3.1 Sequencing analyses
Macroinvertebrates are absolutely predominant faunas in the international rivers of northwest China, but few studies on macroinvertebrates have been carried out in these rivers. In this study, a total of 1,678 individuals were collected and utilized for the generation of DNA barcodes. However, 451 specimens showed poor quality and were excluded from further analyses. Accordingly, a total of 1227 sequences (516-Ephemeroptera, 146-Plecoptera, 81-Trichoptera, 66-Hemiptera, 273-Diptera, 55-Coleoptera, 23-Odonata, 66-Annelida, 17-Mollusca), belonging to 189 species, 123 genera and 59 families, were successfully generated. The lengths of all COI sequences were no less than 600 bp for sequencing analysis. Deletions, insertions and stop codons were not detected in the sequences, suggesting that the COI PCR primers were efficient. All the species exhibited high adenosine and thymine (AT)-rich bias (averaged 63.1%). Specifically, the A+T % in Trichoptera was up to 69.9% and the lowest was shown in Diptera (55.6%).