Molecular Evolution And Phylogeny Of Some Species Of China Aquatics Hemiptera Based On Cytb Gene

With nearly 3738 species grouped in 23 families, aquatics Hemiptera insects play a significant role in the nature. They act as elementary customers or decomposers in water ecology. Most of them are predacious to many small creatures in the water. At present, it becomes a hot point to utilize aquatic insects to supervise and transform water environment. On the other hand, some of the species (such as Nepidae, Belostomatidae ) are pests of fish. So, they have received wide attention from entomologists. Cytochrome b (Cytb) is one of the most widely used molecular markers in animal molecular phylogenetic studies. This paper deals with the molecular system of 11 species 14 samples from 6 families. 485bp Cytb gene was amplified and sequenced .DNA sequences were aligned using CLUSTALX and imported into MEGA2.1 for phylogenetic analysis. The results are as follows:1.Specimens both soked in ethanol and dryly preserved for many years can be used to extract DNA and amplified specific gene. However, temperature should be focused on during the extracting, and physical damage should be avoided, for these factors will lead to DNA decomposing.2.There has a strong AT bias in Cytb gene. This coordinates to the previous reports. Mutations mostly occurred in 3rd positions and 2nd positions. The ratios of transition and transversion diminished gradually corresponding to the divergent time. Among family transitions are higher than transversions interspecies, while it is contrast within families. The gene sequences coded 144 amion acid, and 52.8% of them (namely 75 amion acid) subjected to mutations.3.The phylogenetic relationships of Hemiptera inferred from Cytb gene data indicated that the same genus firstly assembled to one branch. Different genus from one family showed monophyletic. The amount of sequence divergence between clades was greater than within clades. In the Gerridae, Aquarium is the most ancient and earliest-divergencing one. Limnogonus and Potamometra are two orders in evolution history.4.There are various life forms of insects in Gerridae (such as long wing pattern, short wing pattern et), which lead to more difficulties in morphological taxonomy while utilizing molecular method can effectively determinate species, as well as distinguish different life forms intra-species.S.Reconstructed gene tree topologies proved that Diplonychus esakii and Ranatra unicolor formed sister group . According to morphological evolution, their divergence occurred at the same time . Phylogenetic history of Belostomatidae and Nepidae are longer than Corixidae. The evolutional history of Notonectidae is the shortest. All this results are congruent with morphologic analyse.6.The phylogenetic analysis in this paper based on a single gene. The results shows that Cytb gene sequence is suitable for phylogenetic study at intra-familiy level and remains ambiguous at inter-family level.