The Evolutionary Origin of Diversity in Chagas Disease Vectors

Abstract

Chagas disease is amongst the ten most important neglected tropical diseases but knowledge on the diversification of its vectors, Triatominae (Hemiptera: Reduviidae), is very scarce. Most Triatominae species occur in the Americas, and are all considered potential vectors. Despite its amazing ecological vignette, there are remarkably few evolutionary studies of the whole subfamily, and only one genome sequence has been published. The young age of the subfamily, coupled with the high number of independent lineages, are intriguing, yet the lack of genome-wide data makes it a challenge to infer the phylogenetic relationships within Triatominae. Here we synthesize what is known, and suggest the next steps towards a better understanding of how this important group of disease vectors came to be.

Keywords: Triatominae; diversification; phylogeny; taxonomy.

Figure 1. Types of homology

Homology is similarity by descent. When a gene duplication occurs, it generates two distinct types of homology: orthology and paralogy. Assume a gene duplication took place, generating copies A and B. All descendants from copy A will be orthologs among themselves. Same for copy B descendants. However, copy A descendants will be paralogs regarding copy B descendants, and vice-versa. Yet, they are all still homologs, because they all descend from the gene that duplicated in the first place.

Figure 2. Types of taxonomic groups

I) Groups Red and Blue are both monophyletic, because they include all the descendants of a most recent common ancestor (MRCA) and the ancestor. II) Group Blue is polyphyletic, because it includes lineages that evolved independently. III) Groups Red and Blue are paraphyletic because they do not include all the descendants from the MRCA.

Figure 3, Key Figure. Consensus phylogenetic relationships amongst members of the Triatomini and Rhodniini tribes based on published phylogenies

Photos of the specimens represent the type species for all the genera and are not to scale NH Triatoma, Triatoma from the Northern Hemisphere; SH Triatoma, Triatoma from the Southern Hemisphere. Images courtesy of Laboratorio Nacional e Internacional de Referencia em Taxonomia de Triatomineos, LNIRTT, Oswaldo Cruz Institute, FIOCRUZ.