Cytogenetic Study in a Mutant of Triatoma infestans (Hemiptera: Reduviidae) Carrying a Spontaneous Autosomal Fusion and an Extra Chromosome

Abstract

Triatomainfestans (2n = 20 A + XY, male) is a blood-sucking bug and the most important vector of Chagas disease in the Southern Cone countries. A cytogenetic analysis of 14 individuals from the Argentine Gran Chaco has revealed the presence of a naturally heterozygous for an autosomal fusion. The fusion heterozygote (2n = 19 A + 1 extra chromosome + XY, male) presented an autosomal trivalent, 8 bivalents, the X and Y sex univalents, and a minute extra chromosome at meiosis I. The autosomal trivalent divided equationally at first anaphase. At metaphase II, cells had 8 autosomes, X and Y sex chromosomes, and an autosomal pseudo-trivalent composed by 3 different-sized chromatids. The orientation of this pseudo-trivalent led to a reductional segregation. The meiotic behaviour of this new chromosome complement was highly regular. The extra chromosome did not affect the segregation of autosomes and sex chromosomes during both meiotic divisions. We propose that the extra chromosome was originated as a product of an autosomal fusion, and it might become a B chromosome. Many authors suggest that karyotype evolution in Heteroptera has proceeded mainly by fusions and fragmentations. The fact that this rearrangement has been found in a natural population of T. infestans and that it shows a regular meiotic behaviour seems to support the suggested hypothesis.

High Diversity in CMA₃/DAPI-Banding Patterns in Heteropterans

“…We also observed that in E. cornutus the position of a CMA 3 + dot was terminal, while in E. heros this dot was intercalary. This is some evidence of the importance of chromosome rearrangements in Pentatomidae, even when compared with large rearrangements described for the Reduviidae T. infestans [Poggio et al, 2013].…”

Karyotype diversity among predatory Reduviidae (Heteroptera)

“…Rearrangements are more precisely evidenced when trivalents, multivalents or robust cytogenetic markers (heterochromatin, rDNA sites or others) are noted. Samples of these events were reported for species of Belostoma Latreille, 1807 (Papeschi 1994, 1996) and Triatoma infestans (Klug, 1834) (Poggio et al 2013b). Other examples of chromosome changes were reported in insects of the family Aradidae, where fusions were important for karyotype evolution (Jacobs 2003), as well as the dysploidy that originated the neoXneoY sex system in Dysdercus albofasciatus Guérin Meneville, 1831 (Bressa et al 2009).…”

“…Of the 36 species of Pentatomomorpha studied until now, the rDNA loci are preferably located in autosomes with only four species with rDNA loci on the sex chromosomes (González-García et al 1996, Bressa et al 2009, Grozeva et al 2011, Bardella et al 2013). On the contrary, in Cimicomorpha, the location of rDNA loci are more heterogeneous: the hybridization sites are observed on autosomes, sex chromosomes or both simultaneously (Dias de Campos Severi-Aguiar and Azeredo-Oliveira 2005, Severi-Aguiar et al 2006, Morielle-Souza and Azeredo-Oliveira 2007, Grozeva et al 2010, 2011, 2013, 2014, Panzera et al 2012, 2014, Poggio et al 2011, 2013a, 2013b). …”

Entoepidemiology of Chagas disease in northwest São Paulo and cytogenetic analysis of its main vector, Triatoma sordida (Hemiptera: Triatominae)

“…However, the present analysis of mutant organisms revealed peculiar behavior during meiosis: chromosomes condensed and did not show chiasms, chromatin bridges were observed between the autosomes, and some homologous chromosomes did not pair. Cytogenetic analysis of T. infestans mutants was also recently conducted in a previous study that revealed spontaneous fusion and an extra autosomal chromosome in these organisms (Poggio et al, 2013). Noireau et al (1998) proposed that cryptic speciation is occurring among populations of Chicago-Bolivian T. sordida, based on evidence of reproductively isolated populations.…”