Surprisingly Low Limits of Selection in Plant Domestication

Abstract

Current debate concerns the pace at which domesticated plants emerged from cultivated wild populations and how many genes were involved. Using an individual-based model, based on the assumptions of Haldane and Maynard Smith, respectively, we estimate that a surprisingly low number of 50-100 loci are the most that could be under selection in a cultivation regime at the selection strengths observed in the archaeological record. This finding is robust to attempts to rescue populations from extinction through selection from high standing genetic variation, gene flow, and the Maynard Smith-based model of threshold selection. Selective sweeps come at a cost, reducing the capacity of plants to adapt to new environments, which may contribute to the explanation of why selective sweeps have not been detected more frequently and why expansion of the agrarian package during the Neolithic was so frequently associated with collapse.

Keywords: Haldane; Maynard-Smith; cost of selection; domestication.

Figure 1

Probability landscapes of population survival (p) for a given number of loci (g) under a selection coefficient (s). Graphs are colored to show relief only. (A) Inbreeding population with m_f value of 1.5. (B) Out-crossing population with m_f value of 1.5. (C) Inbreeding population with m_f value of 10. (D) Out-crossing population with m_f value of 10.

Figure 2

Landscapes of minimum population bottleneck (b) expressed as a proportion of the original population size for a given number of loci (g) under a selection coefficient (s). Graphs are colored to show relief only. (A) Inbreeding population with m_f value of 1.5. (B) Out-crossing population with m_f value of 1.5. (C) Inbreeding population with m_f value of 10. (D) Out-crossing population with m_f value of 10.