La rizipisciculture au Mali: Pratiques et perspectives de l'innovation piscicole

Rice-Fish Culture in Mali: Practices and Prospects of Piscicultural Innovation. Mali is a country of fishing tradition in its rivers streams. Its fish production is the highest in West Africa, but it is dependent on the flood regime of Niger River. Fish farming appears to be a good alternative for increasing the amount of fish available during drought periods. A new fish production activity has progressively taken place in rural areas, i.e. "rizipisciculture" (rice-fish farming), since 2006. This emergent activity constitutes another challenge for agricultural research in Mali, actually raising up more questions than solutions. Individual surveys were conducted in the area of 'Office du Périmètre Irrigué de Baguinéda (OPIB)', a rice extension service. Fifteen out of 23 farmers, so 65% of those practicing rizipisciculture, were surveyed and monitored in 2011. This investigation showed some disparities in the practices and the results of rice-fish production. Fish yield in the rice compartments varies between 408 and 438 kg.ha-1. This activity is facing environmental, socio-cultural, technic, institutional and financial constraints. In Mali, there is an important potential for irrigated rice production, which is favorable for the development of rice-fish farming. The sustainability of this new technology must however still be proved, and its socio-economic profitability demonstrated

Exceptional Diversity, Maintenance of Polymorphism, and Recent Directional Selection on the APL1 Malaria Resistance Genes of Anopheles gambiae

The three-gene APL1 locus encodes essential components of the mosquito immune defense against malaria parasites. APL1 was originally identified because it lies within a mapped QTL conferring the vector mosquito Anopheles gambiae natural resistance to the human malaria parasite, Plasmodium falciparum, and APL1 genes have subsequently been shown to be involved in defense against several species of Plasmodium. Here, we examine molecular population genetic variation at the APL1 gene cluster in spatially and temporally diverse West African collections of A. gambiae. The locus is extremely polymorphic, showing evidence of adaptive evolutionary maintenance of genetic variation. We hypothesize that this variability aids in defense against genetically diverse pathogens, including Plasmodium. Variation at APL1 is highly structured across geographic and temporal subpopulations. In particular, diversity is exceptionally high during the rainy season, when malaria transmission rates are at their peak. Much less allelic diversity is observed during the dry season when mosquito population sizes and malaria transmission rates are low. APL1 diversity is weakly stratified by the polymorphic 2La chromosomal inversion but is very strongly subdivided between the M and S “molecular forms.” We find evidence that a recent selective sweep has occurred at the APL1 locus in M form mosquitoes only. The independently reported observation of a similar M-form restricted sweep at the Tep1 locus, whose product physically interacts with APL1C, suggests that epistatic selection may act on these two loci causing them to sweep coordinately

Evaluation and optimization of membrane feeding compared to direct feeding as an assay for infectivity

<p>Abstract</p> <p>Background</p> <p>Malaria parasite infectivity to mosquitoes has been measured in a variety of ways and setting, includind direct feeds of and/or membrane feeding blood collected from randomly selected or gametocytemic volunteers. <it>Anopheles gambiae s.l </it>is the main vector responsible of <it>Plasmodium falciparum </it>transmission in Bancoumana and represents about 90% of the laboratory findings, whereas <it>Plasmodium malariae </it>and <it>Plasmodium ovale </it>together represent only 10%.</p> <p>Materials and methods</p> <p>Between August 1996 and December 1998, direct and membrane feeding methods were compared for the infectivity of children and adolescent gametocyte carriers to anopheline mosquitoes in the village of Bancoumana in Mali. Gametocyte carriers were recruited twice a month through a screening of members of 30 families using Giemsa-stained thick blood smears. F1 generation mosquitoes issued from individual female wild mosquitoes from Bancoumana were reared in a controlled insectary conditions and fed 5% sugar solution in the laboratory in Bamako, until the feeding day when they are starved 12 hours before the feeding experiment. These F1 generation mosquitoes were divided in two groups, one group fed directly on gametocyte carriers and the other fed using membrane feeding method.</p> <p>Results</p> <p>Results from 372 <it>Plasmodium falciparum </it>gametocyte carriers showed that children aged 4–9 years were more infectious than adolescents (p = 0.039), especially during the rainy season. Data from 35 carriers showed that mosquitoes which were used for direct feeding were about 1.5 times more likely to feed (p < 0.001) and two times more likely to become infected, if they fed (p < 0.001), than were those which were used for membrane feeding. Overall, infectivity was about three-times higher for direct feeding than for membrane feeding (p < 0.001).</p> <p>Conclusion</p> <p>Although intensity of infectivity was lower for membrane feeding, it could be a surrogate to direct feeding for evaluating transmission-blocking activity of candidate malaria vaccines. An optimization of the method for future trials would involve using about three-times more mosquitoes than would be used for direct feeding.</p

Anopheles Gambiae PRS1 Modulates Plasmodium Development at Both Midgut and Salivary Gland Steps

Background: Invasion of the mosquito salivary glands by Plasmodium is a critical step for malaria transmission. From a SAGE analysis, we previously identified several genes whose expression in salivary glands was regulated coincident with sporozoite invasion of salivary glands. To get insights into the consequences of these salivary gland responses, here we have studied one of the genes, PRS1 (Plasmodium responsive salivary 1), whose expression was upregulated in infected glands, using immunolocalization and functional inactivation approaches. Methodology/Principal Findings: PRS1 belongs to a novel insect superfamily of genes encoding proteins with DM9 repeat motifs of uncharacterized function. We show that PRS1 is induced in response to Plasmodium, not only in the salivary glands but also in the midgut, the other epithelial barrier that Plasmodium has to cross to develop in the mosquito. Furthermore, this induction is observed using either the rodent parasite Plasmodium berghei or the human pathogen Plasmodium falciparum. In the midgut, PRS1 overexpression is associated with a relocalization of the protein at the periphery of invaded cells. We also find that sporozoite invasion of salivary gland cells occurs sequentially and induces intra-cellular modifications that include an increase in PRS1 expression and a relocalization of the corresponding protein into vesicle-like structures. Importantly, PRS1 knockdown during the onset of midgut and salivary gland invasion demonstrates that PRS1 acts as an agonist for the development of both parasite species in the two epithelia, highlighting shared vector/parasite interactions in both tissues. Conclusions/Significance: While providing insights into potential functions of DM9 proteins, our results reveal that PRS1 likely contributes to fundamental interactions between Plasmodium and mosquito epithelia, which do not depend on the specific Anopheles/P. falciparum coevolutionary history

Rethinking the extrinsic incubation period of malaria parasites

The time it takes for malaria parasites to develop within a mosquito, and become transmissible, is known as the extrinsic incubation period, or EIP. EIP is a key parameter influencing transmission intensity as it combines with mosquito mortality rate and competence to determine the number of mosquitoes that ultimately become infectious. In spite of its epidemiological significance, data on EIP are scant. Current approaches to estimate EIP are largely based on temperature-dependent models developed from data collected on parasite development within a single mosquito species in the 1930s. These models assume that the only factor affecting EIP is mean environmental temperature. Here, we review evidence to suggest that in addition to mean temperature, EIP is likely influenced by genetic diversity of the vector, diversity of the parasite, and variation in a range of biotic and abiotic factors that affect mosquito condition. We further demonstrate that the classic approach of measuring EIP as the time at which mosquitoes first become infectious likely misrepresents EIP for a mosquito population. We argue for a better understanding of EIP to improve models of transmission, refine predictions of the possible impacts of climate change, and determine the potential evolutionary responses of malaria parasites to current and future mosquito control tools

Modifications du milieu et expressions de la stratégie adaptative de Brycinus leuciscus (Characidae) dans le bassin du Niger

#Brycinus leuciscus est un petit #Characidae largement répandu dans le bassin du Niger. Au Mali, son milieu originel a subi des transformations anthropiques différentes dans le lac de barrage de Sélingué et dans le Delta Central du Niger. Le stock est affecté par un effort de pêche beaucoup plus faible dans le lac que dans le Delta notamment en ce qui concerne les jeunes qui représentent près de 70 % des captures de l'espèce dans le Delta. La faible prédation des jeunes à Sélingué, alliée aux conditions environnementales lacustres plus favorables, expliquerait les différences de profils démographiques entre les deux populations de #B. leuciscus. Dans le lac de barrage, tous les poissons d'un an entreprennent une deuxième croissance ; la taille et l'âge de première reproduction, la longévité et le coefficient de condition sont plus élevés que le Delta. En outre, l'effort de reproduction, exprimé à travers le rapport gonado-somatique (RGS) de pré-ponte, est très hétérogène dans la population de Sélingué, contrairement à l'homogénéité observée dans le Delta. Cela traduit vraisemblablement une hétérogénéité d'investissement de reproduction dans la population lacustre. Ces variations intraspécifiques du profil démographique traduisent une capacité d'adaptation modulable chez #B. leuciscus. La plasticité phénotypique observée pourrait être un trait caractéristique du patrimoine génétique originel des espèces d'environnements très variables. (Résumé d'auteur

Modifications du milieu et expressions de la stratégie adaptative de Brycinus leuciscus (Characidae) dans le bassin du Niger

#Brycinus leuciscus est un petit #Characidae largement répandu dans le bassin du Niger. Au Mali, son milieu originel a subi des transformations anthropiques différentes dans le lac de barrage de Sélingué et dans le Delta Central du Niger. Le stock est affecté par un effort de pêche beaucoup plus faible dans le lac que dans le Delta notamment en ce qui concerne les jeunes qui représentent près de 70 % des captures de l'espèce dans le Delta. La faible prédation des jeunes à Sélingué, alliée aux conditions environnementales lacustres plus favorables, expliquerait les différences de profils démographiques entre les deux populations de #B. leuciscus. Dans le lac de barrage, tous les poissons d'un an entreprennent une deuxième croissance ; la taille et l'âge de première reproduction, la longévité et le coefficient de condition sont plus élevés que le Delta. En outre, l'effort de reproduction, exprimé à travers le rapport gonado-somatique (RGS) de pré-ponte, est très hétérogène dans la population de Sélingué, contrairement à l'homogénéité observée dans le Delta. Cela traduit vraisemblablement une hétérogénéité d'investissement de reproduction dans la population lacustre. Ces variations intraspécifiques du profil démographique traduisent une capacité d'adaptation modulable chez #B. leuciscus. La plasticité phénotypique observée pourrait être un trait caractéristique du patrimoine génétique originel des espèces d'environnements très variables. (Résumé d'auteur