| Coccindllidae is a large family in Cucujoidea (Coleoptera: Polyphaga) and is a very important group of eccnomic insects. According to their dietary preference, it can be divided into three groups: predatory coccinellids, phytophagous coccinellids and fungivorous coccinellids. Predatory coccinellids dieting on aphids, coccids or other arthropods are important natural enemies of many pests, while many phytophagous coccinellids do great harm to agriculture. There has been much discussion about the classification system at higher level of Coccinellidae because of the limitation of morphological characteristic and coevolution. Diet, as a determinant of coccinellid migration and gene flow, is likely to affect probable modes of speciation in different coccinellid groups. Diet also has a close relationship with agriculture production. So the study on the diet of coccinellids has great value in establishing the classification system of Coccinellidae. Molecular biological techniques were applied to insect systematics and much important progress has been made. However, studies on molecular phylogeny of Coccindllidae are rather few.MtDNA genes are good genetic makers for molecular systematics of insects. The COI gene has a low evolutionary rate among them. It has been used for phylogenetic analyses of a wide range of species and divergence levels for their universal occurrence, sequence and structure conservation and abundance. We adopted PCR products direct sequencing technique to sequence 471bp fragments of COI gene of 19 Coccinellidae species (representing 13 genera of 4 subfamilies) and downloaded the other 11 sequences of coccinellids and one sequence of Chrysolina aurichalcea of Chrysomelidae as an outgroup from GenBank. All the sequences were aligned using ClustalX1.83 and statistics of sequence compositions and nucleotide substitutions were obtained using MEGA3.1. PAUP~*4.0b10 (PPC)was used to evaluate the phylogenetic information content of the data and reconstruct NJ, MP and ML trees and Bayesian analyses were also performed with MrBayesV3.0B4. Dietary characters of coccinellids were mapped on phylogenetic tree. The phylogeny and dietary evolution of Coccinellidae were discussed and conclusions are as follows:1. The 471bp fragments of COI gene of 30 Coccinellidae taxa showed patterns, typical of many insects, such as high A+T content(66.7%). Transition represented the bias of T→C, C→T, and transversion represented the bias of A→T, T→A. Most of them were at the third codon sites. Amino acid sequences were composed of 19 amino acids in lack of Cys. The most common amino acids were Ile, Leu, Ser, Thr, and Asp.2. The ratio of transition and tranversion (R) was 0.868. Transition had a trend to be saturated and tranversion didn't have this trend. The 471bp fragments of COI gene of 30 Coccinellidae taxa showed variable distance-dependent transition/transversion (TS/TV). Analyses of tree length distribution and PTP test of data set showed strong phylogenetic signals and a strong correction of characteristics beyond that expected by random.3.The ML tree and BI tree had a same topology, while NJ tree and MP tree had different topologies with them. Likelihood-based KH and SH tests of four topologies from MP, NJ, ML and BI showed that although the ML tree had the lowest likelihood score, the KH and SH tests showed no significant difference in the -Ln likelihood between four trees. Four trees were all considered good interpretations of the data provided. We concluded that the data couldn't provide enough phylogenetic information to fully resolve the relationship of the 30 species in Coccinellidae.4. The 50% consensus tree of NJ, MP, ML, BI trees showed that: The members of the same species or genus were grouped together with high bootstrap confidence values, and all the 4 subfamilies in Pang's system were monophyletic. Epilachninae was the most ancestral group in Coccinellidae. Scymninae was grouped with Chilocorinae first, showing they had a close relationship, and then they were grouped with Coccinellinae. In Epilachninae, both Epilachna and Henosepilachna were not monophyletic.5. In the aspect of dietary evolution, the species referred here could be divided into two clades from the consensus trees: phytophagous coccinellids clustered together to form the first clade branching from the base of tree; predatory coccinellids and fungivorous coccinellids clustered together to form the second clade. In the second clade, coccinellids with the same dietary preference all clustered together respectively. Aphidophagous coccinellids and fungivorous coccinellids clustered together, showing that they had a close relationship, while coccidophagous, coccinellids and acaridophagous coccinellids clustered together. The larva and diet of phytophagous coccinellids indicate that that they are the most ancestral group of Coccinellidae evolving from ancestors like chrysomelids. Predatory coccinellids shifted to groups with different dietary preferences in an early time. Micraspis discolor and Harmonia axyridis all clustered with other aphidophagous coccinellids. This indicated that the change of diet of these coccinellids is just a temporary dietary shift.6. This study didn't give full resolution in the phylogenetic relationships of 30 species of Coccinellidae. The proble reasons are that taxa sampling is imperfect and the sequence longth of COI fragment is too short. Sequencing the whole COI gene or adding other unlinked genes with better taxa sampling will benefit.This study is the first large scale molecular systematic research in Chinese Coccinellidae insects. By submitting gene sequences, we shared these data with worldwide researchers. We hope that the results of this research will provide molecular evidences for phylogenetic relationships and dietary evolution of Coccinellidae.
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