中国特有果蝇 Drosophila curviceps 种亚组在Drosophila immigrans种组中的种系发生地位

果蝇immigrans种组中的curviceps种亚组是1992年新建立的中国特有果蝇类群。该种亚组中的物种主要分布在中国大陆和台湾。目前除了形态学水平的研究外，还没有其他证据支持建立该种亚组的合理性及其起源和种系发生地位。为了在DNA分子水平上探讨果蝇curviceps种亚组在果蝇immigrans种组中的种系发生地位，从而为今后更深入地研究中国特有果蝇，甚至为果蝇亚属的进化遗传学提供理论依据，测定了immigrans种组5个种亚组（nasuta、immigrans、hypocausta、quadrilineata、curviceps)中12个代表物种的rDNA的ITS1和部分Adh基因的序列。其中ITS1序列的长度为513－587bp,共有191个信息位点；Adh基因片段的长度在714－747bp之间，共99个信息位点。考虑到单个分子提供的信息较少，将两个分子的序列综合起来，组成一个较长的复合序列。分别根据ITS1，Adh和两个分子的复合序列排比（Alignment)结果，和最大简约法和邻接法构建分子系统树，其中根据复合序列构建的系统树与形态学研究结果最为一致。分子树显示curviceps种亚组的特种确定单独形成一个分枝，为种亚组级的分类阶元，支持了形态学将其建立为一个新种亚组。根据Kimura距离，估算了复合分子的替换速率约为每百万年1．48％，进而计算出5个种亚组的分 歧年代。结合各物种的地理分布，推测了immigrans种组的进化历史：curviceps种亚组与quadrilineata种亚组的亲缘关系最近，主要分布在中国南部的温带地区。它们之间的分歧时间大约为3．4百万年，是最年轻的两个种亚组。主要分布在苏门答腊及附近的热带地区的hypocausta种亚组的物种是最早分化出来的，与其他种亚组的分歧时间约为9．2百万年。该结果与形态学和生物地理学研究相吻合。值得一提是的，目前归属仍存在争议的物种D.neohypocausta，在分子系统树中与hypocausta种亚组的物种相距较远，而与immiagrasn种亚组的关系较近，但分枝置信度较低（＜50％）。由于还缺乏其他方面的证据，因此D.neohypocausta的归属有待今后的研究来作定论。

Phylogenetic Position of Chinese Endemic Drosophila curviceps Species Subgroup in the Drosophila immigrans Group

In order to investigate the phylogenetic position of Chinese endemic Drosophila curviceps species subgroup within the D.immigrans group on DNA molecular level,the ITS1 region of ribosomal DNA and part of Adh gene for 12 species represented all the five subgroups in D.immigrans group were sequenced.Molecular phylogenetic trees were constructed by using parsimony and neighbor joining methods based on ITS1, Adh and combined sequences.In the molecular trees,species of the D.curviceps subgroup cluster together,strongly supporting establishment of a separating subgroup suggested in an initial morphologic study. This subgroup is the sister taxa of the D.quadrilineata subgroup.They are the younger subgroups,splitting about 3 4 Mya.The D.hypocausta subgroup is located at the base of the molecular tree,diverged first in this group about 9 2 Mya.Taking the geographic distribution into account,we can conclude that D.curviceps subgroup originated from tropic zones,agreeing with the previous morphologic and biogeographic suggestions.The position of D.neohypocausta was also discussed in this report and it seems that it is closer to the D.immigrans subgroup than to the D.hypocausta subgroup.