Break zones in the distributions of alleles and species in alpine plants

Abstract

Aim We test for the congruence between allele-based range boundaries (break zones) in silicicolous alpine plants and species-based break zones in the silicicolous flora of the European Alps. We also ask whether such break zones coincide with areas of large elevational variation.Location The European Alps.Methods On a regular grid laid across the entire Alps, we determined areas of allele-and species-based break zones using respective clustering algorithms, identifying discontinuities in cluster distributions (breaks), and quantifying integrated break densities (break zones). Discontinuities were identified based on the intra-specific genetic variation of 12 species and on the floristic distribution data from 239 species, respectively. Coincidence between the two types of break zones was tested using Spearman's correlation. Break zone densities were also regressed on topographical complexity to test for the effect of elevational variation. ResultsWe found that two main break zones in the distribution of alleles and species were significantly correlated. Furthermore, we show that these break zones are in topographically complex regions, characterized by massive elevational ranges owing to high mountains and deep glacial valleys. We detected a third break zone in the distribution of species in the eastern Alps, which is not correlated with topographic complexity, and which is also not evident from allelic distribution patterns. Species with the potential for long-distance dispersal tended to show larger distribution ranges than short-distance dispersers.Main conclusions We suggest that the history of Pleistocene glaciations is the main driver of the congruence between allele-based and species-based distribution patterns, because occurrences of both species and alleles were subject to the same processes (such as extinction, migration and drift) that shaped the distributions of species and genetic lineages. Large elevational ranges have had a profound effect as a dispersal barrier for alleles during post-glacial immigration. Because plant species, unlike alleles, cannot spread via pollen but only via seed, and thus disperse less effectively, we conclude that species break zones are maintained over longer time spans and reflect more ancient patterns than allele break zones.

Phylogeography of Alpine populations of Rhytidium rugosum (Bryophyta) in a European context

“…The regional populations A-C in the Alps are similar to each other and differ from population D based on both haplotype and nucleotide data. The differentiation between A-C and D coincides approximately with the eastern major break zone for flowering plants around the Adige valley (Thiel-Egenter et al 2011). Thus, the pattern found for Rhytidium in the east is consistent with the hypothesis that break zones of spore-dispersed organisms should mirror those of genotype patterns in flowering plants.…”

“…More break zones exist at the species compared with the genotype level among flowering plants, due to differences in dispersal potential between species (dispersed by seeds) and genotypes (by pollen and seeds). Two major break zones where species and genotype patterns coincide occur around the Aoste valley in the west and around the Adige valley in the east (Thiel-Egenter et al 2011).…”

“…Many flowering plant species of the Alps seem not yet to have colonized all potential habitats due to limited dispersal abilities (Dullinger et al 2012;Schönswetter et al 2005). Where environmental conditions hinder efficient dispersal of species or intraspecific entities of different origins, break zones are found where the turnover in species and/or genotypes within species is markedly higher than elsewhere (Thiel-Egenter et al 2011). More break zones exist at the species compared with the genotype level among flowering plants, due to differences in dispersal potential between species (dispersed by seeds) and genotypes (by pollen and seeds).…”

“…Several recent studies concerned plants, especially flowering plants, in the European Alps (from here on called 'the Alps') (e.g. Gugerli and Holderegger 2001;Schönswetter et al 2005;Thiel-Egenter et al 2011). Source populations for late-to post-glacial colonization of the Alps by plants occurred in glacial refugia in the lowlands, often along the margins of the glaciated area, or on nunataks within the ice shield, and the molecular evidence for such refugia was summarized by Schönswetter et al (2005).…”

Integrating a Population Genomics Focus into Biogeographic and Macroecological Research

“…By simultaneously studying biogeographic species patterns and population genetic data, these authors gained novel insights into the processes structuring patterns of spatial diversity. Other studies combining genetic with biogeographic and/or macroecological data have made similar advances in inferring the processes underlying spatial diversity (e.g., Bonada et al, 2009;Thiel-Egenter et al, 2011;Eldon et al, 2013).…”