Natural selection drives patterns of lake-stream divergence in stickleback foraging morphology

To what extent are patterns of biological diversification determined by natural selection? We addressed this question by exploring divergence in foraging morphology of threespine stickleback fish inhabiting lake and stream habitats within eight independent watersheds. We found that lake fish generally displayed more developed gill structures and had more streamlined bodies than did stream fish. Diet analysis revealed that these morphological differences were associated with limnetic vs. benthic foraging modes, and that the extent of morphological divergence within watersheds reflected differences in prey resources utilized by lake and stream fish. We also found that patterns of divergence were unrelated to patterns of phenotypic trait (co)variance within populations (i.e. the ‘line of least resistance’). Instead, phenotypic (co)variances were more likely to have been shaped by adaptation to lake vs. stream habitats. Our study thus implicates natural selection as a strong deterministic force driving morphological diversification in lake–stream stickleback. The strength of this inference was obtained by complementing a standard analysis of parallel divergence in means between discrete habitat categories (lake vs. stream) with quantitative estimates of selective forces and information on trait (co)variances.     

Structural characterization of the acid-degraded secondary cell wall polymer of Geobacillus stearothermophilus PV72/p2

The secondary cell wall polymer (SCWP) from Geobacillus stearothermophilus PV72/p2, which is involved in the anchoring of the surface-layer protein to the bacterial cell wall layer, is composed of 2-amino-2-deoxy- and 2-acetamido-2-deoxy-D-glucose, 2-acetamido-2-deoxy-D-mannose, and 2-acetamido-2-deoxy-D-mannuronic acid. The primary structure of the acid-degraded polysaccharide--liberated by HF-treatment from the cell wall--was determined by high-field NMR spectroscopy and mass spectrometry using N-acetylated and hydrolyzed polysaccharide derivatives as well as Smith-degradation. The polysaccharide was shown to consist of a tetrasaccharide repeating unit containing a pyruvic acid acetal at a side-chain 2-acetamido-2-deoxy-alpha-D-mannopyranosyl residue. Substoichiometric substitutions of the repeating unit were observed concerning the degree of N-acetylation of glucosamine residues and the presence of side-chain linked 2-acetamido-2-deoxy-beta-D-glucopyranosyl units: [Formula: see text].     

Entamoeba histolytica: response of the parasite to metronidazole challenge on the levels of mRNA and protein expression

Entamoeba histolytica remains a cause of significant morbidity and mortality in many countries. Although metronidazole has been used for the treatment of amoebiasis for several decades, little is known on how the amoebae react to this challenge on the levels of mRNA and protein expression. In this study, we examined their response using a focused microarray, quantitative RT-PCR, and two-dimensional gel electrophoresis (2DE). The amoebae modestly increased the levels of mRNA coding for superoxide dismutase, peroxiredoxin, ferredoxin, thioredoxin reductase, and the galactose/N-acetylgalactosamine specific lectin light and heavy chains. The mRNAs encoding actin and the 70 kDa and 101 kDa heat shock proteins were decreased. All the changes occured within 1 h of exposition, with very little further changes. In addition, the proteome revealed only very few changes. Taken together, E. histolytica appears to make only modest mRNA and protein expression changes when confronted with an unknown chemical stress.     

Effects of nitric oxide in 5-hydroxytryptamine-, cholera toxin-, enterotoxigenic Escherichia coli- and Salmonella Typhimurium-induced secretion in the porcine small intestine

The effects of nitric oxide (NO) in the secretory response to the endogenous secretagogue 5-hydroxytryptamine (5-HT), the enterotoxins heat-labile enterotoxigenic Escherichia coli (ETEC) toxin (LT) and cholera toxin (CT), and various cultures of ETEC and Salmonella serotype Typhimurium in the porcine small intestine (Sus scrofa) were investigated. In anaesthetized pigs, jejunal tied-off loops were instilled with 5-HT, LT, CT, various cultures of ETEC or S. Typhimurium. Pigs were given intravenously isotonic saline or isotonic saline containing the NO synthase inhibitor, N^ω-nitro-l-arginine methyl ester (L-NAME). L-NAME significantly induced an increased fluid accumulation in loops induced by 5-HT, ETEC and stn-mutated S. Typhimurium. Fluid accumulation in loops instilled with wild-type S. Typhimurium was increased by L-NAME, although not significantly, while there was no effect on fluid accumulation induced by an invH-mutated isogenic strain. No significant effect of L-NAME was observed on the fluid accumulation induced by the purified enterotoxins LT and CT. The results also demonstrated a relatively large difference in the ability to induce fluid accumulation between the bacteria strains. Diastolic, systolic and mean blood pressures were significantly increased and the body temperature was significantly decreased in groups of pigs treated with L-NAME. In conclusion, the results suggest that NO has a proabsorptive effect in the intact porcine jejunum and is involved in the systemic vascular tone.     

Contractile properties,structure and fiber phenotype of intact and regenerating slow-twitch muscles of mice treated with cyclosporin A

We have studied the contractile properties, structure, fiber-type composition, and myosin heavy chain (MyHC) expression pattern of regenerating and intact soleus muscles of adult CBA/J mice treated with cyclosporin A (CsA) or vehicle solutions (Cremophor, saline). A comparison of muscles after 4-7 weeks drug application with those receiving vehicle showed that the isometric contractile force of intact drug-treated muscles was reduced (tetanus, -21%; twitch, -34%) despite normal mass and muscle cross-sectional area. The frequency of fast-twitch fibers was increased, whereas no innervation deficits, histopathological alterations, or changes in fiber numbers were observed. Regeneration after cryolesion of the contralateral soleus proceeded more slowly in CsA-treated than in vehicle-treated animals. Despite this, when muscle properties reached mature levels (4-7 weeks), muscle mass recovery was better in CsA-treated animals (30% higher weight, 50% more fiber profiles in cross-sections). The force production per unit cross-sectional area was deficient, but not the maximum tension. Twitch time-to-peak and half-relaxation time were shorter than controls correlating with a predominance of fast-twitch fibers (98% Type II fibers versus 16%-18% in control muscles) and fast MyHC isoforms. Partial reversal of this fast phenotype and an increase in muscle force were observed when the animals were left to recover without treatment for 5-8 weeks after CsA application over 7 weeks. The high numbers of fiber profiles in CsA-treated regenerated muscles and increased mass remained unchanged after withdrawal. Thus, CsA treatment has a hyperplastic effect on regenerating muscles, and drug-induced phenotype alterations are much more prominent in regenerated muscles.     

Mapping of genetic modifiers affecting the eye phenotype of ocular retardation (Chx10 or-J ) mice

Ocular retardation is a recessive murine mutation whose phenotypic expression is greatly affected by genetic background effects. Mice of the inbred 129/SvJ background that are homozygous for the Chx10^or-J mutation are blind and have a thin, poorly differentiated retina and no optic nerve. A backcross between 129/SvJ and Mus musculus castaneus (CASA/Rk) produced animals that were homozygous for the Chx10^or-J mutation, yet showed a much milder phenotype. Such animals, when brother-sister mated and selected for mild phenotype for several generations, resulted in partial recovery of visual function, including presence of an optic nerve and pupillary response. In this article we report a genome scan of phenotypic extremes of the backcross to identify the genetic loci affecting this phenotype modification. Our scan revealed significant loci on Chromosomes 6 and 14 where the CASA/Rk alleles are maintained selectively. Markers were developed near candidate genes, but no candidate gene could be identified unequivocally. Electronic Supplementary Material Electronic Supplementary material is available for this article at and accessible for authorised users.     

Endozoic algae in shelled gastropods — a new symbiotic association in coral reefs?

Endozoic microalgae were found in most snails collected from coral reefs and beachrock communities in the Red Sea. Algae were identified microscopically as well as by chromatography and spectrophotometry of pigment extracts. The algae were located in the hepatopancreas and the gonads, organs which are permanently concealed within the shell. According to pigment analysis, most of the endozoic algae belong the Chromophyta, perhaps dinoflagellates, except for a few chlorophytes.     

The carbon cycle and carbon dioxide over Phanerozoic time: the role of land plants

A model (GEOCARB) of the long-term, or multimillion year, carbon cycle has been constructed which includes quantitative treatment of (1) uptake of atmospheric CO₂ by the weathering of silicate and carbonate rocks on the continents, and the deposition of carbonate minerals and organic matter in oceanic sediments; and (2) the release of CO₂ to the atmosphere via the weathering of kerogen in sedimentary rocks and degassing resulting from the volcanic-metamorphic-diagenetic breakdown of carbonates and organic matter at depth. Sensitivity analysis indicates that an important factor affecting CO₂ was the rise of vascular plants in the Palaeozoic. A large Devonian drop in CO₂ was brought about primarily by the acceleration of weathering of silicate rock by the development of deeply rooted plants in well-drained upland soils. The quantitative effect of this accelerated weathering has been crudely estimated by present-day field studies where all factors affecting weathering, other than the presence or absence of vascular plants, have been held relatively constant. An important additional factor, bringing about a further CO₂ drop into the Carboniferous and Permian, was enhanced burial of organic matter in sediments, due probably to the production of microbially resistant plant remains (e.g. lignin). Phanerozoic palaeolevels of atmospheric CO₂ calculated from the GEOCARB model generally agree with independent estimates based on measurements of the carbon isotopic composition of palaeosols and the stomatal index for fossil plants. Correlation of CO₂ levels with estimates of palaeoclimate suggests that the atmospheric greenhouse effect has been a major factor in controlling global climate over the past 600 million years.     

Phylogenetic Relationships within Paxillus s. I. (Basidiomycetes, Boletales): Separation of a Southern Hemisphere Genus

Abstract: This study aimed to test the monophyly and present a generic concept of Paxillus s. I. Of special interest were the Southern hemisphere representatives of this genus. Using the primer combination LR0R-LR5, DNA sequence data were generated from the nuclear encoded 28S gene. A data set containing 900 bases was created for 30 different species. Phylogenetic analysis showed 3 main monophyletic groups, also supported by morphological, anatomical, ecological and chemical data. Taxonomic interpretation of these clearly differentiated groups corresponded to the genera PaxilIus s. str. and Tapinella and lead to the proposal of a new Southern hemisphere genus, Austro-paxillus , mycorrhizal with Nothofagus . New combinations are proposed.