Malaria Parasite Sequences from Chimpanzee Support the Co-Speciation Hypothesis for the Origin of Virulent Human Malaria (Plasmodium falciparum)

Phylogenetic analyses of the mitochondrial cytochrome b (cytb), apicoplast caseinolytic protease C (clpC), and 18S rRNA sequences of Plasmodium isolates from chimpanzees along with those of the virulent human malaria parasite P. falciparum showed that the common chimpanzee (Pan troglodytes) malaria parasites, assigned by Rich et al. (2009; Proc. Natl. Acad. Sci. USA 106, 14902–14907) to P. reichenowi, constitute a paraphyletic assemblage. The assumption that P. falciparum diverged from P. reichenowi as recently as 5,000–50,000 years ago would require a rate of synonymous substitution/site/year in cytb and clpC on the order of 10−5–10−6, several orders of magnitude higher than any known from eukaryotic organelle genomes, and would imply an unrealistically recent timing of the most recent common ancestor of P. falciparum mitochondrial genomes. The available data are thus most consistent with the hypothesis that P. reichenowi (in the strict sense) and P. falciparum co-speciated with their hosts about 5–7 million years ago.