[Taxacom] inapplicability of mtDNA barcoding to insects

Doug Yanega dyanega at ucr.edu
Thu Sep 27 12:07:09 CDT 2007

This may be old news to many, but I just came across this paper today:

T.L. Whitworth, R.D. Dawson, H. Magalon, E. Baudry (2007) DNA 
barcoding cannot reliably identify species of the blowfly genus 
Protocalliphora (Diptera: Calliphoridae). Proceedings of the Royal 
Society B: 274: 1731-1739 

This excerpt from the abstract is pretty remarkable:

Here, we investigated the performance of barcoding in a sample 
comprising 12 species of the blow fly genus Protocalliphora, known to 
be infected with the endosymbiotic bacteria Wolbachia. We found that 
the barcoding approach showed very limited success: assignment of 
unknown individuals to species is impossible for 60% of the species, 
while using the technique to identify new species would underestimate 
the species number in the genus by 75%. This very low success of the 
barcoding approach is due to the non-monophyly of many of the species 
at the mitochondrial level. We even observed individuals from four 
different species with identical barcodes, which is, to our 
knowledge, the most extensive case of mtDNA haplotype sharing yet 
described. The pattern of Wolbachia infection strongly suggests that 
the lack of within-species monophyly results from introgressive 
hybridization associated with Wolbachia infection. Given that 
Wolbachia is known to infect between 15 and 75% of insect species, we 
conclude that identification at the species level based on 
mitochondrial sequence might not be possible for many insects.

I'm curious to know how many other studies have come to similar 
conclusions, and how the barcoding community is responding to this 
EXTREMELY serious issue - it could potentially invalidate almost 
every barcoding study ever performed with insects (a brief glance at 
a few such studies indicates that screening for Wolbachia is not part 
of barcoding protocol).


Doug Yanega        Dept. of Entomology         Entomology Research Museum
Univ. of California, Riverside, CA 92521-0314        skype: dyanega
phone: (951) 827-4315 (standard disclaimer: opinions are mine, not UCR's)
   "There are some enterprises in which a careful disorderliness
         is the true method" - Herman Melville, Moby Dick, Chap. 82

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