Competition across diverse taxa: quantitative integration of theory and empirical research using global indices of competition

A main limitation for quantitative assessments of the effect of species richness and competition intensity on ecosystem functions is that the number of model parameters to estimate for a S ‐species community grows at least as S ². We propose and evaluate a novel framework based on a set of global, i.e. for the whole community, indices of competition (GIC) that allows quantitative predictions of community productivity without knowing the entire community matrix. This framework also serves for comparisons among widely different taxa. These GICs were mostly evaluated in communities of primary producers and are expressible in terms of relative yields (mixture biomass/monoculture biomass), such as the relative yield total (RYT ) ? the total sum of relative yields ? and the mean relative yield (MRY ). Specifically: 1) we conducted a meta‐analysis of 166 published competition experiments covering a wide variety of communities ? bacteria, protists, plankton, plants, fish, insects, mammals. For each experiment we computed the set of GICs. 2) We derived from the Lotka–Volterra competition model (LVCM) analytical expressions for the RYT and MRY in terms of the species richness and the mean value of the interspecific interaction coefficients. 3) We tested the agreement of such expressions with the corresponding empirical GICs computed in 1). The main findings are: First, the RYT (significantly different among taxonomic groups) increases with the species richness S; conversely the MRY (not different among groups) decreases with S . Second, these analytical expressions for the RYT and MRY , besides giving the above qualitative dependence on S , reproduce with accuracy these empirical GIC. Third, we thus show that our general formulas can be used to assess the effects of competition on global community attributes in cases with incomplete information on the LVCM parameters (i.e. when only a subset of these parameters is known).     

N2 Fixation (C2H2-Reducing Activity) and Leghaemoglobin Content during Nitrate- and Water-Stress-Induced Senescence of Medicago sativa Root Nodules

Nitrate and water stress were used to induce senescence in rootnodules of alfalfa (Medicago sativa L. cv. Aragon). Nodule senescencewas assessed by determinations of the nitrogenase (C₂H₂-reducing)activity, and the leghaemoglobin (LHb) and total soluble proteincontents of the nodules. Nodules responded similarly to and water stress in many respects, but there was a significant difference.All parameters of nodule activity, expressed on the basis ofnodule dry weight (DW), consistently decreased following treatmentwith or during drought; there was a significant interaction (synergism) between the inhibitory effects of and water stress on nitrogenase activity, but sucheffects were merely additive in the case of LHb content or LHb/solubleprotein ratio. However, caused the selective decay of LHb with respect to other nodular soluble proteins,whereas the decrease of LHb during water stress was due to ageneral inhibition of protein synthesis and to an increasedproteolytic activity in the nodule cytosol rather than to aspecific proteolysis of LHb. Key words: Leghaemoglobin, Medicago saliva, nitrogen fixation, root nodule senescence, water stress     

Complete nucleotide sequence of the messenger RNA coding for chicken muscle glyceraldehyde-3-phosphate dehydrogenase

The complete nucleotide sequence for chicken glyceraldehyde-3-phosphate dehydrogenase mRNA has been determined, thereby extending the longest such sequence previously reported (Dugaiczyk et al. Biochemistry, 1983, 22, 1605-1613) by 27 nucleotides. The complete mRNA with the exclusion of poly(A) is 1284 nucleotides long and contains 56 nucleotides of 5' non coding sequence and 229 nucleotides of 3' non coding region. Knowledge of the complete sequence allows us to propose secondary structures models which may be of biological significance.     

Morphology agrees with molecular data: phylogenetic affinities of Euptychiina butterflies (Nymphalidae: Satyrinae)

Euptychiina is the most species‐rich subtribe of Neotropical Satyrinae, with over 450 known species in 47 genera (14 monotypic). Here, we use morphological characters to examine the phylogenetic relationships within Euptychiina. Taxonomic sampling included 105 species representing the majority of the genera, as well as five outgroups. A total of 103 characters were obtained: 45 from wing pattern, 48 from genitalia and 10 from wing venation. The data matrix was analysed using maximum parsimony under both equal and extended implied weights. Euptychiina was recovered as monophyletic with ten monophyletic genera, contrasting previous DNA sequence‐based phylogenies that did not recover the monophyly of the group. In agreement with sequence‐based hypotheses, however, three main clades were recognized: the ‘Megisto clade’ with six monophyletic and three polyphyletic genera, the ‘Taygetis clade’ with nine genera of which three were monophyletic, and the ‘Pareuptyhia clade’ with four monophyletic and two polyphyletic genera. This is the first morphology‐based phylogenetic hypothesis for Euptychiina and the results will be used to complement molecular data in a combined analysis and to provide critical synapomorphies for clades and genera in this taxonomically confused group.     

Modelling of the qualitative discrimination of odours in the first two layers of olfactory system by Jutten and Hérault algorithm.

The olfactory system discriminates many different odours although membrane receptors, and neuroreceptors that bear them, are only broadly tuned to volatile molecules. We investigated how mixed and redundant information carried by neuroreceptors could be efficiently coded by output neurons in the second neuronal layer in the brain. We showed that a good discrimination is yielded if neuroreceptors that terminate on the same output neuron belong to several types, if these types are in different proportions for each output neuron, and if each output neuron exerts an action on all others so that their independence is maximized, according to the Jutten and Hérault algorithm for separating linear mixtures of independent sources. The proposed model details the computations made by neurons and leads to a better understanding of several observed properties of the olfactory system, among which the inhibitory actions of local neurons of the second layer and the identifiability of insect glomeruli.     

Role of the melanin-concentrating hormone neuropeptide in sleep regulation

Melanin-concentrating hormone (MCH), a neuropeptide secreted by a limited number of neurons within the tuberal hypothalamus, has been drawn in the field of sleep only fairly recently in 2003. Since then, growing experimental evidence indicates that MCH may play a crucial role in the homeostatic regulation of paradoxical sleep (PS). MCH-expressing neurons fire specifically during PS. When injected icv MCH induces a 200% increase in PS quantities in rats and the lack of MCH induces a decrease in sleep quantities in transgenic mice. Here, we review recent studies suggesting a role for MCH in the regulation of the sleep–wake cycle, in particular PS, including insights on (1) the specific activity of MCH neurons during PS; (2) how they might be controlled across the sleep–wake cycle; (3) how they might modulate PS; (4) and finally whether MCH might take part in the expression of some symptoms observed in primary sleep disorders.     

Hypervariable prophage WO sequences describe an unexpected high number of Wolbachia variants in the mosquito Culex pipiens

Wolbachia are maternally inherited endosymbiotic bacteria that infect many arthropod species and may induce cytoplasmic incompatibility (CI) resulting in abortive embryonic development. Among all the described host species, mosquitoes of the Culex pipiens complex display the highest variability of CI crossing types. Paradoxically, searches for polymorphism in Wolbachia infecting strains and field populations hitherto failed or produced very few markers. Here, we show that an abundant source of the long-sought polymorphism lies in WO prophage sequences present in multiple copies dispersed in the genome of Wolbachia infecting C. pipiens (wPip). We identified up to 66 different Wolbachia variants in C. pipiens strains and field populations and no occurrence of superinfection was observed. At least 49 different Wolbachia occurred in Southern Europe C. pipiens populations, and up to 10 different Wolbachia were even detected in a single population. This is in sharp contrast with North African and Cretan samples, which exhibited only six variants. The WO polymorphism appeared stable over time, and was exclusively transferred maternally. Interestingly, we found that the CI pattern previously described correlates with the variability of Gp15, a prophage protein similar to a bacterial virulence protein. WO prophage sequences thus represent variable markers that now open routes for approaching the molecular basis of CI, the host effects, the structure and dynamics of Wolbachia populations.     

Characterization of TCL, a new GTPase of the rho family related to TC10 andCcdc42

GTPases of the Rho family control a wide variety of cellular processes such as cell morphology, motility, proliferation, differentiation, and apoptosis. We report here the characterization of a new Rho member, which shares 85% and 78% amino acid similarity to TC10 and Cdc42, respectively. This GTPase, termed as TC10-like (TCL) is encoded by an unexpectedly large locus, made of five exons spanning over 85 kilobases on human chromosome 14. TCL mRNA is 2.5 kilobases long and is mainly expressed in heart. In vitro, TCL shows rapid GDP/GTP exchange and displays higher GTP dissociation and hydolysis rates than TC10. Using the yeast two-hybrid system and GST pull-down assays, we show that GTP-bound but not GDP-bound TCL protein directly interacts with Cdc42/Rac interacting binding domains, such as those found in PAK and WASP. Despite its overall similarity to TC10 and Cdc42, the constitutively active TCL mutant displays distinct morphogenic activity in REF-52 fibroblasts, producing large and dynamic F-actin-rich ruffles on the dorsal cell membrane. Interestingly, TCL morphogenic activity is blocked by dominant negative Rac1 and Cdc42 mutants, suggesting a cross-talk between these three Rho GTPases.     

Carbon and nitrogen content based estimation of the fat content of animal carcasses in various species

The objective of this study was to explore whether the C and N content can be used to estimate the fat content of animal carcasses. Considering the mean C and N contents of body fat and body protein, the fat content (EE) [%] can be predicted from C and N values [%] according to the generally valid equation EE=1.3038·C – 4.237·N. The application of this equation to estimate the total fat content of all animal carcasses results in significant differences in fat content between predicted and measured values. Therefore, we derived specific equations for rats, pigs, cattle, sheep, broilers and mice to predict the fat content by dual linear regression analysis (y=EE [% DM], x₁=C [% DM], x₂=N [% DM]) based on measured fat, C, and N contents of animal body samples. The specific equations for different animals showed residual standard deviations of 1.55, 1.63, 1.12, 1.35, 1.85 and 0.92% fat for rats, pigs, cattle, sheep, broilers and mice, respectively.