Varying selection differential throughout the climatic range of Norway spruce in Central Europe

Predicting species distribution changes in global warming requires an understanding of how climatic constraints shape the genetic variation of adaptive traits and force local adaptations. To understand the genetic capacity of Norway spruce populations in Central Europe, we analyzed variation of tree heights at the juvenile stage in common-garden experiments established from the species’ warm-dry to cold-moist distribution limits. We report the following findings: first, 47 % of the total tree-height variation at trial sites is attributable to the tree populations irrespective of site climate. Second, tree height variation within populations is higher at cold-moist trial sites than at warm-dry sites and higher within populations originating from cold-moist habitats than from warm-dry habitats. Third, for tree ages of 7 to 15 years, the variation within populations increases at cold-moist trial sites, whereas it remains constant at warm-dry sites. Fourth, tree-height distributions are right-skewed at cold-moist trial sites, whereas they are non-skewed but platykurtic at warm-dry sites. Our results suggest that in cold environments climatic conditions impose stronger selection and probably restrict the distribution of spruce, whereas at the warm distribution limit, the species’ realized niche might rather be controlled by external drivers, for example forest insects

Quantitative genetic analysis of embryo heterosis in faba bean (Vicia faba L.)

Seeds, i.e. embryos, may be genetically different from either of their parents and moreover may express their own heterosis. The objective was to genetically analyse embryo heterosis for their own weight (i.e. seed weight) in comparison with their seedlings’ heterosis, taking the large-seeded crop (Vicia faba L.) as model. A specific diallel mating scheme was used, based on four parental lines, creating 76 seed genotypes in generations P, F(1), F(2) and BC. Mature seed weight was assessed for these embryo genotypes in 3 years at one German location, and young plant biomass yield of seedlings emerging from these seeds in two greenhouse experiments. The quantitative genetic analysis showed an average of 10.6% mid-parent heterosis for mature seed weight and 14.5% mid-parent heterosis for juvenile biomass. In both traits, the embryos contributed markedly and significantly via their own genes to the genetic variation. For mature embryo weight heterosis, apparently the parental difference in seed weight was decisive, whereas for juvenile biomass heterosis, genetic unrelatedness of parents had priority

Contrast Interferometry Using Bose-Einstein Condensates to Measure h/m and the Fine Structure Constant

The kinetic energy of an atom recoiling due to absorption of a photon was measured as a frequency using an interferometric technique called ``contrast interferometry''. Optical standing wave pulses were used as atom-optical elements to create a symmetric three-path interferometer with a Bose-Einstein condensate. The recoil phase accumulated in different paths was measured using a single-shot detection technique. The scheme allows for additional photon recoils within the interferometer and its symmetry suppresses several random and systematic errors including those from vibrations and ac Stark shifts. We have measured the photon recoil frequency of sodium to $7$ppm precision, using a simple realization of this scheme. Plausible extensions should yield a sufficient precision to bring within reach a ppb-level determination of $h/m$ and the fine structure constant $\alpha$

Estimating Reaction Norms for Age and Size at Maturation When Age at First Reproduction is Unknown

We describe a novel method to estimate the probabilities of maturing at age as a function of size; these probabilities can often be interpreted as probabilistic reaction norms for age and size at maturation. Such estimations are useful for describing maturation process independently from the processes of growth and mortality, and they can also help to disentangle phenotypic plasticity from evolutionary changes in maturation. The estimation method can be used when mature and immature individuals are representatively sampled over two consecutive seasons, even when maturing individuals are not distinguished. Confidence intervals are derived for the reaction norm parameters using a bootstrap approach. Using simulated data, the method is shown to be asymptotically unbiased and robust to moderate violations of the main simplifying assumptions. However, it is relatively sensitive to small sample sizes: the method is not robust when fewer than about 100 individuals (mature and immature) are sampled from a cohort at a certain age. The method is illustrated by an application to Georges Bank cod stock (Gadus morhua) but can be used for any type of organism

Standardizing selection strengths to study selection in the wild: A critical comparison and suggestions for the future

We critically review the main approaches for standardizing and comparing selection differentials and gradients among traits, populations, and species and assess their differential merits. In particular, we explain why the most widespread approach to standardizing selection, which measures selection differentials in units of a trait's phenotypic standard deviation, is less appropriate for characterizing strengths of natural selection in wild populations. In contrast, an alternative standardization approach, which uses a trait's phenotypic mean in addition to its standard deviation, results in another dimensionless measure - the mean-standardized selection gradient. This measure offers some key benefits over alternative approaches - such as ease of interpretation, independence of a trait's variance, and the natural interfacing of ecological and evolutionary dynamics - and yet remains rarely used by evolutionary biologists. We explain how the more routine application of this measure will facilitate comparisons of selection strengths in the wild among traits, populations, and species

Assessing Evolutionary Consequences of Size-selective Recreational Fishing on Multiple Life-history Traits, with an Application To Northern Pike (Esox lucius)

Despite mounting recognition of the importance of fishing-induced evolution, methods for quantifying selection pressures on multiple adaptive traits affected by size-selective harvesting are still scarce. We study selection differentials on three life-history traits - reproductive investment, size at maturation, and growth capacity - under size-selective exploitation of northern pike (Esox lucius L.) with recreational-fishing gear. An age-structured population model is presented that accounts for the eco-evolutionary feedback arising from density-dependent and frequency-dependent selection. By introducing minimum-length limits, maximum-length limits, and combinations of such limits (resulting in harvestable-slot length limits) into the model, we examine the potential of simple management tools for mitigating selection pressures induced by recreational fishing. With regard to annual reproductive investment, we find that size-selective fishing mortality exerts relatively small positive selection differentials. By contrast, selection differentials on size at maturation are large and consistently negative. Selection differentials in growth capacity are often large and positive, but become negative when a certain range of minimum-length limits are applied. In general, the strength of selection is reduced by implementing more stringent management policies, but each life-history trait responds differently to the introduction of specific harvest regulations. Based on a simple genetic inheritance model, we examine mid- and long-term evolutionary changes of the three life-history traits and their impacts on the size spectrum and yield of pike. In general, fishing-induced evolution reduces sizes and yields, but details depend on a variety of factors such as the specific regulation in place. We find no regulation that is successful in reducing to zero all selection pressures on life-history traits induced by recreational fishing. Accordingly, we must expect that inducing some degree of evolution through recreational fishing is inevitable

Fifty-fold improvement in the number of quantum degenerate fermionic atoms

We have produced a quantum degenerate Li-6 Fermi gas with up to 7 x 10^7 atoms, an improvement by a factor of fifty over all previous experiments with degenerate Fermi gases. This was achieved by sympathetic cooling with bosonic Na-23 in the F=2, upper hyperfine ground state. We have also achieved Bose-Einstein condensation of F=2 sodium atoms by direct evaporation

Fluctuation Domains in Adaptive Evolution

We derive an expression for the variation between parallel trajectories in phenotypic evolution, extending the well known result that predicts the mean evolutionary path in adaptive dynamics or quantitative genetics. We show how this expression gives rise to the notion of fluctuation domains - parts of the fitness landscape where the rate of evolution is very predictable (due to fluctuation dissipation) and parts where it is highly variable (due to fluctuation enhancement). These fluctuation domains are determined by the curvature of the fitness landscape. Regions of the fitness landscape with positive curvature, such as adaptive valleys or branching points, experience enhancement. Regions with negative curvature, such as adaptive peaks, experience dissipation. We explore these dynamics in the ecological scenarios of implicit and explicit competition for a limiting resource