Studies On Pollination Ecology Of Pedicularis (Orobanchaceae) In Hengduan Mountains Region

Pedicularis L.(Orobanchaceae), estimated over 600 species, is primarily distributed in North Temperate Zone, and majority of species occur in the arctic and alpine areas. It is striking that 352 Pedicularis species, more than half of the genus, occur in China. Among these, more than 3/4 portions, most of which are endemics, are concentrated in Hengduan Mountains and adjacent regions of southwestern China, which was considered as one of central regions of modern distribution and secondary development of Pedicularis. Since a vast of floral diversification within a narrow genetic base, Pedicularis may serve as a model for investigating the issue of speciation and plant adaptive radiation in nature. Flowers of this genus vary considerably and show great diversity. Among numerous flowers, scientists identified four major corolla types: I. edentate: nectariferous, lacking both teeth and echinations; II. dentate: one or two-toothed; III. rostrate-shallow tubed, one with both a shallow corolla tube and a galea prolonged into a short or long beak; IV. deep-corolla-tubed, one with both a beak and a slender, much-elongated tube. To date, it is perplexing on corolla evolution in Pedicularis: what is the selective force in the corolla evolution? Does the high diversity in floral structure correspond to the diversity of pollinators in nature? In this dissertation, we tried to provide some evidence through conducting a lot of pollinator observations and pollination experiments in field.Based on our observations in field, we found Bombus is the most common and most dominant pollinator in Hengduan Mountains region. We also found beetles and honey bees pollinate few Pedicularis species, no lepidopteron was found to probe it.Insects show different pollination behaviors in different corolla types. For shallow-tubed species with galea, insects pollinate it primarily in nototribical way, secondarily in sternotribical way; For species with beak, insects pollinate it dominantly in nototribical way. Several louseworts may share only one primary pollinator. The parts of insects contacting with stigmas during pollinating are different for different Pedicularis species. This is a kind of floral isolation mechanism-mechanical isolation, an import selective force for sympatric speciation in angiosperms.We measured inflorescence number, total flower number (Nt), daily floral display size (Nq), sexual allocation and sexual reproductive success in twenty-six louseworts with varying tube depths in Hengduan mountains region. We also determined the degree of foraging fidelity through the acetic anhydride analysis of pollen loads and pollination efficiency by counting pollen grains transferred to stigmas per visit by the sharing primary pollinator in ten species. We regressed inflorescence number, Nt, Nd, daily display size ratio (Nd / Nt), pollinator fidelity and pollination efficiency on corolla tube depth, respectively. Inflorescence number and Nd increase significantly with corolla tube depth, indicating increased floral attractiveness in deep-tubed Pedicularis. Increased Nd / Nt values in deep-tubed louseworts imply that these plants tend to bloom in a shorter period. Compared with shallow-tubed, deep-tubed louseworts have larger pollen volume and higher reproductive success. Foraging fidelity and pollination efficiency of the primary pollinator also increase significantly with corolla tube depth. We suggest floral traits involved in pollination adaptations have evolved integrally.We conducted pollinator observations to Pedicularis dunniana in field for three years in succession. We found very low pollinator visitation but high seed production that indicates that Pedicularis dunniana is autogamous. We clarified that wilting of the upper lip (galea) brought the pollen laden anthers into contact with the stigma resulting in the deposition of self pollen on the stigma. It is likely that autogamy provides reproductive assurance for P. dunniana under conditions of pollinator scarcity. In the northwest of Yunnan Province, the habitats occupied by P. dunnianaare probably temporary owing to frequent flooding, siltation, and an ongoing process of plant succession. In such unstable environments, taxa that can self will be favored. This reproductive strategy may occur commonly in shallow-tubed louseworts since they have the similar flower structure with P. dunniana.Variation of floral trait is also associated with pollinator adaptation. We examined the effects of the retention of colour-changed flowers on long- and short-distance attractiveness of bumblebees and the likelihood of successive flower visits by bumblebees in Pedicularis monbeigiana. The lower lip changed colour with age from white to purple. Hand geitonogamous pollination significantly reduced seed production. No pollen limitation occurred in this species. Purple-phase flowers contributed minimally to pollinator attractiveness at long distance. The combination of less reproductive flowers with a lower amount of reward and floral colour change enabled plants to direct pollinators to reproductive, highly rewarding white flowers at close range. A high percentage of purple-phase flowers in an inflorescence was associated with a marked reduction in the frequency of successive flower visits to individual plants. We suggest floral colour change in P. monbeigiana may serve as a mechanism for enhancing inter-individual pollen transfer and reducing intra-individual pollen transfer.We performed pollinator observations to Pedicualaris densispica in successive three years. This species is pollinated by bumblebees. Bumblebee composition keep constant but caste composition keep change significantly in different flowering seasons. Pollination efficiency is much higher in queen bumblebees than in worker ones. It suffers greatly from pollen limitation in nature. We recruited honey bees as pollinators, seed production increases largely. Though pollination efficiency of honey bees is lower than bumblebees, great abundance in honey bee number can compensate pollination quality. The successive flower visit number is higher in honey bees than in bumblebees, suggesting honey bee's visit reducing geitonogamy largely. We suggest for shallow-tubed species with nectar subject to pollen limitation and habitat disturbance, recruitment of honey bee benefit for plant since honey bee can enhance reproductive fitness in quantity and quality.We also counted amount of pollen grains deposited on stigmas in nature and observed pollen tube growth along styles in P. densispica and P. siphonantha. The results show that amount of pollen deposited on stigmas in P. densispica is more than the necessary to fertilize ovules, indicating pollen competition occurring. If pollen grains from different sources were deposited on stigmas, the long style (tube) would intensify pollen competition.