Phylogenetic relationships of the genus Frenkelia: a review of its historyand new knowledge gained from comparison of large subunit ribosomal ribonucleic acid gene sequences

The different genera currently classified into the family Sarcocystidae inc lude parasites which are of significant medical, veterinary and economic im portance. The genus Sarcocystis is the largest within the family Sarcocysti dae and consists of species which infect a broad range of animals including mammals, birds and reptiles. Frenkelia, another genus within this family, consists of parasites that use rodents as intermediate hosts and birds of p rey as definitive hosts. Both genera follow an almost identical pattern of life cycle, and their life cycle stages are morphologically very similar. H owever, the relationship between the two genera remains unresolved because previous analyses of phenotypic characters and of small subunit ribosomal r ibonucleic acid gene sequences have questioned the validity of the genus Fr enkelia or the monophyly of the genus Sarcocystis if Frenkelia was recognis ed as a valid genus. We therefore subjected the large subunit ribosomal rib onucleic acid gene sequences of representative taxa in these genera to phyl ogenetic analyses to ascertain a definitive relationship between the two ge nera. The full length large subunit ribosomal ribonucleic acid gene sequenc es obtained were aligned using Clustal W and Dedicated Comparative Sequence Editor secondary structure alignments. The Dedicated Comparative Sequence Editor alignment was then split into two data sets, one including helical r egions, and one including non-helical regions, in order to determine the mo re informative sites. Subsequently, all four alignment data sets were subje cted to different tree-building algorithms. All of the analyses produced tr ees supporting the paraphyly of the genus Sarcocystis if Frenkelia was reco gnised as a valid genus and, thus, call for a revision of the current defin ition of these genera. However, an alternative, more parsimonious and more appropriate solution to the Sarcocystis/Frenkelia controversy is to synonym ise the genus Frenkelia with the genus Sarcocystis. (C) 1999 Published by E lsevier Science Ltd on behalf of the Australian Society for Parasitology In c. All rights reserved.