BackgroundAmong Chagas disease triatomine vectors, the largest genus, Triatoma, includes species of high public health interest. Triatoma dimidiata, the main vector throughout Central America and up to Ecuador, presents extensive phenotypic, genotypic, and behavioral diversity in sylvatic, peridomestic and domestic habitats, and non-domiciliated populations acting as reinfestation sources. DNA sequence analyses, phylogenetic reconstruction methods, and genetic variation approaches are combined to investigate the haplotype profiling, genetic polymorphism, phylogeography, and evolutionary trends of T. dimidiata and its closest relatives within Triatoma. This is the largest interpopulational analysis performed on a triatomine species so far.Methodology and FindingsTriatomines from Mexico, Guatemala, Honduras, Nicaragua, Panama, Cuba, Colombia, Ecuador, and Brazil were used. Triatoma dimidiata populations follow different evolutionary divergences in which geographical isolation appears to have had an important influence. A southern Mexican–northern Guatemalan ancestral form gave rise to two main clades. One clade remained confined to the Yucatan peninsula and northern parts of Chiapas State, Guatemala, and Honduras, with extant descendants deserving specific status. Within the second clade, extant subspecies diversity was shaped by adaptive radiation derived from Guatemalan ancestral populations. Central American populations correspond to subspecies T. d. dimidiata. A southern spread into Panama and Colombia gave the T. d. capitata forms, and a northwestern spread rising from Guatemala into Mexico gave the T. d. maculipennis forms. Triatoma hegneri appears as a subspecific insular form.ConclusionsThe comparison with very numerous Triatoma species allows us to reach highly supported conclusions not only about T. dimidiata, but also on different, important Triatoma species groupings and their evolution. The very large intraspecific genetic variability found in T. dimidiata sensu lato has never been detected in a triatomine species before. The distinction between the five different taxa furnishes a new frame for future analyses of the different vector transmission capacities and epidemiological characteristics of Chagas disease. Results indicate that T. dimidiata will offer problems for control, although dwelling insecticide spraying might be successful against introduced populations in Ecuador.

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Background Triatoma dimidiata is among the main vectors of Chagas disease in Latin America. However, and despite important advances, there is no consensus about the taxonomic status of phenotypically divergent T. dimidiata populations, which in most recent papers are regarded as subspecies.Methodology and FindingsA total of 126 cyt b sequences (621 bp long) were produced for specimens from across the species range. Forty-seven selected specimens representing the main cyt b clades observed (after a preliminary phylogenetic analysis) were also sequenced for an ND4 fragment (554 bp long) and concatenated with their respective cyt b sequences to produce a combined data set totalling 1175 bp/individual. Bayesian and Maximum-Likelihood phylogenetic analyses of both data sets (cyt b, and cyt b+ND4) disclosed four strongly divergent (all pairwise Kimura 2-parameter distances >0.08), monophyletic groups: Group I occurs from Southern Mexico through Central America into Colombia, with Ecuadorian specimens resembling Nicaraguan material; Group II includes samples from Western-Southwestern Mexico; Group III comprises specimens from the Yucatán peninsula; and Group IV consists of sylvatic samples from Belize. The closely-related, yet formally recognized species T. hegneri from the island of Cozumel falls within the divergence range of the T. dimidiata populations studied.ConclusionsWe propose that Groups I–IV, as well as T. hegneri, should be regarded as separate species. In the Petén of Guatemala, representatives of Groups I, II, and III occur in sympatry; the absence of haplotypes with intermediate genetic distances, as shown by multimodal mismatch distribution plots, clearly indicates that reproductive barriers actively promote within-group cohesion. Some sylvatic specimens from Belize belong to a different species – likely the basal lineage of the T. dimidiata complex, originated ∼8.25 Mya. The evidence presented here strongly supports the proposition that T. dimidiata is a complex of five cryptic species (Groups I–IV plus T. hegneri) that play different roles as vectors of Chagas disease in the region.

Summary The wide geographical distribution of Triatoma dimidiata, one of the three major vectors of Chagas disease, ranges from Mexico to northern Peru. Since this species occupies a great diversity of artificial and natural ecotopes, its eradication is extremely difficult. In order to assist control efforts, we used chromosome analyses and DNA amount as taxonomic markers to study genetic variability in populations of T. dimidiata from Mexico, Guatemala, El Salvador and Colombia. We differentiated three groups or cytotypes defined by characteristic chromosome C‐banding patterns and genome size measured by flow cytometry. The three cytotypes are restricted to different geographic locations. Cytotype 1 occurs in Mexico (excluding Yucatán), Guatemala (excluding Petén), El Salvador and Colombia. Cytotype 2 occurs in Yucatán and cytotype 3 occurs in Petén. Cytotype 1, commonly associated with domestic and peridomestic environments but also inhabiting sylvatic ecotopes, is the most widespread and with major epidemiological significance. In contrast, the Yucatán cytotype inhabits wild ecotopes but increasingly enters houses, while the Petén cytotype appears exclusively sylvatic. We suggest that these cytotypes represent cryptic species of T. dimidiata with different epidemiological relevance as Chagas disease vectors. Poor ability to colonize human dwellings, together with their restricted geographic distribution, indicate that the Yucatán and Petén putative species probably have much less epidemiological significance than cytotype 1. Thus, the genetic markers we describe are powerful tools to differentiate cryptic species in T. dimidiata with different epidemiological significance, contributing to planning the most effective control measures.

Eight Triatoma dimidiata populations from different geographic regions were compared along with related species using traditional morphometry of head characters. A method for removing allometric change was used for the intraspecific comparisons, and scaling for the isometric change of size was used for the interspecific comparisons. The intraspecific comparison showed significant head shape differences between T. dimidiata populations correlating with geography, showing a separation between the northern, intermediate, and southern collections (more evident in females), and supporting the idea that this species includes several evolutionarily divergent populations. The positioning of one sylvatic group from Guatemala did not correlate with geography, because it was more closely related to a distinct population of Colombia. This sylvatic group was found in caves, while the Colombian specimens, although collected in houses, may have migrated from nearby caves. Evolutionary and/or ecological influences could be responsible for the head shape similarities between these two groups: a common ancestral origin of both populations or a morphological convergence caused by similar environmental pressures. The interspecific comparisons included four other regional species of the same genus, three of them belonging to the phyllosoma complex (T. pallidipennis, T. mexicana, and T. ryckmani, the latter provisionally) and the fourth one classified in the protracta complex (T. nitida). Both complexes were readily separated by their head dimensions, even after size adjustment, and our data support inclusion of T. dimidiata within the phyllosoma complex.