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

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).

Crossing experiments detect partial reproductive isolation among populations of Triatoma longipennis (Hemiptera: Reduviidae: Triatominae)

Chagas disease is an important vector-borne disease endemic in Mexico. Of the 33 triatomine species found in Mexico, Triatoma longipennis (Usinger) is considered among the most important because of its infection indices, capacity for transmitting Trypanosoma cruzi (Chagas), and its distribution areas. Here, we describe the results of a reproductive isolation analysis among 5 populations of T. longipennis collected from representative areas of Mexico. Fertility and segregation of morphological characteristics were examined in two generations of hybrids. The percentage of pairs with (fertile) offspring varied from 30% to 100% in the parental crosses, while these values varied from 0 to 100% in the intersite crosses. Our results indicate partial reproductive isolation among these populations. These findings shed light on the potential presence of a cryptic species complex of T. longipennis in Mexico.

Dichotomous Keys Based on Cytogenetic Data for Triatomines Reported in Brazilian Regions with Outbreaks of Orally Transmitted Chagas Disease (Pernambuco and Rio Grande Do Norte)

Chagas disease (CD) affects about eight million people worldwide. Brazil has the highest number of estimated cases and the largest number of deaths due to CD. Considering the recent outbreaks of oral CD involving at least 27 cases of acute CD in Pernambuco (PE) as well as 18 cases and 2 deaths in the Rio Grande do Norte (RN), we developed dichotomous keys for the identification of triatomine species in these Brazilian states based on cytogenetic data. All triatomine species could be distinguished by cytogenetic characteristics, emphasizing the importance of the newly developed taxonomic keys for the correct identification of triatomes from PE and RN, particularly for species that exhibit morphological similarities, such as Triatoma brasilensis and T. petrocchiae (present in both states) and T. maculata and T. pseudomaculata (as T. pseudomaculata has been misidentified as T. maculata in PE and RN). These alternative keys are expected to provide a useful tool for the scientific community and, above all, health agents, aimed at preventing mistakes from occurring in the identification of the vectors present in PE and RN related to CD outbreaks caused by oral infection.

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.

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.

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

Simple Summary

Although all triatomines are potential vectors of Chagas disease, there are species with greater or lesser vectorial importance. Therefore, the correct identification of triatomine species is essential for vector control programs. In general, triatomines are identified by external morphological characters. However, some species are very similar or even morphologically identical, making the use of complementary analyses for the correct identification of species important. For this reason, this study focused on the use of experimental crosses to assess the specific status of species of the Triatoma brasiliensis species complex. The crosses did not result in hybrids, demonstrating that there are pre-zygotic reproductive barriers installed between T. petrocchiae and the other species of the T. brasiliensis complex (which confirms the specific status of the species according to the biological species concept). 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.

Abstract

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.