Karyotype and sex chromosome differentiation in two Nalassus species (Coleoptera, Tenebrionidae)

Abstract

Cytogenetic features of Nalassus bozdagus Nabozhenko & Keskin, 2010 and Nalassus plebejus Küster, 1850 were analysed using conventional and differential staining. Mitotic and meiotic chromosomal analysis revealed the diploid number as 2n = 20 (9+Xy_p) in both species. Besides the general resemblance of two Nalassus Mulsant, 1854 karyotypes, important differences related to variations in the number of metacentric/submetacentric chromosomes, localization of highly impregnated regions which are considered as NOR and heterochromatin distribution are clearly observed. The most prominent difference between two species is found related to the X chromosome which is clearly larger in Nalassus bozdagus and has a conspicuous secondary constriction on the long arm. As a result of silver staining, the existence of highly impregnated areas associated with Xy_p of Nalassus bozdagus in both prophase I and metaphase I, suggests that NORs are seemingly located on sex chromosomes. On the other hand, the potential NORs of Nalassus plebejus were observed only in prophase I nuclei. With the application of fluorescence dye DAPI, the AT rich chromosome regions and Xy_p which forms the parachute configuration were shown in both species.

Keywords: DAPI; Helopini; Karyotype; NOR; Nalassus bozdagus; Nalassus plebejus; Tenebrionidae; heterochromatin; sex chromosomes.

Figure 1.

a–b Nalassus bozdagus 2n = 20. a karyotype b idiogram c–d Nalassus plebejus 2n = 20 c karyotype d idiogram. Bar = 5 µm.

Figure 2.

a–b Nalassus bozdagus with dark heterochromatic blocks on all chromosomes. a leptotene–zygotene b pachytene c–d Nalassus plebejus with two distinctive heterochromatic blocks (black arrows); c leptotene–zygotene d pachytene. Orange arrow indicates Xy_p sex bivalent, Bar = 5 µm.

Figure 3.

a diplotene–diakinesis in Nalassus plebejus b–c diakinesis–metaphase I b Nalassus bozdagus c Nalassus plebejus. Bar = 5 µm.

Figure 4.

a–b metaphase I a Nalassus bozdagus b Nalassus plebejus c–d metaphase II c Nalassus bozdagus d Nalassus plebejus. Arrows show Xy_p sex bivalents, Bar = 5 µm.

Figure 5.

Silver nitrate staining a–c Nalassus bozdagus d Nalassus plebejus. Black arrows indicate NOR, red arrows indicate argyrophilic sex bivalents, Bar = 5 µm.

Figure 6.

DAPI staining a metaphase I of Nalassus plebejus b metaphase I of Nalassus bozdagus c prophase I nucleus of Nalassus bozdagus d prophase I nucleus of Nalassus plebejus. Arrows show Xy_p sex bivalents and arrowheads indicate heterochromatic regions, Bars = 5 µm.