gh COCKROACH CLASSIFICATION IS TO BE AMENDED

By applying the DNA-diagnostics the researchers from the Vavilov Institiute of General Genetics, Russian Academy of Sciences, have rectified an error in 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 familiae.

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. The molecular-genetic methods allows to use the 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.

To educe the cockroach DNA, the researchers had to grind into thin gruel a half or a quarter of the thoracal part of the insect (the German cockroach is the smallest, it was used as a whole). The DNA evolved from this slush and thoroughly purified 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 familiae, and their taxonomic position arouses no disputes. 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) - 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 familiae. It has turned out that contrary to existing notion, the German cockroach and oriental cockroach belong to different familiae. The German cockroach stand apart in this classification, its "branch" is not connected to the other five "branches".

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

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