Abstract
We analysed the chromosome complement and male meiosis in a natural population of Mepraia gajardoi (Hemiptera: Reduviidae: Triatominae). The normal karyotype of this species is 20 autosomes plus X1X2Y in males and X1X1X2X2 in females. We confirmed that M. gajardoi is cytogenetically strikingly different from M. spinolai (with which it was previously included), which supports the taxonomic separation of these two species. For the first time in the holocentric chromosomes of the subfamily Triatomi- nae, a structural rearrangement was detected. Observations made during meiosis and mitosis indicated that one of eleven individuals had undergone a fusion between two non-homologous chromosomes, probably before germinal cell development. This autosomal translocation resulted in chromosomal irregularities such as an autosomal trivalent, autosomal univalents and chromosomal frag- ments, which altered the normal segregation of both autosomes and sex chromosomes. The chromosomal fragments resemble super- numerary or B chromosomes, which supports the idea that these chromosomes are remnants of structural rearrangements. The genetic consequences of translocations in holokinetic chromosomes and their role in the evolution of chromosomes in triatomines are also discussed.
Highlights
The Heteroptera, or true bugs, include many species of economical and medical importance
The normal male diploid chromosome complement in M. gajardoi consists of 23 chromosomes (2n = 20A + X1X2Y)
Cytogenetics of Mepraia gajardoi Originally considered as a population of Mepraia
Summary
The Heteroptera, or true bugs, include many species of economical and medical importance. The subfamily Triatominae is relevant because most of their members are vectors of the protozoan Trypanosoma cruzi, causative agent of Chagas disease or American trypanosomiasis This parasitic disease is one of the most important in the tropics and subtropics of the Americas, with about 200,000 cases per year (WHO, 2002). There is little information on the evolution of chromosomes in organisms with holocentric chromosomes because of the difficulty of detecting structural variation, due to the lack of a morphologically differentiated centromere and the scarcity of longitudinal chromosomal differentiation. For these reasons chromosome rearrangements, such as inversions and reciprocal translocations, are rarely reported in Heteroptera (Toledo-Piza, 1944; Papeschi & Mola, 1990; Bressa et al, 1998). Mainly the behaviour of chromosomes during meiosis and C-banding patterns are used to evaluate divergence and chromosomal evolution in the Triatominae (Pérez et al, 2002)
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