Friday, August 7, 2009 - 10:10 AM

OOS 47-7: Biophysical and social drivers interact to shape landscape genetics in an ancient Ethiopian agroecosystem

Leah H. Samberg, University of California, Santa Cruz


In the highlands of southern Ethiopia, a diverse and intensive subsistence agroecosystem dominates a heterogeneous mountain landscape. Biophysical and socioeconomic landscape features affect gene-flow of crop and tree 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 and tree populations are divided or connected by biophysical and socioeconomic features, such as topography or farmer exchange networks. I also ask what the scales and mechanisms of farmer exchange of planting materials are, and how they are related to landscape features.
In a contiguous highland region in southern Ethiopia, I collected leaf samples from three agriculturally important species: barley (Hordeum vulgare), enset (Ensete ventricosum) and East African Juniper (Juniperus procera). Samples were drawn from 130 farms in 12 locations, 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 AFLP techniques. I used geographically-situated Bayesian clustering software to identify distinct populations, correlate population boundaries with landscape features, and determine the relative importance of landscape variables in the genetic distances between individuals.


Each of these three species exhibited distinct population structures within this highland region, and the number and distribution of populations differed between species. Population boundaries were correlated with both biophysical landscape features, namely elevation and north-south location across the range, and socioeconomic landscape features, including farmer-identified seed exchange networks. Several populations exhibited cryptic boundaries that are not correlated with identified landscape features.
In on-farm surveys, 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. 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. In conclusion, I discuss how the molecular and survey-based data sets can be integrated and utilized to identify priorities for conservation in the system and mechanisms by which farmer access to genetic diversity may be enhanced.