Organic matter mineralization in the pore water of a eutrophic lake (Aydat Lake,Puy de Dôme,France)

The chemical composition of the pore water from the sediment of a eutrophic lake is dominated by high concentrations of total dissolved CO₂ (up to 12 mM), reduced soluble iron (up to 2 mM) and dissolved silica (up to 1 mM). The pH lies within the range of 6.70 ± 0.02; this reflects that the pore water is efficiently buffered by the CO₂ acid/base system. This composition is directly related to the main diagenetic reactions which drive the organic matter mineralization i.e. methanogenesis and ferric oxides reduction. Other geochemical processes are of minor importance. A stoichiometric model based on these main reactions allow us: (i) to define a general formula for the organic matter which is close to Redfield's one for the C:N ratio, while the C:P ratio is much higher owing to a probable adsorption of phosphorus onto reactive surfaces of the solid and due to heterotrophic bacterial uptake; (ii) to calculate a global first order kinetic constant which drives the organo-polymers breakdown. Due to the strong influence on the trophic status of the lake caused by an excess of phosphate, special attention is devoted to this species. We show that the sediment-water interface is a source of dissolved phosphate when the hypolimnion is anoxic between May and November. This contribution represents about 17% of the river input and should be taken into account in any attempt toward lake restoration.     

Randomised controlled trial of enalapril and beta blockers in non-diabetic chronic renal failure.

OBJECTIVE--To compare the ability of angiotensin converting enzyme inhibitors and beta blockers to slow the development of end stage renal failure in non-diabetic patients with chronic renal failure. DESIGN--Open randomised multicentre trial with three year follow up. SETTING--Outpatient departments of six French hospitals. PATIENTS--100 hypertensive patients with chronic renal failure (initial serum creatinine 200-400 mumol/l. 52 randomised to enalapril and 48 to beta blockers (conventional treatment). INTERVENTIONS--Enalapril or beta blocker was combined with frusemide and, if necessary, a calcium blocker or centrally acting drug in patients whose diastolic pressure remained above 90 mm Hg. RESULTS--17 patients receiving conventional treatment and 10 receiving enalapril developed end stage renal failure. The cumulative renal survival rate was significantly better in the enalapril group than in the conventional group (P < 0.05). The slope of the reciprocal serum creatinine concentration was steeper in the conventionally treated patients (-6.89 x 10(-5)l/mumol/month) than in the enalapril group (-4.17 x 10(-5)l/mumol/month; P < 0.05). No difference in blood pressure was found between groups. CONCLUSION--In hypertensive patients with chronic renal failure enalapril slows progression towards end stage renal failure compared with beta blockers. This effect was probably not mediated through controlling blood pressure.     

Age-specific survival and reproductive performances in fur seals: evidence of senescence and individual quality

Life history theory hypothesises that breeding events induce reproductive costs that may vary among individuals. However, the growing number of studies addressing this question are taxonomically biased, therefore impeding the generalisation of this hypothesis, especially with regard to marine top predators. This study investigated age‐related survival and breeding performances in subantarctic fur seal (Arctocephalus tropicalis) females from Amsterdam Island, southern Indian Ocean. Using multistate capture–recapture models on data obtained from known‐age tagged females over eight consecutive years, we tested for evidence of senescence, individual quality, and reproductive costs in terms of future survival and fecundity. Adult female yearly survival appeared high and constant throughout time. While a two age‐class model was preferred in non‐breeders, breeding females exhibited three age classes with a maximum survival for the prime‐age class (7–12 years). Survival and reproductive probabilities decreased from 13 years onward, suggesting senescence in this population. Survival was lower for non‐breeders than for breeders, among both prime‐aged (0.938 vs 0.982) and older (0.676 vs 0.855) females. Furthermore, non‐breeders exhibited higher probabilities of being non‐breeders the following year than did breeders (0.555 vs 0.414). Such results suggest consistency in female breeding performance over years, supporting the hypothesis that non‐breeding tend to occur among lower quality individuals rather than representing an alternative strategy to enhance residual reproductive value. However, the high proportion of females that did not breed during two consecutive years, and the lower probability of being a successful breeder after a greater reproductive effort confirmed the existence of reproductive costs, especially during the second half of the lactation. These results also suggest that younger age‐classes included a higher proportion of lower quality individuals, which are likely to face higher costs of reproduction. Such hypotheses lead to consider the first breeding event as a filter generating a within‐cohort selection process in females.     

KCNE1 is an auxiliary subunit of two distinct ion channel superfamilies

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Context-specific calls in wild chimpanzees, Pan troglodytes verus: analysis of barks

Context-specific calls, which have a distinct acoustic structure and are selectively produced in specific contexts, are a prerequisite for calls that function referentially. Functionally referential calls, which convey information to conspecifics about objects and events in the external world, have been found in a number of species, notably primates. Evidence of context-specific calls in apes, however, is largely absent. We analysed whether the barks of wild male chimpanzees in the Ta? Forest, Côte d'Ivoire, are context specific. We examined the acoustic structure of barks, and other calls produced in association with barks, in six contexts, using discriminant function analysis. Chimpanzees produced context-specific signals in two ways. First, they produced two acoustically graded bark subtypes, in hunt and snake contexts, respectively. Second, they produced context-specific signal combinations of barks with acoustically different call types or drums. These signal combinations increased specificity levels in three of the six contexts to over 90%, a level similar to the classic vervet monkey, Cercophithecus aethiops, predator alarm calls. Furthermore, specific chimpanzee signals were produced in contexts other than alarm, such as travel and hunting, where the potential benefits of evolving specific calls are less obvious. These signals may convey specific context information to listeners, and thus function referentially; however, to confirm this, analyses of listeners' responses are required. The results show that two strategies for producing context-specific signals seem to have evolved in a species other than humans: chimpanzees produce context-specific bark subtypes and context-specific signal combinations. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Phenotypic switch of smooth muscle cells in paediatric chronic intestinal pseudo-obstruction syndrome

Smooth Muscle Cells (SMC) are unique amongst all muscle cells in their capacity to modulate their phenotype. Indeed, SMCs do not terminally differentiate but instead harbour a remarkable capacity to dedifferentiate, switching between a quiescent contractile state and a highly proliferative and migratory phenotype, a quality often associated to SMC dysfunction. However, phenotypic plasticity remains poorly examined in the field of gastroenterology in particular in pathologies in which gut motor activity is impaired. Here, we assessed SMC status in biopsies of infants with chronic intestinal pseudo-obstruction (CIPO) syndrome, a life-threatening intestinal motility disorder. We showed that CIPO-SMCs harbour a decreased level of contractile markers. This phenotype is accompanied by an increase in Platelet-Derived Growth Factor Receptor-alpha (PDGFRA) expression. We showed that this modulation occurs without origin-related differences in CIPO circular and longitudinal-derived SMCs. As we characterized PDGFRA as a marker of digestive mesenchymal progenitors during embryogenesis, our results suggest a phenotypic switch of the CIPO-SMC towards an undifferentiated stage. The development of CIPO-SMC culture and the characterization of SMC phenotypic switch should enable us to design therapeutic approaches to promote SMC differentiation in CIPO.