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It is commonly found that individual hybrid, polyploid species originate recurrently and that many polyploid species originated relatively recently. It has been previously hypothesized that the extremely rare allopolyploid peat moss Sphagnum troendelagicum has originated multiple times, possibly after the last glacial maximum in Scandinavia. This conclusion was based on low linkage disequilibrium in anonymous genetic markers within natural populations, in which sexual reproduction has never been observed. Here we employ microsatellite markers and chloroplast DNA (cpDNA)-encoded trnG sequence data to test hypotheses concerning the origin and evolution of this species. We find that S. tenellum is the maternal progenitor and S. balticum is the paternal progenitor of S. troendelagicum. Using various Bayesian approaches, we estimate that S. troendelagicum originated before the Holocene but not before c. 80 000 years ago (median expected time since speciation 40 000 years before present). The observed lack of complete linkage disequilibrium in the genome of this species suggests cryptic sexual reproduction and recombination. Several lines of evidence suggest multiple origins for S. troendelagicum, but a single origin is supported by approximate Bayesian computation analyses. We hypothesize that S. troendelagicum originated in a peat-dominated refugium before last glacial maximum, and subsequently immigrated to central Norway by means of spore flow during the last thousands of years. [ABSTRACT FROM AUTHOR]

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]

Patterns of codon usage bias were studied in the moss model species Physcomitrella patens. A total of 92 nuclear, protein coding genes were employed, and estimated levels of gene expression were tested for association with two measures of codon usage bias and other variables hypothesized to be associated with gene expression. Codon bias was found to be positively associated both with estimated levels of gene expression and GC content in the coding parts of studied genes. However, GC content in noncoding parts, that is, introns and 5'and 3'untranslated regions (UTRs), was not associated with estimated levels of gene expression. It is argued that codon bias is not shaped by mutational bias, but rather by weak natural selection for translational efficiency in P. patens. The possible role of life history characteristics in shaping patterns of codon usage in this species is discussed.Heredity (2005) 94, 87-93. doi:10.1038/sj.hdy.6800547 Published online 13 October 2004 [ABSTRACT FROM AUTHOR]