Does a global DNA barcoding gap exist in Annelida?

Area of Science:

• Zoology
• Genetics
• Bioinformatics

Background:

• Accurate DNA barcoding relies on a 'barcoding gap'—a clear distinction between intra- and interspecific genetic distances.
• The absence of a sufficient barcoding gap can lead to misidentifications (false positives/negatives), reducing DNA barcoding utility.
• Comprehensive analyses of barcoding gaps across broad taxa like Annelida are seldom performed.

Purpose of the Study:

• To comprehensively investigate the existence and size of a global DNA barcoding gap within the animal phylum Annelida.
• To assess the potential for erroneous specimen identifications in Annelida due to insufficient barcoding gaps.
• To analyze intraspecific and interspecific genetic distances for Annelida, Polychaeta, Oligochaeta, and Hirudinea.

Main Methods:

• Downloaded and curated all available cytochrome c oxidase subunit I (cox1) gene sequences for Annelida and its subgroups from GenBank.
• Performed automated global barcoding gap detection analysis on curated datasets (9782 Annelida, 5545 Polychaeta, 3639 Oligochaeta, 598 Hirudinea cox1 sequences).
• Analyzed over 70 million pairwise genetic comparisons, calculating intraspecific and interspecific distances to visualize potential barcoding gaps.

Main Results:

• No distinct or sufficiently sized global barcoding gap was detected across the analyzed Annelida datasets.
• A tendency towards separation between intra- and interspecific distances was observed, but not to a degree ensuring reliable identification.
• Earthworm taxa (Oligochaeta) showed a high proportion (35%) of interspecific comparisons with 0% divergence, indicating significant overlap.

Conclusions:

• The absence of a global barcoding gap in Annelida poses a significant risk of inaccurate specimen identifications in future barcoding efforts.
• While local barcoding gaps may exist for lower taxonomic ranks, a general gap for reliable species-level identification is lacking.
• Findings highlight the critical need for thorough gap analysis before widespread DNA barcoding application in Annelida research.