Dynamique de l’exploitation des crabes nageurs callinectes amnicola, de rochebrune, 1881 (décapode, portuniade) dans le complexe lagunaire de Grand-Lahou (Afrique de l’Ouest, Côte d’Ivoire)

a présente étude a pour but de décrire les pêcheries, les acteurs, les prises par unité d’effort, les captures et les productions de crabes nageurs Callinectes amnicola, De Rochebrune (Crustacé - Decapode – Portunidae) du complexe lagunaire de Grand-Lahou. Pour ce faire, trois enquêteurs de terrain et deux enquêteurs superviseurs enregistraient quotidiennement les débarquements des crabes nageurs dans trois sites Tioko (2001 à 2003), Lauzoua et Lahou Pkanda (2006 à 2009). Trois types d’engins à savoir les balances, les nasses et les filets fixes à pieux sont utilisés par 142 pêcheurs dans le complexe lagunaire de Grand-Lahou pour pêcher les crabes nageurs. Ces engins, dont les plus importants numériquement sont les filets fixes et sont implantés principalement à Tioko dans la lagune de Mackey loin de la passe et capturent essentiellement les crabes femelles. Les deux autres engins ont été introduits selon les témoignages des populations riveraines récemment et sont utilisés dans les eaux calmes et les mangroves.La production des crabes nageurs a fortement baissé car elle est passée de 878 tonnes en 2006 à 852 tonnes en 2009 à cause de la pression exercée sur la ressource. Enfin, la production moyenne annuelle estimée à 823 tonnes /an est faible comparativement aux productions annuelles de la lagune Ebrié et de la lagune Aby et cela est lié à la forte pression exercée par la pêche et la fermeture progressive de la passe qui influence directement le cycle hydrologique lagunaire et par ricochet le recrutement des crabes nageurs de la lagune de Grand-lahou.Mots-clés : crustacés, décapodes, portunidae, crabes nageurs, callinectes amnicola, lagune de Grand-Lahou, Côte d’Ivoire

Etude microscopique de L'ovogenese chez la femelle de Callinectes amnicola de Rochebrune, 1883 (Decapoda Portunidae)

Histological survey showed that the ovary of Callinectes amnicola was made of two elements, lobes of ovogonia and an amorphous zone. Both of them participate into ovogenesis. According to structural and ultrastructural aspects, process of the ovogenesis comprises five stages in which ovogonia change successively in oocytes and in follicles. Follicles are formed at the level of the amorphous zone following the oocytes migration. During the ovary development, maturation of the oocytes takes place with the occurrence of follicle membrane and a single layer of follicular cells, which disappears before realising of eggs from the general cavity of the animal. During this laying, the fertilized egg is surrounded only by fertilization membrane. It then starts directly its embryonic development. Au plan histologique, l’ébauche de l'ovaire chez Callinectes amnicola comporte des lobes d’ovogonies et une zone sans structure, qui interviennent tous les deux dans l’ovogenèse. Abordé sous les aspectsstructural et ultrastructural, le processus de l’ovogenèse comprend cinq étapes au cours desquelles les ovogonies se transforment successivement en ovocytes et en follicules. Les follicules se forment au niveau de la zone amorphe suite à la migration des ovocytes. Au cours de la maturation ovocytaire qui se déroule durant l'évolution de l'ovaire, se forment la membrane ovocytaire et une seule couche de cellules folliculeuses qui disparaît avant la ponte. L’oeuf pondu est donc entouré uniquement de la membrane de fécondation. Etant un oeuf fécondé, il entame directement son développement embryonnaire

Etude Mocroscopique des spematheques des femelles de Callinectes amnicola, de Rochebrune, 1883 (Decapoda portunidae)

The spermathecas or seminal receptacles serve for the storage of spermatophores in the females of Callinectes amnicola. In the microscopic plan, the wall of the spermatheques in the juvenile’s females of stage II consists of three cellular layers recognizable by the nuclei aspect, and the extent of the cytoplasm. The internal layer in the juvenile’s females of stage II is topped by a column-shaped epithelium, which is scaled in the pubescent females of stage III and in the adults of stage IV. In these last, the tripartite structure of the spermatheca is somewhat disorganized. The spermathecas present a broad lumen resulting from the coalescence of inter-epithelial vacuoles and cellular exfoliation and containing spermatophores. They are dilated or reabsorbed at the majority of the females of the stage V. The reconstitution of this organ is noticed in the females of stage VI and VII, which undergo their secondary cycle. Thereconstitution process was not determined. Les spermathèques ou réceptacles séminaux constituent les réservoirs des spermatophores chez les femelles de Callinectes amnicola. Au plan microscopique, la paroi des spermathèques chez les femellesjeunes du stade II est constituée de trois couches cellulaires reconnaissables par l’aspect des noyaux, et l’étendue du cytoplasme. La couche la plus interne est surmontée d’un épithélium columnaire qui est desquamé chez les femelles pubères du stade III et chez les adultes du stade IV. Chez ces dernières, la structure tripartite des spermathèques est désorganisée. Les spermathèques présentent une large lumière résultant de la coalescence de vacuoles inter-épithéliales et de la desquamation cellulaire et contenant des spermatophores. Les spermathèques sont dilatées ou résorbées chez la plupart des femelles du stade V. On note la reconstitution de cet organe chez les femelles des stades VI et VII qui reprennent un nouveau cycle de reproduction. Le processus de reconstitution n’a pu être déterminé

Perennial transmission of malaria by the Anopheles gambiae complex in a North Sudan Savanna area of Mali

[No abstract available

Ecological genetic studies in the chromosomal form Mopti of Anopheles gambiae s.str. in Mali, West Africa.

Among the sibling species of the Afrotropical Anopheles gambiae complex, the nominal taxon (An. gambiae s.str.) is the major malaria vector. Its bionomics suggest a man-dependent speciation process which involves, in West Africa, various incipient species chromosomally recognized by different combinations of 2R paracentric inversions. One of the most recent evolutionary steps of such a speciation process appears to be the chromosomal form Mopti, which is associated with dry season irrigation in arid zones, and is characterized by a remarkable ecological flexibility related to three 2R alternative arrangements, namely bc, u and +, whose expected karyotypes are found in Hardy-Weinberg equilibrium. The study of this chromosomal polymorphism in samples from a 16-locality transect in Mali shows wide variations and highly significant correlation with both temporal and spatial climatic differences. Mosquitoes homokaryotypic for 2Rbc are the actual dry season and arid areas breeders. The regular rise of 2Rbc frequency, up to fixation, during each dry season, corresponds to the South-North clinal increase of the same arrangement along the transect, from about 30% in the humid savanna to near fixation in the South-Saharan zone. This coherent ecological genetics case provides full support to the hypothesis of the adaptive nature of paracentric inversions. Moreover, the very peculiar system of combinations of contiguous 2R inversions, utilized by Mopti as well as by other chromosomal forms of An. gambiae, suggests a process of polygenic reorganization based on linkage disequilibria and involving the inversions as driving selection units

The distribution and inversion polymorphism of chromosomally recognized taxa of the Anopheles gambiae complex in Mali, West Africa

Data from polytene chromosome studies on the Anopheles gambiae complex in Mali were reviewed. The banding pattern was successfully scored in 17,705 specimens from 76 sampling sites representing the main ecological strata of the country. Two members of the complex, namely An. arabiensis and An. gambiae, were found widespread and frequently sympatric, with the latter prevalent in most localities. Population genetic analysis of the inversion polymorphisms indicated the existence of panmictic conditions for An. arabiensis only, whereas the parallel study of An. gambiae supported its splitting into at least three reproductive units, characterized by different 2R chromosome arrangements, designated Bamako, Mopti and Savanna. The chromosomal evidence was consistent with the hypothesis of complete reproductive isolation between Bamako and Mopti. Partial isolation between these two taxa and Savanna was suggested by the scoring of hypothetical hybrid 2R heterokaryotypes in various samples, but the actual hybrid origin of these specimens was not confirmed Different patterns of geographical and seasonal distribution were shown as follows. An. arabiensis prevails in arid savannas (Sahel and Northern Sudan savanna) out of the flooded or irrigated zones: it is able to withstand the most arid conditions of Saharan localities and its breeding might extend throughout the dry season. An. gambiae Savanna and Bamako prevail in relatively humid savannas (Southern Sudan savanna) and their breeding generally occurs only during the rainy season. The Savanna taxon was almost absent in flooded or irrigated zones and in riverine localities; the Bamako taxon is distributed along the upper river Niger and its tributaries. An. gambiae Mopti extends its range in all ecological zones present in Mali including the Sahel and predesertic areas, showing high relative frequencies up to absolute dominance in flooded or irrigated areas; its breeding is highly successful also during the dry season. Rainfall at the sampling sites was found to correlate positively with the frequency of Savanna and negatively with the frequency of Mopti. The remarkable ecological flexibility of the latter was found associated with wide seasonal and geographical variations in its 2R inversion polymorphism bc/u. Higher frequencies of the be arrangement were recorded both in the Southern localities during the dry season and in the Northern more and localities during the rainy season. The absence or scarcity of An arabiensis and An. gambiae Savanna in most flooded or irrigated zones suggests their competitive exclusion by An. gambiae Mopti