The stochastic community and the logistic-J distribution

A new formal model called the multispecies logistical (MSL) system produces species/abundance distributions that are compared statistically with those found in natural communities. The system, which is able to handle thousands of individuals from hundreds of species, iteratively selects random pairs of individuals and transfers a unit of biomass (or energy) between the respective species. Several elaborations of the model, including those with trophic compartments, appear to produce the same distribution. The theoretical distribution underlying the MSL system is a hyperbolic section, here called the logistic-J distribution. In the study reported here, the logistic-J distribution has been fitted to the species-abundance histograms of 125 randomly selected taxocoenoses. Since the overall chi square score of the logistic-J achieved near-optimality in this study, it cannot be distinguished statistically from the J-curves observed by field biologists. For comparison, the log-series distribution was given the same test and scored significantly higher (more poorly) than the mean logistic-J score. If there is a single, major distribution underlying natural communities, it is not the log-series distribution. Nor, owing to a mathematical error in its formulation, can it be the lognormal distribution. In the MSL system each species follows a “stochastic orbit” about the mean abundance producing, in consequence, the logistic-J distribution. Such orbits are produced by any system in which the probabilities of reproduction and death are approximately equal. Accordingly, the “stochastic communities hypothesis” is proposed here as the overall mechanism governing abundances in all natural communities. It is not a single mechanism, per se, but the net effect of all environmental influences.     

Inheritance of resistance to blackmold (Alternaria alternata (Fr.) Keissler) in two interspecific crosses of tomato (Lycopersicon esculentum ×L. cheesmanii f.typicum)

Inheritance of resistance to blackmold, a disease of ripe tomato fruit caused byAlternaria alternata, was studied in two interspecific crosses. The parents, F₁ and F₂ generations of a cross between the susceptibleLycopersicon esculentum Mill. cultivar Hunt 100 and the resistantL. Cheesmanii f.typicum Riley accession LA 422, and the parents, F₁, F₂, F₃, and BC₁ P₂ generations of a cross between the susceptibleL. Esculentum cv. VF 145B-7879 and LA 422 were evaluated. The following disease evaluation traits were used: symptom rating (a symptom severity rating based on visual evaluation of lesions), diseased fruit (the number of diseased fruits divided by the total number of fruit scored), and lesion size (a function derived from the actual lesion diameter). Generation means analysis was used to determine gene action. The data of the Hunt 100 × LA 422 cross fit an additive-dominance model for all three traits. The VF 145B-7879 × LA 422 cross data best fit a model that included the additive × additive and additive × dominance interaction components for the trait diseased fruit, whereas higher-order epistatic models would have to be invoked to fit the data for the traits symptom rating and lesion size. A minimum of one gene segregated for all three traits. Broad-sense heritability estimates ranged from 0.09 to 0.16 for all three traits, indicating that selection for improved resistance to blackmold will require selection on a family performance basis.     

Tropical tree species diversity: a test of the Janzen-Connell model

To test the premises and predictions of the Janzen-Connell model (Janzen's spacing mechanism), seeds of the rainforest canopy tree, Brosimum alicastrum, were placed at different distances from the parent tree and their removal observed over 3 weeks. The number and density of naturally occurring seeds at different distances from the parent tree were also estimated. Predation was not greater near the parent tree, except on the very small spatial scale: the proportion of experimental seeds removed was greater 1 m from the trunk than it was 5–25 m from the trunk. Predation was negatively correlated with seed density, not positively as the Janzen-Connell model assumes-presumably due to predator satiation. The density of seeds after predation peaked 5 m from the tree trunk, but this is well within the crown radius of the parent tree. There is a peak in the number of potential recruits at a distance of 10 m from the parent tree, due to the peaked initial distribution of seeds. This peak is caused by the interaction between the seed density curve and the increasing area of an annulus around the parent tree at increasing distances, not by the product of the density curve and the predation curve. However, it is important to realize that it is not the presence of a peak in recruitment away from the parent that is essential to maintaining tropical tree species diversity, but frequency-dependent recruitment induced by poor recruitment near conspecifics. Predator satiation seems to be an important factor in the survival of B. alicastrum seeds, possibly at several spatial scales. The number of seeds produced by the tree is negatively correlated with the loss to predators, and trees that have a fruiting conspecific nearby also suffer lower levels of predation. Seed predation increases as one moves from the forest edge into the interior, creating an edge effect that may have long-term effects on the forest composition and tree species diversity. More studies are needed, for other species, other localities, and larger spatial and temporal scales, on both the Janzen-Connell mechanism and this edge effect.     

The molecular genetics of Alzheimer's disease

The major pathological characteristic of Alzheimer's disease (AD) is the abnormal deposition of β-amyloid peptide (Aβ) in the brain. In some early onset cases, the disease develops because of mutations in the gene coding for β-amyloid precursor protein (βAPP). However, the majority of AD families in the early onset subgroup are linked to a locus on chromosome 14. The genetic analysis and age of onset correlates of both the βAPP gene and the chromosome 14 locus are discussed. We speculate on the mechanisms by which the βAPP mutations cause the disease and discuss recent advances in βAPP processing that may be relevant to the pathogenesis of the late-onset (common) form of the disease. In addition, we review the association of theAPOE locus with late-onset familial and nonfamilial disease. Further work is required to establish the effects of this locus on disease occurrence, age of onset, and progression. The molecular pathology of ApoE in relation to AD development and the identification of the chromosome 14 gene will greatly contribute to a general pathogenic model of AD, and will clarify the role of βAPP and its derivatives.     

Recombinant Trypanosoma cruzi antigens and Chagas' disease diagnosis: analysis of a workshop

Abstract A workshop organized by the Ibero-American Project of Biotechnology evaluated the diagnostic potential of several cloned Trypanosoma cruzi recombinant antigens for Chagas' disease serodiagnosis. A set of recombinants, Antigen 2, Antigen 13, SAPA, H49, A13, JL5, JL7, JL8, JL9, and RA1 provided by three different South American laboratories were probed with a panel of 236 South American serum samples. Antigens JL7, H49, Antigen 2, and A13 scored as the best diagnostic recombinant reagents. The results suggested that the main advantage of using cloned peptides for chronic Chagas' disease diagnosis resided in their highly specific immunoreactive properties.     

Comparison between woody indexing and a rapid hybridisation assay for the diagnosis of little cherry disease in cherry trees*

Sweet cherry (Prunus avium) and sour cherry (Prunus cerasus) trees from orchards in the Kootenay and Okanagan Valleys of British Columbia, Canada were assayed for the presence of little cherry disease by three different methods: Northern blot analysis of double-stranded RNA, woody indexing for fruit symptoms on sweet cherry cv. Lambert, and woody indexing for foliar symptoms on cv. Canindex 1. Results of the three methods were in agreement for 85% of the samples. Of the 78 orchard trees tested, double-stranded RNA isolated from 48 trees hybridised with a radiolabeled cloned probe specific for little cherry disease. When the 48 trees were tested by woody indexing, buds from 41 trees induced fruit symptoms on cv. Lambert, but only 32 yielded foliar symptoms on cv. Canindex 1 under the conditions of the experiment. Of the 30 orchard trees that did not yield a positive response to the Northern blot analysis, 26 samples were negative on cv. Lambert and 26 were negative on cv. Canindex 1. Northern blot analysis of the 78 cv. Lambert indicator trees revealed that there was an absolute correlation between the presence of little cherry disease-associated double-stranded RNA and the development of typical little cherry disease symptoms on the indicator trees. Reliability of woody indexing of orchard samples was impaired by poor transmission of the disease from the inoculating bud to the indicator tree. Woody indexing with cv. Canindex 1 was particularly prone to a large number of apparently erroneous negative results. Of the three protocols used, diagnosis of little cherry disease by Northern blot analysis was found to be the most reliable and offered a greatly accelerated means of diagnosis.     

A cellular model for drug interactions on hematopoiesis: The use of human umbilical cord blood progenitors as a model for the study of drug-related myelosuppression of normal hematopoiesis

A cellular model of hematopoiesis which would be more convenient than bone marrow (BM) progenitors and directly relevant to human pathology is needed in order to investigate xenobiotic toxicity. Human umbilical cord blood (HCB), previously shown to be able to repopulate BM, provides a powerful in vitro model of normal human hematopoiesis. In order to validate the use of normal HCB progenitors as targets for dose-related myelosuppression, we used clonogenic assays and expansion in a liquid culture of progenitor-enriched cell suspensions from HCB. A series of 8 reference molecules, doxorubicin, cytosine-arabinoside, 5-fluorouracil, 3-azido-3-deoxythymidine, acetylsalicyclic acid, sodium valproate and two cephalosporin antibiotics, were tested. In vitro 50% inhibition concentrations (IC₅₀) were compared to those observed or reported with BM progenitors, and to the values of plasma concentrations from treated patients. HCB progenitors as in vitro targets for cytotoxic molecules were easy to access and handle, and their use was sensitive, specific and reproducible. They gave results similar to BM progenitors and allowed a qualitative approach to cellular metabolism and toxicity using morphological, flow cytometric and chromatographic methods.Abbreviations ARA-CC cytosine arabinoside - AS acetylsalicylic acid - AZTT 3-azido-3-deoxythymidine - BFUU burst-forming units - BM bone marrow - CFU colony-forming units - DOXX doxorubicin - FU 5-fluorouracil - glyAA glyAcophorin A - HCB human umbilical cord blood - IU international units - PCMEM human placenta-conditioned medium - VA sodium valproate     

Further studies on an intermediate host murine model showing that a primary Echinococcus granulosus infection is protective against subsequent oncospheral challenge

We describe the use of a murine model to evaluate resistance against subsequent challenge following a primary infection with oncospheres of Echinococcus granulosus. Mice (Kunming strain) were infected with hatched oncospheres of Echinococcus granulosus; 21 days later a second challenge was given by a different route of infection. A primary infection by intraperitoneal (i.p.) injection stimulated 100 and 90.5% protection in terms of reduced cyst numbers against a secondary infection given subcutaneously (s.c.) or intravenously (i.v.), respectively. A primary infection given s.c. followed by i.p. or i.v. challenge resulted in 84.0 and 100% protection, respectively. Intravenous infection followed by i.p. or s.c. challenge resulted in 98.5 and 69.4% protection, respectively. With the i.v. route of infection, almost all resultant cysts were present in the lungs. The data show that a primary infection with oncospheres can induce total or a high degree of protection against a subsequent challenge and confirms that natural (concomitant) immunity can be stimulated in the intermediate host as the result of a primary infection. This may explain the decline in hydatid infection in sheep older than 2 years in hyper-endemic areas such as those found in Xingjiang, China. These older sheep may have been earlier infected and have subsequently self-cured, with the primary infection stimulating an immune response that protects the intermediate host animals from further infection.     

Small ruminants: Digestive capacity differences among four species weighing less than 20 kg

Small ruminants are generally classified as either browsers or frugivores. We compared intake and digestion in one browsing species, the pudu (Pudu pudu), body weight 9 kg, and three frugivorous species, the red brocket (Mazama americana), 20 kg, the bay duiker (Cephalophus dorsalis), 12 kg, and Maxwell's duiker (C. maxwellii), 9 kg. Rations comprised: a commercial grain and alfalfa pellet, a small amount of vegetables, and mixed hay. Across species, neutral-detergent fiber (insoluble fiber) consumed averaged 34.2 ± 2.6% of dry matter (DM) while the crude protein consumed averaged 16.1 ± 0.5% DM. Apparent DM digestion was similar in pudu (75.2 ± 4.7%), brocket (73.2 ± 1.1%), and Maxwell's duikers (73.0 ± 2.8%), and significantly lower (P = 0.0167) in bay duikers (67.1 ± 4.3%). There were significant differences among species in digestibilities of neutral-detergent fiber, hemicellulose, and cellulose, but they did not follow body size differences, since larger species were expected to show higher digestion coefficients for fiber compared to smaller species. The type of fiber fed may have influenced these results. Frugivores may be adapted to a diet of soluble fibers, as might be found in wild fruits, instead of the insoluble fibers in the diet fed. Passage trials were conducted on the two smallest species. The mean transit time for pudu was 29.9 ± 0.8 hr, and for the Maxwell's duiker was 42.2 ± 6.4 hr. © 1996 Wiley-Liss, Inc.     

Consensus Brain-derived Protein,Extraction Protocol for the Study of Human and Murine Brain Proteome Using Both 2D-DIGE and Mini 2DE Immunoblotting

Two-dimensional gel electrophoresis (2DE) is a powerful tool to uncover proteome modifications potentially related to different physiological or pathological conditions. Basically, this technique is based on the separation of proteins according to their isoelectric point in a first step, and secondly according to their molecular weights by SDS polyacrylamide gel electrophoresis (SDS-PAGE). In this report an optimized sample preparation protocol for little amount of human post-mortem and mouse brain tissue is described. This method enables to perform both two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) and mini 2DE immunoblotting. The combination of these approaches allows one to not only find new proteins and/or protein modifications in their expression thanks to its compatibility with mass spectrometry detection, but also a new insight into markers validation. Thus, mini-2DE coupled to western blotting permits to identify and validate post-translational modifications, proteins catabolism and provides a qualitative comparison among different conditions and/or treatments. Herein, we provide a method to study components of protein aggregates found in AD and Lewy body dementia such as the amyloid-beta peptide and the alpha-synuclein. Our method can thus be adapted for the analysis of the proteome and insoluble proteins extract from human brain tissue and mice models too. In parallel, it may provide useful information for the study of molecular and cellular pathways involved in neurodegenerative diseases as well as potential novel biomarkers and therapeutic targets.