Crops and the seed mass-seed output trade-off in plants

A trade-off between seed mass (SM) and seed output (SO) defines a central axis of ecological variation among plants, with implications for understanding both plant trait evolution and plant responses to environmental change. While an observed negative SM-SO relationship is hypothesized to reflect universal constraints on resource allocation in all plants, domestication has likely fundamentally altered this relationship. Using a dataset of SM and SO for 41 of the world most widespread crops and 1,190 wild plant species, coupled with observational data on these traits in soy (Glycine max) and maize (Zea mays), I show that domestication has systematically rewired SM-SO relationships in crops. Compared to wild plants, virtually all crops express a higher SM for a given SO; this domestication signature is especially prominent in seed crops, and also influences the phylogenetic signal in SM and SO. In maize these traits have become positively related likely due to simultaneous selection for greater SM and SO, while in soy these traits have become decoupled likely due to primary selection for SM only. Evolved relationships between SM and SO in plants have been disrupted by both conscious and unconscious artificial selection, which represents a key aspect of how the functional biology of crops differ fundamentally from wild plants along \"universal\" plant trait spectra.