Biological aspects of crosses between Triatoma recurva (Stål), 1868 (Hemiptera: Reduviidae: Triatominae) and other members of the Phyllosoma complex

Life history data of a Triatoma protracta nahuatlae, T. sinaloensis, and their laboratory hybrids (Hemiptera: Reduviidae)

Chagas disease is one of the most significant vector-borne diseases in Mexico. The presence of "sylvatic" triatomine vectors of Trypanosoma cruzi (Chagas) inside human dwellings necessitates estimating their vectorial capacity. To estimate this capacity in Triatoma protracta nahuatlae (Ryckman), Triatoma sinaloensis (Ryckman), and their laboratory hybrids, 6 biological parameters were examined. Triatoma sinaloensis exhibited the shortest development time (155 days), with a median of 12 blood meals. Mortality rates varied from 35% to 45% in the 3 studied cohorts. All 3 cohorts were aggressive, initiating feeding within 0.5-1 min, and had similar feeding periods ranging from 10 to 18 min. A majority (75.3-97.9%) of the hybrids defecated when feeding, immediately after feeding, or in less than 1 min post-feeding. In contrast, only 7-42% of nymphs of T. sinaloensis defecated during the same period. Our results regarding the 6 parameters studied confirm the potential role of T. p. nahuatlae as an efficient vector of T. cruzi. Triatoma sinaloensis, on the other hand, exhibited limited vectorial capacity primarily due to its poor defecation behavior. Continued surveillance of these "sylvatic" triatomine populations is necessary to prevent an epidemiological problem.

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).

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.

Pattern of climate connectivity and equivalent niche of Triatominae species of the Phyllosoma complex

The Phyllosoma complex is a Triatominae (Hemiptera: Reduviidae) group of medical importance involved in Trypanosoma cruzi (Kinetoplastida: Trypanosomatidae) transmission. Most of the members of this group are endemic and sympatric species with distribution in Mexico and the southern U.S.A. We employed MaxEnt to construct ecological niche models of nine species of Triatominae to test three hypothesis: (a) whether species with a broad climatic niche breadth occupy a broader geographical range than species with a narrow climatic breadth, (b) whether species with broad distribution present high degree of climatic fragmentation/isolation, which was tested through landscape metrics; and (c) whether the species share the same climatic niche space (niche conservatism) considered through an equivalence test implemented in ENMtools. Overall, our results suggest that the geographical distribution of this complex is influenced mainly by temperature seasonality where all suitable areas are places of current and potential transmission of T. cruzi. Niche breadth in the Phyllosoma complex is associated with the geographical distribution range, and the geographical range affects the climatic connectivity. We found no strong evidence of niche climatic divergence in members of this complex. We discuss the epidemiological implications of these results.

"Sweeter than a rose", at least to Triatoma phyllosoma complex males (Triatominae: Reduviidae)

BACKGROUND

The Triatoma phyllosoma complex of Trypanosoma cruzi vectors (Triatominae: Reduviidae) is distributed in both Neotropical and Nearctic bioregions of Mexico.

METHODS

Volatile organic compounds emitted by disturbed Triatoma longipennis, Triatoma pallidipennis and Triatoma phyllosoma, and from their Brindley's and metasternal glands, were identified using solid-phase microextraction coupled with gas chromatography-mass spectrometry.

RESULTS

Disturbed bugs and the metasternal glands from T. phyllosoma released or had significantly fewer compounds than T. longipennis and T. pallidipennis. Isobutyric acid was the most abundant compound secreted by disturbed bugs of the three species, while Brindley's glands of all species produced another four compounds: propanoic acid, isobutyric acid, pentyl butanoate, and 2-methyl hexanoic acid. Two novel compounds, both rose oxide isomers, were produced in MGs and released only by disturbed females of all three species, making this the first report in Triatominae of these monoterpenes. The principal compound in MGs of both sexes of T. longipennis and T. phyllosoma was 3-methyl-2-hexanone, while cis-rose oxide was the principal compound in T. pallidipennis females. The major components in male effluvia of T. pallidipennis were 2-decanol and 3-methyl-2-hexanone.

CONCLUSION

Discriminant analysis of volatile organic compounds was significant, separating the three species and was consistent with morphological and genetic evidence for species distinctions within the complex.

[Biological parameters of Meccus phyllosomus phyllosomus (Burmeister), 1835, Triatoma recurva (Stål), 1868 (Hemiptera, Reduviidae) and their laboratory hybrids]

INTRODUCTION

Hybrids from species and subspecies of Mexican triatomines have shown outstanding biological and behavioral characteristics as compared with their parental groups. This could lead to an increasing risk of transmission of Trypanosoma cruzi to human and animal reservoir hosts.

OBJECTIVE

To describe and compare biological parameters related to the life cycle of Triatoma recurva, Meccus phyllosomus phyllosomus and their laboratory hybrids and estimate their risk as transmitters of T. cruzi to humans.

MATERIALS AND METHODS

We kept a cohort of each one of the three groups (T. recurva, M. p. phyllosomus and their hybrids) under similar laboratory conditions and then compared them to record the data related to their life cycles, number of blood meals to molt, mortality rates, egg eclosion rates and female fecundity.

RESULTS

The hybrid cohort showed the lowest mean time from first-instar nymph to adult (136.6 ± 17.5 days). The number of blood meals from molt to next instar (13.4 ± 1.7; 15.6 ± 5.2) was higher in the hybrid and T. recurva cohorts. The hybrid cohort showed the lowest mortality rate (29.5%) and the highest rate (70%) of adult females at the end of the biological cycle. Fecundity per day per female (range: 1.1 ± 0.6- 1.6 ± 0.7 eggs) was similar in the three cohorts. Egg hatching rate was higher than 70% in both hybrid and M. p. phyllosomus cohorts.

CONCLUSION

The hybrid cohort showed some outstanding biological characteristics, which would entail a higher risk of transmission of T. cruzi to hosts than their parentals.

Experimental crosses between Mepraia gajardoi and M. spinolai and hybrid chromosome analyses reveal the occurrence of several isolation mechanisms

Hematophagous insects of the subfamily Triatominae include several species with a large variety of shapes, behavior and distribution. They have great epidemiological importance since most of them transmit the flagellated protozoan Trypanosoma cruzi, the etiologic agent of Chagas disease. In this subfamily several cases of species hybridization have been reported under experimental and natural conditions. Mepraia is a genus of Triatominae endemic in Chile, responsible for transmitting T. cruzi in the sylvatic cycle. This genus includes three species, M. gajardoi, M. spinolai and M. parapatrica; however, the differentiation of M. parapatrica as a separate species remains controversial considering the possible occurrence of introgression/hybridization processes in some populations of this putative species. Mepraia species show conspicuous wing polymorphism, and it has been proposed that the genes related to wings are linked to the Y chromosome, thus wingless males could not engender winged progeny. In order to determine the degree of reproductive isolation and to assess the wing phenotype in the offspring, we performed experimental crosses between the two most divergent Mepraia species (M. gajardoi and M. spinolai) together with chromosome analyses of hybrid progenies. Although fertile F₁ hybrids were obtained in only one direction of crossing, we verified the existence of different isolation mechanisms between parental species, including hybrid breakdown. The occurrence of winged males in the offspring of wingless parental males suggests that the wing character is not linked to the Y chromosome.

Comparative egg morphology of six Meccus species and Triatoma recurva (Stål, 1868) Hemiptera: Reduviidae

We investigated the morphology and morphometry of eggs from the colonies of the Entomology Laboratory at ENCB-IPN belonging to six species of the genus Meccus and Triatoma recurva, using both light and scanning electron microscopy. Egg ornamentation is an important parameter to consider in the differentiation of species. Samples were observed under a scanning electron microscope. Measurements of fifty eggs per species included length, width, and opercular diameter, which were used for the morphometric analysis. The results showed that the seven species display a polygonal ornamentation dominated by hexagons; the operculum shows also a polygonal ornamental characteristic in each species. Morphometry provided valuable information for discriminating between closely related species of the genus Meccus and Triatoma recurva, a species akin to this group, thereby facilitating the complete discrimination of these species.