The Barcode Blog

Thrips are tiny (.5 to 2 mm) plant feeding insects; approximately 4500 species are known, and some are serious agricultural pests. Kladothrips is an Australian genus of at least 35 species which form galls on Acacia trees. In Biol J Linn Soc 2006 88:555 researchers from Flinders University, Australia, apply mtDNA analysis to show that two gall morpho-types of Kladothrips rugosus represent different species. 

Originally described in 1907, K. rugosus is widely distributed across south and western Australia. Two gall types were noted, but no morphologic differences could be found in the thrips themselves. McLeish, Chapman, and Mound found pairwise uncorrected mtCOI p-distances were 0.0-0.6% within gall morphotypes, and 7.4-7.8% between, similar to distances within and among other gall thrips species. The authors aver the usual taxonomic distaste for distance measures (“Distance values are not intended as a means of identifying different species here, which is a problematic approach for species depiction, but as useful descriptors of genetic variation”). I translate this as distance measures can be used help discover new species, but are verboten in official species descriptions. 

The only morphologic differences are that “abdominal segments I-III are as brown as IV-VII, the metathorax is scarcely paler than the brown mesothorax and prothorax, and the sculptured reticles on the posterior half of of tergites II-III are all small and equiangular.” Phew! Not many persons could decipher such abstruse morphologic terminology, whereas DNA-based identification promises more democratic access to species identification. The main limiting factors are technological and likely solvable: establishing reference libraries and developing inexpensive DNA analytic methods. 

The authors found a third genetic cluster in K. rugosus, but were unable to discover any morphologic characters, so did not describe this as a new species. This seems scientifically inconsistent, and the authors seem to agree: “This lack of morphologic divergence has evident problems for traditional taxonomy..we suggest that “morpho-taxonomy” is little more than an historical artifact in the methodology of species recognition, despite commonly providing the most practical methods”

I hope the large data sets emerging from the barcode initiative and other genetic surveys will enable taxonomists to develop consistent methods of species delimitation, whether in thrips or thresher sharks, and the sequences themselves or their diagnostic nucleotide characters will be routinely incorporated into species descriptions.

This entry was posted on Thursday, November 16th, 2006 at 9:03 pm and is filed under General. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.