial history. Adaptive trait differentiation was observed due to altitude and as a
consequence of different land use. Selection pressure in contrasting habitats is not
always strong enough for pronounced differentiaton. Factors like land use or local
conditions may override altitude. To conclude: 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. Plasticity in growth and
reproduction help plants to survive in the alpine landscape.
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