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

Morales-Hojas, R., Cheke, Robert A. and Post, R.J. (2006) Molecular systematics of five Onchocerca species (Nematoda: Filarioidea) including the human parasite, O. volvulus, suggest sympatric speciation. Journal of Helminthology, 80 (3). pp. 281-290. ISSN 0022-149X

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

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