Genetic heterogeneity underlying variation in a locally adaptive clinal trait in Pinus sylvestris revealed by a Bayesian multipopulation analysis.

Local adaptation is a common feature of plant and animal populations. Adaptive phenotypic traits are genetically differentiated along environmental gradients, but the genetic basis of such adaptation is still poorly known. Genetic association studies of local adaptation combine data over populations. Correcting for population structure in these studies can be problematic since both selection and neutral demographic events can create similar allele frequency differences between populations. Correcting for demography with traditional methods may lead to eliminating some true associations. We developed a new Bayesian approach for identifying the loci underlying an adaptive trait in a multipopulation situation in the presence of possible double confounding due to population stratification and adaptation. With this method we studied the genetic basis of timing of bud set, a surrogate trait for timing of yearly growth cessation that confers local adaptation to the populations of Scots pine (Pinus sylvestris). Population means of timing of bud set were highly correlated with latitude. Most effects at individual loci were small. Interestingly, we found genetic heterogeneity (that is, different sets of loci associated with the trait) between the northern and central European parts of the cline. We also found indications of stronger stabilizing selection toward the northern part of the range. The harsh northern conditions may impose greater selective pressure on timing of growth cessation, and the relative importance of different environmental cues used for tracking the seasons might differ depending on latitude of origin.

Mixtures of Bose gases confined in a ring potential.

The rotational properties of a mixture of two distinguishable Bose gases that are confined in a ring potential provide novel physical effects that we demonstrate in this study. Persistent currents are shown to be stable for a range of the population imbalance between the two components at low angular momentum. At higher values of the angular momentum, even small admixtures of a second species of atoms make the persistent currents highly fragile.

Energy gaps and interaction blockade in confined quantum systems.

We investigate universal properties of strongly confined particles that turn out to be dramatically different from what is observed for electrons in atoms and molecules. For a large class of harmonically confined systems, such as small quantum dots and optically trapped atoms, many-body particle addition and removal energies, and energy gaps, are accurately obtained from single-particle eigenvalues. Transport blockade phenomena are related to the derivative discontinuity of the exchange-correlation functional. This implies that they occur very generally, with Coulomb blockade being a particular realization of a more general phenomenon. In particular, we predict a van der Waals blockade in cold atom gases in traps.

Genotype-environment interactions in pollen competitive ability in an anemophilous tree, Betula pendula Roth.

This study describes genotype-environment interactions in pollen competitive ability expressed as pollen-tube growth rate and seed-siring success in Betula pendula Roth. A factorial crossing design was applied using the same maternal and paternal clones in two different environmental conditions, in a B. pendula seed orchard established in a greenhouse and at an outdoor clone collection. Both single donor and two-donor pollinations were employed. Female inflorescences were collected after a fixed time of germination, pollen-tube lengths were measured for each cross, and paternity of the seeds sired by two-donor pollen mixtures was analyzed using isozyme markers. The pollination site had a significant influence on pollen-tube growth rate and seed-siring success. Significant interactions between pollination site and pollen donor indicated genotype-environment interactions in pollen-tube growth rate and seed-siring success. A highly significant positive correlation between pollen-tube growth rate and seed-siring success was found in the greenhouse but not at the outdoor clone collection. These results suggest that the pollen-tube growth rate can be a predictor of seed-siring success in controlled greenhouse conditions, where differences among maternal plants are mainly of genetic origin, but not in more heterogeneous outdoor conditions. In natural birch stands, environmental maternal effects probably diminish the significance of pollen competition for sexual selection in Betula pendula. At seed orchards, the effects of environmental conditions on pollen competitive ability can have important consequences for the genetic composition of the seed crop.

Factors influencing the extent of inbreeding depression: an example from scots pine

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, approximately 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.

Evolution of microsatellites in Arabis petraea and Arabis lyrata, outcrossing relatives of Arabidopsis thaliana.

We examined microsatellite variation in two diploid, outcrossing relatives of Arabidopsis thaliana, Arabis petraea and Arabis lyrata. The primer sequences were derived from A. thaliana. About 50% (14 loci) of the A. thaliana primers could successfully amplify microsatellites in the related species. Analysis of microsatellite structure in the related species showed that there had been large changes in the microsatellites: there were large differences in repeat numbers and many of the A. thaliana simple repeats were shorter in the related species. For the loci we compared, the related species had a much lower level of variability at the microsatellites than Japanese wild populations of A. thaliana. This is presumably related to the different microsatellite structures, because allozyme data showed that the outcrossing relatives were highly polymorphic compared to other outcrossing herbaceous species. Use of microsatellites in assessing variability or phylogenetic relationships between different species requires caution, because changes in microsatellite structure may alter evolutionary rates.

Do molecular markers reflect patterns of differentiation in adaptive traits of conifers?

We have examined patterns of variation of several kinds of molecular markers (isozymes, RFLPs of ribosomal DNA and anonymous low-copy number DNA, RAPDs and microsatellites) and an adaptive trait [date of bud set in Scots pine (Pinus sylvestris L.)]. The study included Finnish Scots pine populations (from latitude 60°N to 70°N) which experience a steep climatic gradient. Common garden experiments show that these populations are adapted to the location of their origin and genetically differentiated in adaptive quantitative traits, e.g. the date of bud set in first-year seedlings. In the northernmost population, bud set took place about 21 days earlier than in the southernmost population. Of the total variation in bud set, 36.4% was found among the populations. All molecular markers showed high levels of within-population variation, while differentiation among populations was low. Among all the studied markers, microsatellites were the most variable (He=0.77). Differences between populations were small, GST was less than 0.02. Our study suggests that molecular markers may be poor predictors of the population differentiation of quantitative traits in Scots pine, as exemplified here by bud-set date.