Karyotype evolution in holocentric chromosomes of three related species of triatomines (Hemiptera-Reduviidae)

Abstract

C-banded karyotypes, DNA content and the male meiiotic process of Triatoma platensis and Triatoma delpontei are compared with those of Triatoma infestans, the main vector of Chagas disease in South America. These three species present the same diploid chromosome number 2n = 22 (20 autosomes + XX male/XY female). They also have several cytogenetic traits that differ from all other triatomines: large autosomes, C-heterochromatic blocks and meiotic heteropycnotic chromocenters formed by autosomes and sex chromosomes. In spite of these similarities, each species presents different chromosomal behavior during male meiosis, distinct DNA content and a specific amount and localization of the C-heterochromatin. The differences in DNA content are mainly due to the variation in C-heterochromatin amount, which may be interpreted as loss and/or gain of C-regions. This interpretation is supported by the presence of meiotic and mitotic chromocenters that facilitate the transference of C-positive material. The cytogenetic data presented in this work suggest that T. infestans and T. platensis are more closely related to each other than to T. delpontei. It can also be inferred that the differences in distribution and amount of heterochromatin do not play a direct role in speciation in this group.

Chromosomal evolution trends of the genus Panstrongylus (Hemiptera, Reduviidae), vectors of Chagas disease

“…During the past decade, our research group has carried out cytogenetic studies on triatomines, including intra-and inter-populations analysis (Panzera et al, 1992, comparison of species of the same and different genera (Pérez et al, 1992;Panzera et al, 1995Panzera et al, , 1998 as well as chromosomal behaviour during meiosis . These results give insights both in the chromosomal evolution of the subfamily and in the establishment of the taxonomic status of some taxa.…”

“…In Triatoma, the heterochromatic regions show different behaviour depending on the species analysed, possibly reflecting the polyphyletic nature of this large genus (Dujardin et al, 2000). In some Triatoma species, particularly those of the infestans sub-complex (T. melanosoma, T. infestans, T. platensis and T. delpontei), the heterochromatic regions are generally associated to form a single chromocentre (Panzera et al, 1995). In others, the heterochromatic regions appear scattered through the nucleus and multiple chromocentres are formed, such as in T. barberi, T. rubrofasciata, T. tibiamaculata, T. brasiliensis and in some species of sordida sub-complex .…”

“…In order to compare the species and populations, we considered several cytogenetic markers previously used to differentiate triatomine species (Pérez et al, 1992;Panzera et al, 1995Panzera et al, , 1997. Those traits based on relative size (autosomal size and autosomes versus sex chromosomes) were determined by observing first and second metaphases.…”

Chromosome homogeneity in populations of Triatoma brasiliensis Neiva 1911 (Hemiptera - Reduviidae - Triatominae)

“…Isoenzymatic data not only confirmed the specific status of both species but also suggested they have been evolving independently for considerable time . On the contrary, other groups of closely related species show clear chromosomal divergences such as the ones that belong to infestans subcomplex (T. infestans, Triatoma platensis, and Triatoma delpontei) and the sordida subcomplex (T. sordida, Triatoma patagonica, and T. guasayana) (Panzera et al, 1995 and1997 respectively). All this is evidence that several groups of Triatoma species show different chromosome evolution rates that may reflect adaptation to different environments or some intrinsic property of their chromosome complement.…”

“…In order to determine the existence of chromosome differentiation between these chromatic forms, we analyzed them in terms of cytogenetic characters previously used to differentiate triatomine species (Pérez et al, 1992;Panzera et al, 1995Panzera et al, , 1997 and to detect intraspecific variation . This group of heteropteran insects exhibits holocentric chromosomes, which do not have a morphologically differentiated centromere.…”