Poleward increase in feeding efficiency of leafminer Stigmella lapponica (Lepidoptera: Nepticulidae) in a latitudinal gradient crossing a boreal forest zone

Damage to plant communities imposed by insect herbivores generally decreases from low to high latitudes. This decrease is routinely attributed to declines in herbivore abundance and/or diversity, whereas latitudinal changes in per capita food consumption remain virtually unknown. Here, we tested the hypothesis that the lifetime food consumption by a herbivore individual decreases from low to high latitudes due to a temperature-driven decrease in metabolic expenses. From 2016 to 2019, we explored latitudinal changes in multiple characteristics of linear (gallery) mines made by larvae of the pygmy moth, Stigmella lapponica, in leaves of downy birch, Betula pubescens. The mined leaves were larger than intact leaves at the southern end of our latitudinal gradient (at 60°N) but smaller than intact leaves at its northern end (at 69°N), suggesting that female oviposition preference changes with latitude. No latitudinal changes were observed in larval size, mine length or area, and in per capita food consumption, but the larval feeding efficiency (quantified as the ratio between larval size and mine size) increased with latitude. Consequently, S. lapponica larvae consumed less foliar biomass at higher latitudes than at lower latitudes to reach the same size. Based on space-for-time substitution, we suggest that climate warming will increase metabolic expenses of insect herbivores with uncertain consequences for plant–herbivore interactions.     

Indirect determination of magnetic susceptibility tensors in peroxidases: a novel approach to structure elucidation by NMR

 The chemical shifts of several ¹³C nuclei positioned α to the haems in oxidised cyanide complexes of horseradish peroxidase and lignin peroxidase are reported and analysed in terms of π molecular orbitals with perturbed D_4h symmetry. The additional contributions to the paramagnetic shifts of ¹³C nuclei in the vinyl groups which arise from conjugation with the porphyrin π molecular orbitals are discussed, and an empirical correction factor is derived from a number of other compounds which contain haems b. The orbital mixing parameter which is obtained from the analysis of the experimental ¹³C shifts is compared with the orientation of the axial histidine ligands in X-ray structures of related compounds and found to be close to the orientation of the normal to the histidine ring. Comparison with the magnetic axes determined by fitting the dipolar shifts of several protons which have been assigned previously also shows close agreement with the negative in-plane rotation of the magnetic y axis. It is therefore possible to obtain the approximate orientation of the magnetic axes from ¹³C resonances of the haem and hence to determine the dipolar shifts at any point in space with respect to the haem by using these axes together with the anisotropy of the magnetic susceptibility, which can be obtained by extrapolation from EPR g values. Excellent agreement is found between dipolar shifts obtained by fitting an empirical magnetic susceptibility tensor and predictions based on ¹³C NMR and EPR in the case of lignin peroxidase. The agreement is less good in the case of horseradish peroxidase, in which the empirical magnetic z axis appears to be tilted significantly away from the haem normal, though this may be due in part to the lack of accurate atomic coordinates. It is concluded that useful estimates of the magnetic susceptibility tensor may be obtained from ¹³C NMR and EPR studies even in large mammalian peroxidases for which no structural models are available. Received: 27 December 1995 / Accepted: 17 April 1996     

Studies on the catalytic mechanism of H2-forming methylenetetrahydromethanopterin dehydrogenase: para-ortho H2 conversion rates in H2O and D2O

H₂–forming N ⁵,N ¹⁰ –methylenetetrahydromethanopterin dehydrogenase is a novel type of hydrogenase that contains neither nickel nor iron-sulfur clusters. Evidence has been presented that the reaction mechanism catalyzed by the enzyme is very similar to that of the formation of carbocations and H₂ from alkanes under superacidic conditions. We present here further results in support of this mechanism. It was found that the purified enzyme per se did not catalyze the conversion of para H₂ to ortho H₂, a reaction catalyzed by all other hydrogenases known to date. However, it catalyzed the conversion in the presence of the substrate N ⁵,N ¹⁰ –methenyltetrahydromethanopterin (CH≡H₄MPT⁺), indicating that for heterolytic cleavage of H₂ the enzyme-CH≡H₄MPT⁺ complex is required. In D₂O, the formation of HD and D₂ from H₂ rather than a para–ortho H₂ conversion was observed, indicating that after heterolytic cleavage of H₂ the dissociation of the proton from the enzyme-substrate complex is fast relative to the re-formation of free H₂.     

Stability of α-chymotrypsin conjugated with poly (ethylene glycols) and proxanols at high temperature and in watercosolvent mixtures

Summary -Chymotrypsin has been modified with poly(ethylene glycols) and proxanols, block-copolymers of poly(propylene oxide) and poly(ethylene oxide). These conjugates were several-fold more thermostable and showed high catalytic activity at elevated concentrations of water-miscible organic cosolvents (alcohols and dimethyl sulfoxide) which caused inactivation of free (non-modified) -chymotrypsin.     

A transposon insertion in the Arabidopsis SSR16 gene causes an embryo-defective lethal mutation

The SSR16 gene of Arabidopsis has been identified as a gene encoding a ribosomal protein S16 homolog through analysis of a transposon insertion mutation. The insertion mutation is lethal, arresting embryonic development at approximately the transition from the globular to the heart stage of embryonic development. Co-segregation of the mutant phenotype with the transposon-borne drug-resistance marker and loss of the inserted transposon concomitant with phenotypic reversion provided evidence that the transposon had caused the mutation. Sequences flanking the insertion site were amplified from DNA of viable heterozygotes by thermal asymmetric interlaced (TAIL) PCR. The amplified fragment flanking the 3' end of the inserted element was sequenced and found to be identical to an Arabidopsis expressed sequence tag (EST). The EST, in turn, contained a coding sequence homologous to the ribosomal protein S16 (RPS16) of bacteria such as Escherichia coli, Bacillus subtilis and Salmonella typhimurium , as well as Neurospora crassa mitochondria and higher plant plastids. Thus the gene identified by the embryo-defective lethal insertion mutation encodes an RPS16 homolog and has been designated the SSR16 gene.     

Size of genetic bottlenecks leading to virus fitness loss is determined by mean initial population fitness.

Genetic bottlenecks are important events in the genetic diversification of organisms and colonization of new ecological niches. Repeated bottlenecking of RNA viruses often leads to fitness losses due to the operation of Muller's ratchet. Herein we use vesicular stomatitis virus to determine the transmission population size which leads to fitness decreases of virus populations. Remarkably, the effective size of a genetic bottleneck associated with fitness loss is greater when the fitness of the parental population increases. For example, for starting virus populations with low fitness, population transfers of five-clone-to-five-clone passages resulted in a fitness increase. However, when a parental population with high fitness was transferred, 30-clone-to-30-clone passages were required simply to maintain fitness values.     

Extreme fitness differences in mammalian and insect hosts after continuous replication of vesicular stomatitis virus in sandfly cells.

Continuous, persistent replication of a wild-type strain of vesicular stomatitis virus in cultured sandfly cells for 10 months profoundly decreased virus replicative fitness in mammalian cells and greatly increased fitness in sandfly cells. After persistent infection of sandfly cells, fitness was over 2,000,000-fold greater than that in mammalian cells, indicating extreme selective differences in the environmental conditions provided by insect and mammalian cells. The sandfly-adapted virus also showed extremely low fitness in mouse brain cells (comparable to that in mammalian cell cultures). It also showed an attenuated phenotype, requiring a nearly millionfold higher intracranial dose than that of its parent clone to kill mice. A single passage of this adapted virus in BHK-21 cells at 37 degrees C restored fitness to near neutrality and also restored mouse neurovirulence. These results clearly illustrate the enormous capacity of RNA viruses to adapt to changing selective environments.