Larger is better: The effects of floral display on reproductive success in two populations of Caladenia (Stegostyla) gracilis R. Br

Abstract

Floral display can affect pollinator visitation and reproductive success. If floral display is genetically regulated and if pollinators preferentially visit some types of displays more frequently than others, then there are opportunities for selection. The effect of variable numbers of flowers in the terrestrial orchid Caladenia (Stegostyla) gracilis R.Br. on reproductive fitness was investigated in two populations. Fitness measures included the number of male (pollinaria removal) and female (pollinaria deposition and fruit set) reproductive successes. In both populations studied, all three fitness indices demonstrated the same trends that inflorescences with a greater number of flowers have a higher probability of having pollinaria removed, deposited and of producing fruits. This trend of increased reproductive success of plants with larger inflorescences was not expected in this mostly few-flowered clade, the Caladeniinae. If no other counter selective fitness measures are present, then inflorescences with greater number of flowers in C. gracilis can be expected in future generations, however, the increased fitness advantage for larger displays may be mediated by a reduction in lifetime fitness or survival of larger individuals, moreover flower number may be a response to phenotypic plasticity to environmental resources and may not be easily inherited if at all.