Water erosion, caused by water acting on soils, leads to the transport of sediments and can contaminate waterways, thereby harming hydraulic infrastructures and the quality of water for humans and ecosystems. An effective understanding of this phenomenon requires the use of reliable and accurate tools. The objective of this study validate flow estimates as well as assess the soil erosion potential in the watershed of the Sanaga water intake at Nachtigal. The results of the SWAT modeling demonstrate its ability to accurately reproduce the temporal variations of flows. Moreover, the model proves to be effective in identifying the areas of the watershed most exposed to erosion. Soil loss rates vary from 0.7 to 27 t/ha/year, with an average of 10.41 t/ha/year. This rate is more pronounced in areas where steep slopes are combined with agricultural zones. This model provides a rigorous framework for prioritizing soil conservation interventions by identifying critical areas of the watershed and assessing the impact of different management practices on erosion dynamics. To reduce soil erosion in this watershed, it is advisable to implement conservation practices, particularly direct seeding and soil conservation agriculture. It is imperative to establish protection zones around hydraulic structures to prevent any contamination and ensure their proper functioning.

Soil erosion threatens the planet, compromising natural resources and sustainable development, with irreversible consequences on fertility loss, water pollution, and biodiversity depletion. In Cameroon, the Sanaga basin at Nachtigal harbors strategic resources for the country's development (drinking water, hydroelectric dam), which suffer the harmful effects of erosion; hindering the country's socio-economic progress. This study aimed to evaluate the spatial and temporal dynamics of soil loss in the Sanaga basin at Nachtigal from 1980 to 2023. The method employed is based on the Revised Universal Soil Loss Equation (RUSLE). The results show that between 1980 and 2023, forests decreased by 15% among the five land use types, giving way to urbanized areas, cultivated lands, and bare soils. The analysis of soil loss reveals a significant increase in erosion rates, ranging from 0 t/ha/year in non-eroded areas to 1989.82 t/ha/year in the most affected. The average soil loss rate increased by 173.8%, rising from 25.17 t/ha/year in 1980 to 68.97 t/ha/year in 2023. Notably, more than 33% of the basin's area has experienced intolerable soil loss rates exceeding 10 t/ha/year. Steep slope areas, areas with unsustainable agricultural practices, and areas with high rainfall erosivity represent the majority of the basin's area affected by intolerable soil loss. The AUC (Area Under the Curve) method confirms the high accuracy of the erosion susceptibility maps, with a score ranging from 0.81 to 0.85. The maps generated from the study results are valuable tools for the implementation of soil and water conservation strategies in this region.

Soil erosion caused by water is the result of several factors whose specific contributions include erosivity, terrain characteristics, soil properties and vegetation cover. These factors are highly variable in space and time. The rainfall aggressiveness and its erosive effects on soils is a strategic basis for water and soil conservation, agricultural development and water management. This study assesses and maps the erosive power of rainfall in the Sanaga River Basin (SRB) at Nachtigal using the local Arnoldus index applied to TAMSAT 1985-2020 satellite data. Two types of data were used: rainfall data collected in the field and satellite rainfall data (TAMSAT). The formers were obtained from the National Meteorological Directorate of the Ministry of Transport, and the second, made up of TAMSAT precipitation downloaded online via the website https: //www.tamsat.org.uk. This data set consists of monthly and annual rainfall data. The results obtained show an average annual erosivity of 181.696 MJ. mm/ha.h.y. for the observed data and 206.59 MJ. mm/ha.h.y. with the TAMSAT data. Spatially, the precipitation erosivity shows a gradient of decreasing intensity from the north-west to the south-east which follows that of precipitation. The basin northwestern part presents a high erosion risk with values of the order of 215.18 mm/ha.h.y. compared to the south-eastern part where values are of the order of 169 MJ. mm/ha.h.y. As for the temporal plan, the maximum values of erosivity, i.e. 120 MJ. mm/ha.h.y. are observed during the period from September to November, the southeast being less sure of the aggressiveness of precipitation given the agricultural development activities. Given the high risk of erosion observed in this basin, this problem is likely to disrupt the functioning of the hydraulic works that have been and are being built. It is urgent to mention the safety measures, namely the protection perimeters around these works.

Résumé : Dans cet article, il est question d’évaluer la déforestation dans la périphérie Ouest de la réserve de Biosphère du Dja à travers les techniques de Télédétection et de Système d’Information Géographique. Pour cela, 08 images Landsat de date différentes (2011 à 2018) ont été utilisées pour produire les cartes d’occupation du sol, à travers la méthode de classification supervisée et l’algorithme « maximum likelihood ». Les classes d’occupation de sol retenues pour cette classification sont : forêt dense, forêt dégradée, zone de culture, zone marécageuse, zone d’habitation, sol nu et eau. L’analyse des changements a été faite avec la technique de « change detection ». Les résultats de cette étude ont montré que la déforestation a été importante pendant la période d’étude (2011 – 2018). Les surfaces forestières se sont principalement transformées en zone de culture, marécage, forêt dégradée, sol nu. Le taux de déforestation observé est de 6,8% et dénote une importante baisse du couvert forestier dense. L’étude a montré des tendances de déforestation dans cette périphérie. Elle a permis d’observer que les zones tendancieuses sont concentrées principalement autour de certaines activités anthropiques présentes dans cette zone (la plantation agricole SUDCAM, le barrage de Mekin, les lieux habités). Mots-clés : Déforestation, Changement climatique, forêt, tendances de déforestation, images satellites

The Batouri area is located in the Adamawa-Yade domain in East Cameroon region, and has a high geological potential as a host for gold deposits. It is covered by thick forest where outcrops are sometime scarce. The purpose of this study is to generate and combine different geological information which makes up the specificity of the Batouri gold District, in order to contribute to the better knowledge of its geological setting. From satellite imageries, GIS tools and field data; lithological units, lineament and density maps have been dressed at regional-scale of 1/400.000. The mapping has enabled the discovery of spatial and topologic relationships between shear zones, lineaments, gold occurrences and often mineralized granitic intrusions. According to the field data, lithological and lineament maps, the lithology of the Batouri gold District is characterized by alkali granitoids (tonalite, granodiorite, syenomonzo-granite, alkaline granite) hosted by orthogneisses and migmatites as gold mineralization hosts; while the lineaments show a major shear zones trending NE-SW defined by presence of mylonites. The shear zones crosscut all lithologies, mostly granodiorite where majority of gold occurrences is observed; locally, nearest these shear zones, rocks are transformed to the mylonites and gold is concentrated along. From density map, it is shown that the high gold mineralization zone corresponds to highest lineaments density. All those data suggest that gold mineralization in the Batouri district is controlled by tectonic and lithology. It is conclusive that Batouri gold deposit is epigenetic gold set emplaced in orogenic setting, during the post-collisional stage of the Central African Fold Belt (CAFB) and the Congo Craton (CC).

The potential of Radarsat-1 beam mode Synthetic Aperture Radar (SAR) data processing for geological investigation in an equatorial environment has been evaluated. This approach used textural analysis based on Grey Level Co-occurrence Matrix (GLCM) on our image, followed by Principal Component Analysis (PCA) performed on eight normalized co-occurrence indices created (mean, variance, homogeneity, contrast, dissimilarity, entropy, second moment and correlation) and directional filters for lithological discriminations and lineament investigations. Red-Green-Blue (RGB) color-composite was applied to three of the indices, the mean, variance and homogeneity, highlighting the morphostructure of the study area and facilitate lithology discrimination. The PC1 band was multiplied by itself (as PC1 x PC1 image) to enhance the information contained in this neo-canal and to reduce noise during filtering. Directional filters were then applied to the PC1 x PC1 image at 0 degrees, 45 degrees, 90 degrees and 135 degrees directions and the structure lines were extracted manually in a GIS software. From the results obtained, color-composite produced image map containing lithological units easily identified formations such as continental and coastal deposits, sedimentary stack, micaschists, garnet micaschists, micaceous quartzites, charnockitic orthogneisses, and coincided with those already existing on published geological map from Maurizot et al. (1986) and non-published geological map after IRGM geological field campaign. A total of 572 lineaments features (fractures and major faults) were identified on the filtered images and mapped. Major structures (faults) were considered as those clearly identified in the four directions while minor structures (fractures) were those observed in at least two directions. They are oriented in one of the two main directions: NE-SW (N040-N060) and NNW-SSE (N345-N360). The lineament result showed those that already existed on the reference maps and the newly updated lineaments. Spatial relationships between mapped lineaments and areas of current and historical mining exploration were examined by overall lineament density. GPS points of gold indices existing in the area correlate with areas of high lineament density particularly around the Ngovayang massif within the Paleoproterozoic Nyong unit. This study stresses the usefulness of remote sensing data and methods in field campaign, improvement of published geological maps and mining prospecting in areas with an equatorial climate. (C) 2018 National Authority for Remote Sensing and Space Sciences. Production and hosting by Elsevier B.V.

Douala, the most important metropolis of Cameroon, is a sub-Saharan wet coastal environment of which the anarchic urbanization is a socio-economic and environmental problem, significantly influencing the local climate. In this study, three Landsat images from 1986 (TM), 2007 (ETM+) and 2016 (LDCM), were utilized to investigate the effect of this urbanization on the increasing land surface temperature (LST) between these dates. Thus, the urban indices (UI), determined from the Landsat Visible and NIR channels were used to identify impervious areas (Urban Fabric and bare soil) of urban area. It has been shown from the UI images that, impervious areas have been increased from 1986 to 2016. The LST images derived have a continual expansion of zones and points of heat throughout these dates. The correlation analysis of LST and UI, at the pixel-scale, indicated the positive relationship between these parameters, which could show a real impact of urbanization on the increasing temperature in the area. These correlations are fairly low in 1986 (maximum R-square value is about 0.35) and in 2007 (maximum R-square value is about 0.44. In 2016, a high positive correlation (maximum R-square value is about 0.77) confirm that, the impervious areas strengthen the temperature and the Urban Heat Island effect in Douala urban zone. Overall, the earth observation images and the geographic information system techniques were effective approaches for aiming at environment monitoring and analyzing urban growth patterns and evaluating their impacts on urban climates.

In accordance with the implementation of forest management sustainability of protected areas, this work is based on detection of changes in the vegetation of the Mozogo-Gokoro National Park, located in ecologically fragile semiarid region of the Far North of Cameroon, as well as a search for explanatory mechanisms. A processing of Landsat images of years 1982, 1987, 2001 and 2015 have been done and then put in combination with demographic and rainfall data. Three large vegetable mosaics classes are distinguished over the years. The analysis of their spatiotemporal evolution translated a decrease in area of galleries forests in favor of dense to clear dry forests or more open vegetation, with an annual reduction rate of -0.33 % between 1982 and 2015. The vegetation indices (Normalized Difference Vegetation Index and Generalized Difference Vegetation Index) have a decreasing trend between 1982 and 2001 and an increase between 2001 and 2015, proof of a reforestation. A few significant differences of their values are observed between years showing certain stability of the vegetation, but not in account statistically with rainfall and population density. There is a worry about the 1.73 % per year expansion speed in surface of more open vegetation. Therefore, control actions are envisaged to limit this extension of savannah, most likely related to human impacts. *Corresponding Author: Rodrigue Constant Sandjong Sani  sanirocos@yahoo.fr Journal of Biodiversity and Environmental Sciences (JBES) ISSN: 2220-6663 (Print) 2222-3045 (Online) Vol. 11, No. 5, p. 74-91, 2017 http://www.innspub.net J. Bio. Env. Sci. 2017 75 | Sani et al. Introduction The nonstop anthropisation and climate variability affecting dry land ecosystems are often detrimental to the vitality and development of their populations. Changes in natural ecosystems are generally harmful to human societies that live there, because of the fragility of these environments. Poccard-Leclercq and Xue (2004) particularly assert the sensitivity of these dry areas to any environmental changes, related to climate variability and anthropogenic pressures. The deterioration of vegetation is here due to population growth (Potapov et al., 2012; Mayaux et al., 2013) to urbanization and climate change (Gonzalez et al., 2012). Rapid population growth, which increases the land requirements and spontaneous urbanization, are identified as one of the major ecological scourges that the Earth faces (Rossi, 1999). Despite varying sociocultural influences between human societies over time, deforestation is generally seen in close correlation with the contacting forests population growth. It is recognized that the increase or decrease in population density in a given area is closely correlated with the evolution of vegetation (Megevand, 2013). Climate variability, defined as natural intra and interannual variation of climate (Al Hamndou and Requier-Desjardins, 2008), has a great influence in the dynamics of vegetation in dry areas. Rainfall is a climate factor, representing an indicator adapted to local studies in these areas. It is established that in semi-arid and arid environments, the vegetation is especially sensitive to rainfall variations (Diello et al., 2005; Philippon et al., 2008). The scarcity of rainfall, variability in its distribution and its unpredictability, are climatic constraints, which increase in the Sudanian and Sahelian areas, and are determining factors controlling ecosystem and vegetation change (Ozer et al., 2010). These disturbance factors of ecosystem stability are taken into account in Cameroon, in the strategic environmental and forest policies, with the wake of incentive international initiatives (Republic of Cameroon, 2015). There can be cited as examples the National Plan for Adaptation to Climate Change, the National Action Plan for the Fight against Desertification, and the National Action Plan on biodiversity (Republic of Cameroon, 2012). These planning documents stress that in the Sudanian and Sahelian northern part of the country, where the study site, the Mozogo-Gokoro National Park (MGNP) is located, such factors like wood energy consumption and overgrazing are major direct causes of deforestation and degradation of vegetation. These reports also call for more efficient management of protected areas considered as biodiversity hotspots. The sustainable conservation of vegetation and in this perspective the increase in the carbon sequestered are related to the international mechanism REDD+ (Reducing Emissions due to Deforestation and forest Degradation, sustainable forest management and forest conservation). This article is undertaken in accordance with the various national sectorial strategies conducive to sustainable forestry management in Cameroon. The detection of changes in vegetation can be considered as important criteria of alarm, to trigger adaptation and/or mitigation strategies, or control of this vegetable dynamics. Remote sensing is one of the right tools for the global direct monitoring of degradation of vegetation or apprehension of changes in plant cover (Aman et al., 2001; Xue and Su, 2017) and implementation of sustainable development (Franklin, 2001). Spatiotemporal dynamics studies of vegetation using remote sensing are numerous in the Sudanian and Sahelian zones in Africa like those of Diallo et al. (2011), Maârouhi et al. (2011) and in the same area in Cameroon (Yengué, 2000; Wafo, 2008). But, studies of interactions between vegetation and environmental factors has been relatively low (Karlson and Ostwald, 2015). The aims of this paper are firstly, a description and a projection into the future of spatial and spectral evolution of the vegetation of MGNP; secondly, a seeking of explicative mechanisms in such way to assess links with population density and rainfall, two factors likely to be involved in vegetation dynamics; J. Bio. Env. Sci. 2017 76 | Sani et al. thirdly, finish with some proposals measures for a sustainable management of the park. Material and methods Study site The study site was created as a protected area since 1932 and built in a national park in 1968. It is located in the far North region of Cameroon, 10° 56' to 10° 96' North latitude and 13° 54' 13° 58' East longitude, and covers an area of 1,400 ha with lack of a buffer zone (Figure 1). Fig. 1. Location of Mozogo-Gokoro National Park with peripheral localities. This park is peripheral to the Mandara Mountains, and belongs to a geomorphologic unit comprising the plains of Diamaré, Mora and Kaélé, with an altitude of around 450 m (Sandjong Sani et al., 2013a). Advanced soils such as gleyic solonetz and planosols on anatexie granite and gneiss, poorly developed soils dewatered from ancient alluvial of temporary water courses (Mayo) and flooded soils of clay settling plain (vertisols waterlogged) can be found in the study zone (Brabant and Gavaud, 1985). The climate is a sudano-sahelian type, with oscillating annual rainfall between 800 to 1000 mm, and average temperatures from 27 to 28° C (Sandjong Sani et al., 2013b). The analysis of the Standardized Precipitation Index (SPI) from known criteria (World Meteorological Organization, 2012), suggests an interannual variability of rainfall in the study area, with observation of majority years of slight dryness and mild humidity from 1982 to 2015 (Table 1 and Figure 2). A large period of drought is observed, from 1982 to 1990. It is consistent with the rainfall data obtained in the Sahelian and Sudanian regions. Indeed, the space of time (1970-1990), is deemed as being marked by a long episode of drought in these environments (Ozer et al., 2010; Diallo et al., 2011). The vegetation consists mainly of a mosaic of dense dry forests, gallery forests and shrub thickets. A birdlife, reptiles and some mammals have been identified in the park. The MGNP shows several indications of a reference ecosystem in the SudanoSahelian zone (Sandjong Sani et al., 2013a). However, it suffers from significant anthropogenic threats (Sandjong Sani et al., 2013b). J. Bio. Env. Sci. 2017 77 | Sani et al. The largely agricultural local population is quite dense and exponentially growing (Figure 3). There is obviously a very important human pressure in the riparian zone of MGNP, likely to impact on the park vegetation. A very large land pressure may also be exercised on the outskirts of the park, especially with the lack of a buffer zone. Methods Determination of diachronic vegetation covering and explicative elements Selection and acquisition of satellite images The space of time selected for image acquisition is the dry season, on January and February especially. Jensen (1983) recommends that period, in studies to detect observable change in vegetation. He argues that pictures acquired during sunny periods for the detection of change in land covering, have a high contrast and reduce problems related to differences in sun angles, the dissimilarities in soil moisture and vegetation phenological changes. During this time too, the vegetation cover and chlorophyll activity is still discernible, and the presence of naked spaces also distinguishable, with the advantage of a reduction in cloudiness, one of the factoring that could affect the picture quality. The inter-annual variation of rainfall, by exerting a great impact on the vegetation (Diallo et al., 2011), constitutes another criterion that has allowed the choice of pictures. Selected pictures cover all the major periods observed in rainfall variability. The spatial resolution, another indicator for the selection of image data, must be quite high. The downloaded images, come from different sensors: MSS (Multi Spectral Scanner), TM (Thematic Mapper), ETM + (Enhance Thematic Mapper) OLI (Operational Land Imager) and TIRS (Thermal Infrared Sensor) Landsat (Table 2). These sensors are recognized having resolutions, considered as acceptable and workable scale of observation, in the study ar

This paper aimed to assess the status of land degradation in arid and semi-arid areas based on a correlation analysis between spectral and statistical neo-bands. The methodology uses vegetation and soil spectral indices as the second Modified Soil Adjusted Vegetation Index (MSAVI2), Normalized Difference Bare Soil Index (NDBSI), Texture Index (NDTeI), Crust Index (CI), Top Soil Grain Size Index (GSI), Normalized Difference Sand Dune Index (NDSDI) and the first Specific Principal Component of the red, near infrared, shortwave infrared bands stacking (SPC1 R-NIR-SWIR1-SWIR2 ). The vegetation is considered here as the main object of soil sub-surface. Thus after all the spectral and the statistic neo-bands are performed on Landsat8 OLI sensor image, a linear regression is generated to assess their correlation with MSAVI2. Based on the visual interpretation and the regression curves the results show that the determination coefficient R 2 and the P values all significant as less than 0.0001. Each neo-band is weighted with its R 2 to improve its contribution to the model and the synthesis image obtained enhances the land degradation sensing in six classes; these are respectively named as ‘‘severe’’ (3139 km 2 ), ‘‘high’’ (6763 km 2 ), ‘‘moderate’’ (8341 km 2 ), ‘‘low’’ (7454 km 2 ), ‘‘very low’’ (6947 km 2 ) and ‘‘close to nil’’ (5437 km 2 ). This last image is summed with population layer to produce a decision map helpful for further government decision. At the end the degradation image has given interesting results for the detection of land degradation comparatively to derivation and comparison of individual indices.

In this paper, Analytic Hierarchy Process (AHP) is used as the method of criteria choice and classification for the delimitation of a protected area. Starting from the hypothesis that the space define for protected areas of Cameroon must integrate in priority wildlife, the density of spatial distribution of medium and large mammals in the Campo Ma'an National Park is used here as the main criterion analysis. Its combination in raster mode with other layers of information such as vegetation, streams, tracks, surrounding localities and areas of human activities provides a map on which the park area increased by 88.6%. This result is discussed on the basis of socio-spatial impact which is assessed in terms of three levels of relocation of the surrounding villages and their populations.

This work aims at identifying and mapping using Earth Observation (EO) and Geographic Information Systems (GIS), the water-erosion risk areas. The RUSLE (Revised Universal Soil Loss Equation) model, which can be used to estimate the water-erosion risk of soil, was applied to the productive Sangu

BACKGROUND:Anthropogenic habitat disturbance is a prime cause in the current trend of the Earth's reduction in biodiversity. Here we show that the human footprint on the Central African rainforest, which is resulting in deforestation and growth of densely populated urban agglomerates, is associated to ecological divergence and cryptic speciation leading to adaptive radiation within the major malaria mosquito Anopheles gambiae.METHODOLOGY/PRINCIPAL FINDINGS:In southern Cameroon, the frequency of two molecular forms--M and S--among which reproductive isolation is strong but still incomplete, was correlated to an index of urbanisation extracted from remotely sensed data, expressed as the proportion of built-up surface in each sampling unit. The two forms markedly segregated along an urbanisation gradient forming a bimodal cline of ∼6-km width: the S form was exclusive to the rural habitat, whereas only the M form was present in the core of densely urbanised settings, co-occurring at times in the same polluted larval habitats of the southern house mosquito Culex quinquefasciatus--a species association that was not historically recorded before.CONCLUSIONS/SIGNIFICANCE:Our results indicate that when humans create novel habitats and ecological heterogeneities, they can provide evolutionary opportunities for rapid adaptive niche shifts associated with lineage divergence, whose consequences upon malaria transmission might be significant.

Background The question of sampling and spatial aggregation of malaria vectors is central to vector control efforts and estimates of transmission. Spatial patterns of anopheline populations are complex because mosquitoes' habitats and behaviors are strongly heterogeneous. Analyses of spatially referenced counts provide a powerful approach to delineate complex distribution patterns, and contributions of these methods in the study and control of malaria vectors must be carefully evaluated. Methodology/Principal Findings We used correlograms, directional variograms, Local Indicators of Spatial Association (LISA) and the Spatial Analysis by Distance IndicEs (SADIE) to examine spatial patterns of Indoor Resting Densities (IRD) in two dominant malaria vectors sampled with a 5×5 km grid over a 2500 km2 area in the forest domain of Cameroon. SADIE analyses revealed that the distribution of Anopheles gambiae was different from regular or random, whereas there was no evidence of spatial pattern in Anopheles funestus (Ia = 1.644, Pa<0.05 and Ia = 1.464, Pa>0.05, respectively). Correlograms and variograms showed significant spatial autocorrelations at small distance lags, and indicated the presence of large clusters of similar values of abundance in An. gambiae while An. funestus was characterized by smaller clusters. The examination of spatial patterns at a finer spatial scale with SADIE and LISA identified several patches of higher than average IRD (hot spots) and clusters of lower than average IRD (cold spots) for the two species. Significant changes occurred in the overall spatial pattern, spatial trends and clusters when IRDs were aggregated at the house level rather than the locality level. All spatial analyses unveiled scale-dependent patterns that could not be identified by traditional aggregation indices. Conclusions/Significance Our study illustrates the importance of spatial analyses in unraveling the complex spatial patterns of malaria vectors, and highlights the potential contributions of these methods in malaria control.

BACKGROUND:Speciation among members of the Anopheles gambiae complex is thought to be promoted by disruptive selection and ecological divergence acting on sets of adaptation genes protected from recombination by polymorphic paracentric chromosomal inversions. However, shared chromosomal polymorphisms between the M and S molecular forms of An. gambiae and insufficient information about their relationship with ecological divergence challenge this view. We used Geographic Information Systems, Ecological Niche Factor Analysis, and Bayesian multilocus genetic clustering to explore the nature and extent of ecological and chromosomal differentiation of M and S across all the biogeographic domains of Cameroon in Central Africa, in order to understand the role of chromosomal arrangements in ecological specialisation within and among molecular forms.RESULTS:Species distribution modelling with presence-only data revealed differences in the ecological niche of both molecular forms and the sibling species, An. arabiensis. The fundamental environmental envelope of the two molecular forms, however, overlapped to a large extent in the rainforest, where they occurred in sympatry. The S form had the greatest niche breadth of all three taxa, whereas An. arabiensis and the M form had the smallest niche overlap. Correspondence analysis of M and S karyotypes confirmed that molecular forms shared similar combinations of chromosomal inversion arrangements in response to the eco-climatic gradient defining the main biogeographic domains occurring across Cameroon. Savanna karyotypes of M and S, however, segregated along the smaller-scale environmental gradient defined by the second ordination axis. Population structure analysis identified three chromosomal clusters, each containing a mixture of M and S specimens. In both M and S, alternative karyotypes were segregating in contrasted environments, in agreement with a strong ecological adaptive value of chromosomal inversions.CONCLUSION:Our data suggest that inversions on the second chromosome of An. gambiae are not causal to the evolution of reproductive isolation between the M and S forms. Rather, they are involved in ecological specialization to a similar extent in both genetic backgrounds, and most probably predated lineage splitting between molecular forms. However, because chromosome-2 inversions promote ecological divergence, resulting in spatial and/or temporal isolation between ecotypes, they might favour mutations in other ecologically significant genes to accumulate in unlinked chromosomal regions. When such mutations occur in portions of the genome where recombination is suppressed, such as the pericentromeric regions known as speciation islands in An. gambiae, they would contribute further to the development of reproductive isolation.