Linking Herbivory and Pollination: Defoliation and Selective Fruit Abortion in Lindera Benzoin

Abstract

It has been predicted that plants will selectively mature fruit from flowers in which there has been the most intense pollen tube competition. The degree of this selectivity should increase as resources become more constrained and fruit abortion rates increase. One way in which resources could become more constrained is through defoliation by herbivores. The effect of defoliation on selective fruit abortion was tested by examining fruit set and pollen tube numbers in naturally pollinated flowers on defoliated and control branches of Lindera benzoin. Defoliating branches after fruit initiation significantly increased subsequent fruit abortion. Flowers that matured fruit had significantly more pollen tubes per style than those that initiated but then aborted fruit, but greater levels of pollen competition did not result in the production of larger seeds. On undefoliated control branches, selective abortion occurred only among flowers opening during the second half of the flowering season. On defoliated branches selective abortion occurred throughout the entire flowering season. Although defoliation increased abortion rate, it did not increase selectivity based on pollen tube number. When resources were depleted at the branch level, the position of the flower along the branch influenced whether a flower matured a fruit. Floral phenology was unrelated to position. The influence of position on fruit abortion was likely due to the patterns of resource acquisition and use.