Taking more care in using different species concepts - an opinion

Some articles recently published in "Parasitology Research" concern the pro blem of using morphological or molecular traits to award defined population s of parasites the taxonomic level of being separate species. Differences i n or (alternatively) the lack of distinguishing features in oocyst morpholo gy (McAllister 2000) and different ultrastructural or serological data (Fre nkel and Dubey 2000; Mehlhorn and Heydorn 2000) in Toxoplasma and some rela ted genera have been considered to have a species-specific value. Also, sim ilarities or differences observed in 18S rDNA sequences in dinoflagellates have been used as species-specific traits (Janson et al. 2000); and the mag nitude of any difference in the internal transcribed spacer (ITS) of the ri bosomal DNA sequence among related Trichuris groups (Oliveros et al. 2000) and in the Contracaecum osculatum complex (Ascaridoidea) has been used to a ward some taxa the status of species.