Postive and Relaxed Selection on Chickpea during Domestication and Post-Domestication Diversification

Like many other annual crops, chickpea (Cicer arietinum) underwent a substantial population bottleneck when domesticated from its wild progenitor (Cicer reticulatum) approximately 10 thousand years ago.  During this bottleneck several key domestication traits such as indehiscence were positively selected by early farmers.  However, the small effective population sizes of early agriculture and the ecological transition to the protected habitat of a cultivated field likely relaxed selection on much of the cultivated chickpea genome. We document both positive and relaxed selection on the cultivated chickpea genome, utilizing a recently assembled expanded collection of the wild progenitor of chickpea as well as its sister taxa Cicer echinospermum. A thorough survey of the source populations for the wild relatives as well as their habitats allows inference into the levels of standing variation available to early farmers, and environmental factors that shifted with the advent of agriculture in the fertile crescent.  Our work shows the need for in-depth collections of crop wild relatives and landraces shielded from modern breeding to make informed inferences about domestication.