Extensive variation at the α-glycerophosphate dehydrogenase locus in species of waterstriders (Gerridae: Hemiptera)

Variation at the -glycerophosphate dehydrogenase (-Gpdh; EC 1.1.1.8) locus was surveyed in 11 species of waterstriders (Gerridae: Hemiptera) and five other species of aquatic Hemiptera. Species of waterstriders exhibited considerable inter- and intraspecific variation in degree of winglessness. Average heterozygosity (0.401±0.090) and average number of observed electromorphs (5.36±0.96) for the 11 gerrid species were well above values reported for nearly all other insect species surveyed to date. Wing-monomorphic and wing-polymorphic species did not differ in average -Gpdh heterozygosity. Of the three wing-polymorphic species surveyed geographically, two species exhibited marked variation in wing-morph frequencies but homogeneous -Gpdh allele frequencies. The third species exhibited geographically homogeneous -Gpdh and wing-morph frequencies, but no significant association between -Gpdh phenotype and wing morph was observed in any surveyed population. These results are consistent with hypotheses evoking either relaxed purifying selection at the -Gpdh locus in species of Gerridae due to the apparent reduced importance of flight, or selective maintenance of common -Gpdh electromorphs.This work was supported by NSF Grant DEB 76-20967 to Alan H. Brush, funds from the Research Foundation of the University of Connecticut to Carl W. Schaefer, and USPHS Grant GM 21133 to Richard K. Koehn.     

The synthesis of 6-deoxy-6-fluoro-α,α-trehalose and related analogues

Selective acid-catalysed methanolysis of 2,3,2′,3′-tetra-O-benzyl-4,6:4′,6′-di-O-benzylidene-α,α-trehalose yielded the monobenzylidene derivative, which was converted into the 4,6-dimesylate. Selective nucleophilic displacement of the primary sulphonyloxy group then gave 2,3-di-O-benzyl-6-deoxy-6-fluoro-4-O-mesyl-α-d-glucopyranosyl 2,3-di-O-benzyl-4,6-O-benzylidene-α-d-glucopyranoside. Removal of the protecting groups then yielded 6-deoxy-6-fluoro-α,α-trehalose. In addition, 6-deoxy-6-fluoro-4-O-mesyl-α,α-trehalose and a derivative of 4-chloro-4,6-dideoxy-6-fluoro-α-d-galactopyranosyl α-d-glucopyranoside were also prepared from the same substrate. Iodide displacement of 2,3-di-O-benzyl-4,6-di-O-mesyl-α-d-glucopyranosyl 2,3-di-O-benzyl-4,6-di-O-mesyl-α-d-glucopyranoside afforded the 6-iodide and 6,6′-di-iodide in yields of 31 and 36%, respectively. Similarly, the 6-azide and 6,6′-diazide were isolated in yields of 17 and 21%, respectively.     

The oxidation of methyl α-D-glucopyranoside with methyl sulproxide and acetic anhydride

The relative proportions of carbonyl, O-acetyl, and O-(methylthio)methylsugars resulting from the partial oxidation of methyl α-D-glucopyranoside with methyl sulphoxide and acetic anhydride have been investigated@ the preparation of the 2- and 6-(methylthio)methyl ethers of methyl α-D-glucopyranoside is described.     

The reaction of phosphorus pentachloride with amides,in particular 2-acetamido-2-deoxyaldohexopyranoses

2-acetamido-2-deoxyaldohexopyranose polyacetates are transformed by the action of phosphorus pentachloride into 2-tetrachloroethylideneamino derivatives, the trans-2-acetamido-l-acetate system reacting more rapidly than the cis. A 1-acetamido-pyranosyl polyacetate afforded the 1-tetrachloroethylideneamino derivative and 2-O-trichloroacetyl-β-D-glucopyranosyl chloride. The latter was also observed, amongst other products, from the reaction of β-D-glucopyranosyl azide tetra-acetate with phosphorus pentachloride. Similar reactions on acetamidocyclohexane and its 2-acetoxy derivative afforded dichloroacetamido, trichloroacetamido, and tetrachloroethylideneamino derivatives. Likewise, 1-acetamido-2-acetoxyethane gave the 1-dichloroacetamido derivative.     

Assessment of the stream invertebrate β‐diversity along an elevation gradient using a bidimensional null model analysis

β‐Diversity, commonly defined as the compositional variation among localities that links local diversity (α‐diversity) and regional diversity (γ‐diversity), can arise from two different ecological phenomena, namely the spatial species turnover (i.e., species replacement) and the nestedness of assemblages (i.e., species loss). However, any assessment that does not account for stochasticity in community assembly could be biased and misinform conservation management. In this study, we aimed to provide a better understanding of the overall ecological phenomena underlying stream β‐diversity along elevation gradients and to contribute to the rich debate on null model approaches to identify nonrandom patterns in the distribution of taxa. Based on presence‐absence data of 78 stream invertebrate families from 309 sites located in the Swiss Alpine region, we analyzed the effect size of nonrandom spatial distribution of stream invertebrates on the β‐diversity and its two components (i.e., turnover and nestedness). We used a modeling framework that allows exploring the complete range of existing algorithms used in null model analysis and assessing how distribution patterns vary according to an array of possible ecological assumptions. Overall, the turnover of stream invertebrates and the nestedness of assemblages were significantly lower and higher, respectively, than the ones expected by chance. This pattern increased with elevation, and the consistent trend observed along the altitudinal gradient, even in the most conservative analysis, strengthened our findings. Our study suggests that deterministic distribution of stream invertebrates in the Swiss Alpine region is significantly driven by differential dispersal capacity and environmental stress gradients. As long as the ecological assumptions for constructing the null models and their implications are acknowledged, we believe that they still represent useful tools to measure the effect size of nonrandom spatial distribution of taxa on β‐diversity.     

HIV Reactivation from Latency after Treatment Interruption Occurs on Average Every 5-8 Days—Implications for HIV Remission

HIV infection can be effectively controlled by anti-retroviral therapy (ART) in most patients. However therapy must be continued for life, because interruption of ART leads to rapid recrudescence of infection from long-lived latently infected cells. A number of approaches are currently being developed to ‘purge’ the reservoir of latently infected cells in order to either eliminate infection completely, or significantly delay the time to viral recrudescence after therapy interruption. A fundamental question in HIV research is how frequently the virus reactivates from latency, and thus how much the reservoir might need to be reduced to produce a prolonged antiretroviral-free HIV remission. Here we provide the first direct estimates of the frequency of viral recrudescence after ART interruption, combining data from four independent cohorts of patients undergoing treatment interruption, comprising 100 patients in total. We estimate that viral replication is initiated on average once every ≈6 days (range 5.1- 7.6 days). This rate is around 24 times lower than previous thought, and is very similar across the cohorts. In addition, we analyse data on the ratios of different ‘reactivation founder’ viruses in a separate cohort of patients undergoing ART-interruption, and estimate the frequency of successful reactivation to be once every 3.6 days. This suggests that a reduction in the reservoir size of around 50-70-fold would be required to increase the average time-to-recrudescence to about one year, and thus achieve at least a short period of anti-retroviral free HIV remission. Our analyses suggests that time-to-recrudescence studies will need to be large in order to detect modest changes in the reservoir, and that macaque models of SIV latency may have much higher frequencies of viral recrudescence after ART interruption than seen in human HIV infection. Understanding the mean frequency of recrudescence from latency is an important first step in approaches to prolong antiretroviral-free viral remission in HIV.