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Cockroach classification is to be amended

August 22, 2003

Now it is difficult to imagine how people managed without DNA-diagnostics. Russian scientists hope to apply this method for eliminating differences in classification of the most ancient inhabitants of the earth - cockroaches.

By applying DNA-diagnostics the researchers from the Vavilov Institiute of General Genetics, Russian Academy of Sciences, have rectified an error in the classification of domestic cockroaches. According to the taxonomists' new data, two inhabitants of the kitchens, the German cockroach (Blatta germanica) and oriental cockroach (Blatta orientalis), belong to different families.

Any detail is important if it dates back to ancient times. Already three hundred and fifty million years back, when there was no trace of human beings and even dinosaurs, cockroaches already inhabited the Earth. The cockroach class counts about 4,000 species now, out of which only few accompany people. Having survived multiple changes of the climate, natural catastrophes and even outright murder, cockroaches have existed up to the present time, thus provoking surprise, admiration and desire for investigation. However, animal research is impossible without classification, but the scientists are not unanimous on this matter. Molecular-genetic methods allow the use of DNA structure peculiarities as diagnostic signs. Foreign researchers have made several attempts to apply these methods to the cockroach taxonomy, but failed to resolve the contradictions in classifications by different authors. Now, the specialists of the Vavilov Institiute of General Genetics, Russian Academy of Sciences, are trying to address the issue.

Purified DNA was decomposed by special enzymes into several fragments and the scientists tried to ascertain which of the fragments contained evolutionary conservative successions of ribosomal genes, i.e. the one that had not practically changed for millions of years. Proceeding from the number and size of the DNA fragments which contain these ancient "conserved" successions, the researches have calculated the coefficients of pair resemblance between the individuals belonging to different species, and based on the obtained coefficients the researchers have produced the dendrogram of genetic similarity.

The researchers started to try a new method on six species which belong to three different families, and whose taxonomic position is indisputed. If in this case the molecular diagnostics results coinside with the traditional taxonomy data, the new method can be applied to solving vexed questions. The species selected by the researchers included among others American cockroach (Periplaneta americana) - a traditional laboratory insect; Nauphoeta cinerea, which inhabits woods in the south of the Moscow Region, and in tropical areas - populates the human dwellings; and the well-known German cockroach (Blatta germanica) and oriental cockroach (Blatta orientalis). The Moscow geneticist obtained the German cockroaches by themselves, other species were sent to them from the University of Northern Carolina, USA. Having analyzed the DNA of cockroaches, the researchers easily distinguished all six species and grouped them into families. Contrary to existing notions, the German cockroach and oriental cockroach belong to different families. The German cockroach stands apart in this classification, its "branch" is not connected to the other five "branches".

The researchers hope that the method they propose (that does not require significant economic expenses) will allow the comparison of all species and make the existing multiple cockroach classifications more precise. Several thousand species form a branch evolutionary tree, which can be watched for hours with gradual plunging in the depths of geological epochs.

Informnauka (Informscience) Agency