Species Diversification And Phylogeography In The Lordiphosa Clarofinis Species Complex(Diptera:Drosophilidae)

The Lordiphosa clarofinis species complex comprises L. clarofinis and a few morphologically allied species.In this thesis, we first investigated the species composition of the complex based on morphological data and DNA sequence data of the mitochondrial COI (cytochrome c oxidase subunit I) gene and the nuclear ribosomal ITS1(first internal transcribed spacer) region. It proved that the complex comprises four species, L. clarofinis widely distributed in the continental East Asian, L. sp.l aff. clarofinis (sp.l) endemic to Japan, L. sp.2aff.clarofinis (sp.2) geographically restricted to the Sichuan Basin, and L. sp.3aff.clarofinis (sp.3) found in Yunnan only. Our phylogenetic reconstruction revealed that, within the complex, sp.1spit first, following by clarofinis, and then the divergence between sp.2and sp.3. Polyphenisms of paramere were observed in sp.2and sp.3, indicating that polyphenism evolved in the most recent common ancestor (MRCA) of these two species. In the clarofinis complex, there is size variation in male sex comb, which may develops by rotation and fusion of transverse bristle rows (TBRs) on the tarsomeres; shorter1st sex comb was found in sp.2probably due to fewer TRBs involved; the bristle pattern on the the fore tarsomeres of sp.3is similar to that in the females, but different from that in the females of clarofinis, sp.1, and sp.2, indicating that, its foreleg is completely feminized, a sitation similar to that in D. lucipennis, which has also lost male sex combs secondarily. Based on the estimates of divergence times, phylogeography, population genetic diversity and genetic constructure, we assumed that, the MRCA of the clarofinis complex started to diversify near or posterior to Pliocene, during which the onset Norther Hemisphere Glaciation occurred. We hypothesize that, during the quaternary glaciation:the ancestral populations of the MRCA of the clarofinis complex or the descendant species had been isolated in different refugia, thus facilitate the speciation and intraspecific differentiation in the complex. It is likely that the Sichuan Basin had served as the refugium of the MRCA of sp.2and sp.3, thus facilitated its divergence from clarofinis; and then, the two daughter species, sp.2and sp.3, diverged from each other due to adaptation of environments of different elevation. Among the species in the complex, clarofinis has the highest genetic diversity. This is probably due to that, the diversity of this species had been preserved in multiple refugia during the glaciation, and the lineages from separate refugia can admixed via postglacial colonization, thus maintained the diversity of the species. We also hypothesize that, some purifying selection may have deprived the genetic diversity in sp.3,leading to low diversity in this species, and the low differentiation among its populations.