DNA-barcoding for the inference of larval community structure of non-biting midges (chironomidae) from the River Stour, Kent

Chironomids, or non-biting midges (Chironomidae), belong to the order of true flies (Diptera), and are the most abundant freshwater macroinvertebrates with an estimated 20,000 species worldwide. With the use of the taxonomic identification tool DNA barcoding, it is possible to identify new species and identify specimens without the need for expert knowledge in morphological identification. In this study, DNA barcoding using the mitochondrial (mt) DNA cytochrome oxidase I gene (CO1) was used to identify non-biting midge larvae from the River Stour, Kent. Chironomid larvae were collected by kick sampling at three different sites: Bingley Island (BI), Rheims Way (RW) and Westgate Towers (WT). A total of 93 DNA extractions were carried out including 36 samples from Bingley Island, 30 from Rheims Way and 27 from Westgate Towers. From these, only 33 samples (BI = 8, RW = 12, WT = 13) gave successful PCR amplifications and provided mtDNA sequences for analysis (35.5% success rate).

Reasons for the low success rate were discussed; and could be due to the small tissue sample left after the head capsule and final abdominal segments were removed (for morphological analysis), or because of amplification failure due to contamination in the specimen (PCR inhibitors in some samples). Nonetheless, the sequence data obtained was robust enough for analysis. The mtDNA sequences were compared to the public data base GenBank (NCBI) using the Basic Local Alignment Search Tool (BLAST). A similarity score was obtained for each sample, and the first hit was used to provide a ‘putative’ (tentative or provisional) genus name to the mtDNA sequences from the River Stour. Using phylogenetic methods, the evolutionary relationships of the chironomids obtained in this study were assessed alongside other sequence data obtained from GenBank. Also, genetic diversity and differentiation values among the three sites and GenBank data were obtained. The presence and abundance of chironomids from the River Stour (with their putative genus names) were also used to study the generic richness and diversity in each site, as well as the community structure among the sites.

Results showed that it was possible to obtain a putative identification of chironomid larvae, i.e. DNA barcoding, as shown by the similarity scores obtained with BLAST. The phylogenetic analyses also showed the relative similarities of the DNA sequences of chironomids from the River Stour to all other chironomids from GenBank; and also showed the still unexplored non-biting midge phylogenetic relationships. Overall, the three sites in the River Stour were very similar and showed little richness and diversity, although this could be due to the low success obtaining DNA sequences. This study represented the first DNA characterisation of chironomids from the River Stour, and the results could be interpreted as representative of the chironomid larval community. As a first attempt to DNA barcode chironomids from the River Stour, the results and could be useful for monitoring purposes, or as a comparison of biodiversity among other rivers in the region.