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Gallala W.,Faculte des science de Gabes | Gaied M.E.,University of Sfax | Essefi E.,Ecole Nationale des Ingenieurs de Sfax ENIS | Montacer M.,University of Sfax
Journal of African Earth Sciences | Year: 2010

This paper is meant to study the stratigraphy, the mineralogy, the microstructure and the geochemistry of Pleistocene calcretes from eastern Tunisia in order to infer the environmental factors intervening in their formation.Samples of eight profiles of Pleistocene calcretes from eastern Tunisia were examined on the basis of a variety of techniques including Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), chemical analysis and Atomic Absorption Spectrophotometer (AAS) techniques. Then, the obtained data underwent a statistical analysis on the basis of Factor Analysis (FA) and Principal Component Analysis (PCA).On the basis of field missions, five different horizons have been differentiated from bottom to top of all profiles: nodular, powdery, massive Brecciated and laminar horizon. The mineralogical study shows two minerals categories inversely proportional: calcite and (quartz and the clay). It shows also shows that Palygorskite is the dominant clay mineral. The escarpment edge is capped by a limestone containing fibrous palygorskite. Finally, superficial calcrete are described: a brecciated horizon which occurs in pockets on the plateau surface. This study about eastern Tunisia revealed the occurrence of successive cycles of calcretisation. Pedogenesis, water table oscillation, sedimentogenesis and stromatogenesis are the intervening factors in the calcretisation process. During the Pleistocene, they interfered with each other according to the climatic pulsations. From the studied case, it may be noticed that the formation of each calcrete horizon is the result of a dominating process that takes place during a distinguishable stage. In the first stage, the pedogenic process is developed by palygorskite formation including authigenic replacement or formation from a precursor mineral, neoformation from the breakdown products of such minerals or neoformation from suitable solutions. In the second stage, the powdery horizon is formed in the slope of the distal zone which presents a drained environment. In the third stage, several diagenetic processes (cementing, compaction, dissolution...) contribute to the formation of the laminar and massive horizon. Since it is exposed to dryness for a long period, the massive horizon is harder and more compact. In the fourth stage, the banding of light-dark in the laminar horizons reflects a dry-wet season alternation seasons. Dark beds are formed by the stromatolitic cover were developed during the wet season, whereas light beds were developed in an extremely arid climate argued by the presence of the detrital grains. In the fifth stage, the brecciated horizon, which occupies the channels, is formed by well rolled concretions, which present a dismantling material of Early and Middle Pleistocene calcretes after the Post-Villafranchian compressive phase. Thus, calcretisation seems to have been controlled by periods of uplift and stability of the slope, given that calcrete formation might be inhibited by the activation of the sedimentation of colluvial materials as a consequence of the tectonic activity. We also suggest that groundwater and biological activity may play a significant role in the development of pedogenic, sedimentological and polygenetic calcrete cycles within the same sedimentary basin. The alternation of dry and wet climatic periods may be responsible for the calcrete genesis. © 2010 Elsevier Ltd.

Leclaire S.,CNRS Center of Evolutionary and Functional Ecology | Czirjak G.A,Leibniz Institute for Zoo and Wildlife Research | Hammouda A.,Faculte des science de Gabes | Gasparini J.,University Pierre and Marie Curie
BMC evolutionary biology | Year: 2015

BACKGROUND: Complex communities of bacteria inhabit the feathers of all birds. Under normal conditions, individuals maintain a healthy state by defending themselves against these potential invaders by preening. The immune system is only triggered when bacteria gain access into the body. Preening is, however, costly and may trade-off with investment in the immune system. To shed light on how birds balance the trade-off between immunity and preen secretions when facing high or low feather bacterial load, we experimentally manipulated feather bacteria load of feral pigeons (Columba livia), and investigated the effects on immune defenses.RESULTS: Birds facing high feather bacterial load had lower immune response to PHA skin-swelling test (a measure of induced pro-inflammatory capacity) than controls, while birds facing low feather bacterial load had higher blood bacterial killing ability (a measure of the capacity to eliminate bacterial pathogens) than controls. No other components of the immune system (i.e., hemagglutination and hemolysis capacity of plasma, primary and secondary responses to KLH and quantity of blood parasites) were found to be affected by feather bacterial load.CONCLUSION: Pigeons had previously been shown to adjust preening to feather bacterial load. The decrease in the energetically costly inflammatory response of birds experiencing high bacterial load suggests a trade-off between investment in preen secretion and immunity and reinforces the idea that feather microbiota may have a strong impact on the ecology and evolution of the avian host.

Hammouda A.,Faculte des science de Gabes | Selmi S.,Faculte des science de Gabes | Pearce-Duvet J.,CNRS Center of Evolutionary and Functional Ecology | Chokri M.A.,Faculte des science de Gabes | And 2 more authors.
PLoS ONE | Year: 2012

Female birds transfer antibodies to their offspring via the egg yolk, thus possibly providing passive immunity against infectious diseases to which hatchlings may be exposed, thereby affecting their fitness. It is nonetheless unclear whether the amount of maternal antibodies transmitted into egg yolks varies with female quality and egg laying order. In this paper, we investigated the transfer of maternal antibodies against type A influenza viruses (anti-AIV antibodies) by a long-lived colonial seabird, the yellow-legged gull (Larus michahellis), in relation to fluctuating asymmetry in females, i.e. the random deviation from perfect symmetry in bilaterally symmetric morphological and anatomical traits. In particular, we tested whether females with greater asymmetry transmitted fewer antibodies to their eggs, and whether within-clutch variation in yolk antibodies varied according to the maternal level of fluctuating asymmetry. We found that asymmetric females were in worse physical condition, produced fewer antibodies, and transmitted lower amounts of antibodies to their eggs. We also found that, within a given clutch, yolk antibody level decreased with egg laying order, but this laying order effect was more pronounced in clutches laid by the more asymmetric females. Overall, our results support the hypothesis that maternal quality interacts with egg laying order in determining the amount of maternal antibodies transmitted to the yolks. They also highlight the usefulness of fluctuating asymmetry as a sensitive indicator of female quality and immunocompetence in birds. © 2012 Hammouda et al.

Ammar S.,Institute Superieur Dinformatique Et Du Multimedia Of Sfax | Mabrouk M.,Faculte des science de Gabes
International Journal of Control | Year: 2010

The objective of the work is twofold. First, we investigate the problem of observer design for a class of systems in cascade form. We suppose that an observer exists for each subsystem and then prove that this interconnection is an observer for the overall system. One of both nonlinear functions is assumed to be not Lipschitz (e.g. to satisfy a quadratic constraint on the unmeasured part of the state). This first main result may be viewed as an improvement of Besancon and Hammouri (Besancon, G., and Hammouri, H. (1998), 'On Observers Design for Interconnected Systems', Journal of Mathematical Systems, Estimation and Control, 8, 377-380) in which the authors discussed the problem of the synthesis of interconnected observers. The second part is a generalisation of Ammar, Mabrouk, and Vivalda (Ammar, S., Mabrouk, M., and Vivalda, J.-C. (2009), 'Observer and Global Output Feedback Stabilisation for Some mechanical Systems', International Journal of Control, 82, 1070-1081) in which the authors study the problem of output feedback stabilisation for a class of Euler-Lagrange systems. The problem of global output feedback stabilisation of the practical system called the two-link manipulator system is solved. The output feedback scheme presented has better performance than the one exhibited in Ammar et al. (2009). © 2010 Taylor & Francis.

Frigui M.,Center des Recherches et des Technologies des Eaux | Ben Youssef M.,Center des Recherches et des Technologies des Eaux | Ouaja M.,Faculte des science de Gabes
Journal of African Earth Sciences | Year: 2016

Eight stratigraphic sections, located in northeastern part of the Sahel area of Tunisia recorded evidences of “Lago-Mare” episode and events related to the Messinian-Late Pliocene interval. A comparison with previous studies carried on sections from neighboring areas and boreholes data drilled within the Gulf of Hammamet and the Gulf of Gabès, is conducted and gives useful information to characterize the Late Messinian to Late Pliocene events. The most notable feature distinguished in the studied area consists on the lack of gypsum, commonly recorded in relation with the crucial event of the Messinian Salinity Crisis. However, only lagoonal deposits, bearing messinian brackish fauna, are encountered. These sediments are usually attributed to the “Segui” formation or the so called “Mio-Pliocene continental”. Thin sections samples and field observations have recognized sands, marls, clays, lacustrine limestone, some gypsum lenses, mud-cracks, lignite and Messinian brackish fauna. Similar deposits were previously described in the Kechabta basin from the Northern Tunisia and in some wells from the Gulf of Gabès and the Gulf of Hammamet. We suggest that all these facies belong to the coeval of the “Lago-Mare” facies within Eastern and Western Mediterranean basins (e.g. Sicily, Mallorca, Libya and Cyprus). Finally, four major erosional surfaces have been recorded within the Late Messinian-Late Pliocene deposits, aged post-Tortonian, intra-Messinian, Late Messinian and intra-Pliocene times. They seem to be the result of local tectonic uplifts and eustatic fluctuations. © 2016

Mahmoudi S.,Faculte des science de Gabes | Srasra E.,Center des Materiaux | Zargouni F.,Departement de Geologie
Journal of African Earth Sciences | Year: 2010

The Valangenian-Hauterivian clays of Tunisia located at Djebel Oust were characterised by chemical analysis, X-ray diffraction and scanning electron microscopy in order to determine if these clays are appropriate for the manufacturing of ceramic products for construction. The mineralogical study shows that these clays are mainly of illitic type. However, other clay minerals, such as kaolinite, I/Sm mixed-layer, and chlorite, are also present. The chemical analysis indicates that the clays are notably siliceous, carbonated and aluminous. The content of iron is variable. Under firing tests on clay raw material until 1200. °C, quartz, cristobalite, hematite, mullite and sillimanite minerals were also identified. The amount of interstratified I/Sm and chlorite is higher in the samples located at the west zone of Djebel Oust than those located at the east. However, under firing behaviour of both types of raw samples seems to be similar. As conclusion of this study, these clays meet the firing specifications required for the manufacturing of ceramic products for construction. © 2010.

Urbain X.,Catholic University of Louvain | Lecointre J.,Catholic University of Louvain | Mezdari F.,Faculte des science de Gabes | Miller K.A.,Columbia University | Savin D.W.,Columbia University
Journal of Physics: Conference Series | Year: 2012

Total and partial cross sections have been measured for the mutual neutralization of H- and H+ by means of a merged and inclined beam set-up. The low energy data between 10 meV and 5 eV contradict one previous set of measurements, while above 5 eV the data fall in excellent agreement with previously published results by two other groups.

Alaya-Ltifi L.,Faculte des science de Gabes | Selmi S.,Faculte des science de Gabes
European Journal of Wildlife Research | Year: 2014

Gabès region, in south-eastern Tunisia, is nowadays considered as one of the most remarkable pollution hotspots in the Mediterranean due to the emissions of the Gabès-Ghannouche factory complex of phosphate treatment. However, because of the lack of detailed studies, the impact of such pollution on the terrestrial wildlife inhabiting this area still remains unknown. In this work, we checked whether the proximity to Gabès-Ghannouche factory complex was associated with a decreased abundance of passerines breeding in the neighbouring oasis habitat. Overall, passerine abundance was found to decrease in the proximity of the factory complex, but this decrease was more pronounced in insectivorous species than in granivorous ones. The latter species seemed to be more dependent on vegetation structure. Moreover, we found that in the sites close to the factory complex, the studied passerine community was dominated by the Sparrow Passer domesticus × hispaniolensis, which seemed to be the less sensitive species to pollution. However, in the more distant sites, passerine abundance was more equitably distributed among species due to the increase in the densities of pollution-sensitive ones. Our findings give support to those reported in polluted European forest habitats and stress once again the usefulness of passerines as reliable biomonitors of polluted terrestrial environments. © 2014 Springer-Verlag Berlin Heidelberg.

Chokri M.A.,Faculte des science de Gabes | Hammouda A.,Faculte des science de Gabes | Tavecchia G.,CSIC - Mediterranean Institute for Advanced Studies
Bird Study | Year: 2011

Capsule Crèches formed early in the season lasted longer than those formed later, but a longer crèching period did not appear to confer higher chick survival. Aims To investigate the ecological factors influencing the benefit to parents of crèching behaviour by measuring chick survival. Methods Mark-recapture was used to model apparent daily survival of 505 chicks during the crèching period in three different crèches. We contrasted models with different tipping points to assess possible differences across crèches in chick survival during the first week and in the moment at which chick departures began. Results We did not find a clear difference across crèches on daily chick survival during the first stages of the crèche. By modelling chick apparent survival as a linear function of time we showed that the latest formed crèche dispersed more rapidly. Conclusions The two crèches formed early in the season lasted longer than the one formed later but chicks did not appear to have a higher survival over the first week of crèching. We suggest that a longer period at the crèche should result in a higher survival in the period soon after fledging because chicks leave the crèche 4-7 days older than other chicks. Furthermore, early crèches are synchronous with those of other species breeding in the same area, thus perhaps diluting predation. We discuss the limitations of our analysis and the possible implications for the community of waterbirds breeding at our study site. © 2011 British Trust for Ornithology.

Ali Chokri M.,Faculte des science de Gabes | Selmi S.,Faculte des science de Gabes
Bird Study | Year: 2011

Capsule The edge effect hypothesis of nest predation in habitat patches and colonies is supported Aims To test whether nest predation rates in Pied Avocet colonies are a function of distance from the colony edge. Methods The study was conducted in Sfax salina (3439'N, 1042'E) in Tunisia. We monitored Pied Avocet nests in 30 colonies established at different distances from the salina-suburbs edge. Using the Mayfield method, we estimated nest predation rate in each monitored colony. Regression analyses were used to investigate the relationship between nest predation rate and distance from colony edge. Results Predation by stray dogs coming from Sfax suburbs was responsible for the failure of a significant number of monitored nests. Nest predation rate varied among colonies and was found to be negatively correlated with distance to salina-suburbs edge. Conclusion The results support the edge effect hypothesis. Pied Avocet colonies located near the edge between Sfax salina and the suburbs of Sfax city suffered higher predation rates than those situated in the salina interior. The installation of fences separating the salina from Sfax suburbs is likely to promote the nesting success of waterbirds in this important bird-rich habitat. © 2011 British Trust for Ornithology.

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