Spatial and density-dependent multilevel selection on weed-infested maize
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RESEARCH ARTICLE
Spatial and density-dependent multilevel selection on weedinfested maize Ce´sar Marı´n
Received: 29 February 2020 / Accepted: 21 September 2020 Springer Nature B.V. 2020
Abstract Artificial group selection has long been proposed as a useful method for crop breeding, yet the possibility that group selection occurs naturally in agroecosystems has not been explored. Due to natural and/or artificial selection, the fitness of an individual can depend on both the individual’s traits, the traits of neighboring individuals, and on group’s emergent traits (as density). This process is defined as multilevel selection type I. Using contextual analysis, I detected significant multilevel selection type I at the individual and group levels on weed-infested maize (Zea mays L.) genotypes with different spatial patterns and densities. In general, uniformity promoted multilevel selection type I, but this response varied within maize varieties and years. The results herein presented show that crop productivity and weed suppression increased at high density-uniformity conditions, but this also depends on variety. Multilevel selection type II is defined as the differential reproduction of entire groups, a process that in agronomic settings is implemented by humans. A reduced phenotypic variation in the angle of insertion of the oldest living C. Marı´n (&) Institute of Agri-food, Animal and Environmental Sciences (ICA3), Universidad de O’Higgins, 3070000 San Fernando, Chile e-mail: [email protected] C. Marı´n Center of Applied Ecology and Sustainability, 8331150 Santiago, Chile
leaf at harvest was identified as a group attribute to be selected for artificial multilevel selection type II. This trait experienced stabilizing selection at the individual level, which significantly increased crop productivity. Keywords Artificial selection Contextual analysis Crop-weed competition Densitydependence Multilevel selection Spatial uniformity
Introduction Two of the main architects of the Green Revolution, C.M. Donald and J.L. Harper, argued that the selection of entire crop groups should be the strategy implemented in agronomic breeding programs instead of the traditional selection of more-fit individuals (Harper 1977; Donald 1968, 1981). Harper suggested that ‘‘…group selection, which is believed to be extremely rare in or absent in nature … may be the most proper type of selection for improving the productivity of crop and forest plants’’ (Harper 1977; p. 892). Currently, ‘group selection’ is better understood as multilevel selection, which occurs when natural selection acts simultaneously on two or more levels of the biological hierarchy (Heisler and Damuth 1987; Marı´n 2016). Donald’s concepts of ‘‘ideotype’’ and ‘‘communal plant’’ reaffirmed the possible role of multilevel selection in agroecosystems: ‘‘…a
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Genet Resour Crop Evol
successful crop ideotype will be a weak competitor … [so] … plants in the crop community will compete with each other to a min
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