Chromosome Morphology and Meiosis in Zonocerus Variegatus L. (Orthoptera, Pyrgomorphidae).

Abstract

The grasshopper, Zonocerus variegatus of the family Pyrogomorphidae has a male diploid chromosome number of 19, with an XO constitution (Oyidi 1968, Lasebikan andOlorode 1972). Although these investigators described the chromosomes as acrocentric, Nwankiti (1983b) described them as metacentric. The meiotic aberrations detected by Lasebikan and Olorode (1972) and Olorode and Akingbohungbe (1975) were not reported by Nwankiti, (1983a, b). Since the chromosomes of Z. variegatus are relatively large and not too many, it is not expected that there would be any disagreement on the morphology of the chromosomes. It should also be possible to detect consistent meiotic aberrations. This paper re-examines these issues. Materials and methodsThe fifty grasshoppers used for this study were adult males collected between January and May on the University of Lagos campus. They were killed with chloroform either on the day they were captured or on the next day. The grasshoppers were then dissected in 0.67% NaCI solution.Five fresh testicular follicles were placed on each glass slide, cut into three or four pieces and covered with a drop of 2% lactic-propionic orcein stain. After about 15 min, a cover glass was placed on the material. The cover glass was held in place while it was tapped gently with a dissecting needle, to disperse the cells and force out the excess stain. The preparation was squashed further between folds of bibulous paper to absorb the excess stain. The edges of the cover glass were sealed with nail varnish. Photomicrographs were made under the 100x oil immersion objective of a Wild M20 microscope with MPS 55 photoautomat attachment. Results and discussionChromosome Morphology:In spite of the fact that the grasshoppers were not treated with colchicine the individual chromosomes could be identified and counted in a polar view of the mitotic metaphase (Fig. la). The chromosomes appeared to be in C-metaphase because there was no relational coiling between sister chromatids. This appearance and the fact that what should be the short arms of the chromosomes were not clearly visible as paired structures (chromatids) could lead to misinterpretation, as by Nwankiti (1983b), that a pair of sister chromatids are instead the two arms of a folded metacentric chromosome. Close examination however, shows that there is a constriction separating the long arm from the short arm which also has some of the lampbrush appearance of the long arm. In addition, in some cases, the two chromatids of the short arm can be detected (Fig. la). The interpretation of folded metacentric chromosomes would be plausible only if the figure which Nwankiti (1983b) called mitotic telophase were so, but that is in fact a polar view of metaphase as in the present case. Furthermore, the mitotic anaphase/

Cytogenetic and Meiotic Studies Reveal Conservatism in Acrida turrita (Linnaeus 1758) (Orthoptera: Acrididae) from Lagos, Nigeria

“…In Anaphase I, the chromosomes were seen to be V-shaped and consist of two sister chromatids. Repulsion between the sister chromatids confers the V shape characteristic of acrocentric chromosomes; while in Anaphase II (Plate 4F), the chromatids have fully separated and appeared I-shaped confirming that the chromosomes are acrocentric morphologically (Williams and Ogunbiyi, 1995;Seino et al, 2008), or acrotelocentric as suggested by Adekoya (2009) and Seino and Akongnui (2010).…”

“…Five cells or slides were prepared for each specimen and were examined for chromosome number and morphology. The chromosomes were identified on the basis of their length (Stace, 1980) and their morphology was determined by examining the shapes of the chromosomes in meiotic anaphase I, anaphase II and metaphase II according to Williams and Ogunbiyi (1995) and Seino et al (2008). Ocular and stage micrometers were used in determining the chromosomes' lengths.…”

Cytogenetic studies in Dictyophorus griseus (Reiche & Fairmaire, 1849) (Orthoptera: Pyrgomorphidae) from Cameroon. II. Karyotype

“…6) the chromatids were separated and the chromosomes appeared I -shaped. As per the criteria of Williams and Ogunbiyi (1995) these chromosomes could be judged to be acrocentric in morphology. From this study, the standard karyotype of D. griseus comprises of 2n = 19 XO acrocentric chromosomes which is the same as that described for representatives and basic for the family Pyrgomorphidae.…”

“…These chromosome smears were examined using the Fisher laboratory microscope by first scanning with the 10X objective and nuclei of interest further examined with the high power objective 40X. Chromosome morphology was determined by examining the shapes of chromosome in meiotic Anaphase-I, Metaphase-II and Anaphase-II and classified as per the criteria of Williams and Ogunbiyi, (1995) and Seino et al, (2008). Photographs of mitotic chromosome smears were taken with the Lietz digital photomicroscope using the oil immersion lens, 100X.…”

Comparative analysis of chromosomal localization of ribosomal and telomeric DNA markers in three species of Pyrgomorphidae grasshoppers

“…This is partially related to the poor degree of karyological study of Pyrgomorphidae grasshoppers. The karyotypes of only about 30 species are known from tropical and subtropical regions of the Old World (Makino 1951, Sannomiya 1973; Nankivell 1976, John and King 1983, Fossey et al 1989, Williams and Ogunbiyi 1995, Seino et al 2013, Seino and Dongmo 2015). The vast majority of species have a 19-chromosome karyotype, but a few species have been shown to have a different karyotype, resulting from one, two or three Robertsonian translocations (White 1973, Fossey et al 1989).…”