Flower number and floral components in ten angiosperm species: an examination of assumptions about trade-offs in reproductive evolution

A common approach to modelling reproductive evolution in flowering plants includes an implicit assumption that module number and resource allocation per module follow an inverse hyperbolic trade-off. This assumption has not been thoroughly tested. In ten herbaceous and small woody species I examined phenotypic partial correlations between flower number (measured in relation to vegetative biomass) and each of three floral components: pollen number per flower, ovule number per flower, and corolla size. Significantly negative correlations between flower number and at least one of the floral components occurred in four of the ten species. These phenotypic correlations suggest the existence of true (genetically based) trade-offs, because environmental correlations are likely to be positive, but the significant negative relationships are linear except in one case. Thus, evolutionary tradeoffs involving flower number seem likely in some cases, but there is little to indicate that hyperbolic trade-offs are common. The phenotypic patterns investigated here cannot provide definitive answers about the form of trade-offs. Nonetheless, theoretical attention to the potential evolutionary consequences of trade-offs other than the implicit hyperbolic form is needed.