Floral reduction in Crepis tectorum (Asteraceae): tradeoffs and dominance relationships

Abstract

The present investigation of Crepis tectorum examines the extent to which tradeoffs and patterns of dominance contribute to the association between flower size (head width) and degree of self-fertility among populations adapted to rock outcrops. Partial correlation analyses of phenotypic data from a F2 generation derived from a cross between two outcrop plants and of family means representing one of the parent populations indicate that small-flowered plants fail to reallocate resources to flower and fruit production, that small flower size offers little or no advantage in terms of autofertility, and that floral reduction has little influence on the rate of flower development. Hence, it may be necessary to invoke factors other than tradeoffs to explain the decline in flower size associated with the evolution of autogamy in C. tectorum. Comparison of parent and Fl hybrid means in the crossing experiment suggests incomplete dominance in the alleles for large flower size. Under the assumption that Fl hybrid means reflect the average degree of dominance across loci, I propose inbreeding depression as the basis for some of the reduction in floral morphology.