Perceptions de la variabilité climati que et stratégies d’adaptation dans le système oasien de Gouré (Sud-est Niger)

Les savoirs liés au temps et à l’espace, et l’identification des stratégies paysannes pour affronter les problèmes climatiques sont indispensables pour toute compréhension des questions climatiques. Pour mieux apprécier les perceptions de la variabilité climatique et les stratégies d’adaptation utilisées, une enquête semi structuré qui a concerné 60 personnes repartie dans 4 villages du département de Gouré, situé dans l’Est du Niger est conduite selon une approche qualitative et quantitative. Les effets de la variabilité climatique ressentis par les agriculteurs sont l’aridité du climat, l’augmentation de la température et le caractère aléatoire des pluies. Les éleveurs la perçoivent de façon indirecte à travers la réduction du fourrage et de la disponibilité d’eau. Ces effets ont poussé ces populations à adopter des stratégies d’adaptation comme la recherche de nouvelles variétés à cycle court et supportant les poches de sécheresse, la pratique des techniques de fixation des dunes pour la restauration du couvert herbacé, l’utilisation de la fumure organique, la modification des dates de semis, le stockage de fourrage, le déstockage des animaux pendant la soudure, les prières collectives de demande de pluies. Elles sont toutefois insuffisantes du fait de la persistance des effets négatifs de la variabilité climatiques au Niger.Mots clés: Variabilité climatique, perception, stratégies d’adaptation, Gouré, NigerEnglish Title: Farmers perception and adaptation strategies to climate change in the oasis system of Goure (Southeast Niger)English AbstractKnowledge related to the perception of time and space, and identification of farmers’ strategies for dealing with climate change is a perequisite for a good understanding of climate issues. Farmers’ climate variability perceptions and adaptation strategies was studied using a survey conducted with sixty (60) farmers in the department of Gouré, located in eastern Niger. Results showed that farmers directly experience changes in  climate variability through temperature increase, frequent drought and erratic rainfall. By contrast, herders sense the effects of climate change indirectly through fodder reduction and scarce water availability. These effects have prompted farmers to adopt coping strategies such as the use of improved varieties, early and drought tolerant, sand dune stabilization and land reclamation, use of organic manure, changing of planting dates, storage of fodder, the destocking of animals during drought periods, collective prayers for rain. These strategies, however, appear to be insufficient for addressing the negative effects of climate change in this part of Niger.Keywords: climate variability, perception, strategies of adaptation, Goure, Nige

Accurate Shapley Values for explaining tree-based models

Although Shapley Values (SV) are widely used in explainable AI, they can be poorly understood and estimated, implying that their analysis may lead to spurious inferences and explanations. As a starting point, we remind an invariance principle for SV and derive the correct approach for computing the SV of categorical variables that are particularly sensitive to the encoding used. In the case of tree-based models, we introduce two estimators of Shapley Values that exploit the tree structure efficiently and are more accurate than state-of-the-art methods. Simulations and comparisons are performed with state-of-the-art algorithms and show the practical gain of our approach. Finally, we discuss the ability of SV to provide reliable local explanations. We also provide a Python package that computes our estimators at https://github.com/salimamoukou/acv00.Comment: Accepted at the 25th International Conference on Artificial Intelligence and Statistics (AISTATS), 2022. V2: The section on Active Shapley Values has been removed in this updated versio

Farmers perception and adaptation strategies to climate change in the oasis system of Goure (Southeast Niger)

Les savoirs liés au temps et à l’espace, et l’identification des stratégies paysannes pour affronter les problèmes climatiques sont indispensables pour toute compréhension des questions climatiques. Pour mieux apprécier les perceptions de la variabilité climatique et les stratégies d’adaptation utilisées, une enquête semi structurée qui a concerné 60 personnes réparties dans 4 villages du département de Gouré, situé dans l’Est du Niger, est conduite selon une approche qualitative et quantitative. Les effets de la variabilité climatique ressentis par les agriculteurs sont l’aridité du climat, l’augmentation de la température et le caractère aléatoire des pluies. Les éleveurs la perçoivent de façon indirecte à travers la réduction du fourrage et de la disponibilité d’eau. Ces effets ont poussé ces populations à adopter des stratégies d’adaptation comme la recherche de nouvelles variétés à cycle court et supportant les poches de sécheresse, la pratique des techniques de fixation des dunes pour la restauration du couvert herbacé, l’utilisation de la fumure organique, la modification des dates de semis, le stockage de fourrage, le déstockage des animaux pendant la soudure, les prières collectives de demande de pluies. Elles sont toutefois insuffisantes du fait de la persistance des effets négatifs de la variabilité climatique au Niger.Knowledge related to the perception of time and space, and identification of farmers’ strategies for dealing with climate change is a perequisite for a good understanding of climate issues. Farmers’ climate variability perceptions and adaptation strategies was studied using a survey conducted with sixty (60) farmers in the department of Gouré, located in eastern Niger. Results showed that farmers directly experience changes in climate variability through temperature increase, frequent drought and erratic rainfall. By contrast, herders sense the effects of climate change indirectly through fodder reduction and scarce water availability. These effects have prompted farmers to adopt coping strategies such as the use of improved varieties, early and drought tolerant, sand dune stabilization and land reclamation, use of organic manure, changing of planting dates, storage of fodder, the destocking of animals during drought periods, collective prayers for rain. These strategies, however, appear to be insufficient for addressing the negative effects of climate change in this part of Niger

Association mapping, patterns of linkage disequilibrium and selection in the vicinity of the phytochrome C gene in pearl millet

Key message Linkage analysis confirmed the association in the region of PHYC in pearl millet. The comparison of genes found in this region suggests that PHYC is the best candidate. Major efforts are currently underway to dissect the phenotype-genotype relationship in plants and animals using existing populations. This method exploits historical recombinations accumulated in these populations. However, linkage disequilibrium sometimes extends over a relatively long distance, particularly in genomic regions containing polymorphisms that have been targets for selection. In this case, many genes in the region could be statistically associated with the trait shaped by the selected polymorphism. Statistical analyses could help in identifying the best candidate genes into such a region where an association is found. In a previous study, we proposed that a fragment of the PHYTOCHROME C gene (PHYC) is associated with flowering time and morphological variations in pearl millet. In the present study, we first performed linkage analyses using three pearl millet F-2 families to confirm the presence of a QTL in the vicinity of PHYC. We then analyzed a wider genomic region of similar to 100 kb around PHYC to pinpoint the gene that best explains the association with the trait in this region. A panel of 90 pearl millet inbred lines was used to assess the association. We used a Markov chain Monte Carlo approach to compare 75 markers distributed along this 100-kb region. We found the best candidate markers on the PHYC gene. Signatures of selection in this region were assessed in an independent data set and pointed to the same gene. These results foster confidence in the likely role of PHYC in phenotypic variation and encourage the development of functional studies

Influence des facteurs anthropiques et des flux de gènes sur la variabilité génétique des formes cultivées et spontanées du mil dans deux localités du Niger

Le projet a été réalisé au Niger (pays Zarma-Songhai) à l’aide d’analyses anthropologiques et génétiques, autour de deux axes de recherche : i) l’étude des relations entre la diversité des pratiques agricoles, les flux de gènes entre variétés et l’organisation de la diversité aux niveaux agromorphologique et moléculaire ; ii) l’analyse des relations génétiques entre formes cultivées, sauvages et intermédiaires (soun). Les résultats montrent que les pratiques agricoles favorisent les brassages génétiques entre populations variétales, et la dissémination des soun à l’échelle du village et de la région, via les flux de semences. Ceci expliquerait l’abondance des soun dans les champs de la région. L’absence de différenciation génétique (au niveau des marqueurs moléculaires) entre variétés démontre aussi l’importance quantitative des flux de gènes par le biais des hybridations. Ainsi, la gestion des semences, sans doute moins autarcique qu’auparavant, les pratiques culturales et la forte allogamie du mil conduisent à un processus d’homogénéisation, au niveau régional, des variétés cultivées par les agriculteurs. Il est toutefois difficile de savoir s’il s’agit d’un processus récent. Ce processus aurait pour conséquences une déstructuration rapide des qualités d’adaptation des variétés aux conditions locales, et une augmentation de l’introgression par des gènes des formes sauvages dont la présence des soun est une manifestation. Il pourrait à l’extrême conduire à une « dé-domestication » du mil dans ces régions soumises à des pénuries de production chroniques et donc participer à l’aggravation du phénomène.The project was settled mainly in two localities in West Niger (Zarma-Songhai region). It includes both anthropologic and genetic analyses and aims at: i) studying the relationships between farmers’ practices, gene flow and the organization of diversity at morphological and molecular levels: ii) analysing the genetic relationships between domesticated, wild and intermediate forms (soun) of pearl millet based on their genetic and morphological evaluation at the field level. The purpose was to understand the origin of so-called soun (plants with intermediate domesticated/ wild phenotypes) and to evaluate the level of introgression of cultivated populations by genes from the wild. The results showed that, although diverse, farmer practices favour very large genetic admixture at the village and even regional scale, through important seed flows (seed exchanges and supply networks). A consequence of this is the near-absence of any genetic differentiation (at the molecular level) between populations of the same variety cultivated by different farmers, even in remote villages. Both the abundant seed flows and the existence of a large seed bank in the soil could explain why soun are so abundant in large areas in the region, even where no wild forms are found. Moreover, the very low level of genetic differentiation between different varieties (including between early and semi–late flowering ones) can be used as a proof of the sizeable gene flow through hybridization at the field level (different varieties are often found in the vicinity of each other or even in the same field). Farmers are able to identify the different varieties they grow and to manage them separetely. Nevertheless, different factors act together to lead both to the homogeneization of the cultivated gene pools, and then varieties, at large geographical scales and to the existence of gene flow between domesticated and non domesticated forms of pearl millet. In particular, farmers pressures during the seed selection process cannot be neither strong nor evenly applied due to the scarcity in production. We think also they are probably less strong that they used to be; cultural practices and the largely preponderant outcrossing mating system promote hybridization between different varieties; weeding is not efficient and/or discriminant enough to remote all the soun growing in the field, so that the proportion of these plants can sometimes reach several tens per cent. However, it is difficult to ascertain whether we are facing a recent evolutionary process due to dramatic social and ecological (repeated drought) changes. If this were the case, this could lead to a decrease in the level of adaptation of cultivated populations to their local environment and to an increase in their introgression by genes from the wild. At the end, this could lead to a “de-domestication” of pearl millet in this region that already suffers of scarcity in the production of this crop, reinforcing therefore this situation

Ressources génétiques des mils en Afrique de l’Ouest

Le mil constitue, avec le sorgho, la base de l’alimentation d’une part importante des populations indiennes et africaines. Au Niger, deuxième pays producteur en Afrique, cette culture représente les trois quarts de la production céréalière et occupe plus de la moitié des terres cultivées. C’est en Afrique de l’Ouest que se situent les zones d’origine et de diversification des mils cultivés (Penniselum glaucum subsp. glaucum) et l’on peut encore y trouver des populations de la forme sauvage (P. glaucum subsp. monodii). Mieux conserver, évaluer et valoriser ces ressources génétiques, tels sont les enjeux exposés lors de l’atelier « Ressources génétiques des mils et plantes associées en Afrique de l’Ouest » organisé à Niamey en 2002. L’IRD et ses partenaires y ont présenté une synthèse des résultats de recherches pluridisciplinaires (génétique, agronomie, anthropologie) sur le rôle des pratiques paysannes dans la dynamique de la diversité génétique des mils sauvages et cultivés au Niger. Cet atelier a également permis de confronter les expériences et conclusions d’autres équipes et a contribué à la réflexion sur les stratégies de conservation (in et ex situ) et de valorisation des ressources génétiques des mils et de quelques autres plantes cultivées dans les agrosystèmes sahéliens.Pearl millet is, along with sorghum, the staple food for a large part of Indian and African populations. In Niger, the second producing country in Africa, this crop accounts for three quarters of the cereals production and more than half of cultivated land. Regions of origin and diversification of pearl millet (Pennisetum glaucum subsp. glaucum) are located in West Africa, where wild millet populations (P. glaucum subsp. monodii) can still be found. A better conservation, evaluation and valorisation of this diversity is therefore an important challenge, that was adressed during a workshop on genetic resources of pearl millet and associated crops in West Africa, held in Niamey in 2002. IRD and its partners presented there a synthesis of their multidisciplinary research (genetics, agronomy, anthropology) on the role of farmers' practices in the dynamics of genetic diversity of wild and cultivated millets in Niger. The workshop allowed exchanges and comparisons of experience and conclusions of other teams and contributed to the debate on strategies of conservation (in and ex situ) and utilisation of genetic resources of pearl millet and other crops in Sahelian agrosystems.© IRD Éditions, 200