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

Abstract

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. Graphical abstract

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

“…The generation of hybrids is relatively common between the species of this subfamily, with the main evolutionary events responsible for the decline of the hybrid lineage (postzygotic barriers) being inviability (offspring mortality before reaching adulthood) [ 8 ], sterility (partially or completely infertile offspring) [ 9 , 10 ] and the collapse of the hybrid (high offspring mortality from the second generation) [ 11 , 12 ]. Several studies involving experimental crosses have already been carried out among the triatomines, focusing mainly on taxonomic [ 8 , 11 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ] and epidemiological aspects [ 24 , 25 , 26 , 27 ]. On the other hand, although prezygotic barriers are less frequent and, generally, are present in only one direction of the crossings, as observed between Rhodnius colombiensis Mejia, Galvão and Jurberg, 1999 and R. pallescens Barber, 1932 [ 28 ], Triatoma pseudomaculata Corrêa and Espínola, 1964 and T. infestans (Klug, 1834) [ 29 ], T. delpontei Romaña and Abalos, 1947 and T. platensis Neiva, 1913 [ 30 ] and T. longipennis Usinger, 1939 and T. mopan Dorn et al, 2018 [ 17 ], they may be present between species that are very distant from the phylogenetic point of view [ 29 , 31 ] and between species of different genera ( Triatoma Laporte, 1832 × Panstrongylus Berg, 1879, Triatoma × Rhodnius Stål, 1859 and Rhodnius × Psammolestes Bergroth, 1911 [ 18 , 23 , 31 ]).…”