Abstract
Background and Aims The effects of habitat fragmentation on quantitative genetic variation in plant populations are still poorly known. Saxifraga sponhemica is a rare endemic of Central Europe with a disjunct distribution, and a stable and specialized habitat of treeless screes and cliffs. This study therefore used S. sponhemica as a model species to compare quantitative and molecular variation in order to explore (1) the relative importance of drift and selection in shaping the distribution of quantitative genetic variation along climatic gradients; (2) the relationship between plant fitness, quantitative genetic variation, molecular genetic variation and population size; and (3) the relationship between the differentiation of a trait among populations and its evolvability.Methods Genetic variation within and among 22 populations from the whole distribution area of S. sponhemica was studied using RAPD (random amplified polymorphic DNA) markers, and climatic variables were obtained for each site. Seeds were collected from each population and germinated, and seedlings were transplanted into a common garden for determination of variation in plant traits.Key Results In contrast to previous results from rare plant species, strong evidence was found for divergent selection. Most population trait means of S. sponhemica were significantly related to climate gradients, indicating adaptation. Quantitative genetic differentiation increased with geographical distance, even when neutral molecular divergence was controlled for, and QST exceeded FST for some traits. The evolvability of traits was negatively correlated with the degree of differentiation among populations (QST), i.e. traits under strong selection showed little genetic variation within populations. The evolutionary potential of a population was not related to its size, the performance of the population or its neutral genetic diversity. However, performance in the common garden was lower for plants from populations with reduced molecular genetic variation, suggesting inbreeding depression due to genetic erosion.Conclusions The findings suggest that studies of molecular and quantitative genetic variation may provide complementary insights important for the conservation of rare species. The strong differentiation of quantitative traits among populations shows that selection can be an important force for structuring variation in evolutionarily important traits even for rare endemic species restricted to very specific habitats.
Highlights
Selection, drift and gene flow shape genetic variation within and among natural populations and their study is important for conservation and evolutionary biology (Merilaand Crnokrak, 2001; Leinonen et al, 2008, 2013)
We found that selection has strongly influenced the variation in quantitative traits within and among populations of S. sponhemica
Our results indicate that selection can be an important force for structuring variation in evolutionarily important traits even for rare endemic species restricted to very specific habitats, if climatic conditions vary
Summary
Drift and gene flow shape genetic variation within and among natural populations and their study is important for conservation and evolutionary biology (Merilaand Crnokrak, 2001; Leinonen et al, 2008, 2013). Plants in small and isolated populations often have a lower performance than those in larger, interconnected populations due to increased inbreeding (Ellstrand and Elam, 1993; Fischer and Matthies, 1998; Kery and Matthies, 2004) They have lower levels of genetic variation, limited evolutionary potential (Schemske et al, 1994; Young et al, 1996; Willi et al, 2006; Aguilar et al, 2008; Weber and Kolb, 2014) and they are more strongly threatened by random environmental fluctuations (Matthies et al, 2004). This study used S. sponhemica as a model species to compare quantitative and molecular variation in order to explore (1) the relative importance of drift and selection in shaping the distribution of quantitative genetic variation along climatic gradients; (2) the relationship between plant fitness, quantitative genetic variation, molecular genetic variation and population size; and (3) the relationship between the differentiation of a trait among populations and its evolvability
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