Analysis of the maternal inheritance hypothesis of the exochorium in eggs from hybrids of Chagas disease vectors.

Morphological studies applied to the taxonomy of the Triatominae cover various structures (head, wing, thorax, genitalia, and eggs). Exochorial structures of hybrid eggs were characterized and compared with the parents, demonstrating that hybrids presented characteristics identical to the exochorial pattern observed in the females of the crosses, which resulted in the hypothesis that the pattern of triatomine eggs is possibly a characteristic inherited from females. Thus, we characterized the exochorium of the eggs of several triatomine hybrids and compared them with the parents, to assess the pattern of segregation and test the hypothesis of maternal inheritance. Hybrids were obtained in at least one direction from all crosses. The analysis of the exochorium of the eggs of the hybrids showed different patterns of segregation: "exclusively paternal", "predominantly maternal", "predominantly paternal", "mutual", and "differential". Curiously, none of the hybrids evaluated presented characteristics that segregated exclusively from the female parental species. Thus, we demonstrate that the hypothesis of maternal inheritance of the exochorium pattern of eggs is not valid and we emphasize the importance of alternative/combined tools (such as integrative taxonomy) for the correct identification of these insect vectors (mainly in view of possible natural hybridization events due to climate and environmental changes).

First evidence of gonadal hybrid dysgenesis in Chagas disease vectors (Hemiptera, Triatominae): gonad atrophy prevents events of interspecific gene flow and introgression.

BACKGROUND: Hybridization events between Triatoma spp. have been observed under both natural and laboratory conditions. The ability to produce hybrids can influence different aspects of the parent species, and may even result in events of introgression, speciation and extinction. Hybrid sterility is caused by unviable gametes (due to errors in chromosomal pairing [meiosis]) or by gonadal dysgenesis (GD). All of the triatomine hybrids analyzed so far have not presented GD. We describe here for the first time GD events in triatomine hybrids and highlight these taxonomic and evolutionary implications of these events. METHODS: Reciprocal experimental crosses were performed between Triatoma longipennis and Triatoma mopan. Intercrosses were also performed between the hybrids, and backcrosses were performed between the hybrids and the parent species. In addition, morphological and cytological analyzes were performed on the atrophied gonads of the hybrids. RESULTS: Hybrids were obtained only for the crosses T. mopan♀ × T. longipennis♂. Intercrosses and backcrosses did not result in offspring. Morphological analyses of the male gonads of the hybrids confirmed that the phenomenon that resulted in sterility of the hybrid was bilateral GD (the gonads of the hybrids were completely atrophied). Cytological analyses of the testes of the hybrids also confirmed GD, with no germ cells observed (only somatic cells, which make up the peritoneal sheath). CONCLUSIONS: The observations made during this study allowed us to characterize, for the first time, GD in triatomines and demonstrated that gametogenesis does not occur in atrophied gonads. The characterization of GD in male hybrids resulting from the crossing of T. mopan♀ × T. longipennis♂ highlights the importance of evaluating both the morphology and the cytology of the gonads to confirm which event resulted in the sterility of the hybrid: GD (which results in no gamete production) or meiotic errors (which results in non-viable gametes).

Climate and Environmental Changes and Their Potential Effects on the Dynamics of Chagas Disease: Hybridization in Rhodniini (Hemiptera, Triatominae).

Chagas disease affects about eight million people. In view of the issues related to the influence of anthropogenic changes in the dynamics of the distribution and reproductive interaction of triatomines, we performed experimental crosses between species of the Rhodniini tribe in order to evaluate interspecific reproductive interactions and hybrid production capacity. Reciprocal crossing experiments were conducted among Rhodnius brethesi × R. pictipes, R. colombiensis × R. ecuadoriensis, R. neivai × R. prolixus, R. robustus × R. prolixus, R. montenegrensis × R. marabaensis; R. montenegrensis × R. robustus, R. prolixus × R. nasutus and R. neglectus × R. milesi. With the exception of crosses between R. pictipes ♀ × R. brethesi ♂, R. ecuadoriensis ♀ × R. colombiensis ♂ and R. prolixus ♀ × R. neivai ♂, all experimental crosses resulted in hybrids. Our results demonstrate that both allopatric and sympatric species produce hybrids, which can generate concern for public health agencies in the face of current anthropogenic events. Thus, we demonstrate that species of the Rhodniini tribe are capable of producing hybrids under laboratory conditions. These results are of great epidemiological importance and raise an important discussion about the influence of climatic and environmental interactions on Chagas disease dynamics.

Karyotype Evolution in Triatominae (Hemiptera, Reduviidae): The Role of Chromosomal Rearrangements in the Diversification of Chagas Disease Vectors.

Several cytogenetic studies have already been performed in Triatominae, such that different karyotypes could be characterized (ranging from 2n = 21 to 25 chromosomes), being the changes in the number of chromosomes related mainly to fusion and fission events. These changes have been associated with reproductive isolation and speciation events in other insect groups. Thus, we evaluated whether different karyotypes could act in the reproductive isolation of triatomines and we analyzed how the events of karyotypic evolution occurred along the diversification of these vectors. For this, experimental crosses were carried out between triatomine species with different karyotypes. Furthermore, based on a phylogeny with 88 triatomine taxa (developed with different molecular markers), a reconstruction of ancestral karyotypes and of anagenetic and cladogenetic events related to karyotypic alterations was performed through the ChromoSSE chromosomal evolution model. All crosses performed did not result in hybrids (prezygotic isolation in both directions). Our modeling results suggest that during Triatominae diversification, at least nine cladogenetic events may be associated with karyotype change. Thus, we emphasize that these alterations in the number of chromosomes can act as a prezygotic barrier in Triatominae (karyotypic isolation), being important evolutionary events during the diversification of the species of Chagas disease vectors.

Trends in evolution of the Triatomini tribe (Hemiptera, Triatominae): reproductive incompatibility between four species of geniculatus clade.

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).

Morphological, Cytological and Molecular Studies and Feeding and Defecation Pattern of Hybrids from Experimental Crosses between Triatoma sordida and T. rosai (Hemiptera, Triatominae).

Under laboratory conditions, Triatoma rosai and T. sordida are able to cross and produce hybrids. In the face of climate and environmental changes, the study of hybrids of triatomines has evolutionary and epidemiological implications. Therefore, we performed morphological, cytological and molecular studies and characterized the feeding and defecation pattern of hybrids from crosses between T. sordida and T. rosai. The morphological characterization of the female genitalia of the hybrids showed that characteristics of both parental species segregated in the hybrids. Cytogenetic analyzes of hybrids showed regular metaphases. According to molecular studies, the mitochondrial marker Cytochrome B (CytB) related the hybrids with T. sordida and the nuclear marker Internal Transcribed Spacer 1 (ITS-1) related the hybrids with T. rosai. Both parents and hybrids defecated during the blood meal. Thus, the hybrids resulting from the cross between T. sordida and T. rosai presented segregation of phenotypic characters of both parental species, 100% homeology between homeologous chromosomes, phylogenetic relationship with T sordida and with T. rosai (with CytB and ITS-1, respectively), and, finally, feeding and defecation patterns similar to the parents.

Do not judge a book by its cover: would Triatoma tibiamaculata (Pinto, 1926) belong to Triatoma Laporte, 1832, or to Panstrongylus Berg, 1879, with misleading homoplasies?

BACKGROUND: Triatoma tibiamaculata is a species distributed in ten Brazilian states which has epidemiological importance as it has already been found infecting household areas. The taxonomy of this triatomine has been quite unstable: it was initially described as Eutriatoma tibiamaculata. Later, the species was transferred from the genus Eutriatoma to Triatoma. Although included in the genus Triatoma, the phylogenetic position of T. tibiamaculata in relation to other species of this genus has always been uncertain once this triatomine was grouped in all phylogenies with the genus Panstrongylus, rescuing T. tibiamaculata and P. megistus as sister species. Thus, we evaluated the generic status of T. tibiamaculata using phylogenetic and chromosomal analysis. METHODS: Chromosomal (karyotype) and phylogenetic (with mitochondrial and nuclear markers) analyses were performed to assess the relationship between T. tibiamaculata and Panstrongylus spp. RESULTS: The chromosomal and phylogenetic relationship of T. tibiamaculata and Panstrongylus spp. confirms the transfer of the species to Panstrongylus with the new combination: Panstrongylus tibiamaculatus. CONCLUSIONS: Based on chromosomal and phylogenetic characteristics, we state that P. tibiamaculatus comb. nov. belongs to the genus Panstrongylus and that the morphological features shared with Triatoma spp. represent homoplasies.

Revisiting the Hybridization Processes in the Triatoma brasiliensis Complex (Hemiptera, Triatominae): Reproductive Isolation between Triatoma petrocchiae and T. b. brasiliensis and T. lenti.

Triatoma petrocchiae is a species morphologically similar to T. b. brasiliensis (which resulted in a synonymization event); despite this similarity, genetic, morphological, and experimental crossbreeding studies confirmed the specific status of T. petrocchiae. Considering that both species have been reported living in sympatry and that, for a long time, most species of the T. brasiliensis complex were considered only chromatic variants of T. b. brasiliensis, we carried out experimental crosses between T. b. brasiliensis and T. petrocchiae (to confirm whether these species are reproductively isolated) and between T. lenti and T. petrocchiae (to assess whether T. petrocchiae also presents prezygotic isolation with the other species of the T. brasiliensis complex). Reciprocal experimental crosses were conducted, and weekly, the eggs were collected, counted, and separated in new containers to assess the hatch rate. Neither cross resulted in hybrids, demonstrating that there are pre-zygotic reproductive barriers installed between T. petrocchiae and the other species of the T. brasiliensis complex. On the basis of the results above, we demonstrated that T. petrocchiae is reproductively isolated from T. b. brasiliensis and T. lenti. Furthermore, we suggest that T. petrocchiae is the species most derived from the T. brasiliensis complex.

Revisiting the hybridization processes in the Triatoma brasiliensis complex (Hemiptera, Triatominae): Interspecific genomic compatibility point to a possible recent diversification of the species grouped in this monophyletic complex.

Triatomines are hematophagous insects of great epidemiological importance, since they are vectors of the protozoan Trypanosoma cruzi, the etiological agent of Chagas disease. Triatoma brasiliensis complex is a monophyletic group formed by two subspecies and six species: T. b. brasiliensis, T. b. macromelasoma, T. bahiensis, T. juazeirensis, T. lenti, T. melanica, T. petrocchiae and T. sherlocki. The specific status of several species grouped in the T. brasiliensis complex was confirmed from experimental crossing and analysis of reproductive barriers. Thus, we perform interspecific experimental crosses between T. lenti and other species and subspecies of the T. brasiliensis complex and perform morphological analysis of the gonads and cytogenetic analysis in the homeologous chromosomes of the hybrids of first generation (F1). Besides that, we rescue all the literature data associated with the study of reproductive barriers in this monophyletic complex of species and subspecies. For all crosses performed between T. b. brasiliensis, T. b. macromelasoma, T. juazeirensis and T. melanica with T. lenti, interspecific copulas occurred (showing absence of mechanical isolation), hybrids were obtained, none of the male hybrids presented the phenomenon of gonadal dysgenesis and 100% pairing between the chromosomes homeologous of the hybrids was observed. Thus, we demonstrate that there are no pre-zygotic reproductive barriers installed between T. lenti and the species and subspecies of the T. brasiliensis complex. In addition, we demonstrate that the hybrids obtained between these crosses have high genomic compatibility and the absence of gonadal dysgenesis. These results point to reproductive compatibility between T. lenti and species and subspecies of the T. brasiliensis complex (confirming its inclusion in the complex) and lead us to suggest a possible recent diversification of the taxa of this monophyletic group.

Triatoma sordida (Hemiptera, Triatominae) from La Paz, Bolivia: an incipient species or an intraspecific chromosomal polymorphism?

BACKGROUND: Triatoma sordida is one of the main Chagas disease vectors in Brazil. In addition to Brazil, this species has already been reported in Bolivia, Argentina, Paraguay, and Uruguay. It is hypothesized that the insects currently identified as T. sordida are a species subcomplex formed by three cytotypes (T. sordida sensu stricto [s.s.], T. sordida La Paz, and T. sordida Argentina). With the recent description of T. rosai from the Argentinean specimens, it became necessary to assess the taxonomic status of T. sordida from La Paz, Bolivia, since it was suggested that it may represent a new species, which has taxonomic, evolutionary, and epidemiological implications. Based on the above, we carried out molecular and experimental crossover studies to assess the specific status of T. sordida La Paz. METHODS: To evaluate the pre- and postzygotic barriers between T. sordida La Paz and T. sordida s.s., experimental crosses and intercrosses between F1 hybrids and between F2 hybrids were conducted. In addition, cytogenetic analyses of the F1 and F2 hybrids were applied with an emphasis on the degree of pairing between the homeologous chromosomes, and morphological analyses of the male gonads were performed to evaluate the presence of gonadal dysgenesis. Lastly, the genetic distance between T. sordida La Paz and T. sordida s.s. was calculated for the CYTB, ND1, and ITS1 genes. RESULTS: Regardless of the gene used, T. sordida La Paz showed low genetic distance compared to T. sordida s.s. (below 2%). Experimental crosses resulted in offspring for both directions, demonstrating that there are no prezygotic barriers installed between these allopatric populations. Furthermore, postzygotic barriers were not observed either (since the F1 × F1 and F2 × F2 intercrosses resulted in viable offspring). Morphological and cytogenetic analyses of the male gonads of the F1 and F2 offspring demonstrated that the testes were not atrophied and did not show chromosome pairing errors. CONCLUSION: Based on the low genetic distance (which configures intraspecific variation), associated with the absence of prezygotic and postzygotic reproductive barriers, we confirm that T. sordida La Paz represents only a chromosomal polymorphism of T. sordida s.s.

Trends in evolution of the Rhodniini tribe (Hemiptera, Triatominae): experimental crosses between Psammolestes tertius Lent & Jurberg, 1965 and P. coreodes Bergroth, 1911 and analysis of the reproductive isolating mechanisms.

BACKGROUND: The tribe Rhodniini is a monophyletic group composed of 24 species grouped into two genera: Rhodnius and Psammolestes. The genus Psammolestes includes only three species, namely P. coreodes, P. tertius and P. arthuri. Natural hybridization events have been reported for the Rhodniini tribe (for genus Rhodnius specifically). Information obtained from hybridization studies can improve our understanding of the taxonomy and systematics of species. Here we report the results from experimental crosses performed between P. tertius and P. coreodes and from subsequent analyses of the reproductive and morphological aspects of the hybrids. METHODS: Crossing experiments were conducted between P. tertius and P. coreodes to evaluate the pre- and post-zygotic barriers between species of the Rhodniini tribe. We also performed cytogenetic analyses of the F1 hybrids, with a focus on the degree of pairing between the homeologous chromosomes, and morphology studies of the male gonads to evaluate the presence of gonadal dysgenesis. Lastly, we analyzed the segregation of phenotypic characteristics. RESULTS: Interspecific experimental crosses demonstrated intrageneric genomic compatibility since hybrids were produced in both directions. However, these hybrids showed a high mortality rate, suggesting a post-zygotic barrier resulting in hybrid unviability. The F1 hybrids that reached adulthood presented the dominant phenotypic segregation pattern for P. tertius in both directions. These insects were then intercrossed; the hybrids were used in the cross between P. tertius ♀ × P. coreodes ♂ died before oviposition, and the F1 hybrids of P. coreodes ♀ x P. tertius ♂ oviposited and their F2 hybrids hatched (however, all specimens died after hatching, still in first-generation nymph stage, pointing to a hybrid collapse event). Morphological analyses of male gonads from F1 hybrids showed that they did not have gonadal dysgenesis. Cytogenetic analyses of these triatomines showed that there were metaphases with 100% pairing between homeologous chromosomes and metaphases with pairing errors. CONCLUSION: The results of this study demonstrate that Psammolestes spp. have intrageneric genomic compatibility and that post-zygotic barriers, namely unviability of hybrid and hybrid collapse, resulted in the breakdown of the hybrids of P. tertius and P. coreodes, confirming the specific status of species based on the biological concept of species.

Trends in taxonomy of Triatomini (Hemiptera, Reduviidae, Triatominae): reproductive compatibility reinforces the synonymization of Meccus Stål, 1859 with Triatoma Laporte, 1832.

BACKGROUND: Meccus' taxonomy has been quite complex since the first species of this genus was described by Burmeister in 1835 as Conorhinus phyllosoma. In 1859 the species was transferred to the genus Meccus and in 1930 to Triatoma. However, in the twentieth century, the Meccus genus was revalidated (alteration corroborated by molecular studies) and, in the twenty-first century, through a comprehensive study including more sophisticated phylogenetic reconstruction methods, Meccus was again synonymous with Triatoma. Events of natural hybridization with production of fertile offspring have already been reported among sympatric species of the T. phyllosoma subcomplex, and experimental crosses demonstrated reproductive viability among practically all species of the T. phyllosoma subcomplex that were considered as belonging to the genus Meccus, as well as between these species and species of Triatoma. Based on the above, we carried out experimental crosses between T. longipennis (considered M. longipennis in some literature) and T. mopan (always considered as belonging to Triatoma) to evaluate the reproductive compatibility between species of the T. phyllosoma complex. In addition, we have grouped our results with information from the literature regarding crosses between species that were grouped in the genus Meccus with Triatoma, in order to discuss the importance of experimental crosses to confirm the generic reorganization of species. RESULTS: The crosses between T. mopan female and T. longipennis male resulted in viable offspring. The hatching of hybrids, even if only in one direction and/or at low frequency, demonstrates reproductive compatibility and homeology between the genomes of the parents. CONCLUSION: Considering that intergeneric crosses usually do not result in viable offspring in Triatominae, the reproductive compatibility observed between the T. phyllosoma subcomplex species considered in the Meccus genus with species of the Triatoma genus shows that there is "intergeneric" genomic compatibility, which corroborates the generic reorganization of Meccus in Triatoma.

Segregation of phenotypic characteristics in hybrids of Triatoma brasiliensis species complex (Hemiptera, Reduviidae, Triatominae).

There are currently 156 species, grouped into 18 genera and five tribes included in the subfamily Triatominae. All of them are potential vectors of Chagas disease. Triatoma is paraphyletic and the species of this genus have been grouped into complexes and subcomplexes. Triatoma brasiliensis complex is a monophyletic group composed of eight taxa: T. b. brasiliensis, T. b. macromelanosoma, T. juazeirensis, T. sherlocki, T. petrocchiae, T. lenti, T. bahiensis, T. melanica. Experimental crosses have helped in systematic, taxonomic and evolutionary issues of these vectors. Based on this, we carried out experimental crosses between T. lenti and four other species of the T. brasiliensis complex and analyzed the segregation pattern of phenotypic characteristics of T. lenti, T. b. brasiliensis, T. b. macromelasoma, T. juazeirensis and T. melanica in the hybrids. The hybrids resulting from the crosses between T. b. brasiliensis ♀ x T. lenti ♂, T. juazeirensis ♀ x T. lenti ♂, and T. melanica ♀ x T. lenti ♂ showed segregation of characteristics of both parental species. On the other hand, the hybrids between T. lenti ♀ x T. juazeirensis ♂, T. b. macromelasoma ♀ x T. lenti ♂, and T. lenti ♀ x T. melanica ♂ showed a specific pattern of T. lenti, T. lenti and T. melanica, respectively. Thus, the pattern of segregation of morphological characteristics between species of the T. brasiliensis complex was characterized. These results highlight the importance of integrative taxonomy for the correct identification of Chagas disease vectors grouped in the T. brasiliensis complex if natural hybridization events occur.

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

Although all triatomines are considered as potential vectors of the Chagas disease, the Triatoma, Panstrongylus, and Rhodnius genera are the most important from the epidemiological point of view. Based on cytogenetic analyzes carried out so far (C banding and FISH), the species of the genus Rhodnius show little interspecific chromosomal variation. Thus, we analyzed the distribution of AT- and CG-rich DNA in the chromatin and chromosomes of the genus Rhodnius and discuss the chromosome evolution of these vectors. Except for Rhodnius domesticus, Rhodnius nasutus, Rhodnius pictipes, Rhodnius colombiensis, and Rhodnius pallescens, all Rhodnius species have euchromatic autosomes with the absence of AT- and CG-rich blocks. Curiously, the same species that have heterochromatin blocks in the autosomes also have chromomycin A3 (CMA3 +) blocks dispersed in the prophasic nucleus (demonstrating that the heterochromatin of these species is rich in CG). Thus, we characterize the AT- and CG-rich DNA pattern for the genus Rhodnius, and we suggest that the pattern of CG-rich heterochromatin in the autosomes of these vectors evolved independently in pallescens, pictipes, and prolixus groups.

Triatoma rosai sp. nov. (Hemiptera, Triatominae): A New Species of Argentinian Chagas Disease Vector Described Based on Integrative Taxonomy.

Chagas disease is the most prevalent neglected tropical disease in the Americas and makes an important contribution to morbidity and mortality rates in countries where it is endemic since 30 to 40% of patients develop cardiac diseases, gastrointestinal disorders, or both. In this paper, a new species of the genus Triatoma is described based on specimens collected in the Department San Miguel, Province of Corrientes, Argentina. Triatoma rosai sp. nov. is closely related to T. sordida (Stål, 1859), and was characterized based on integrative taxonomy using morphological, morphometric, molecular data, and experimental crosses. These analyses, combined with data from the literature (cytogenetics, electrophoresis pattern, molecular analyses, cuticular hydrocarbons pattern, geometric morphometry, cycle, and average time of life as well as geographic distribution) confirm the specific status of T. rosai sp. nov. Natural Trypanosoma cruzi infection, coupled with its presence mostly in peridomestic habitats, indicates that this species can be considered as an important Chagas disease vector from Argentina.

Revisiting the genetic variability of Brazilian peridomestic populations of the Chagas disease vector Triatoma sordida () (Hemiptera, Triatominae).

Triatoma sordida is an endemic species to South America, currently considered the species most frequently found in the peridomestic environment in Brazil. This triatomine has a wide ecological tolerability that allows it to inhabit several ecotopes and use different food sources. Although the species is considered predominantly peridomestic, it is also capable of colonizing households and forming numerous intra-household colonies, leading to its inclusion among the priorities for triatomine control campaigns in Brazil. All Brazilian populations of T. sordida are considered as T. sordida sensu stricto by chromosomal analyses (which highlights their epidemiological importance), although molecular studies that characterize the genetic diversity of these populations are scarce, being restricted only to the region of Minas Gerais. Thus, several populations of this vector distributed in the states of Bahia, Goiás, Mato Grosso do Sul, and Minas Gerais were analyzed using mitochondrial markers (cyt b and nd1). Low nucleotide diversity, high haplotypic diversity, low genetic distance, and high FST value were observed, as well as the formation of a monophyletic clade of the Brazilian populations of T. sordida, which confirms that this species has low genetic variability, with all specimens in Brazil grouped in T. sordida sensu stricto. In addition to the genetic and evolutionary importance for the knowledge of the biology of these vectors, these results are important from an epidemiological point of view, thus being able to direct vector control programs.

Parasite × vector relationship in Chagas disease: does Trypanosoma cruzi (Chagas, 1909) infection affect the spermatogenesis of Triatoma infestans (Klug, 1834)?

The parasite-vector interaction of Chagas disease is still poorly understood and the understanding of this relationship can help in the development of new strategies to control Trypanosoma cruzi transmission, which is the etiological agent of this disease. Considering the need to know if T. cruzi can cause some pathology in the reproductive system of the Chagas disease vectors, we investigated the spermatogenesis of Triatoma infestans infected by T. cruzi through histological and cytogenetic analysis. Trypanosoma cruzi Bolivia strain infection was not pathogenic for the reproductive system of T. infestans, because all the analyzed males had normal spermatogenesis, with all phases (spermatocytogenesis, meiosis and spermiogenesis) happening without any change. Thus, we demonstrated that the presence of T. cruzi Bolivia strain does not have influence in the spermatogenesis of T. infestans and we suggest that the influences on reproductive system observed for other species were a result of the action of the parasite on gametogenesis of females.

Molecular cytotaxonomy of the Triatoma brasiliensis species subcomplex (Hemiptera, Triatominae).

The Triatoma genus is paraphyletic, and its species are grouped into complexes and subcomplexes. Given the fact that species that make up a given subcomplex generally share chromosomal traits, we analyzed the distribution of AT- and CG-rich DNA of the T. brasiliensis species subcomplex, in order to establish affinities among members of the T. brasiliensis subcomplex based on chromatin and chromosome traits and develop an identification key for the four monophyletic Triatoma subcomplexes from South America. All species exhibited a CG-rich X sex chromosome and autosomes, as well as an AT-rich Y sex chromosome. This feature can be used as a diagnostic characteristic to determine whether a given species is a member of the T. brasiliensis subcomplex, because it enables the differentiation of these species from all Triatoma of South America. Thus, we confirmed the chromosomal relationship of the T. brasiliensis species subcomplex and developed a dichotomous key based on the chromocenter to differentiate the species from this subcomplex from the other monophyletic Triatoma subcomplexes from South America.

Prezygotic isolation confirms the exclusion of Triatoma melanocephala, T. vitticeps and T. tibiamaculata of the T. brasiliensis subcomplex (Hemiptera, Triatominae).

Chagas disease is caused by the Trypanosoma cruzi and transmitted mainly by triatomines. Triatoma is a paraphyletic group and the species of this genus are grouped into complexes and subcomplexes. Morphological data and geographical distribution grouped initially T. melanocephala, T. vitticeps and T. tibiamaculata in the T. brasiliensis subcomplex. However, karyotypic and phylogenetic analysis suggested the exclusion of T. melanocephala, T. vitticeps and T. tibiamaculata from this subcomplex. Considering that studies of experimental crosses can help to understand the systematics of species, we performed experimental crosses between T. melanocephala, T. vitticeps and T. tibiamaculata with T. b. brasiliensis. No crosses resulted in hybrids. Taking into account that the species of the T. brasiliensis subcomplex do not present interspecific prezygotic barriers, the characterization of reproductive barriers shows that T. melanocephala, T. vitticeps and T. tibiamaculata do not present an evolutionary proximity relationship with the species of this subcomplex. Thus, we confirmed the exclusion of these species from the T. brasiliensis subcomplex and we emphasize the importance of experimental crosses for evolutionary studies.

Reproductive Aspects of Chagas Disease Vectors: Evidence of Transcriptional Activity during the Nucleolar Persistence Phenomenon in the Spermatogenesis of Triatomines.

The subfamily Triatominae currently consists of 154 species, most of them being of great importance for public health because they are considered potential vectors of the protozoan Trypanosoma cruzi, the etiologic agent of Chagas disease. In addition to their epidemiological importance, these insects are considered important biological models for cell studies because they have peculiar characteristics in their cells, for example, persistence of the nucleolus during spermatogenesis. This phenomenon is characterized by the presence of the nucleolus or nucleolar corpuscles during all phases of meiosis. To date, all knowledge is restricted to the study of the presence/absence of the nucleolus during the triatomine meiosis, so the present work aimed to analyze if this persistent nucleolar material has transcriptional activity. Analysis of the meiotic metaphases of Rhodnius montenegrensis and Panstrongylus megistus by using fluorochrome acridine orange made it possible to characterize the presence of RNA in the nucleolar material. Thus, it was demonstrated, for the first time, that the persistent nucleolar material during triatomine meiosis is transcriptionally active, supporting the hypothesis of the relationship between nucleolar persistence during meiosis of these insects and the formation of the chromoid body, an organelle responsible for the support of all transcriptional activities during spermiogenesis.