Journal of Helminthology

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Research Article

Molecular systematics of five Onchocerca species (Nematoda: Filarioidea) including the human parasite, O. volvulus, suggest sympatric speciation


R. Morales-Hojasa1 c1, R.A. Chekea1 and R.J. Posta2



a1 Natural Resources Institute, University of Greenwich at Medway, Central Avenue, Chatham Maritime, Kent, ME4 4TB, UK

a2 Department of Entomology, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK

Article author query

Morales-Hojas R [PubMed]  [Google Scholar]
Cheke RA [PubMed]  [Google Scholar]
Post RJ [PubMed]  [Google Scholar]

Abstract

The genus Onchocerca (Nematoda: Filarioidea) consists of parasites of ungulate mammals with the exception of O. volvulus, which is a human parasite. The relationship between O. volvulus, O. ochengi and O. gibsoni remains unresolved. Based on morphology of the microfilariae and infective larvae, vector transmission and geographical distribution, O. ochengi and O. volvulus have been placed as sister species. Nevertheless, the cuticle morphology and chromosomal data (O. volvulus and O. gibsoni have n=4 while O. ochengi is n=5) suggest that O. gibsoni could be more closely related to O. volvulus than O. ochengi. Sequences from the 12S rRNA, 16S rRNA and ND5 mitochondrial genes have been used to reconstruct the phylogeny of five Onchocerca species including O. volvulus. Analyses with maximum likelihood and maximum parsimony showed that O. ochengi is the sister species of O. volvulus, in accordance with the classification based on morphology and geographical location. The separate specific status of the species O. gutturosa and O. lienalis was supported, although their phylogenetic relationship was not well resolved. The analyses indicated that the basal species was O. gibsoni, a South-East Asian and Australasian species, but this result was not statistically significant. The possible involvement of sympatric speciation in the evolution of this group of parasites is discussed.

(Accepted October 17 2005)

Correspondence:

c1 Fax: +351 22 609 9157 Email: rmhojas@ibmc.up.pt