Effects of herbivores and pollinators on fruit yield and survival in a cleistogamous herb

Abstract

Although the way in which multiple biotic interactions affect plant reproductive success has been assessed in sexually monomorphic plants, little is known about the joint influence of these interactions on the reproductive success and the consequences to the mating system of plants with sexual heteromorphisms. Dimorphic cleistogamy is a sexual heteromorphism where a single plant produces open, potentially out-crossed chasmogamous (CH) flowers and closed, obligately self-pollinated, cleistogamous (CL) flowers. Fruits produced are also dimorphic with CH fruit being larger and having more seeds than CL fruit. The effects of defoliation and enhancement of the pollination environment on CH and CL fruit yield and plant survival were experimentally assessed in a dimorphic cleistogamous herb (Ruellia nudiflora Engel. & Gray). We predicted that defoliation would have a stronger effect on CH fruit than on CL fruit owing to the high cost of maintaining the former. However, the negative effects of defoliation on CH fruit may be overcome by compensatory mechanisms in an enhanced pollination environment. Lower survival is expected in defoliated plants, particularly in an enhanced pollination environment owing to greater investment in reproduction. As expected, we found that defoliation had a greater negative effect on CH fruit production; however, this effect was absent in the enhanced pollination environment. Enhancement of the pollination environment also increased survival, but only when plants were not defoliated. Although herbivores may increase inbreeding (via reduction of CH fruit production) in plants with dimorphic cleistogamy, this effect may be negligible in environments where pollination service is optimal.