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However, morphologically well defined but recently radiated species could suffer from incomplete lineage sorting; a natural phenomenon that could give rise to high intraspecific variation when both derived and ancestral alleles were sampled within species, and low interspecific variations when ancestral alleles were sampled across species. Despite rarer, convergence might cause distantly related species to share COI with similar sequence. Many researchers have since pointed out that DNA barcoding can only be successful if it is based on a solid taxonomic foundation, which is elusive for many taxa given that most animal species are undescribed and few are well studied. This also applies to the numerous species in the ornamental species trade that has recently become a source of many invasive species.
4 Many criticisms of DNA barcoding have been methodological and numerous researchers have pointed out that the analysis techniques were poorly developed. In addition, as more sequences have become available, the initial proposal of a universal COI barcode for each species was revealed to be incorrect. Indeed, quite a few studies have provided evidence that COI has limitations for species identification and delimitation, and that there is no barcoding gap in most taxa. For example, Mallet and Willmott (2003) mentioned that closely related species often share COI sequences and that a tendency to hybridize can make the situation even more confusing. Meier et al. (2006) pointed out that the lack of a barcoding gap was even more apparent when the smallest interspecific pairwise distances was used instead of average pairwise distances. Further studies by Wiemers and Fiedler (2007) demonstrated that not all butterflies can be readily identified by their COI DNA barcode. Their analysis showed that there was an 18% overlap between the intra- and interspecific COI sequence divergence due to low interspecific divergence between many closely related species in the Lycaenidae which includes the well-sampled clade of Agrodiaetus. The authors showed that the lack of a barcoding gap resulted in a misidentification rate of 16%. Wiemers and Fiedler (2007) concluded that the “barcoding gap” is an artefact of insufficient sampling across taxa (Martin, 2007). Another test of the applicability of DNA barcoding to a diverse community of butterflies from the upper Amazon only
5 yielded a 77% identification success rate, a figure that dropped to 68% for species represented in the analyses by more than one geographical race and at least one congener (Elias et al., 2007). These studies as well as many other studies on Lepidoptera (Kaila & Stahls, 2006; Roe & Sperling, 2007) indicated that the initial claim of 100% identification success for lepidopterans was due to insufficient sampling.