Potential contribution of natural enemies to patterns of local adaptation in plants

Genetic differentiation among plant populations and adaptation to local environmental conditions are well documented. However, few studies have examined the potential contribution of plant antagonists, such as insect herbivores and pathogens, to the pattern of local adaptation. Here, a reciprocal transplant experiment was set up at three sites across Europe using two common plant species, Holcus lanatus and Plantago lanceolata. The amount of damage by the main above-ground plant antagonists was measured: a rust fungus infecting Holcus and a specialist beetle feeding on Plantago, both in low-density monoculture plots and in competition with interspecific neighbours. Strong genetic differentiation among provenances in the amount of damage by antagonists in both species was found. Local provenances of Holcus had significantly higher amounts of rust infection than foreign provenances, whereas local provenances of Plantago were significantly less damaged by the specialist beetle than the foreign provenances. The presence of surrounding vegetation affected the amount of damage but had little influence on the ranking of plant provenances. The opposite pattern of population differentiation in resistance to local antagonists in the two species suggests that it will be difficult to predict the consequences of plant translocations for interactions with organisms of higher trophic levels.     

Low beta diversity of ambrosia beetles (Coleoptera: Curculionidae: Scolytinae and Platypodinae) in lowland rainforests of Papua New Guinea

We assessed the effect of geographical distance on insect species turnover in a situation where other major environmental factors, including host plant species, altitude, and climate, were constant. We sampled ambrosia beetles (Coleoptera, Curculionidae: Scolytinae and Platypodinae) from four tree species: Artocarpus altilis , Ficus nodosa , Leea indica and Nauclea orientalis , at three sites forming a 1000 km transect in lowland rainforests of northern Papua New Guinea. A standardized volume of wood from trunk, branches and twigs was sampled for ambrosia beetles from three individuals of the four tree species at each site. Each tree was killed standing and left exposed to beetle colonization for 20 days prior to sampling. We obtained 12 751 individuals from 84 morphospecies of ambrosia beetles. We surveyed most of the local species richness at each site, predicted by Chao 2 species richness estimates. The similarity of ambrosia beetle communities, estimated by Chao-Sorensen index, was not correlated with their geographical distance. Likelihood analysis and Q-mode analysis using Monte Carlo-generated null distribution of beetles among sites supported the hypothesis that the assemblages of ambrosia beetles at different sites are drawn from the same species pool, regardless of their geographical distance. Tree part (trunk, branch, or twig) was more important predictor of the composition of ambrosia beetle communities than was the host species or geographical location. All three variables, however, explained only a small portion of variability in ambrosia assemblages. The distribution of ambrosia beetles among tree parts, tree species and study sites was mostly random, suggesting limited importance of host specificity or dispersal limitation.     

Occurrence of bifidobacteria in faeces of calves fed milk or a combined diet

The development of faecal bacteria composition in calves fed milk or a combined diet was investigated from 4 to 21 days of age. On day 7, bifidobacteria in faeces of milk-fed calves already increased from about 7.6 to 9.2 log CFU/g and did not change until the end of the study, whereas in calves fed the combined diet bifidobacteria only moderately increased to 7.9 log CFU/g and decreased slowly until day 21. The counts of bifidobacteria in calves on a combined diet were significantly (p < 0.01) lower compared to those in milk-fed calves. Bifidobacterial counts determined by cultivation or by fluorescence in situ hybridisation (FISH) did not differ significantly. Our results showed that the occurrence of bifidobacteria in calf faeces is highly dependent on the diet composition. Faecal bacteria flora of calves fed exclusively by milk is rich in bifidobacteria, but in calves on a combined diet coliforms dominated.     

Selection and screening for enzymes of nitrile metabolism

This work critically reviews the assays of nitrile-converting and nitrile-forming enzymes (nitrilases, nitrile hydratases, amidases, aldoxime dehydratases). Most of the strains producing such enzymes were obtained by selection on media with nitriles, amides or aldoximes as nitrogen sources. Activity and enantioselectivity of the enzymes was usually assayed by time-consuming chromatographic analysis of substrates and the corresponding reaction products. Attempts at introducing faster assays resulted in several spectrophotometric methods for reaction product (ammonia, hydroxamate, methacrylamide, benzamide, etc.) determination. Recently, new methods for colorimetric and fluorimetric determination of ammonia have been developed, which appear promising for high-throughput assays. Alternatively, methods consisting in determination of NADH consumed in a coupled amination reaction or pH-responsive methods are promising for this purpose. All the above selection and screening methods establish fundamental conditions for the design of hierarchical screening projects. However, the potential of these principles, in particular spectrophotometric and fluorimetric methods, will be probably further exploited and adapted to multiwell plate and robotic systems.     

Community structure of insect herbivores is driven by conservatism,escalation and divergence of defensive traits in Ficus

Escalation (macroevolutionary increase) or divergence (disparity between relatives) in trait values are two frequent outcomes of the plant‐herbivore arms race. We studied the defences and caterpillars associated with 21 sympatric New Guinean figs. Herbivore generalists were concentrated on hosts with low protease and oxidative activity. The distribution of specialists correlated with phylogeny, protease and trichomes. Additionally, highly specialised Asota moths used alkaloid rich plants. The evolution of proteases was conserved, alkaloid diversity has escalated across the studied species, oxidative activity has escalated within one clade, and trichomes have diverged across the phylogeny. Herbivore specificity correlated with their response to host defences: escalating traits largely affected generalists and divergent traits specialists; but the effect of escalating traits on extreme specialists was positive. In turn, the evolution of defences in Ficus can be driven towards both escalation and divergence in individual traits, in combination providing protection against a broad spectrum of herbivores.     

Seasonality of sap-sucking insects (Auchenorrhyncha, Hemiptera) feeding on Ficus (Moraceae) in a lowland rain forest in New Guinea

Sap-sucking insects (Auchenorrhyncha, Hemiptera) were sampled quantitatively from the foliage of 15 species of Ficus (Moraceae) in a lowland rain forest in Papua New Guinea. Continuous sampling throughout 12 months produced 61,777 individuals and 491 species. Two seasonality parameters, circular statistics and Lloyd's index, were calculated for 139 species with a sample size of more than 36 individuals. Most of the species were present in the adult stage for at least half of the year, and many of them continuously throughout the year. However, almost all species exhibited marked seasonal changes in abundance. The abundance peaks of species were scattered throughout most of the year, but more species reached their population maximum during the wet, especially early wet, season than during the dry season. Overall species richness and abundance of Auchenorrhyncha were also higher during the wet than the dry season. A significant correlation between seasonality and host specificity was revealed in the auchenorrhynchan community. In particular, species evenly distributed throughout the year had a tendency to feed on a larger number of Ficus species than seasonally more restricted species. The seasonality, and the seasonality versus specificity correlation, were independent of species abundance. Among the most abundant species (n > 300) there was a marginally significant negative correlation between abundance and host specificity, so that polyphagous species had, on average, larger populations than specialists. There was no similar correlation among rarer species. The Auchenorrhyncha comprises three feeding guilds, which were also analysed separately. The mesophyll-feeding guild exhibited more pronounced seasonality than the phloem- and xylem-feeders. This difference could be explained as a part of the overall correlation between seasonality and host specificity as mesophyll-feeders were significantly more host specific than the other two guilds. Received: 26 January 1998 / Accepted: 9 March 1998     

Some biochemical threshold mechanisms

Certain arrangements of enzymatic (bimolecular) subsystems lead to characteristic threshold-type response. Two simple cases of such systems are studied here in terms of steady state behavior and explicit relationships between system and curve parameters. It is found that the curvature of the threshold curve is directly related to the equivalent Michaelis constant and, in the case of saturated threshold curve, the slope of the curve at the idealized threshold is limited by the ratio of saturation to threshold. This slope may be appreciably increased up to a stepwise response at the threshold if a multisubstrate complex of the enzyme is the only species which affects the enzyme mediated transport.     

Zeptomole Electrochemical Detection of Metallothioneins

Background

Thiol-rich peptides and proteins possess a large number of biological activities and may serve as markers for numerous health problems including cancer. Metallothionein (MT), a small molecular mass protein rich in cysteine, may be considered as one of the promising tumour markers. The aim of this paper was to employ chronopotentiometric stripping analysis (CPSA) for highly sensitive detection of MT.

Methodology/Principal Findings

In this study, we used adsorptive transfer stripping technique coupled with CPSA for detection of cysteine, glutathione oxidized and reduced, phytochelatin, bovine serum albumin, and metallothionein. Under the optimal conditions, we were able to estimate detection limits down to tens of fg per ml. Further, this method was applied to detect metallothioneins in blood serum obtained from patients with breast cancer and in neuroblastoma cells resistant and sensitive to cisplatin in order to show the possible role of metallothioneins in carcinogenesis. It was found that MT level in blood serum was almost twice higher as compared to the level determined in healthy individuals.

Conclusions/Significance

This paper brings unique results on the application of ultra-sensitive electroanalytical method for metallothionein detection. The detection limit and other analytical parameters are the best among the parameters of other techniques. In spite of the fact that the paper is mainly focused on metallothionein, it is worth mentioning that successful detection of other biologically important molecules is possible by this method. Coupling of this method with simple isolation methods such as antibody-modified paramagnetic particles may be implemented to lab–on-chip instrument.