Ecological niche and geographic distribution of the Chagas disease vector, Triatoma dimidiata (Reduviidae: Triatominae): Evidence for niche differentiation among cryptic species

- Ecological niche differentiation of the Chagas disease vector, Triatoma dimidiata complex was tested.
- Niche divergence of one of the groups in the Triatoma dimidiata complex suggests ecological evolution.
- Based on Triatoma dimidiata complex niches sympatric and vicariant speciation events are postulated.

The principal vector of Chagas disease in Central America, Triatoma dimidiata, shows considerable diversity of habitat, phenotype, and genotype across its geographic range (central Mexico to southern Ecuador), suggesting that it constitutes a complex of cryptic species. However, no consistent picture of the magnitude of ecological differentiation among populations of this complex has yet been developed. To assess ecological variation across the complex, we broadened the geographic coverage of phylogeographic data and analyses for the complex into Colombia and Mexico, with additional nuclear (ITS-2) and mitochondrial (ND4) DNA sequences. This information allowed us to describe distributions of previously documented clades in greater detail: Group I, from central Guatemala south to Ecuador; Group II, across Mexico south through the Yucatán Peninsula to Belize and northern Guatemala; and Group III, in northern Guatemala, Belize, and the Yucatán Peninsula. Using ecological niche modeling, we assessed ecological niche differentiation among the groups using four hypotheses of accessible areas (M) across the distribution of the complex. Results indicated clear niche divergence of Group I from Group II: the speciation process thus appears to have involved genetic and ecological changes, suggesting divergence in populations in response to environmental conditions.

Niche divergence among groups in the Triatoma dimidiata complex, based on background similarity tests (Warren et al., 2008) based on the accessible area hypothesis of ecoregion + 100 km (see text). Observed niche overlap values (arrows) were compared to null distributions of background divergence levels. Each pairwise comparison produces two reciprocal analyses: one in which the niche model for one group is compared to a niche model generated from random points from the background of the other, and vice versa. Overlap values falling in or below the lower left 5% of the null distribution are interpreted as indicative of significant niche divergence.42