The genus Anopheles comprises about 460 species. Over 100 can transmit human malaria, but only 30–40 commonly transmit parasites of the genus Plasmodium, which cause malaria in humans. The major vector of malaria in India, Anopheles fluviatilis has been described as a complex of three closely related species, named as S, T and U, based on variations in chromosomal inversions. Over-sized chromosomes, so called polytene chromosomes, have developed from standard chromosomes and are commonly found in the salivary glands of flies (and their close relatives, the mosquitoes). These polytene chromosomes are also used to identify species e.g. of Chironomid larvae that are notoriously difficult to identify. This method is not free of error and researchers have been trying to find reliable DNA markers that confirm the species S, T, U in the case of Anopheles fluviatilis. Two DNA regions (ITS2 and the D3 region of 28S) had been used by some researchers whereas others showed that both show insufficient variation and in one case even a 100% similarity to another congener Anopheles minimus.
A group of colleagues from India have now published a study that shows that two members of this 'species complex' rather represent genetically con-specific intermixing populations with negligible genetic differentiation. The third 'species' had previously been shown to be a phenotypic variant of Anopheles minimus.