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Understanding the natural history of model organisms is important for the effective use of their genomic resourses. Arabidopsis lyrata has emerged as a useful plant for studying ecological and evolutionary genetics, based on its extensive natural variation, sequenced genome and close relationship to A. thaliana. We studied genetic diversity across the entire range of European Arabidopsis lyrata ssp. petraea, in order to explore how population history has influenced population structure. We sampled multiple populations from each region, using nuclear and chloroplast genome markers, and combined population genetic and phylogeographic approaches. Within-population diversity is substantial for nuclear allozyme markers (mean P=0.610, Ae=1.580, He=0.277) and significantly partitioned among populations (FST=0.271). The Northern populations have modestly increased inbreeding (FIS=0.163 verses FIS=0.093), but retain comparable diversity to central European populations. Bottlenecks are common among central and northern Europe populations, indicating recent demographic history as a dominant factor in structuring the European diversity. Although the genetic structure was detected at all geographic scales, two clear differentiated units covering northern and central European areas (FCT =0.155) were identified by Bayesian analysis and supported by regional pairwise FCT calculations. A highly similar geographic pattern was observed from the distribution of chloroplast haplotypes, with the dominant northern haplotypes absent from central Europe. We conclude A. l. petraea's cold-tolerance and preference for disturbed habitats enabled glacial survival between the alpine and Nordic glaciers in central Europe and an additional cryptic refugium. While German populations are probable peri-glacial leftovers, Eastern Austrian populations have diversity patterns possibly compatible with longer-term survival. [ABSTRACT FROM AUTHOR]

Species colonizing new areas disjunct from their original habitat may be subject to novel selection pressures, and exhibit adaptive genetic changes. However, if colonization occurs through a small number of founders, the genetic composition of the colonized population may differ from that of the original population simply due to genetic drift. Disentangling the effects of founder drift and selection after colonization is crucial to understanding the adaptive process. Drosophila buzzatii colonized Australia some 600–700 generations ago, and spread rapidly over a wide geographical range. Genetic variation for 15 microsatellite loci in each of nine populations in eastern Australia was used to estimate the size of the bottleneck, and to determine if any of these microsatellites marked genomic regions subject to recent selection. We estimate that on its introduction to Australia, D. buzzatii went through a moderate bottleneck (approximately 30–40 founders). Linkage disequilibrium was common, both intrachromosomal and between loci on different chromosomes. Of the 15 loci, 2 showed evidence of selection, one exhibiting local adaptation in different populations and the other balancing selection. We conclude that linkage disequilibria may be far more common in natural populations than is generally assumed, and the loci apparently affected by selection may well be marking selection in large genome regions including many loci that are not necessarily closely linked.Heredity (2009) 102, 389–401; doi:10.1038/hdy.2008.127; published online 14 January 2009 [ABSTRACT FROM AUTHOR]

Undoubtedly, viruses represent a major threat faced by human and veterinary medicines and by agronomy. The rapid evolution of viruses enables them to escape from natural immunities and from state-of-the-art antiviral treatments, with new viruses periodically emerging with deadly consequences. Viruses have also become powerful and are increasingly used tools in the field of experimental evolution. A growing body of evidence points that the evolution of viruses is mainly determined by key features such as their compacted genomes, enormous population sizes, and short generation times. In addition, RNA viruses also present large selection coefficients, antagonistic epistasis, and high mutation rates. Most of this knowledge comes from studies that have used either bacteriophages or animal viruses in cell cultures as experimental systems. However, plant viruses provide almost identical advantages for evolutionary studies and, in addition, offer an invaluable tool for studying the interplay between viruses and pluricellular hosts. Without seeking to be exhaustive, here we summarize some peculiarities of plant viruses and review recent experiments that have explored important questions on evolution, such as the role of deleterious mutation and neutrality, the effect of different transmission modes in the evolution of virulence, and the heterogeneous selective constraints imposed by multiple hosts.Heredity (2008) 100, 478–483; doi:10.1038/sj.hdy.6801088; published online 6 February 2008 [ABSTRACT FROM AUTHOR]

Detailed studies suggest that the level of inbreeding depression may vary between populations. In a study of Scots pine from Finland, the level of inbreeding depression was much lower in northern than in southern populations. We have examined theoretically whether population genetic factors, such as the level of selfing, intensity of selection against heterozygotes or homozygotes, level of mutation, a bottleneck, finite population size, or the level of polyembryony could account for this difference. Higher selfing or stronger selection against heterozygotes in the north, both at biologically reasonable levels, appear to produce changes consistent with the observed differences and we consider these to be the most likely explanations. In addition, the differences could have accumulated by these mechanisms over the age of the northern population, ≈100 generations. Finally, the differences generated by these factors could still be maintained in the face of reasonable levels of gene flow from the south. Such a comprehensive theoretical investigation of this example has given some general insight into the potential influence of these evolutionary factors on the level of inbreeding depression and provides an approach that could be used to understand similar phenomena in other examples. [ABSTRACT FROM AUTHOR]

The genetic architectures of four morphometric traits in the housefly, Musca domestica L., were analysed using a paternal half-sib design on a large outbred base population and on two populations each established with two pairs of flies from the base population. By including parents with the offspring in the analysis, phenotypic variance was subdivided into components for additive, dominance, additive-by-additive epistasis and environmental variation. In relation to the nonbottlenecked base population, narrow sense hertitability was lower in the bottlenecked populations, largely because of an increase in the level of the environmental component of variance. Averaged over the four traits in the nonbottlenecked base population, nonadditive components contributed nearly 60 per cent of the phenotypic variance, with more than half of this being attributable to epistasis. Two of the four traits showed reduced additive genetic variance in the bottlenecked lines, whereas two of the traits showed increased additive genetic variance. A major difference in the genetic architecture between traits showing these two disparate bottleneck effects was the presence of epistasis in the nonbottlenecked base population for the traits which showed an increase in the additive component. Overall, there was a significant positive relationship between the initial percentage contribution of epistasis in the base population and the gain in the additive component in the bottleneck lines, as predicted by models incorporating additive-by-additive epistasis. [ABSTRACT FROM AUTHOR]