Experimental demonstration of floral allocation costs in Crepis tectorum

Abstract

Information on floral resource costs is fundamental for understanding how selection operates on floral morphology. In this study, I explored the cost of maturing flowers in a self-incompatible population of the ligulate composite Crepis tectorum L. by experimentally manipulating floral investment and then monitoring the response in reproductive effort. Plants on which the heads were removed during the initial stage of ligule expansion had a higher reproductive effort than plants whose heads were removed immediately after flower maturation, and the latter plants had a higher reproductive effort than plants on which all flowers were permitted to set fruit. Judging from biomass estimates and the magnitude of the observed tradeoffs, the amount of resources allocated to maturing flowers was about half as great as the amount of resources devoted to fruit maturation. These and other results suggest that floral tradeoffs may exert negative selection on floral size variables.