_??_1994 The Japan Mendel Society Cytologia 59 : 285-287, 1994

Karyotypes of Two Indian Grasshoppers of (-)

N. V. Aswathanarayana* and S. K. Ashwath

Deprtment of Studies in Zoology, University of Mysore, Manasa Gangotri , Mysore, 570 006, India

Accepted June 2, 1994

Variation in the chromosome number and form in closely related groups are of great interest and importance in the karyotype evolution. Robertsonian rearrangements and peri centric inversions are both considered to be the principle modes of chromosomal change in . (Imai et al. 1977). There are instances where the karyotypes are relatively stable as in the Acrididae. However, in the related family of Tettigonidae there is a wide range of variation in the diploid numbers from 12 to 39 (Ferreira 1977, Ashwath 1981, Aswathanara yana and Ashwath 1985). In the present paper, the karyotype diversity in two species of the less studied subgroup Mecopodiane is described and discussed.

Material and methods

A total of 29 males of elongata and 27 males of Mecopoda sp. were collected in and around Mysore (S. W. India) for karyological studies. The chromosome preparations were made from testes as well as from hepatic caecae adopting the method of Imai et al. (1977). The C-banding was induced applying technique of Summer (1972) with minor modifications.

Observations

A. Karyotype: (1) : The mitotic metaphases from hepatic caecae show 29 chromosomes in the males (2n= 28+XO). The karyotype possesses 8 pairs of metacentrics of which one pair is large (chrm. 1) and others are smaller in size. Of the other 6 pairs, 5 pairs are subacrocentric having one large pair (chrm. 9), one medium-sized (chrm. 10) and three small pairs (chrm. 11-13) and one pair is acrocentric (chrm. 14). The X chromosome is a large metacentric and is about 20% of the haploid set (Fig. 1). (2) Mecopoda sp. The spermatagonial metaphases reveal 27 chromosomes (2n=26+XO). The karyotype has all biarmed chromosomes consisting of 8 pairs of metacentrics which includes one large (chrm. 1) and seven small pairs of chromosomes (chrm. 2-8) one heteromorphic pair having a secondary constriction in one homologue (chrm. 9) and 4 pairs of subacrocentric chromo somes (chrm. 10-13). The X chromosome is large and metacentric measuring about 18% of the haploid set (Fig. 2).

B. C-Banding: The distribution of the constitutive heterochromatin of Mecopoda sp. is characteristic. The centromeric bands are clear only in chromosomes 1, 9 and X. In others they are either faint or

* No . 290/3, 34 'A' Cross, 9th Main, IV Block, Jayanagar, Bangalore, 560 011, India. 286 N. V. Aswathanarayana and S. K. Ashwath Cytologia 59

Fig. 1. Karyotype of Mecopoda elongata Fig. 2. Karyotype of Mecopoda sp.

absent. In the heteromorphic chromosome 9, the centromeric band is conspicuous only in one homologue. There are deeply stained heterochromatin blocks at the telomeric reg ions in chromosomes 1, 3, 4, 6 and 10-13 and the X. The X chromosome resembles chro mosome 1 except for the presence of intersti tial band near the centromere and the ab sence of the faint telomeric band at the distal end of the long arm (Fig. 3).

Discussion

Relatively very little is known of the chromosomes of the subfamily Mecopodinae. The first report on this group is of Hareyama Fig. 3. C-banded karyotype of Mecopoda sp. (1932) who reported a diploid number of 27 chromosomes in the males of Mecopoda elo ngata nipponensis from Japan but without figures. Later Asana et al, (1938) described the karyotype of the same species collected from Jogeswari (N. India) as having 2n=27 consisting of 2 pairs of V-shaped (one with submedian and one with subterminal constriction), 11 pairs of rod-shaped chromosomes and a V-shaped X chromosome. Though the North Indian from is somewhat closer to Mecopoda sp. of the present study further investigations are needed. We can consider the karyotype evolution of Mecopodinae as has been done by Ferreira (1977) for Pheneropterinae. He assumes that there are at least two basic karyotypes (2n=31 and 2n=21) in the family Tettigonidae with all acrocentric chromosomes from which karyo type diversification must have occurred by centric fusions and pericentric inversions. Since the karyotype of Mecopoda sp. is having 2n=27 and M. elongata 2n=29, the basic karyotype of the genus Mecopoda is assumed to have 31 acrocentric chromosomes which has undergone repatterning. The large metacentric chromosome 1 in both species and the submetacentric chromosomes 9 in Mecopoda sp. could be the products of centric fusions from the basic karyotype and all the small metacentric and submetacentric chromosomes are due to pericentric inversions. We propose that the terminal C-bands of chromosomes 3, 4 and 6 as cytological evidence for pericentric inversions. The C-banding in tettigonids is much wanting for comparison. As the authors are aware the only report on this aspect is of Euhexacentrus annulicornis (2n=10+XY), a tettigonid with 1994 Karyotypes of Two Indian Grasshoppers of Mecopodinae 287 least number of chromosomes with all metacentrics (Aswathanarayana and Ashwath 1985) where the centromeric bands and the heterochromatin blocks at the terminal and interstitial regions are large and district.

Summary

(1) The chromosomes of two species of the genus Mecopoda are described. (2) Mecopoda elongata has 2n=29 with 8 pairs of metacentric, 5 pairs of subacrocentric and one pair of acrocentric chromosomes. The karyotype of Mecopoda sp . consists of 2n=27 with all biarmed chromosomes 8 pairs of metacentric , one pair of heteromorphic sub metacentric with a secondary constriction in one homologue and 4 pairs of subacrocentric chromosomes. In both, the X chromosome is large and metacentric . (3) The basic karyotype of the genus Mecopoda is assumed to be 2n=31 with all acrocentric chromosomes and the karyotypes of M. elongata and Mecopoda sp. are considered to be derived from such a basic karyotype by the mechanisms of centric fusion and pericentric inverson. (4) The C-banded karyotype of Mecopoda sp. is presented showing the characteristic distribution of C-heterochromatin.

Acknowledgement

The authors are grateful to the University Grants Commission-New Delhi for the award of a Research Fellowship (to SKA). Thanks are due to the Chairman, Department of Zoology, University of Mysore, Mysore for the facilities and to the Zoological Survey of India for the identification of the specimens.

References

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