Does the DNA barcoding gap exist? - a case study in blue butterflies (Lepidoptera: Lycaenidae).

Martin Wiemers,Konrad Fiedler

doi:10.1186/1742-9994-4-8

Abstract

BackgroundDNA barcoding, i.e. the use of a 648 bp section of the mitochondrial gene cytochrome c oxidase I, has recently been promoted as useful for the rapid identification and discovery of species. Its success is dependent either on the strength of the claim that interspecific variation exceeds intraspecific variation by one order of magnitude, thus establishing a "barcoding gap", or on the reciprocal monophyly of species.ResultsWe present an analysis of intra- and interspecific variation in the butterfly family Lycaenidae which includes a well-sampled clade (genus Agrodiaetus) with a peculiar characteristic: most of its members are karyologically differentiated from each other which facilitates the recognition of species as reproductively isolated units even in allopatric populations. The analysis shows that there is an 18% overlap in the range of intra- and interspecific COI sequence divergence due to low interspecific divergence between many closely related species. In a Neighbour-Joining tree profile approach which does not depend on a barcoding gap, but on comprehensive sampling of taxa and the reciprocal monophyly of species, at least 16% of specimens with conspecific sequences in the profile were misidentified. This is due to paraphyly or polyphyly of conspecific DNA sequences probably caused by incomplete lineage sorting.ConclusionOur results indicate that the "barcoding gap" is an artifact of insufficient sampling across taxa. Although DNA barcodes can help to identify and distinguish species, we advocate using them in combination with other data, since otherwise there would be a high probability that sequences are misidentified. Although high differences in DNA sequences can help to identify cryptic species, a high percentage of well-differentiated species has similar or even identical COI sequences and would be overlooked in an isolated DNA barcoding approach.

Highlights

DNA barcoding, i.e. the use of a 648 bp section of the mitochondrial gene cytochrome c oxidase I, has recently been promoted as useful for the rapid identification and discovery of species
Apart from a single unpublished sequence (AB192475), all other c oxidase subunit I (COI) GenBank sequences of this species are identical with each other or only differ in a single nucleotide (= 0.15% divergence). They are nearly identical to two specimens of Lampides boeticus in the CBOL database (BOLD) [43] from Tanzania and another sequence of this species from Papua New Guinea (Wiemers, unpubl. data)
We found an upper limit for intraspecific sequence divergences in a wide range of species of the diverse butterfly family Lycaenidae, but no lower limit for interspecific divergences and no barcoding gap

Summary

Introduction

DNA barcoding, i.e. the use of a 648 bp section of the mitochondrial gene cytochrome c oxidase I, has recently been promoted as useful for the rapid identification and discovery of species. Frontiers in Zoology 2007, 4:8 http://www.frontiersinzoology.com/content/4/1/8 this approach received opposition, especially from the taxonomists' community [3,4,5,6,7,8] Some arguments in this debate are political in nature, others have a scientific basis. The existence of a barcoding gap would even enable the identification of previously undescribed species ([11,12,13] but see [14]) Possible errors of this approach include false positives and false negatives. False positives occur if populations within one species are genetically quite distinct, e.g. in distant populations with limited gene flow or in allopatric populations with interrupted gene flow In the latter case it must be noted that, depending on the amount of morphological differentiation and the species concept to be applied, such populations may qualify as 'cryptic species' in the view of some scientists. False negatives are more critical for the barcoding approach, because the existence of such cases would reveal examples where the barcoding approach is less powerful than the use of other and more holistic approaches to delimit species boundaries

Methods

Results

Conclusion