‘Sax‐sess’— genetics of primary succession in a pioneer species on two parallel glacier forelands

Abstract

The primary succession on glacier forelands is characterized by a sequence of early and late successional species, but whether there is also a chronosequence at the intraspecific, genetic level is a matter of debate. Two opposing hypotheses differ in their prediction of genetic diversity in colonizing populations due to founder effects and postcolonization gene immigration. The development of genetic diversity in the pioneer Saxifraga aizoides was investigated along a successional gradient on two parallel glacier forelands, in order to test whether populations from older successional stages were less genetically diverse than populations from younger successional stages, and to locate the sources of the propagules that originally colonized new glacier foreland. Genetic diversity was determined with amplified fragment length polymorphisms, and potential sources of colonizing propagules were assessed via assignment tests. Our results indicate considerable postcolonization gene flow among populations on glacier forelands, since population differentiation was low and genetic diversity within populations was significantly higher. Molecular diversity and differentiation of populations did not develop linearly. Dispersal events within the glacier foreland, from the adjacent valley slopes, and from parallel glacier valleys were identified. In summary, it seems that the colonization of glacier forelands in the European Alps is highly dynamic and stochastic.

Contrasting genetic diversity and differentiation of populations of two successional stages in a Neotropical pioneer tree (Eremanthus erythropappus, Asteraceae)

“…The two indices used to estimate within population diversity in the two successional stages were concordant, and none indicated differences in degree of genetic diversity between populations from "candeial" and populations from forest. These results do not support the hypothesis that the selection of genotypes during succession leads to genetic depletion (Gray, 1987), but they are in accordance with several other studies indicating that populations maintain equal levels of intra-populational genetic diversity during succession (Aarssen and Turkington, 1985;Hartnett et al, 1987;Peroni, 1994;Pluess and Stöcklin, 2004;Solé et al, 2004;Goulart et al, 2005;Raffl et al, 2006). These results suggest that if an increase in selection intensity occurred during succession it did not result in a decrease in genetic diversity or that the selection effect was balanced by other factors, such as gene flow.…”

“…However, in evaluating within same species, we did not detect higher significant differentiation among H. erythropappus populations from an early successional stage in relation to that among populations from middle successional one. Differentiation among colonizing populations depends on the type of colonization (one versus several source populations) and the amount of post-colonizing recurrent gene flow, as reviewed by Raffl et al (2006). Considering the spatial proximity among "candeial" populations studied here, gene flow among them can be considerable, and thus "candeial" populations must receive genes from different sources (populations).…”

Genetic and morphological diversity in <i>Armeria</i> (Plumbaginaceae) is shaped by glacial cycles in Mediterranean refugia

“…The genetic diversity values of Armeria filicaulis subsp. nevadensis and A. splendens also decrease with increasing altitude, an effect observed in alpine plants during the colonization of glacier forelands along the successional series following ice retreat (Raffl & al., 2006). Another possible explanation for the low genetic diversity of A. splendens and A. filicaulis, as compared with A. villosa subsp.…”

Land ahead: using genome scans to identify molecular markers of adaptive relevance

“…(Photo location: Aletsch, Switzerland.) scales in alpine plants (Raffl et al 2006(Raffl et al , 2008 are more frequent and wide-ranging than hitherto thought. Now, we also have the tools to determine the adaptive potential of arctic and alpine species using genome scans in a landscape genomic set-up (Bonin et al 2007b) along with selection experiments.…”