Selection for domestication favored taxa characterized by fast growth and tolerance of high intraspecific density

Abstract

In spite of a large history of research, it is still unclear which functional traits may have mediated plant domestication. Solving this problem requires consideration of the ecological and demographic disparities between natural plant populations and cultivated fields. Since population density tends to be higher in the latter, we hypothesized that traits facilitating growth and survival in dense, monospecific populations might have been relevant for initial domestication. We investigated whether functional traits that respond to population density varied across three different domestication stages: undomesticated crop wild relatives, natural populations of crop progenitors, and landraces. To do this, we compared traits influencing competition (lodging; growth rate), resource acquisition (plant height; total aerial and root biomass) and yield (fruit number) in three annual legume crops—lentil, grasspea, and vetch—grown without resource limitation at three different densities. Our results showed clear differences among species, likely reflective of the distinct uses of the crops and their domestication pathways. Nevertheless, undomesticated relatives consistently differed from crop progenitors and landraces, producing smaller, slower-growing plants that were more prostrate and allocated less biomass to roots. The effect of selection under domestication on these vegetative traits appeared to be largely negligible. Conversely, landraces produced more fruits. We conclude that early agriculturalists selected for domestication wild legumes that performed well in dense monocultures and were more effective in resource capture. Later domestication and breeding efforts likely had more significant effects on reproductive traits, such as fruit and seed production.