4.4. Predicting evolutionary change based on genetic variation
We assumed that KG species will conserve its cultivated areas over space and time. Our results however, found evidence of variability in the species response to future environmental conditions. This corroborates many other studies which showed the impact of future climatic conditions on crops production, such as cereals, legumes, vegetables (Burke et al. 2009; Pironon et al. 2019; Ramirez-Cabral et al. 2017; Ramirez-Cabral et al. 2016; Syfert et al. 2016).
We also combined genetic information to ENM to test hypothesis that genetic divergent groups differ in their adaptive potential to respond to environmental change. The projection under future climatic scenarios RCP4.5 and RCP8.5 clearly indicate that the response of Kersting’s groundnut and genetic groups varied significantly across agroclimatic zones. Our results confirmed the idea that different genetic clusters potentially showed adaptive variation to different abiotic conditions within the geographical range of the species (Hancock et al. 2011). Globally, although Central Benin is presumed to be a centre of origin for the crop, we observed a loss in suitable areas for the species production in the Southern-Sudanian zone of the country. The genetic Pop 1 is the mostly concerned by the negative impact of environmental evolution as it was generally found in these regions of the country. Similarly, Ikeda et al. (2016) tested and demonstrated the hypothesis that species locally adapted to current environments are likely to become maladapted in the future. The same trends were reported on other cereals such as maize, wheat, sorghum and barley which tend to decrease their area of suitability in their centres of origin (Bellon & van Etten 2014; Lane & Jarvis 2007). In the context of an inevitable agricultural reduction in these agroclimatic zones, the earlier the mitigation actions are taken, more successful will be the collection and conservation efforts of KG’ resources. On the other hand, severe environmental conditions (RCP8.5) of the Northern-Guinean zone in Southern Benin and Togo remain, even become more favorable to the species cultivation (Pop2). Likewise, the Southern-Sudanian zone of Ghana, Burkina Faso, Togo and Northern Benin, and Northern-Sudanian zone increased in cultivable areas of Pop2. Out of the 361 individuals included in this study, 101 belong to the genetic Pop2, distributed mostly in the Southern-Sudanian zone and counts all the landraces grown - diversity based on seed coat color - (Akohoué et al. 2019; Coulibaly et al. 2020). Such diversity in this population may explain the adaptive response of the Pop2 to climate variation. This is supported by the conclusion of Vigouroux et al. (2011) who described the evolution and adaptation of pearl millet in West-Africa. However, the cultivable area of this genetic Pop2 is predicted to decline in the Southern-Sudanian zone of Central Benin. With regards to these results, significant headway can be made by creating more favorable policy environments. Two strategies proposed by Ramirez-Cabral et al. (2016) can be used in order to mitigate loss in KG resources and diversity: first, the use of all the resources of Pop2 in regions where the stress of climate conditions become unsuitable for the species production. Examples of this is the Southern-Sudanian zone of Central Benin, where the use of KG is more important than other regions. And the second option was to address future loss of suitability by shifting the current cultivation areas of Pop1 to new regions, where the future climatic conditions is projected to become more cultivable for KG, the Northern-Guinean zone of Southern Benin, the southern-Sudanian and northern-Sudanian zones.