Abstract
The island-like distribution of subalpine habitats across mountain ranges can trigger the parallel evolution of locally adapted ecotypes. Such naturally replicated scenarios allow testing hypotheses on how elevational differentiation structures genetic diversity within species. Nevertheless, the parallel colonization of subalpine habitats across different mountain ranges has only rarely been documented with molecular data. We chose Primula elatior (Primulaceae), naturally spanning entire elevation range in multiple mountain regions of central Europe, to test for the origin of its scattered subalpine populations. Nuclear microsatellite variation revealed three genetic groups corresponding with the distinct study regions. We found that genetic differentiation between foothill and subalpine populations within each region was relatively low, suggesting that the colonization of subalpine habitats occurred independently within each mountain range. Furthermore, the strongest differentiation was usually found between the subalpine populations suggesting that mountain ridges may act as migration barriers that can reduce gene flow more strongly than elevational differences between foothill and subalpine populations. Finally, we found that subalpine colonization did not result in a loss of genetic diversity relative to foothill populations in agreement with the high migration rates that we document here between the subalpine and the foothill populations. In summary, our study shows subalpine Primula elatior populations are genetically diverse and distinct results of parallel colonization events from multiple foothill gene pools.
Highlights
Alpine and subalpine habitats represent challenging and often unpredictable environments for plants
We address the genetic consequences of elevational differentiation in Primula elatior (Primulaceae), a species with broad ecological preferences including a large elevational range in several mountain ranges in Europe[24]
We explored the genetic structure of P. elatior populations across the three target mountain ranges, where it occupies both foothill and subalpine habitats, using Bayesian clustering, distance networks (Neighbor-joining networks), and ordinations
Summary
Alpine and subalpine habitats represent challenging and often unpredictable environments for plants. The restriction of gene flow between lower and higher elevations as well as the reduction or absence of gene flow among mountain ridges can lead to the accumulation of reproductive barriers and/or hybrid incompatibilities[9] This process is but one of several potential explanations for relatively high species diversity in alpine/subalpine habitats throughout the world[10]. The influence of habitat differentiation on the genetic diversity of populations has been previously studied mainly at lower elevations[16,17,18] It is poorly known how the colonization of alpine/subalpine h abitats has shaped the genetic diversity of populations, but it is hypothesized that alpine/subalpine populations would be genetically depauperate relative to lowland populations due to the effects of genetic bottleneck, genetic drift, reduced gene flow, and habitat fragmentation[19], all of which can promote the genetic isolation of alpine/subalpine populations from their foothill relatives[20]. Our assumption of upslope colonization is likely because temperate species are highly unlikely to have survived past glaciations that affected these subalpine habitats[30]
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