Regulation of the mutualism between yuccas and yucca moths: intrinsic and extrinsic patterns of fruit set

Abstract

In plants that produce many more flowers than fruit, nonrandom patterns of fruit set arise from (1) factors intrinsic to inflorescence architecture, such as flower position or timing in the blooming sequence, and (2) factors extrinsic to the plant, such as pollinator visitation patterns. Here, we address how intrinsic and extrinsic factors drive fruit set in the interaction between Yucca kanabensis McKelvey and its pollinating moths. On inflorescences from which moths were excluded and all flowers were hand pollinated, the flowers most likely to produce fruit were (1) flowers from the first of three waves of flowering, (2) earlier opening flowers but not the earliest, and (3) flowers lower on the inflorescence but not the lowest. However, inflorescences experiencing natural levels of pollination and oviposition showed no effect of flowering wave, and flowers later in the flowering sequence and higher on the inflorescence were the ones most likely to produce fruit. The intrinsic patterns of fruit set were associated with differences among flowers, with the largest flowers being wave 1 flowers and flowers lower on the inflorescence. However, these differences among flowers did not translate into commensurate differences among fruit.Key words: mutualism, abscission, fruit, yucca, yucca moth.