Adaptive introgression: an untapped evolutionary mechanism for crop adaptation

Abstract

29Global environmental changes strongly impact wild and domesticated species biology and their 30 associated ecosystem services. For crops, global warming has led to significant changes in terms of 31 phenology and/or yield. To respond to the agricultural challenges of this century, there is a strong 32 need for harnessing the genetic variability of crops and adapting them to new conditions. Gene 33 flow, from either the same species or a different species, may be an immediate primary source to 34 widen genetic diversity and adaptions to various environments. When the incorporation of a foreign 35 variant leads to an increase of the fitness of the recipient pool, it is referred to as "adaptive 36 introgression". Crop species are excellent case studies of this phenomenon since their genetic 37 variability has been considerably reduced over space and time but most of them continue 38 exchanging genetic material with their wild relatives. In this paper, we review studies of adaptive 39 introgression, presenting methodological approaches and challenges to detecting it. We pay 40 particular attention to the potential of this evolutionary mechanism for the adaptation of crops. 41Furthermore, we discuss the importance of farmers' knowledge and practices in shaping wild-to-42 crop gene flow. Finally, we argue that screening the wild introgression already existing in the 43 cultivated gene pool may be an effective strategy for uncovering wild diversity relevant for crop 44 adaptation to current environmental changes and for informing new breeding directions. 45 46 93 94 In the context of species conservation and management a large body of literature discuss how gene 95 flow could also be associated with negative effects. Undesirable consequences of gene flow are 96 4 associated with the risks of invasiveness (Ellstrand and Schierenbeck, 2000; Whitney et al., 2006), 97 transgene escape (Ellstrand et al., 2013 and references therein), or genetic erosion of native 98 populations (Wolf et al., 2001). Little attention has been paid to the potential of managed gene flow 99to increase genetic variation for species rescue (Hedrick, 2009) and adaptation (Aitken and 100 Whitlock, 2013). Up to now, the potential of adaptive introgression as a source of adaptation to on-101 going global changes for domesticated species has been overlooked. 103In this paper, we review studies of adaptive introgression, paying particular attention to the potential 104 of this evolutionary mechanism for the adaptation of crops. By the term 'introgression' we mean the 105 consequence of gene flow, at both the interspecific and the intraspecific level, i.e. independently of 106 the taxonomic classification of the gene pools exchanging genetic material. We focus on sexually 107 reproductive organisms; and we did not directly discuss horizontal gene transfer (reviewed in 108 Arnold and Kunte, 2017). Within this framework, we report on 34 case studies addressing adaptive 109 introgression ( Table 1). After discussing methodological approaches and challenges ...

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“…Differentiation of early-and late-owering millets may have occurred after the domestication of pearl millet, as a consequence of a center of specialization across the Sahel belt. This assumption is supported by previous observations reporting migrations, exchanges and gene ow that led to a wider genetic diversity as an adaptive mechanism (3,17). These ndings and assumption make the identi ed subgroups within early-owering Souna and late-owering Sanio genuine heterotic groups for breeding for earliness or biomass, respectively.…”

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