THE INFLUENCE OF ENVIRONMENTAL VARIATION ON GROUP AND INDIVIDUAL SELECTION IN A CRESS.

An experimental study of group and individual selection for leaf area under different patterns of environmental variation is presented. This study, which uses the cress Arabidopsis thaliana, demonstrates that group selection can occur in plants. The response to group selection was always in the expected direction, but surprisingly, the response to individual selection was not. Furthermore the interaction between group and individual selection was significant. Individual selection interfered with the response to group selection whether the two forces were acting in concert or were opposed. The effects of the environmental variation treatments were detected mainly as three-way interactions with group and individual selection. Group selection was more effective in environments that interfered with individual selection, as well as in environments that did not interfere with group selection. These results suggest that the ability of a character to respond to group selection, individual selection, or both will depend on a great many factors and that the relative importance of the different levels of selection can only be determined empirically.