Revisiting the Chromosomal Diversification of the Genus Rhodnius (Stål, 1859) (Hemiptera, Triatominae)

Geometric morphometry of the Rhodniusprolixus complex (Hemiptera, Triatominae): patterns of intraspecific and interspecific allometry and their taxonomic implications

In the subfamily Triatominae, the genus Rhodnius is one of the most studied, not only because of its epidemiological importance, but also because of the difficulty in differentiating its species. Currently, one of the strategies to control Chagas disease, besides other initiatives such as the analysis of donated blood, is focused on fighting the vector. Correctly identifying triatomines is essential for the entomoepidemiological surveillance of Chagas disease. The objective of the present work was to compare the species of the R.prolixus complex using geometric morphometry of hemelytra and heads to evaluate the patterns of intraspecific and interspecific allometry and their taxonomic implications. This method can help in the diagnosis of close species, whose morphological characteristics are insufficient for correct identification. Specimens from five different collections were used, covering the species included in the R.prolixus complex (R.barretti, R.dalessandroi, R.domesticus, R.marabaensis, R.milesi, R.montenegrensis, R.nasutus, R.neglectus, R.neivai, R.prolixus and R.robustus). Morphometric analyses indicated that the hemelytra are not structures with good resolution for separating species and, for this reason, the use of the heads proved to be more adequate for this group (thus allowing differentiation of all species of the R.prolixus complex). The results suggest that R.milesi is a variant of R.neglectus and confirms that R.prolixus and R.robustus are distinct species. Furthermore, we propose the creation of the R.neivai complex comprising R.domesticus and R.neivai.

Genome Size Variation of Chagas Disease Vectors of the Rhodniini Tribe

The genome size of five Rhodnius species (R. milesi, R. nasutus, R. neivai, R. prolixus, and R. robustus) and two Psammolestes species (P. coroedes and P. tertius) were estimated using flow cytometry and/or k-mer distributions in genome sequences. Phylogenetic generalized linear mixed models highlighted significant genome size variations among species and between sexes, with R. prolixus showing the largest genome. In this study we provide the first data on female genome size in Triatominae. For five species, female genome size did not differ from males, except for R. robustus, where females had smaller genomes. Genome size estimations based on the k-mer distribution method were less than those estimated from flow cytometry, but both methods exhibited the same pattern of sexual differences. Further genomic studies are needed to infer whether genome size variation could be an adaptive trait in Rhodnius.

Biology of Chagas disease vectors: biological cycle and emergence rates of Rhodnius marabaensis Souza et al., 2016 (Hemiptera, Reduviidae, Triatominae) under laboratory conditions

In Latin America, Chagas disease has been mostly transmitted to humans by contact with the feces or urine of triatomine species infected with the protozoan Trypanosoma cruzi. There are currently 156 species in the subfamily Triatominae, distributed in 18 genera and five tribes. The prolixus group of the genus Rhodnius is composed of 11 species. Rhodnius marabaensis was the last species described and considered in this grouping of vectors. Knowledge about the biology, ecology, and behavior of these vectors is of great epidemiological importance, and in order to expand the knowledge of the biology of R. marabaensis, this paper describes the biological cycle and emergence rates of the species under laboratory conditions. The experiment was carried out at temperatures ranging from 15.5 to 29 °C (average of 24 °C) and humidity ranging from 51.4 to 72.2 (average of 63). For each of the fifteen couples, the egg emergence rate was calculated throughout the oviposition period. The oviposition period lasted from February to September, and the emergence rate varied between 13.9 and 53.3%. R. marabaensis presented an emergence rate of 46.7% and a total biological cycle of 193 days (the mean time required for emergence (25.1 days), 1st nymphal instar (19.4 days), 2nd nymphal instar (22.1 days), 3rd nymphal instar (26.2 days), 4th nymphal instar (29.3 days), and 5th nymphal instar (70.9 days)). Based on the biological cycle of R. marabaensis and 14 other Rhodnius species already described in the literature, it was also possible to calculate the averages for the groups prolixus, pictipes, and pallescens and, mainly, for the genus Rhodnius, contributing to the knowledge of this important group of Chagas disease vectors.

Historical Biogeography and the Evolution of Hematophagy in Rhodniini (Heteroptera: Reduviidae: Triatominae)

The Rhodniini tribe is one of the five tribes in the subfamily Triatominae and is notorious for its domestic blood-sucking pests and vectors of Trypanosoma cruzi across Latin America. The human and economic costs of the Chagas disease in the American tropics are considerable, and these insects are of unquestionable importance to humans. We used mitochondrial rDNA (16S), nuclear ribosomal RNA (28S) and wingless (Wg) sequences to perform phylogenetic analysis to derive trees based on parsimony and maximum likelihood. Nucleotide sequences were used in molecular-clock analyses to estimate time divergence between species of Rhodniini. The potential distribution of each species was modeled and compared with Kappa statistic. Multivariate niches with bioclimatic variables were used to describe differences between the species using discriminant analysis. The results of this study indicate that the Rhodniini originated 17.91 Mya ago. Rhodnius domesticus is the oldest species having its origin at 9.13 Mya. Rhodniini are closely related to Salyavatinae that are specialist termite predators and diverged from this subfamily 30.43 Mya. Most species are clearly allopatric and have distinct bioclimatic niches. The colonization of bromeliads, palms trees and bird nests represent important events for the speciation of these taxa. The hematophagous habit can be described as a scenario where Rhodniini’s ancestor could be pre-adapted for the invasion of bromeliads, palm trees, and bird nests where they would find significant water availability and thermal damping. These environments are widely used by vertebrate inquilines that would be the source of food for the species of Rhodniini. Lastly, our results show an alternative position of Psammolestes in the phylogenetic tree.