Two distinct Triatoma dimidiata (Latreille, 1811) taxa are found in sympatry in Guatemala and Mexico

Abstract

Approximately 10 million people are infected with Trypanosoma cruzi, the causative agent of Chagas disease, which remains the most serious parasitic disease in the Americas. Most people are infected via triatomine vectors. Transmission has been largely halted in South America in areas with predominantly domestic vectors. However, one of the main Chagas vectors in Mesoamerica, Triatoma dimidiata, poses special challenges to control due to its diversity across its large geographic range (from Mexico into northern South America), and peridomestic and sylvatic populations that repopulate houses following pesticide treatment. Recent evidence suggests T. dimidiata may be a complex of species, perhaps including cryptic species; taxonomic ambiguity which confounds control. The nuclear sequence of the internal transcribed spacer 2 (ITS2) of the ribosomal DNA and the mitochondrial cytochrome b (mt cyt b) gene were used to analyze the taxonomy of T. dimidiata from southern Mexico throughout Central America. ITS2 sequence divides T. dimidiata into four taxa. The first three are found mostly localized to specific geographic regions with some overlap: (1) southern Mexico and Guatemala (Group 2); (2) Guatemala, Honduras, El Salvador, Nicaragua, and Costa Rica (Group 1A); (3) and Panama (Group 1B). We extend ITS2 Group 1A south into Costa Rica, Group 2 into southern Guatemala and show the first information on isolates in Belize, identifying Groups 2 and 3 in that country. The fourth group (Group 3), a potential cryptic species, is dispersed across parts of Mexico, Guatemala, and Belize. We show it exists in sympatry with other groups in Peten, Guatemala, and Yucatan, Mexico. Mitochondrial cyt b data supports this putative cryptic species in sympatry with others. However, unlike the clear distinction of the remaining groups by ITS2, the remaining groups are not separated by mt cyt b. This work contributes to an understanding of the taxonomy and population subdivision of T. dimidiata, essential for designing effective control strategies.

Figure 1. Haplotype sequence differences found in all 190 Triatoma dimidiata ITS2 sequences (39 haplotypes).

Haplotypes are separated into the 4 ITS2 groups described in the text. Nucleotide positions are given (read vertically) at the top based on Clustal W alignment. “.” = identity, †S-singleton sites, P-parsimony informative sites, *newly identified haplotypes.

Figure 2. Map showing location of 53 Triatoma dimidiata isolates collected (see Table 1 for details).

ITS2 groups: Group 1A (red), Group 1B (blue), Group 2 (yellow), Group 3 (green). Numbers identify individuals (Table 1).

Figure 3. Phylogenetic maximum likelihood tree of all 39 haplotypes of T. dimidiata ITS2 sequence.

Number of substitutions per site is indicated by the bar and bootstrap values higher than 75% / Bayesian posterior probabilities larger than 85% are indicated at the nodes. Yuc = Yucatan, Mexico (MX); Chiapas = Chiapas, MX; Peten = Peten, Guatemala (GT); Bel = Belize; Hon = Honduras; Ecu = Ecuador; Nic = Nicaragua; Lanquin = Lanquin, Alta Verapaz, Guatemala; Mex = Mexico; Pan = Panama; Col = Colombia. T. pallidipennis is the outgroup. ITS2 Groups coded as follows: 1A (red), 1B (blue), 2 (yellow), 3 (green).

Figure 4. Network analysis of all 22 haplotypes of T. dimidiata mt cyt b.

The size of the circle indicates how many individuals shared that haplotype. The colors indicate the country of the sample: Mexico-yellow, Honduras-red, Guatemala-green, Belize-black.

Figure 5. Phylogenetic maximum likelihood tree of all 23 distinct mt cyt b sequences of T. dimidiata.

Number of substitutions per site is indicated by the bar and bootstrap values higher than 75% are indicated at the nodes. See Table 2 for sample ID. T. pallidipennis is the outgroup. ITS2 Group 2 is shown in yellow and Group 3 in green.