Title Spatial isolation and genetic differentiation in naturally fragmented alpine plant populations of the Swiss Alps
Author/s Patrick Kuss, Andrea R. Pluess, Hafdís Hanna Ægisdóttir, and Jürg Stöcklin
Year 2008
Journal Journal of Plant Ecology 1: 149-159
Abstract Aims: The effect of anthropogenic landscape fragmentation on the genetic diversity and adaptive potential of plant populations is a major issue in conservation biology. However, little is known about the partitioning of genetic diversity in alpine species which occur in naturally fragmented habitats. Here, we investigate molecular patterns of three Alpine plants (Epilobium fleischeri, Geum reptans, Campanula thyrsoides) across Switzerland and ask whether spatial isolation has led to high levels of population differentiation, increasing over distance, and to a decrease of within-population variability. We further hypothesize that the contrasting potential for long-distance (LDD) seed dispersal in these species will considerably influence and explain diversity partitioning.
Methods: For each study species we sampled 20-23 individuals from each of 20-32 populations across entire Switzerland. We applied RAPD markers to assess genetic diversity within (Nei’s expected heterozygosity, He, percentage of polymorphic bands, Pp) and among (AMOVA, Fst) populations and correlated population size and altitude with within population diversity. Spatial patterns of genetic relatedness were investigated using Mantel tests and standardized major axis regression as well as UPGMA cluster analyses and Monmonier's algorithm. To avoid known biases we standardized the numbers of populations, individuals and markers using multiple random reductions. We modelled LDD with a high alpine wind data set using the terminal velocity and height of seed release as key parameters. Additionally we assessed a number of important life-history traits and factors that potentially influence genetic diversity partitioning (e.g. breeding system, longevity, population size).
Main findings: For all three species we found a significant isolation-by-distance relationship but only a moderately high differentiation among populations (Fst: 22.7 %, 14.8 %, 16.8 %, for E. fleischeri, G. reptans and C. thyrsoides respectively). Within-population diversity (He: 0.19-0.21, Pp: 62-75 %) was not reduced in comparison to known results from lowland species and even small populations with less than 50 reproductive individuals contained high levels of genetic diversity. We further found no indication that a high long-distance seed dispersal potential enhances genetic connectivity among populations. Gene flow seems to have a strong stochastic component causing large dissimilarity between population pairs irrespective of the spatial distance. Our results suggest that other life-history traits, especially the breeding system, may play an important role in genetic diversity partitioning. We conclude that spatial isolation in the alpine environment has a strong influence on population relatedness but that a number of factors can considerably influence the strength of this relationship.
Keywords Campanula thyrsoides, Epilobium fleischeri, Geum reptans, isolation by distance, life-history traits, molecular diversity
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