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The significance of variation in floral traits and mating system for local adaptation in alpine plants
Third-party funded project
Project title The significance of variation in floral traits and mating system for local adaptation in alpine plants
Principal Investigator(s) Stöcklin, Jürg
Project Members Kesselring, Halil
Bichsel, Hannah Noemi
Organisation / Research unit Departement Umweltwissenschaften / Pflanzenökologie (Körner)
Project start 01.04.2015
Probable end 30.09.2016
Status Completed

Alpine biodiversity is particularly rich and the flora of the Alps includes more than five hundred endemic species, i.e. plants unique to a particular mountain region where they have probably evolved. The particular environmental conditions at high elevation required unique plant adaptations, and the richness of endemics is highlighting the strength of selective forces and evolu­t­­­io­­nary processes in the alpine landscape. While patterns of Alpine species diversity are fairly well known, this is less so for intra-specific genetic and phenotypic variability.

It is usually assumed that plants are locally adapted, but how much this is really the case has rarely been rigorously tested. Phenotypic differentiation among populations of alpine plants is abundant. To some degree phenotypic differentiation may be ecologically relevant and adaptive, but it may also result from random evolutionary processes, or from past selection. Clearly, the generality of local adaptation in alpine plants, and how it is influenced by regional climatic conditions, by environmental heterogeneity, or by biotic interactions is insufficiently known.

My recent research focused on the respective importance of genotypic variability and phenotypic plasticity for local adaptation by using reciprocal transplant experiments and QST-FST comparisons, testing the hypothesis that coarse-grained environmental heterogeneity selects for fixed genetic variability, while in response to fine-grained environ­mental heterogeneity natural selection should favour phenotypic plasticity.

In continuity of this research on local adaptation in alpine plants and its underlying functional mechanisms, I propose here two reciprocal transplant experiments that are designed to test the general hypothesis, that population variability in floral traits and mating systems are the result of natural selection and local adaptation, and not only a result of random evolutionary processes. Because of my retirement in Oct. 2016, the duration of this research proposal is 18 month.

We will perform reciprocal transplantations among field sites of populations’ origin to test for local adaptation. We will genotype plants with microsatellites to determine outcrossing rates, which will be related to pollinator activity, and measure key flower and mating system parameters such as autonomous selfing and inbreeding depression in the common garden. The project includes two parts:

(1) The adaptive significance of mating system variability: We will test the particular hypothesis that variation in protandry and flower phenology in mixed-mating populations of Anthyllis vulneraria results from fine-tuning to local conditions, particularly the timing and abundance of pollinator availability. We suggest that protandry evolved to adjust flowers to the optimum degree of out­crossing, determined by inbreeding depression, pollinator service and reproduc­tive insurance. We will use popula­tions of Anthyllis vulneraria from two regions that differ strongly in their degree of protandry and flower phenology. The degree of protandry and the realized outcrossing rates will be measured at population and genotype level and tested for correlations.

(2) The adaptive significance of flower size variability: We will test the hypothesis that populations of Campanula scheuchzeri/rotundifolia are locally adapted to the regional climate, and that variation in flower size (and shape) is an adaptation to pollinator environment at different elevations within regions. We suggest that larger flowers evolved to better attract scarce pollinators or to fit better the particular pollinators at higher elevation. We will use twelve populations in total, one each from four different elevations in three regions, and test for local adaptation in general, local adaptation across elevation, and local adaptation across regions. The strength of current natural selection on flower size will be measured at each site using selection gradient analysis.

This project will contribute to knowledge on fundamental, but still insufficiently understood questions of evolutionary biology. It will reveal the general degree of local adaptation, and the specific degree to which variability in flower size across elevation in Campanula and in protandry and flower phenology in Anthyllis is due to local adaptation. Such knowledge will add to the understanding of how alpine plants will be able to respond to global change and will thereby contribute to urgent conservation issues.

Financed by Swiss National Science Foundation (SNSF)

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