Detection of Plasmodium sporozoites in mosquitoes by polymerase chain reaction and oligonucleotide rDNA probe, without dissection of the salivary glands

Dried Anopheles gambiae mosquito head + thorax portions, infected with Plasmodium falciparum sporozoites, were processed by the polymerase chain reaction. The PCR product was hybridized to an oligonucleotide probe (known as 114R or AW34) diagnostic for Plasmodium . The detection level by autoradiography was ten sporozoites per mosquito. Head + thorax of mosquitoes that contained mature P.falciparum oocysts, without sporozoites, gave no positive signal, indicating that the test detects only infective mosquitoes. This test can be applied to wild mosquito specimens collected, prepared and processed at different time intervals. The technique is convenient, highly sensitive, and could be used with a non-radioactive detection system and specific probes to differentiate Plasmodium spp.     

The impact of planktivorous flsh on the structure of a plankton community

SUMMARY. 1. The abundance of pianktivorous juvenile yellow perch, Perca flavescens , was manipulated in three 750 m³ enclosures in a eutrophic lake.
2. There was a significant negative relationship between fish and zoopiankton biomasses. At high fish densities the zooplankton community was dominated by small filter-feeding cladocera. primarily bosmi- nids. At low fish densities the zooplankton community was dominated by large filter-feeding cladocera, primarily daphnids.
3. There was no significant relationship between zooplankton and phytoplankton biomasses when considered over the whole experiment but there was a trend towards lower phytoplankton biomass in the enclosure dominated by daphnids during mid-summer.
4. We conclude that although planktivorous fish have a strong negative impact on zooplankton community biomass and size structure, the relationship at the next lower trophic level, zooplankton and phytoplankton, is much weaker. Therefore, the biomanipulation of planktivorous fish populations as a management technique to control phytoplankton abundance is largely ineffective.     

Temperature-independent diel variation in soil respiration observed from a temperate deciduous forest

The response of soil respiration (R_s) to temperature depends largely on the temporal and spatial scales of interest and how other environmental factors interact with this response. They are often represented by empirical exponential equations in many ecosystem analyses because of the difficulties in separating covarying environmental responses and in observing below ground processes. The objective of this study was to quantify a soil temperature‐independent component in R_s by examining the diel variation of an R_s time series measured in a temperate deciduous forest located at Oak Ridge, TN, USA between March and December 2003. By fitting 2 hourly, continuous automatic chamber measurements of CO₂ efflux at the soil surface to a Q₁₀ function to obtain the temperature‐dependent respiration (R_t) and plotting the diel cycles of R_t, R_s, and their difference (R_i), we found that an obvious temperature‐independent component exists in R_s during the growing season. The diel cycle of this component has a distinct day/night pattern and agrees well with diel variations in photosynthetically active radiation (PAR) and air temperature. Elevated canopy CO₂ concentration resulted in similar patterns in the diel cycle of the temperature‐independent component but with different daily average rates in different stages of growing season. We speculate that photosynthesis of the stand is one of the main contributors to this temperature‐independent respiration component although more experiments are needed to draw a firm conclusion. We also found that despite its relatively small magnitude compared with the temperature‐dependent component, the diel variation in the temperature‐independent component can lead to significantly different estimates of the temperature sensitivity of soil respiration in the study forest. As a result, the common practice of using fitted temperature‐dependent function from night‐time measurements to extrapolate soil respiration during the daytime may underestimate daytime soil respiration.     

A critical analysis of the causes of boron toxicity in plants

This study investigated the main factors contributing to boron toxicity in plants. Growth was rapidly inhibited by internal B concentrations in the range 1–5 m m across a range of plant types that included monocot, dicot and algal species. In contrast, mature cells were able to withstand up to 60 m m B for several days. In wheat, rapid inhibition of root growth occurred if high B was applied to the root tip, but not if high B was applied to mature sections of the root. In leaves, there were gradations in B concentrations that correlated with visible symptoms of toxicity. However, there was no evidence to support the hypothesis that toxicity in leaves is due to osmotic stress induced by the accumulation of B. Analysis of the sensitivity to B of a range of metabolic processes including photosynthesis, respiration and protein synthesis leads to the conclusion that growth is not restricted by effects of B on energy supply and not directly by inhibition of protein synthesis. At higher B concentrations, many cellular activities were found to be partially inhibited and the toxicity to mature tissues was therefore considered not to arise from the disruption of a single process, but from the accumulated retardation of many cellular processes, exacerbated in light by photo‐oxidative stress.     

High concentration of long‐snouted beaked whales (genus Messapicetus) from the Miocene of Peru

Abstract: Eight skulls of beaked whales (Cetacea, Odontoceti, Ziphiidae), in six cases associated with elements of the mandible, were collected from a limited area (about 1.5 km²) and roughly from the same stratigraphic horizon at Cerro Colorado, 35 km south‐south‐west of the city of Ica (Peru), where the late Middle Miocene basal strata of the Pisco Formation crop out. They represent the highest concentration reported of fossil Ziphiidae. These finely preserved Cerro Colorado fossils are described and assigned to a new species Messapicetus gregarius, together with another specimen collected from sediments of the same age at Cerro la Bruja (33 km south‐east to Cerro Colorado). Messapicetus gregarius shares with M. longirostris Bianucci, Landini and Varola, 1992 (Tortonian of Italy), an extremely elongated rostrum, but is clearly different from the Italian species in the more distinct maxillary tubercle and prominential notch, the more robust premaxillary crest, and the abrupt ventrolateral descent of the medial margin of the maxilla from the vertex. A parsimony analysis reveals that Messapicetus belongs to a basal clade, which includes other ziphiids with a dorsally closed mesorostral groove and prenarial basin. The high concentration of specimens belonging to the same species (some of them tentatively identified as adult males and females), combined with the presence of a calf, supports the hypothesis of site fidelity; these cetaceans might have lived in a limited region for a long period for both breeding and feeding. Besides the eight specimens of M. gregarius, strata at Cerro Colorado include many other cetacean remains (with several specimens of the pontoporiid Brachydelphis including a foetus), pinnipeds, turtles, fishes, and birds.     

Resolution of phylogenetic relationships of the major subfamilies of the Delphacidae （Homoptera： Fulgoroidea） using the mitochondrial ribosomal DNA

Delphacid relationships from the genus level to the subfamily have been completely resolved （among those taxa examined） using sequence data from the 3＇ end of the 12S gene. Monophyly of the non-asiracine subfamilies was strongly supported and the asiracine Ugyops was placed in the most basal position of the tree. Support levels for monophyly of the Delphacini increased after weighting transversions more heavily than transitions and after removing the cixiid outgroup from the dataset. Among the Delphacini, Conomelus and Megamelus were more closely related to each other than either was to Chloriona. These results are in agreement with the tree based on morphological characters. However, in contrast to morphological data our results strongly supported a sister group relationship between the Stenocraninae and the Kelisiinae. Although the 12S gene fragment gave some information about the species relationships within Chloriona, neither this fragment nor the 5＇ end of the 16S gene appear to be very useful for this level. Molecular evolutionary patterns provided evidence that there has been a shift in base composition from T to A during the early evolution of the non-Asiracinae. The non-Asiracinae also had comparatively fast substitution rates and these two observations are possibly correlated. In the ‘ modem＇ delphacid Chloriona, the AT content was comparatively low in regions free of constraints but this was not the case for ‘ non-modem＇ delphacids. The tRNA for valine has been translocated elsewhere, probably before the Delphacidae and Cixiidae diverged from each other.