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Background: The geniculatus clade, composed by the rufotuberculatus, lignarius, geniculatus and megistus groups, relates evolutionarily the species of the genus Panstrongylus and Nesotriatoma. Several studies have shown that triatomine hybrids can play an important role in the transmission of Chagas disease. Natural hybrids between species of the geniculatus clade have never been reported to our knowledge. Thus, carrying out experimental crosses between species of the geniculatus clade can help to elucidate the taxonomic issues as well as contribute to the epidemiological knowledge of this group. Methods: Experimental crosses were carried out between species of the megistus and lignarius groups to evaluate the reproductive compatibility between them. A phylogenetic reconstruction was also performed with data available in GenBank for the species of the geniculatus clade to show the relationships among the crossed species. Results: Phylogenetic analysis grouped the species of the geniculatus clade into four groups, as previously reported. In the interspecific crosses performed there was no hatching of eggs, demonstrating the presence of prezygotic barriers between the crossed species and confirming their specific status. Conclusions: In contrast to the other groups of the Triatomini tribe, as well as the Rhodniini, there are prezygotic barriers that prevent the formation of hybrids between species of the megistus and lignarius groups. Thus, the geniculatus clade may represent an important evolutionary model for Triatominae, highlighting the need for further studies with greater sample efforts for this clade (grouping the 17 species of Panstrongylus and the three of Nesotriatoma). [ABSTRACT FROM AUTHOR]

Background: The analysis of the chromosomal and genome evolution in organisms with holocentric chromosomes is restricted by the lack of primary constriction or centromere. An interesting group is the hemipteran subfamily Triatominae, vectors of Chagas disease, which affects around 6 to 7 million people worldwide. This group exhibits extensive variability in the number and chromosomal location of repeated sequences such as heterochromatin and ribosomal genes. This paper tries to reveal the significant differences of the repeated sequences among Triatoma species through the use of genomic DNA probes. Methods: We analysed the chromosomal distribution and evolution of repeated sequences in Triatoma species by genomic in situ hybridization (GISH) using genomic DNA probes from two North American Triatoma species. These genomic probes were hybridized both on their own chromosomes and on other Triatoma species from North and South America, with different amounts and chromosome location of C-heterochromatin. The results were compared with those previously described using South American Triatoma genomic probes. Results: We observed two chromosomal hybridization patterns: (i) very intense hybridization signals concentrated on specific chromosomal regions or particular chromosomes; and (ii) lower intensity hybridization signals dispersed along all chromosomes. Self-GISH on T. rubrofasciata and T. dimidiata chromosomes presented strong hybridization signals on all C-heterochromatin regions. However, when we perform genomic cross-hybridizations, only strong signals are detected on the Y chromosome, leaving the C-heterochromatic autosomal regions unmarked. Conclusions: We confirm that repeated DNA of the Y chromosome is shared among Triatoma species and probably represents an ancestral character of the Triatomini tribe. On the contrary, autosomal heterochromatic regions are constituted by species-specific DNA repeats, most probably satDNA families, suggesting that Triatoma speciation involved the amplification of diverse types of autosomal repeats. Molecular characterization of principal repetitive DNAs seems to be an appropriate approach to infer evolutionary relationships in triatomines. [ABSTRACT FROM AUTHOR]

Background: Chagas disease vectors (Hemiptera-Reduviidae) comprise more than 140 blood-sucking insect species of the Triatominae subfamily. The largest genus is Triatoma, subdivided in several complexes and subcomplexes according to morphology, ecology and genetic features. One of them is the sordida subcomplex, involving four species: Triatoma sordida, T. guasayana, T. garciabesi and T. patagonica. Given the great morphological similarity of these species, their taxonomic identification, evolutionary relationships and population differentiation have been controversial for many years and even today remain under discussion. Methods: We simultaneously analyzed two chromosomal markers, C-heterochromatin distribution and 45S ribosomal genes chromosomal position, of 139 specimens from several sordida subcomplex populations from Argentina, Bolivia, Brazil and Paraguay, collected both in nature and from several established insectaries. Our results were compared with COI sequences deposited in GenBank. Results: We recognized five chromosomal taxa with putative hybrids, which each differ in at least one chromosome marker. Most of them present significant differences in their mtDNA sequences. Conclusion: The chromosomal taxa here show a significant chromosome differentiation involving changes in the C-heterochromatin content and in the ribosomal clusters position. This paper identifies several erroneously classified populations by morphological methods, delimits the geographical distribution of each taxon and proposes the existence of a new cryptic species, widely distributed in Argentina. We also suggest that sordida sibling species involve closely related as well as evolutionary distant species. Taxonomic status of each chromosomal taxon is discussed considering phenotypic and genetic results previously published [ABSTRACT FROM AUTHOR]