25 research outputs found
A cytogenetic and pollen study of annual Medicago species from Soummam Valley (Northeastern of Algeria)
This paper reports a cytogenetic study of eight Medicago L. species sampled from the Soummam Valley (northeastern Algeria). Chromosome numbers and meiosis irregularities during microsporogenesis were explored. Pollen viability rate and pollen size were also examined. The studied taxa are diploid and display bivalent
pairing and regular chromosome segregation during meiosis. Although meiosis appears regular, some anomalies were detected in relatively high cumulated rates (14.66%â26.14%). The most common meiotic abnormality examined here is related to cytomixis (from 14.66% in M. littoralis to 25.83% in M. laciniata). Other anomalies were also etected, including chromatic bridges, asynchronous divisions, micronuclei and multipolar cells. Consequently, the species exhibited varying ercentages of pollen viability (from 70.11% in M. laciniata to
99.14% in M. littoralis). Pollen viability was negatively correlated with meiotic abnormalities (Pearson correlation coefficient R = â0.72, p = 0.043). The pollen grains were also heterogeneous in size. Medicago truncatula Gaertn. and M. laciniata (L.) Miller presented the most variable pollen size (relative standard deviation exceeding 19%). Medicago littoralis is distinguished from other species by possessing homogeneous and large sized pollen (relative standard deviation RSD = 6.73 %). The cytogenetic and pollen data provided by this study are
discussed in the context of species systematics and in the perspective of genetic improvement
STR-based genetic structure of the Berber population of Bejaia (Northern Algeria) and its relationships to various ethnic groups
Patterns of genetic variation in human populations have been described for decades. However, North Africa has received little attention and Algeria, in particular, is poorly studied, Here we genotyped a Berber-speaking population from Algeria using 15 short tandem repeat (STR) loci D8S1179, D21S11, D7S820, CSF1PO, D3S1358, TH01, D13S317, D16S539, D2S1338, D19S433, vWA, TPOX, D18S51, D5S818 and FGA from the commercially available AmpF/STR Identifiler kit. Altogether 150 unrelated North Algerian individuals were sampled across 10 administrative regions or towns from the Bejaia Wilaya (administrative district). We found that all of the STR loci met Hardy-Weinberg equilibrium expectations, after Bonferroni correction and that the Berber-speaking population of Bejaia presented a high level of observed heterozygosity for the 15 STR system (>0.7). Genetic parameters of forensic interest such as combined power of discrimination (PD) and combined probability of exclusion (PE) showed values higher than 0.999, suggesting that this set of STRs can be used for forensic studies. Our results were also compared to those published for 42 other human populations analyzed with the same set. We found that the Bejaia sample clustered with several North African populations but that some geographically close populations, including the Berber-speaking Mozabite from Algeria were closer to Near-Eastern populations. While we were able to detect some genetic structure among samples, we found that it was not correlated to language (Berber-speaking versus Arab-speaking) or to geography (east versus west). In other words, no significant genetic differences were found between the Berber-speaking and the Arab-speaking populations of North Africa. The genetic closeness of European, North African and Near-Eastern populations suggest that North Africa should be integrated in models aiming at reconstructing the demographic history of Europe. Similarly, the genetic proximity with sub-Saharan Africa is a reminder of the links that connect all African regions.Instituto Gulbenkian de CiĂȘncia, Laboratoire d'Excellence (LABEX) entitled TULIP: (ANR-10-LABX-41)
Influence de la date dâĂ©chantillonnage sur la reproduction de lâescargot terrestre Helix aperta maintenu en conditions contrĂŽlĂ©es de tempĂ©rature et de photopĂ©riode
Reproductive traits of Helix aperta snails were investigated under four combinations
of temperature and photoperiod (20°C/16hL:8hD; 20°C/8hL:16hD; 15°C/16hL:8hD and 15°C/ 8hL:16hD).
Three samples were used: Sample 1 and Sample 2 collected from Annaba (Northeastern Algeria) during
and after hibernation respectively; Sample 3, previously studied (unpublished data), collected from BejaĂŻa
(near Northeastern Algeria) during aestivation. All the snails began to mate on the first week and to lay on
the 3rd-4th week of setting under conditions of reproduction. Sample 1 and Sample 2 were characterized by
shorter reproduction periods (4-6 weeks) than Sample 3 (5-7 weeks). Strikingly, although most of the snails
collected during and after hibernation mated at a high rate (56-87 %) in comparison with those collected
during aestivation (32-92 %), their rates of egg-laying were drastically lower (6-25 % against 12-80 %). Among the snails that had mated, only 11-36 % laid eggs in Samples 1 and 2 against 38-87 % in Sample 3.
The mean numbers of eggs per clutch were higher in Sample 1 (293-323) and Sample 3 (337-348) than in
Sample 2 (237-248) (P < 0.05). Inversely, the mean egg weights per clutch were heavier in Sample 2 (17.5-
17.8 mg) than in Sample 1 (16.1-16.3 mg) and Sample 3 (16.3-16.6 mg) (P < 0.05). After the reproduction
period, as a consequence of differential reproductive yields, the mean weights of snails very significantly
increased in Sample 1 and Sample 2 (P < 0.001) and significantly decreased in Sample 3 (P < 0.05). Reproductive
performances were more affected and lethality rates higher under low temperature and short day
photoperiod. The best combination of temperature and photoperiod was mostly 20°C/16hL:8hD, conditions
closer to those in the field during autumn, especially overnight, the phase of snail activity. After the reproduction
period, the lethality was becoming higher and higher and the surviving snails were less active or
trying to burrow themselves into the soil of the egg-laying pots. All these arguments plead that H. aperta
snails are better adapted to reproduce in autumn (decreasing days and higher temperatures) after a long aestivation
stimulating gametogenesis than in spring (increasing days and lower temperatures) after hibernation
inhibiting gametogenesisLes caractÚres reproductifs des escargots Helix aperta ont été étudiés sous quatre combinaisons de température et photopériode (20°C/16hL 8hD ; 20°C/8hL:16hD ; 15°C/16hL:8hD and 15°C/ 8hL:16hD). Trois échantillons ont été
utilisés: Ech. 1 et Ech. 2 collectés à Annaba (Nord-Est Algérien) respectivement durant et aprÚs l'hibernation ; Ech. 3, précédemment analysé (données non publiées), collecté à Béjaïa (proche Nord-Est Algérien) durant l'estivation. Tous les escargots ont commencé à s'accoupler dÚs la 1Úre
semaine et à pondre durant la 3Úme ou la 4Úme semaine de leur mise en conditions de reproduction. Ech. 1 et Ech. 2 se sont distingués par leur plus courte période de reproduction (4-6 semaines) en comparaison avec Ech. 3 (5-7 semaines). D'une maniÚre frappante, bien que les escargots
collectés durant ou aprÚs hibernation (Ech. 1 et Ech. 2) se soient accouplés, dans la plupart des cas, à des taux plus élevés (56-87 %) que ceux échantillonnés durant l'estivation (32-92 %), leurs taux de pontes ont été dramatiquement plus faibles (6-25 % contre 12-80 %). Autrement dit,
parmi les escargots qui se sont accouplĂ©s dans Ech. 1 et Ech. 2, seulement 11-36 % ont pondu, contre 38-87 % dans Ech. 3. Les nombres moyens d'Ćufs par ponte Ă©taient plus Ă©levĂ©s en Ech. 1 (293-323) et Ech. 3 (337-348) qu'en Ech. 2 (237-248) (P < 0.05). Inversement, les poids moyens des
Ćufs par ponte Ă©taient plus Ă©levĂ©s en Ech. 2 (17.5-17.8 mg) qu'en Ech. 1 (16.1-16.3 mg) et Ech. 3 (16.3-16.6 mg) (P<0.05). AprĂšs la pĂ©riode de reproduction, en consĂ©quence des rendements reproductifs diffĂ©rentiels, les poids moyens des escargots ont trĂšs significativement augmentĂ© en Ech.
1 et Ech. 2 (P < 0.001) et significativement baissé en Ech. 3 (P < 0.05). Les performances reproductives étaient plus affectées et les taux de mortalité plus élevés sous basse température et courte photopériode. La meilleure combinaison de ces deux facteurs était souvent 20°C/16hL:8hD,
plus proche des conditions sur le terrain en automne, surtout durant la nuit, phase d'activité des escargots. AprÚs la période de reproduction, la mortalité devenait de plus en plus élevée et les survivants moins actifs ou essayant de s'enfouir dans le sol des pots de ponte. Tous ces
arguments plaident que les escargots H. aperta sont mieux adaptés à se reproduire en automne (jours décroissants et températures plus élevées) aprÚs une longue estivation stimulant la gamétogenÚse qu'au printemps (jours croissants et températures basses) aprÚs l'hibernation inhibant la
gamétogenÚse
Effets de la tempĂ©rature et de la photopĂ©riode sur la croissance et la reproduction de lâescargot Petit-gris Helix aperta Born (Gastropoda, Pulmonata)
Body growth and reproductive activity of Helix aperta were studied in laboratory conditions over 40 weeks, from hatching to maturity at 15°C and 20°C, and under two photoperiods: 16h-Light /8h-Dark and 8h-Light/16h-Dark. Only
temperature, but not photoperiod, had significant effects on body growth; snails reared at 15°C grew slower, took more time to develop and reached a smaller adult body weight than those raised at 20°C. In contrast, the results showed some interaction between photoperiod and temperature on
reproduction (length of reproductive activity, numbers of matings and layings) and revealed a predominant effect of photoperiod. Number of eggs per clutch was linked to body weight of snails. The best conditions for growth and reproduction of Helix aperta snails were the combination of a
temperature of 20°C and a long-day photoperiod (16h L/8h D)La croissance corporelle et l'activité reproductrice de Helix aperta ont été étudiées en laboratoire de l'éclosion à la maturité, à 15°C et 20°C durant 40 semaines et selon deux photopériodes: 16 h de jour / 8 h de nuit et 8 h de
jour / 16 h de nuit. Seule la température, pas la photopériode, a eu des effets significatifs sur la croissance corporelle; les escargots élevés à 15°C se sont développés plus lentement et ont atteint un poids adulte plus petit que ceux élevés à 20°C. En revanche, les résultats ont montré
une certaine interaction entre photopĂ©riode et tempĂ©rature dans la reproduction (durĂ©e de l'activitĂ© reproductrice, nombre d'accouplements et de pontes) ainsi qu'un effet prĂ©dominant de la photopĂ©riode. Le nombre d'Ćufs par ponte est apparu liĂ© au poids des escargots. Les meilleures
conditions de croissance et de reproduction de Helix aperta furent la combinaison d'une température de 20°C et d'une photopériode de 16 h de jour / 8 h de nuit
Contribution des LĂ©gumineuses Ă la rĂ©gĂ©nĂ©ration aprĂšs feu des forĂȘts de Quercus suber et Pinus halepensis du Nord-Est AlgĂ©rien
The role of legumes in post-fire forest regeneration has been extensively studied in
the northern Mediterranean basin but no published data are available concerning the southern part of the
area. The aim of the present paper is to analyse the dynamics of the leguminous species in a Q. suber and
a P. halepensis forests in northeastern Algeria during the first months after a wildfire of low intensity.
The aspects of seedling demography of legumes, their contribution to total biomass and species richness
were considered. No major differences were detected between the two communities. They presented similar
demographic patterns: legume seedlings began to emerge very early (November) after the fire (October) and
continued to increase massively with a peak in December and another in March, and a significant slowdown
in January and February; in April, they resumed to gradually decrease again to reach their minimum in May
and completely stop in early June. This pattern with two peaks rather than only one in seedling demography
was likely due to the exceptional coldness of January and February 2005 (snow down to sea level) whereby
the germination slowdown and its delay to March. Eight months after the fire (towards the end of June, as
the herbaceous vegetation began to dry), the above-ground biomass of legumes reached a maximum of 37.8
± 1.83 g/m2 in the Q. suber forest and 26.7 ± 1.63 g/m2 in the P. halepensis one. Seven months after the disturbance, in comparison with the other taxa, the legumes were floristically well represented with 19.8 ±
1.11 % and 24.3 ± 2.05 % of species in the Cork oak and the Allepo pine forests respectively. These richness
values are far higher than those reported for other Mediterranean-type ecosystems (3.8 - 13.3 %) probably
because of the geographic location (lower latitude) of our study area and the overgrazing pressure favouring
installation of leguminous speciesLe rÎle des Légumineuses dans la régénération aprÚs feu a été largement étudié sur la rive nord de la Méditerranée, mais aucune donnée n'est disponible concernant la rive sud. Le but de cet article est d'analyser la dynamique des
Légumineuses dans une subéraie et une pinÚde à Pin d'Alep du Nord-Est Algérien durant les premiers mois aprÚs un feu de faible intensité. Les aspects de la démographie des germinations des Légumineuses, leur contribution à la biomasse totale et la richesse spécifique sont considérés. Les
deux communautés ne présentent pas de différences majeures. Toutes deux montrent des modÚles démographiques similaires: les germinations de Légumineuses commencent à émerger trÚs tÎt (novembre) aprÚs le feu (octobre) et continuent à s'établir abondamment avec un premier pic en décembre et un
deuxiĂšme en mars, avec un ralentissement significatif en janvier et fĂ©vrier. La germination diminue Ă partir d'avril pour atteindre son minimum en mai et complĂštement s'arrĂȘter en dĂ©but juin. Ce modĂšle en deux pics plutĂŽt qu'un seul, comme dĂ©jĂ rapportĂ©, serait vraisemblablement dĂ» au froid
exceptionnel durant janvier et fĂ©vrier 2005 (neige jusqu'au niveau de la mer) d'oĂč un ralentissement de la germination et son dĂ©calage Ă mars. Huit mois aprĂšs l'incendie (vers la fin juin, pĂ©riode oĂč la vĂ©gĂ©tation herbacĂ©e commence Ă sĂ©cher), la biomasse aĂ©rienne des LĂ©gumineuses affiche un
maximum de 37,8 ± 1,83 g/m2 dans la subéraie et 26,7 ± 1,63 g/m2 dans la pinÚde. Sept mois aprÚs le feu, relativement aux autres familles de plantes, les Légumineuses sont floristiquement bien représentées avec 19,8 ± 1,11 % des espÚces dans la subéraie et 24,3 ± 2,05 % dans la pinÚde,
valeurs nettement supérieures à celles rapportées pour d'autres écosystÚmes de type méditerranéen (3,8 - 13,3 %), probablement en raison de la localisation géographique (basse latitude) de notre aire d'étude et la pression de surpùturage qui favorise l'installation des
LĂ©gumineuses
Phytogeographical study of the forest massifs of KĂ©frida, a neglected sector of the Babors important plant area (Northeastern Algeria)
Afin dâapporter une meilleure connaissance sur la flore de Petite Kabylie (BĂ©jaĂŻa, AlgĂ©rie), dans lâobjectif de conservation du patrimoine naturel, une Ă©tude phytogĂ©ographique a Ă©tĂ© menĂ©e sur la vĂ©gĂ©tation forestiĂšre dans deux massifs montagneux peu Ă©tudiĂ©s du secteur de KĂ©frida, mitoyen de la ZIP (zone importante pour les plantes) des Babors. Lâinventaire floristique rĂ©alisĂ© au niveau des groupements forestiers de ChĂȘne zĂ©en (Quercus canariensis Willd.), de ChĂȘne afarĂšs (Q. afares Pomel) et des pelouses de montagne a permis de comptabiliser 332 espĂšces de plantes vasculaires. En plus des 205 (62 %) espĂšces mĂ©diterranĂ©ennes quâil abrite, le site est remarquable par la prĂ©sence de 37 (11 %) endĂ©miques ou sub-endĂ©miques algĂ©riennes et surtout 79 (23 %) espĂšces de lâensemble holarctique non mĂ©diterranĂ©en. Lâanalyse du spectre biologique brut montre une dominance significative des hĂ©micryptophytes (48 %) sur les autres formes de vie (7,2 â 22,5 %). Cette zone constitue un refuge actuel exceptionnel pour une flore dâorigine non mĂ©diterranĂ©enne et/ou endĂ©mique, dans un contexte de rĂ©chauffement climatique. On note la prĂ©sence de quatorze espĂšces dĂ©terminantes pour le secteur de KĂ©frida Ă©tudiĂ©, dont huit en commun avec la ZIP des Babors et celle dâAkfadou et quatre en commun avec les ZIPs de Djurdjura et des monts de la Medjerda. La zone Ă©tudiĂ©e prĂ©sente aussi un nombre apprĂ©ciable de plantes importantes pour lâAlgĂ©rie. Cette prĂ©sence dâespĂšces dĂ©terminantes et/ou importantes pour le pays permet de classer le secteur de KĂ©frida comme une extension de la ZIP des Babors.In order to provide a better knowledge of the flora of Little Kabylia (BejaĂŻa, Algeria), with an objective of conservation of natural heritage, a phytogeographical study was conducted on forest vegetation in two understudied mountains in the area of KĂ©frida, adjoining the IPA (important plants area) of the Babors. The floristic surveys were conducted in a Zeen and an Afares oak (Quercus canariensis Willd. and Q. afares Pomel respectively) forests as well as mountain grasslands. The sampling allowed us to inventory 332 species of vascular plants. Besides the 205 (62 %) Mediterranean species it houses, the site is remarkable by the presence of 37 (11 %) Algerian endemics or sub-endemics and, above all, 79 (23 %) species from the non-Mediterranean Holarctic subset. Analysis of the global biological spectrum showed the significant dominance of hemicryptophytes (48 %) over the other life-forms (7.2 - 22.5 %). This area is an exceptional current refuge for non-Mediterranean and/or endemic flora, in a context of global warming. We note the presence of fourteen trigger species, including eight in common with the Babors and the Akfadou IPAs and four in common with the Djurdjura and the Medjerda ones. Besides, the investigated area has a significant number of plants important for Algeria. This presence of trigger species and/or plants important for the country allows to classifying the sector of KĂ©frida as an extension of the Babors IPA
Tribological and mechanical properties of polyamide-11/halloysite nanotube nanocomposites
This article reports some morphological, tribological, and mechanical data on polyamide-11(PA11)/ halloysite nanotube (HNT) nanocomposites prepared by melt-compounding. HNTs extracted from the Djebel Deb- bagh deposit in Algeria were incorporated into the polymer at 1, 3, and 5 wt%. For comparison, commercial HNTs were also used under the same processing conditions. Scanning electron microscopy showed that both HNTs were homogeneously dispersed in the PA11 matrix, despite the presence of few aggregates, in particular at higher filler contents. The tribological properties were significantly improved, resulting in a decrease in the friction coefficient and the wear rate characteristics due to the lubricating effect of HNTs. This is consistent with optical profilometry data, which evidenced the impact of both types of HNTs on the surface topography of the nanocomposite samples, in which the main wear process was plastic deformation. Furthermore, Youngâs modulus and tensile strength were observed to increase with the filler content, but to the detriment of elongation at break and impact strength. Regarding the whole data, the raw Algerian halloysite led to interesting results in PA11 nanocomposites, thus reveal- ing its potential in polymer engineering nanotechnology
Etude de la morphologie, des propriétés et de la durabilité de nanocomposites à base de polyamide-11/halloysite
The thesis is on the study of the properties and the sustainability of different nanocomposites systems based on polyamide-11 (PA11) and Algerian halloysite. The first part is devoted to the assessment of the potential as nanofiller of the Algerian halloysite by comparing it to another commercial one, through the study of PA11/halloysite nanocomposites prepared by melt mixing. In view of the different techniques, the results show the full potential of the Algerian halloysite with improvements in both thermal and mechanical properties after incorporation of the nanocharge. The second focuses on the use of halloysite, after functionalization, as compatibilisant agent in PA11 based polymers blends. Two functionalizations have been tested successfully via grafting on the surface of P(S-co-MAPC1(OH)2) and SEBS chains. The incorporation of these two modified halloysites in PS/PA11 and PA11/SEBS-g-MA, blends, respectively, led to ternary systems where the modified halloysite plays the role of compatibilizing agent by its localization at the interface. The third and final part of the work focuses on the sustainability of the PA11/halloysite nanocomposites. First, the impact of halloysite up to 6 weeks of immersion on the kinetics of the hygrothermal aging has been studied, as well as the effects of aging on the morphology and properties of samples. The study reveals that halloysite increases water sorption while delaying its diffusion in the PA11 due to the tortuosity induced by its presence. An evolution of the outward appearance of the material is observed with a decrease of the mechanical properties of the PA11. Finally, the study of the fire reaction of the PA11/halloysite nanocomposites with and without presence of phosphorus flame retardants has highlighted the inhibitory effect of halloysite after its functionalization with methylphosphonic acid. The results show that at comparable incorporation rate, the modified halloysite has a better effect on the fire behavior than ammonium polyphosphate or raw halloysite.La thĂšse porte sur lâĂ©tude des propriĂ©tĂ©s et de la durabilitĂ© de diffĂ©rents systĂšmes nanocomposites Ă base de polyamide-11 (PA11) et dâhalloysite algĂ©rienne. La premiĂšre partie est consacrĂ©e Ă lâĂ©valuation du potentiel comme nanocharge de lâhalloysite algĂ©rienne, en la comparant Ă une autre commerciale, et ce Ă travers lâĂ©tude de nanocomposites PA11/halloysite prĂ©parĂ©s par voie fondue. Au vu des diffĂ©rentes techniques utilisĂ©es, les rĂ©sultats rĂ©vĂšlent le plein potentiel de lâhalloysite algĂ©rienne avec des amĂ©liorations Ă la fois des propriĂ©tĂ©s thermiques et mĂ©caniques aprĂšs incorporation de la nanocharge. La seconde sâintĂ©resse Ă lâutilisation de lâhalloysite, aprĂšs fonctionnalisation, comme agent compatibilisant dans des mĂ©langes de polymĂšres Ă base de PA11. Deux fonctionnalisations ont Ă©tĂ© testĂ©es avec succĂšs, via greffage en surface de chaĂźnes de P(S-co-MAPC1(OH)2) et de SEBS. Lâincorporation de ces deux halloysites modifiĂ©es dans des mĂ©langes PS/PA11 et PA11/SEBS-g-MA, respectivement, a permis dâobtenir des systĂšmes ternaires ou lâhalloysite modifiĂ©e joue le rĂŽle de compatibilisant en se plaçant Ă lâinterface. La troisiĂšme et derniĂšre partie du travail se concentre sur la durabilitĂ© des nanocomposites PA11/halloysite. Dâabord, lâimpact de lâhalloysite jusquâĂ 6 semaines dâimmersion, sur la cinĂ©tique du vieillissement hygrothermique a Ă©tĂ© Ă©tudiĂ©, ainsi que les effets de ce vieillissement sur la morphologie et les propriĂ©tĂ©s des Ă©chantillons. LâĂ©tude rĂ©vĂšle que lâhalloysite augmente la sorption en eau tout en retardant sa diffusion dans le PA11 du fait de la tortuositĂ© induite par sa prĂ©sence. Une Ă©volution de l'aspect extĂ©rieur du matĂ©riau est observĂ©e avec une diminution des propriĂ©tĂ©s mĂ©caniques du PA11. Enfin, lâĂ©tude de la rĂ©action au feu de nanocomposites PA11/halloysite avec et sans prĂ©sence de retardateurs de flamme phosphorĂ©s a mis en Ă©vidence lâeffet inhibiteur de lâhalloysite aprĂšs sa fonctionnalisation avec de lâacide mĂ©thylphosphonique. Les rĂ©sultats montrent quâĂ taux dâincorporation comparable, lâhalloysite modifiĂ©e possĂšde un meilleur effet sur le comportement au feu que le polyphosphate dâammonium ou lâhalloysite brute