ORAL PRESENTATION: Geographic and environmental determinants of neutral and adaptive genomic variation in Swiss stone pine

Submitted by : Fady Bruno
Abstract type : Oral presentation
Session type : Conference session 3: CONSERVING and USING GENETIC DIVERSITY
Author Speaker : Christian Rellstab

Information about other authors :

Christian Rellstab, WSL Swiss Federal Research Institute, Switzerland

Rafael O. Wüest, WSL Swiss Federal Research Institute, Switzerland

Sabine Brodbeck, WSL Swiss Federal Research Institute, Switzerland

Stefan Zoller, Genetic Diversity Centre (GDC), ETH Zurich, Switzerland

Martin C. Fischer, Institute of Integrative Biology (IBZ), ETH Zurich, Switzerland

Rolf Holderegger, WSL Swiss Federal Research Institute, Switzerland and Institute of Integrative Biology (IBZ), ETH Zurich, Switzerland

Felix Gugerli, WSL Swiss Federal Research Institute, Switzerland

Benjamin Dauphin, WSL Swiss Federal Research Institute, Switzerland

Abstract :

Disentangling the factors that govern the distribution of genetic diversity is crucial to set measures for conserving species genetic diversity. It is generally accepted that the distribution of neutral genetic diversity of a species mostly depends, among other factors, on effective population size, the degree of population fragmentation (i.e. gene flow), geographic position (i.e. peripherality/centrality) within its native range, and habitat suitability within its ecological niche. However, it remains unclear to what degree genetic diversity at neutral and adaptive loci correlates with geographic peripherality or habitat suitability. Using range-wide distribution maps and exome-based genomic data, we first tested whether geographic peripherality explains population genetic diversity at >17,000 neutral and adaptive SNPs in 24 Alpine populations (480 individuals) of Pinus cembra, a keystone species of the timberline ecotone. To define neutral and adaptive SNP sets, we used various approaches (gene diversity estimates, FST outlier test, and environmental association analysis) that identify signatures of selection. We then established ecological niche models for the study species and investigated the relationship between habitat suitability and genetic diversity at both neutral and adaptive loci. Our results show that geographic peripherality and habitat suitability were not highly correlated. Various estimates of neutral genetic diversity decreased with geographic peripherality, but were usually not correlated with habitat suitability. In contrast, genetic diversity (He) declined with increasingly suitable conditions at loci showing a strong signal for positive selection based on Tajima’s D. Our results suggest that populations at the edge of the geographic distribution harbor less neutral genetic diversity due to small population sizes and restricted gene flow. Moreover, we argue that populations from highly suitable habitats already went through strong selection processes, are adapted to local conditions, and therefore exhibit reduced genetic diversity at adaptive loci compared to populations at the niche edge. Our findings provide new insights into the relationships between adaptive genetic variation, geographic position, and habitat suitability, and on spatial patterns of adaptive genetic variation. We discuss the importance of disentangling neutral and adaptive genetic variation to better refine a species’ adaptive capacity. This is highly important for conservation projects in which forest and conservation managers or other stakeholders need reliable estimates of population genetic diversity for drawing recommendations in the context of environmental change.

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Keywords : conifers, environmental association analysis, exome capture, genetic diversity, geographic peripherality, habitat suitability, outlier test, Pinus cembra
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