Stochastic determinants of assemblage patterns in coral reef fishes: a quantification by means of two models

Synopsis One perspective emphasizing the importance of stochastic processes in determining coral reef fish assemblages implies that there is little organization in species richness, abundance structure, and spatial distribution. We examine the degree to which this perspective is correct by analyzing distribution of fishes on a collection of patch reefs (Discovery Bay, Jamaica). We ask the question whether these patches accumulate species and individuals in a manner consistent with stochastic expectations. To address this question we use two conceptual models, each permitting a different insight. One assumes that fish are distributed stochastically on patches while the other assumes presence of restrictions on fish distribution due to habitat structure. For each conceptual model we use two types of benchmark: we compare observed patterns to those predicted by theoretical models, and we also compare observed patterns to those obtained from a random reallocation of fish individuals to patches. We found that the conceptual model assuming stochastic processes appeared to provide weaker explanation of patterns than the conceptual model that includes restrictions due to habitat structure. Further, and more importantly, we found that (i) the community is shaped by a mixture of stochastic and non-stochastic mechanisms, and (ii) the stochastic assembly processes decrease in importance for species restricted to fewer microhabitat types and sites. Our study therefore indicates that patches do accumulate individuals and species in a manner consistent with stochastic expectations, however, this applies primarily to the habitat generalists (unrestricted species). By the same token, increased habitat specialization by some species imposes constraints on the stochastic model such that it eventually fails.     

Diversity concept in ecology

Hierarchy of systems organization is used as a framework in advancing methodological guidelines for posing correct questions related to ecological diversity.Diversity if defined in general terms as a property of a set of elements dependent on and determines: by the epistemological perspective. Ontological diversity, because it is indefinite, is regarded as unmeasurable.Ecological diversity — be it species, spatial, reproductive or trophic, is a particular case of diversity of matter and must be precisely defined on the studied level of system organization.Diversity measurements combining more than one level of organization are information-void, for data become irretrievable as a result of such a treatment.Hypotheses explaining diversity sources are briefly surveyed. An integrated model interrelating them is constructed as a result of some basic views on the structure of matter coupled with the empirical knowledge of involved factors. The model reflects hierarchies of systems, their dynamics, and the complexities of factors affecting diversity. The model's properties suggest that it is conceptually related to an imaginary model of organization of ecological systems. Parameters recognized as invariant components of this complexity are: habitat differentiation, ecological specialization of species, ambiental changes, and integration of this system.Finally, it is shown that the peculiar shape of the species abundances curve is a necessary consequence of stratification of the system structure, which is an intrinsic attribute of hierarchical organization.     

Adrenalectomy Potentiates Immediate Early Gene Expression in Rat Brain

Administration of kainate or pentylenetetrazole increased c-fos, c-jun, junB, and junD mRNA levels in rat brain in a dose-dependent manner. Kainate increased these mRNA levels predominantly in the hippocampus, and pentylenetetrazole was more effective in the cortex. Adrenalectomy (3 days) was used to eliminate endogenous glucocorticoid hormones. Adrenalectomy significantly potentiated kainate-induced increases, compared with increases caused by kainate (4 mg/kg) alone, in the hippocampal mRNA levels of c-fos and junB by 6.5-fold and of junD by twofold and tended to augment c-jun mRNA. Corticosterone administration blocked the potentiated stimulation of these mRNA levels caused by adrenalectomy. Adrenalectomy also significantly increased pentylenetetrazole-induced levels of c-fos mRNA in the cortex. These results demonstrate that glucocorticoids modulate immediate early gene expression in the brain, raising the possibility that this interaction contributes to interneuronal and interindividual differences in responses to stimuli and to the effects of stress- or disease-induced changes in glucocorticoid concentrations.     

Hymenolepis diminuta: Analysis of the expression of Toll-like receptor genes (TLR2 and TLR4) in the small and large intestines of rats. Part II

Toll-like receptors in the gastrointestinal tract can influence intestinal homeostasis and play a role in the repair and restitution of intestinal epithelium following tissue damage. In our previous study a statistically significant increase in the level of TLR4 and TLR2 gene expression was observed in rats in early stages of hymenolepidosis. Moreover, the immunopositive cell number and the intensity of immunohistochemical staining (indicating the presence of TLRs within intestinal epithelial cells) increased over the infection period.     

Predicting the occurrence of persistent hotspots in ecosystem variables

Ecological resources and services (e.g. organisms, nutrient cycling) are distributed heterogeneously across landscapes. While spatial variation has been studied extensively, the pattern of hotspots and coolspots persisting over time – called persistent spatial variation (PSV) – has not. Yet this pattern imparts key information to managers about whether resources will be found consistently in certain locations or vary unpredictably. Anticipating whether an ecosystem variable will display PSV is thus a valuable prospect. We tested the ability of attributes of variables (e.g. niche breadth, abundance, temporal scale) to predict the occurrence of PSV. Using a new measure of PSV based on the F‐value of analysis of variance, we were able to 1) decompose the pattern of persistent hotspots into spatial and temporal components – ‘spatial variation’ of site mean values and ‘stability’ of time series at each site – and 2) identify predictors of these patterns in temperate lakes and tropical coastal rock pools. We found PSV to be highly predictable (R2 = up to 0.80) from an estimate of stability taken at a single site, as well as from other factors related to stability. These factors included whether the variable was environmental (stable, slow) or was an aggregate of other variables (stabilized by statistical averaging). Species properties like niche position and abundance were modest predictors because they correlated with PSV components of site occupancy, spatial variation and stability. We conclude that PSV and the distribution of resources in space and time might be predicted from simple temporal indicators (e.g. stability at a single location) when data are scarce.     

A-350619: a novel activator of soluble guanylyl cyclase

Nitric oxide (NO) is a key mediator in many physiological processes and one of the major receptors through which NO exerts its effects is soluble guanylyl cyclase. Guanylyl cyclase converts GTP to cyclic GMP as part of the cascade that results in physiological processes such as smooth muscle relaxation, neurotransmission, inhibition of platelet aggregation and immune response. The properties of A-350619, a novel soluble guanylyl cyclase activator, were examined to determine the modulatory effect on the catalytic properties of soluble guanylyl cyclase. A-350619 increased V(max) from 0.1 to 14.5 micromol/min/mg (145 fold increase), and lowered K(m) from 300 to 50 microM (6 fold decrease). When YC-1 (another sGC activator) and A-350619 were combined, a 156 fold increase in V(max) and a 5 fold decrease in Km were observed, indicating that the modulation of the enzyme brought about by YC-1 and A-350619 are not additive, suggesting a common binding site. Activation of soluble guanylyl cyclase by A-350619 was partially inhibited by ODQ, a specific inhibitor of soluble guanylyl cyclase by oxidation of the enzyme heme. YC-1 and A-350619 after pre-treatment with N-omega-nitro-L-arginine, an NO-synthase inhibitor, relaxed cavernosum tissue strips in a dose-dependent manner with EC(50) of 50 microM and 80 microM, respectively. Addition of SNP potentiated the relaxation effect of YC-1 and A-350619, shifting the dose-response curve to the left to 3 microM and 10 microM, respectively. Consistent with its biochemical activity, A-350619 (1 micromol/kg) alone induced penile erection in a conscious rat model. Activation of soluble guanylyl cyclase in cavernosum tissue as an alternate method of enhancing the effect of NO may provide a novel treatment of sexual dysfunction.     

Rapid hit to lead evaluation of pyrazolo[3,4-d]pyrimidin-4-one as selective and orally bioavailable mGluR1 antagonists

Our HTS effort yielded a preferential mGluR1 pyrimidinone antagonist 1 with lead-like characteristics. Rapid hit to lead (HTL) study identified compounds with improved functional activity and selectivity such as 1b with little improvements in ADME properties. Addition of an aminosulfonyl group on the N-1 aromatic ring led to 2f, a compound with similar in vitro biochemical profiles as those of 1b but drastically improved in vitro ADME properties. These improvements were paralleled by rat PK study characterized by low clearance and quantitative bioavailability. Compound 2f represented a true lead-like molecule that is amenable for further lead optimization (LO) evaluation.     

Hormonal status of male reproductive system: androgens and estrogens in the testis and epididymis. In vivo and in vitro approaches

The purpose of this article was to summarize our results on the role of androgens and estrogens in human, rodent and equine testes and epididymides, in both, physiological and patological conditions, obtained in the space of the Solicited Project (084/PO6/2002) financially supported by the State Committee for Scientific Research during the last three years. Testosterone produced by Leydig cells of the testes is clearly the major androgen in the circulation of men and adult males of most mammalian species. However, androgen metabolites make up a significant fraction of total circulating steroids. Moreover, androgen metabolism may proceed to amplify the action of testosterone through its conversion to dihydrotestosterone (DHT) or its aromatization to estradiol. The distribution of androgen and estrogen receptors (ARs and ERs) within male reproductive tissues is important because of their crucial role in mediating androgen and/or estrogen action. Attempts were undertaken to discuss not only the role of aromatase and ERs in mediating the action of estrogens in the male, but also the importance of DHT in hormonal regulation of the epididymis. In the latter, alterations caused by finasteride treatment and lead-induced oxidative stress are described. Male reproductive function of the testis and epididymis reflected by the alterations in enzymatic activity, distribution of steroid hormone receptors, differences in steroid hormone levels and altered gene expression of antioxidant enzymes are also discussed.     

Environmental Productivity and Biodiversity Effects on Invertebrate Community Invasibility

Productivity influences the availability of resources for colonizing species. Biodiversity may also influence invasibility of communities because of more complete use of resource types with increasing species richness. We hypothesized that communities with higher environmental productivity and lower species richness should be more invasible by a competitor than those where productivity is low or where richness is high. We experimentally examined the invasion resistance of herbivorous meiofauna of Jamaican rock pools by a competitor crustacean (Ostracoda: Potamocypris sp. (Brady)) by contrasting three levels of nutrient input and four levels of species richness. Although relative abundance (dominance) of the invasive was largely unaffected by resource availability, increasing resources did increase the success rate of establishment. Effects of species richness on dominance were more pronounced with a trend towards the lowest species richness treatment of 2 resident species being more invasible than those with 4, 6, or 7 species. These results can be attributed to a ‘sampling effect associated with the introduction of Alona davidii (Richard) into the higher biodiversity treatments. Alona dominated the communities where it established and precluded dominance by the introduced ostracod. Our experimental study supports the idea that niche availability and community interactions define community invasibility and does not support the application of a neutral community model for local food web management where predictions of exotic species impacts are needed.     

Hymenolepis diminuta: analysis of the expression of Toll-like receptor genes (TLR2 and TLR4) in the small and large intestines of rats

Toll receptors play a critical role in the rapid activation of innate immune responses to a variety of pathogens. In mammals, Toll-like receptors (TLR) have been found in both immune related cells and other cells. At present little is known about the participation of TLR in host defense mechanisms during parasitic infections. The aim of this study was to determine the expression of TLR2 and TLR4 genes in rat intestines during experimental hymenolepidosis. There is difference in expression of TLR2 and TLR4 genes in the colon and jejunum in uninfected rats: in the colon, mRNA of the examined TLR is present in much higher amounts than the jejunum, while the protein of the TLR also had a segmented specific distribution. In the jejunum isolated rats infected with Hymeolepis diminuta 6 and 8 days post infection (dpi), mRNA for TLR4 and TLR2 were significantly more strongly expressed in comparison with the uninfected controls. In the colon, a statistically significantly increased expression of TLR4 gene was observed only at 6 dpi, and at 8 dpi for the TLR2 gene. Moreover, we observed that during inflammation, the immunopositive cell number and the intensity of immunohistochemical staining (indicating the presence of TLR within intestinal epithelial cells), increased together with the duration of the infection period.