Stable version is available from CRAN: http://cran.r-project.org/. Development version is available from the R-forge repository: http://r-forge.r-project.org/projects/rehh. Both versions can be installed directly from R. Function documentation and example data files are provided within the package and a tutorial is available as Supplementary Material. rehh is distributed under the GNU General Public Licence (GPL ≥ 2).

Bottlenecks in population size can reduce fitness and evolutionary potential, yet introduced species often become invasive. This poses a dilemma referred to as the genetic paradox of invasion. Three characteristics must hold true for an introduced population to be considered paradoxical in this sense. First, it must pass through a bottleneck that reduces genetic variation. Second, despite the bottleneck, the introduced population must not succumb to the many problems associated with low genetic variation. Third, it must adapt to the novel environment. Some introduced populations are not paradoxical as they do not combine these conditions. In some cases, an apparent paradox is spurious, as seen in introduced populations with low diversity in neutral markers that maintain high genetic variation in ecologically relevant traits. Even when the genetic paradox is genuine, unique aspects of a species' biology can allow a population to thrive. We propose research directions into remaining paradoxical aspects of invasion genetics.

Rapid phenotypic evolution of quantitative traits can occur within years, but its underlying genetic architecture remains uncharacterized. Here we test the theoretical prediction that genes with intermediate pleiotropy drive adaptive evolution in nature. Through a resurrection experiment, we grew Arabidopsis thaliana accessions collected across an 8-year period in six micro-habitats representative of that local population. We then used genome-wide association mapping to identify the single-nucleotide polymorphisms (SNPs) associated with evolved and unevolved traits in each micro-habitat. Finally, we performed a selection scan by testing for temporal differentiation in these SNPs. Phenotypic evolution was consistent across micro-habitats, but its associated genetic bases were largely distinct. Adaptive evolutionary change was most strongly driven by a small number of quantitative trait loci (QTLs) with intermediate degrees of pleiotropy; this pleiotropy was synergistic with the per-trait effect size of the SNPs, increasing with the degree of pleiotropy. In addition, weak selection was detected for frequent micro-habitat-specific QTLs that shape single traits. In this population, A. thaliana probably responded to local warming and increased competition, in part mediated by central regulators of flowering time. This genetic architecture, which includes both synergistic pleiotropic QTLs and distinct QTLs within particular micro-habitats, enables rapid phenotypic evolution while still maintaining genetic variation in wild populations.

Central Africa is currently peopled by numerous sedentary agriculturalist populations neighboring the largest group of mobile hunter-gatherers, the Pygmies [1-3]. Although archeological remains attest to Homo sapiens' presence in the Congo Basin for at least 30,000 years, the demographic history of these groups, including divergence and admixture, remains widely unknown [4-6]. Moreover, it is still debated whether common history or convergent adaptation to a forest environment resulted in the short stature characterizing the pygmies [2, 7]. We genotyped 604 individuals at 28 autosomal tetranucleotide microsatellite loci in 12 nonpygmy and 9 neighboring pygmy populations. We found a high level of genetic heterogeneity among Western Central African pygmies, as well as evidence of heterogeneous levels of asymmetrical gene flow from nonpygmies to pygmies, consistent with the variable sociocultural barriers against intermarriages. Using approximate Bayesian computation (ABC) methods [8], we compared several historical scenarios. The most likely points toward a unique ancestral pygmy population that diversified approximately 2800 years ago, contemporarily with the Neolithic expansion of nonpygmy agriculturalists [9, 10]. Our results show that recent isolation, genetic drift, and heterogeneous admixture enabled a rapid and substantial genetic differentiation among Western Central African pygmies. Such an admixture pattern is consistent with the various sociocultural behaviors related to intermariages between pygmies and nonpygmies.