Revision And Molecular Phylogenetics Of The Bumblebees Of Subgenus Megabombus(Hymenoptera: Apidae)

Bumblebees of the subgenus Megabombus belong to the genus Bombus within the family Apidae. Bees of the subgenus Megabombus are often large,colourful and have long tongues. They are among the most important pollinators for highland and mountain flowering plants in Asia and Europe,especially for the long corolla plants. Therefore, they play an important role in ecological systems. There is strong evidence for convergent evolution of morphology within Megabombus. Moreover, the color pattern varies greatly within and between some species. As a result, it is hard to diagnose species from morphology and color pattern alone. The history of Megabombus is reviewed briefly at the beginning of this thesis. Species are recognized based on COI barcodes in the second chapter. Keys for the identification of species for males and females are provided in the third chapter. Finally, variation in food specialization within this group is explored. The most important results were listed as follows:1. Species recognition and phylogeny of MegabombusOne hundred and seventeen haplotypes of COI barcodes were extracted, amplified and sequenced from Megabombus specimens. The alignment of the COI barcodes shows that it comprised of 389 conserved sites, 269 variable sites, 221 phylogenetically informative sites, with 48 singleton(autapomorphic) sites. GMYC model analysis supports 22 species including one new species. We apply the oldest available names to the constituent taxa as the valid names for the species according to the International Code on Zoological Nomenclature. The support values for the nodes to each species are all greater than 0.9. Therefore, each species is strongly supported as a monophyletic group. The tree topologies from the analysis results of Bayesian inference and from Maximum Likelihood analysis are almost the same. Both methods support two groups in Megabombus with posterior support values of 1. The first group includes the species of the former subgenus Diversobombus of Richards’ subgeneric system. The second group includes the species of the former subgenera Senexibombus and Megabombus(in the narrow sense) of Richards’ subgeneric system. These two groups together form a single large monophylogenetic group. As a result, the former subgenera Diversobombus, Senexibombus and Megabombus of Richards’ subgeneric system are included in the new subgenus Megabombus. 2. TaxomonyAdopting the species recognised here, the distribution of Megabombus was investigated basing on the museum specimens and published records. This shows that all bees of the subgenus Megabombus are indigenous only in the Old World. There are 16 species in China. The centre of species richness is located in the eastern region of the Qinghai-Tibetan Plateau. Diagnosis of the morphology for the subgenus Megabombus is described. All of the bees in this subgenus have long tongues and large body sizes. The oculo-malar distance is more than 1.5 times the proximal breadth of the mandible in most of the species. The key for the identification of species for males and females was written using the species recognized from the GMYC analysis in this chapter. 3. DNA barcoding shows the variability of the colour pattern of Bombus koreanusBombus koreanus Skorikov is an efficient pollinator for plants with long-corolla flowers. In order to document the distribution, colour pattern variation, and food plants of this species, I checked specimens in museum collections and records in the literature. Results show that B. koreanus is distributed only in Korea and China. The species is distributed by elevation from 500-2000 m. The abundance of individuals is highest between 1000 m to 1500 m. Analysis of DNA barcodes shows that there are nine different color patterns in workers and three in queens within the species. The colour pattern of the thorax varies from completely brown to completely black witheveral intermediate color patterns. Phylogenetic analysis shows that B. koreanus is one of the species to have diverged most recently and is the sister species of B. consobrinus. Bombus koreanus has been recorded visiting 11 species of food plant. 4. Food specialisation in the evolution of MegabombusBumblebees of the subgenus Megabombus have unusually long tongues and are generally more specialised than other bumblebees in their choice of food plants. The phylogeny of Megabombus bumblebees shows that speciation occurred primarily within two periods. Speciation in the first period(ca 4.25-1.5 Ma) is associated with the late rise of the Hengduan Mountains at the eastern end of the Qinghai-Tibetan plateau. Speciation in the second period(1.2-0.3 Ma) is associated with climatic cooling in the northern forests. The most extreme food-specialist species belong to the second group, which may point to climate as a factor contributing to specialisation. The most extreme specialist species occur either in the far north(B. consobrinus), or at high elevations(B. gerstaeckeri), in situations where long tongues coincide with the shortest nesting seasons. Species with the longest tongues but occurring further south(even at high elevations) use a broader range of food plants.The season available for colony development measured as growing-degree days varied not only between species but also within species. Global ANOVA analysis showed a significant effect of GDD among different species(F=19.9, P<0.01). The mean value of GDD for the more specialised B. consobrinus-EU + B. gerstaeckeri group was significantly lower than for the less specialised B. religiosus + B. securus + B. koreanus group(P<0.01).Molecular phylogenetic analysis to revise the species of the subgenus Megabombus is reported in this study. Keys for the identification of species for male and female specimens were presented based on characters of morphology and color pattern. Moreover, the evolution of specialization in the use of food plants is also investigated. This will contribute to the taxonomy of bumblebees and to the conservation of these long-tongued pollinators.