L. Tomazi, S.Y. Kawashita, P.M. Pereira, B. Zingales, M.R.S. Briones
Published: April 28, 2009
Genet. Mol. Res. 8 (2) : 458-476
DOI: https://doi.org/10.4238/vol8-2gmr591
Cite this Article:
L. Tomazi, S.Y. Kawashita, P.M. Pereira, B. Zingales, M.R.S. Briones (2009). Haplotype distribution of five nuclear genes based on network genealogies and Bayesian inference indicates that Trypanosoma cruzi hybrid strains are polyphyletic. Genet. Mol. Res. 8(2): 458-476. https://doi.org/10.4238/vol8-2gmr591
About the Authors
L. Tomazi, S.Y. Kawashita, P.M. Pereira, B. Zingales, M.R.S. Briones
Corresponding author
M.R.S. Briones
E-mail: marcelo.briones@unifesp.br
ABSTRACT
Chagas disease is still a major public health problem in Latin America. Its causative agent, Trypanosoma cruzi, can be typed into three major groups, T. cruzi I, T. cruzi II and hybrids. These groups each have specific genetic characteristics and epidemiological distributions. Several highly virulent strains are found in the hybrid group; their origin is still a matter of debate. The null hypothesis is that the hybrids are of polyphyletic origin, evolving independently from various hybridization events. The alternative hypothesis is that all extant hybrid strains originated from a single hybridization event. We sequenced both alleles of genes encoding EF-1α, actin and SSU rDNA of 26 T. cruzi strains and DHFR-TS and TR of 12 strains. This information was used for network genealogy analysis and Bayesian phylogenies. We found T. cruzi I and T. cruzi II to be monophyletic and that all hybrids had different combinations of T. cruzi I and T. cruzi II haplotypes plus hybrid-specif-ic haplotypes. Bootstrap values (networks) and posterior probabilities (Bayesian phylogenies) of clades supporting the monophyly of hybrids were far below the 95% confidence interval, indicating that the hybrid group is polyphyletic. We hypothesize that T. cruzi I and T. cruzi II are two different species and that the hybrids are extant representatives of independent events of genome hybridization, which sporadically have sufficient fitness to impact on the epidemiology of Chagas disease.
Key words: Trypanosoma cruzi, Molecular evolution, Phylogeny, Chagas disease, Small subunit rDNA, Trypanosoma cruzi.