Heterochromatin characterization and ribosomal gene location in two monotypic genera of bloodsucker bugs (Cimicidae, Heteroptera) with holokinetic chromosomes and achiasmatic male meiosis.

Members of the family Cimicidae (Heteroptera: Cimicomorpha) are temporary bloodsuckers on birds and bats as primary hosts and humans as secondary hosts. Acanthocrios furnarii (2n=12=10+XY, male) and Psitticimex uritui (2n=31=28+X1X2Y, male) are two monotypic genera of the subfamily Haematosiphoninae, which have achiasmatic male meiosis of collochore type. Here, we examined chromatin organization and constitution of cimicid holokinetic chromosomes by determining the amount, composition and distribution of constitutive heterochromatin, and number and location of nucleolus organizer regions (NORs) in both species. Results showed that these two bloodsucker bugs possess high heterochromatin content and have an achiasmatic male meiosis, in which three regions can be differentiated in each autosomal bivalent: (i) terminal heterochromatic regions in repulsion; (ii) a central region, where the homologous chromosomes are located parallel but without contact between them; and (iii) small areas within the central region, where collochores are detected. Acanthocrios furnarii presented a single NOR on an autosomal pair, whereas P. uritui presented two NORs, one on an autosomal pair and the other on a sex chromosome. All NORs were found to be associated with CMA3 bright bands, indicating that the whole rDNA repeating unit is rich in G+C base pairs. Based on the variations in the diploid autosomal number, the presence of simple and multiple sex chromosome systems, and the number and location of 18S rDNA loci in the two Cimicidae species studied, we might infer that rDNA clusters and genome are highly dynamic among the representatives of this family.

Cytogenetic study in a mutant of Triatoma infestans (Hemiptera: Reduviidae) carrying a spontaneous autosomal fusion and an extra chromosome.

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.