The roles of nectar variation, hawkmoth behavior, and pollen movement in natural selection for nectar production in Mirabilis multiflora.

摘要

The success of the angiosperms is thought to be largely due to their ability to ensure reproduction by using animals for the transfer of pollen among plants. Pollinators visit flowers searching for rewards, such as nectar, and consequently pollen is removed from anthers and deposited on stigmas. Nectar volume can influence pollinator foraging patterns and thus pollen movement. Therefore, if nectar production has a heritable component, selection will act on nectar production to optimize pollen transfer. Despite the central role of nectar production in the reproduction of many angiosperms, the extent of interplant variation in nectar production and its effect on pollinator behavior, pollen movement, and plant fitness is largely unknown.; In order to determine how selection may influence nectar production, I measured the nectar production of individuals of Mirabilis multiflora in the White Mountains of California. By manipulating nectar levels, I determined how nectar influenced the behavior of the hawkmoth pollinator, Hyles lineata. The effect of pollinator behavior on pollen movement was studied by measuring pollen removal from anthers and deposition on stigmas. Self vs. outcross pollen movement was determined using pollen marked with fluorescent dye.; I found that individuals had consistent and widely varying nectar productions which environmental factors could not explain. Ramets of clones separated by up to several meters had similar nectar productions while genetically distinct near-neighbors did not; thus indicating a strong genetic component to nectar production. Increased nectar levels resulted in increased numbers of flowers visited consecutively by H. lineata and consequently increased pollen deposition on stigmas and removal from anthers. However, moderate producing plants had higher percentage seed set than either low or high producing plants indicating that stabilizing selection is acting on nectar production. Consecutive flower visits quickly increased self pollen on stigmas and reduced seed set. By modeling the movement of pollen among plants, consecutive flower visits were found to quickly maximize pollen dispersal. Therefore, stabilizing selection will operate on nectar production to ensure enough pollinator visits for seed set and pollen dispersal but not too many flower visits which would reduce fitness by increasing self pollination and pollen wastage.