Embryonic Development in House Fly Eggs Fertilized with Genetically Deficient Sperm

In house flies, Musca domestica L., eggs fertilized with sperm that have chromosome deficiencies and duplications do not hatch, but develop to a stage where a fully differentiated, prehatch larva is formed. Fifteen different chromosome translocations involving most of the 10 arms of the 5 autosomes were studied by crossing male translocation heterozygotes to normal females. Egg hatch was reduced to 36–66% depending on the translocation used. Eggs that did not hatch after 24 hours were fixed, stained, and examined for stage of development. Several translocations involving the right arm of chromosome 4 indicate that the region closest to the centromere contains genes that affect the process of syngamy or early cleavage divisions, but do not reduce the ability of the sperm to compete for egg fertilization. Approximately 70% of the autosomal genes can be absent from sperm (not simultaneously but in different crosses) without inhibiting embryonic development.     

Spatial patterns and competition of tree species in a Douglas-fir chronosequence on Vancouver Island

While the successional dynamics and large-scale structure of Douglas-fir forest in the Pacific Northwest region is well studied, the fine-scale spatial characteristics at the stand level are still poorly understood. Here we investigated the fine-scale spatial structure of forest on Vancouver Island, in order to understand how the three dominant species, Douglas-fir, western hemlock, and western redcedar, coexist and partition space along a chronosequence comprised of immature, mature, and old-growth stands. We quantified the changes in spatial distribution and association of the species along the chronosequence using the scale-dependent point pattern analyses pair-correlation function g(r) and Ripley's L-function. Evidence on intra- and inter-specific competition was also inferred from correlations between nearest-neighbor distances and tree size. Our results show that 1) the aggregation of Douglas-fir in old-growth was primarily caused by variation in local site characteristics, 2) only surviving hemlock were more regular than their pre-mortality patterns, a result consistent with strong intra-specific competition, 3) inter-specific competition declined rapidly with stand age due to spatial resource partitioning, and (4) tree death was spatially randomly distributed among larger overstory trees. The study highlights the importance of spatial heterogeneity for the long-term coexistence of shade-intolerant pioneer Douglas-fir and shade-tolerant western hemlock and western redcedar.     

Macromolecular crowding effects on the kinetics of opposing reactions catalyzed by alcohol dehydrogenase

In order to better understand how the complex, densely packed, heterogeneous milieu of a cell influences enzyme kinetics, we exposed opposing reactions catalyzed by yeast alcohol dehydrogenase (YADH) to both synthetic and protein crowders ranging from 10 to 550 kDa. The results reveal that the effects from macromolecular crowding depend on the direction of the reaction. The presence of the synthetic polymers, Ficoll and dextran, decrease V_max and K_m for ethanol oxidation. In contrast, these crowders have little effect or even increase these kinetic parameters for acetaldehyde reduction. This increase in V_max is likely due to excluded volume effects, which are partially counteracted by viscosity hindering release of the NAD⁺ product. Macromolecular crowding is further complicated by the presence of a depletion layer in solutions of dextran larger than YADH, which diminishes the hindrance from viscosity. The disparate effects from 25 g/L dextran or glucose compared to 25 g/L Ficoll or sucrose reveals that soft interactions must also be considered. Data from binary mixtures of glucose, dextran, and Ficoll support this “tuning” of opposing factors. While macromolecular crowding was originally proposed to influence proteins mainly through excluded volume effects, this work compliments the growing body of evidence revealing that other factors, such as preferential hydration, chemical interactions, and the presence of a depletion layer also contribute to the overall effect of crowding.