Landscape genetics in an ancient Ethiopian agroecosystem: patterns of seed flow and forces of change

Background/Question/Methods In the highlands of southern Ethiopia, a diverse and intensive subsistence agroecosystem dominates a rugged mountainous landscape. Biophysical and socioeconomic landscape features affect gene-flow of crop species and determine the extent and structure of genetic diversity. Understanding how genetic diversity is distributed allows us to predict ways in which traditional agroecosystems are vulnerable to changing conditions. My research applies a landscape genetics approach to relate gene-flow patterns to landscape structure in a global center of diversity. I ask whether and in what ways crop populations are structured in relation to biophysical and socioeconomic features. I examine two central species in the region, barley (Hordeum vulgare), and enset (Ensete ventricosum), which are exchanged and propagated through very different methods and pathways.  I ask what effects these different management systems have on population structure of the two crops. I then use this information to assess the vulnerability of crop diversity to changing environmental and socioeconomic conditions in the region.
This study was carried out in the remote Gamo highlands of southwest Ethiopia. Samples were drawn from 130 farms in 12 communities, representing gradients of elevation, accessibility, and agroecological zones. Plant sampling was accompanied by farmer surveys on seed sourcing and exchange. DNA from leaf samples was extracted, amplified, and analyzed via microsatellite and AFLP techniques. Genetic data was analyzed through multivariate statistical and ordination methods. Genetic and landscape data were analyzed in GIS software to determine spatial patterns and processes.

Results/Conclusions

These two species exhibited distinct population structures within this highland region. Patterns of isolation-by-distance were evident in both species, though the relationship was considerably more pronounced in enset than in barley. Barley populations largely reflected elevation gradients and farmer preferences for elevation-specific barley varieties. Enset population structure more closely reflected farmer-identified variety names, and differentiation between communities was much greater.
Farmers identified elevation and social networks as primary factors influencing their seed-sourcing decisions. The scale of seed movement ranged from local to long-distance, and was dependent on farmer socioeconomic status, plant species, elevation, and location. Farmers also identified several forces of change in the region, including changing social structures, market orientation, adoption of new crops, and increasingly unpredictable rainfall. Exchange of planting material within and between agroecological zones has the potential to provide agroecosystem resilience in the face of environmental or land-use change.