Drivers of genetic differentiation and recent evolutionary history of an Eurasian wild pea

Aim: Genetic diversity is a major determinant for the capacity of species to persist and adapt to their environments. Unravelling the factors affecting genetic differentiation is crucial to understand how genetic diversity is shaped and species may react to changing environments. We investigated the drivers of genetic differentiation and their interplay with the evolutionary history in a wild pea to test how those may have affected the distribution of genetic diversity. Location: Mediterranean basin, western Asia. Taxon: Pisum sativum (Fabaceae). Methods: We employed restriction site associated DNA (RAD) sequencing of a collection of 81 wild pea samples. The influence of environmental factors on genetic differentiation was tested by estimating the association of these factors and genetic variation using gradient forest analysis. Stairwayplots were used to estimate past effective population sizes and clines of allele frequencies were analysed to detect past expansion patterns. Association of single nucleotide polymorphisms with environmental variables was tested to find signatures of local adaptation. Results: The effect of the tested factors influencing genetic differentiation was variable among genetic clusters. Climate predictors were most important in all clusters. Land cover was more important in clusters from areas strongly influenced by human land use. We found statistically significant associations of 3623 SNPs with environmental variables. Most of these SNPs were correlated with latitude followed by temperature. Wild peas went through a genetic bottleneck during the last glacial period followed by population recovery. The detected range expansion patterns suggested an eastward range expansion of the European cluster to Turkey and thereof southwards and eastwards. Main conclusion: Drivers of genetic differentiation do not act in a uniform manner within a species. The distribution of genetic variation and the processes affecting this distribution have to be viewed in the context of the hierarchical structure of genetic variation and the environment of its entities to understand how genetic diversity was shaped and may change in the future.