Meiotic Behavior of Chromosomes in Two Species of Coreinae (Coreidae: Heteroptera)

Harbhajan Kaur* and Nidhi Bansal

Department of Zoology and Environmental Sciences, Punjabi University, Patiala, 147 002, Punjab, India

Received April 6, 2012; accepted August 1, 2012

Summary Coreinae, the largest subfamily of Coreidae, is distributed worldwide but is most abun- dant in the tropics. Its 2 tribes, Homoeocerini and Petascelini, are speciﬁcally found in the Eastern Hemisphere. In 118 species of Coreinae cytogenetically analysed so far, male diploid number ranges from 15 to 29 and variations are reported in chiasma frequency, metaphase arrangement pattern and anaphasic movement of sex chromosomes during meiosis. In view of this, meiotic behavior of chromosomes in 2 North Indian species of Coreinae viz. Homoeocerus signatus Walker (Homoeocerini) and Petillopsis patulicollis (Walker) (Petascelini) has been described for the ﬁrst time and characteristic features are discussed in the present paper. The male diploid chromosome complement of H. signatus Walker is 2n=21=18A+2m+X0

while that of P. patulicollis (Walker) is 2n=28=24A+2m+X1X20. The general course of meiosis is fairly uniform and is typical for heteropteran types. During diplotene, a single chiasma per bivalent is observed in H. signatus Walker whereas 2 chiasmata are observed in 2 to 3 bivalents in P. patulicollis (Walker). In both the species, the arrangement of chromosomes at metaphase I is typical of coreid types. In P. patulicollis (Walker), however, a few metaphase I plates are observed with an al- ternate arrangement.

Key words Heteroptera, Coreinae, Chromosomes, Meiosis.

Coreidae, one of the major families of Heteroptera (Insecta:Hemiptera), includes 2,200 species belonging to 500 genera distributed worldwide (Dursun and Fent 2009). Members of this family are phytophagous feeding on legumes, cucurbit crops, nuts and soft fruits, and thus are called pod bugs or squash bugs. Coreidae is divided into 4 subfamilies: Coreinae, Pseudophloeinae, Meropachydinae and Agriopocorinae. Subfamily Coreinae, the largest of all, is distributed worldwide but most abundantly in the tropics. Its 2 tribes, Homoeocerini and Petascelini, are speciﬁcally found in the Eastern Hemisphere (Schuh and Slater 1995). Cytogenetically, Heteroptera is characterized by possession of holokinetic chromosomes. A diffuse stage with decondensed autosomes and condensed sex chromosomes and post-reductional division of sex chromosomes are characteristic features of meiosis. In Coreidae, besides heteropteran features, genetic complements show, with few exceptions, the presence of microchromosomes, the absence of Y chromosome and X chromosome multiplicity. So far, 118 species of Coreinae have been cytogenetically analysed. In them, male diploid number ranges from 15 to 29 with X0 as the dominant sex mechanism (Ueshima 1979, Papeschi and Bressa 2006, Kaur and Bansal 2012). Variations in chiasma frequency, chromosome arrangement on metaphase I and II plates and anaphasic movement (precocious or lagging) of sex chromosomes are reported in Coreinae. In view of this, meiotic behavior of chromosomes has been studied in 2 species of

* Corresponding author, e-mail: [email protected] DOI: 10.1508/cytologia.77.373 374 H. Kaur and N. Bansal Cytologia 77(3)

Coreinae viz. Homoeocerus signatus Walker (Homoeocerini) and Petillopsis patulicollis (Walker) (Petascelini), for the ﬁrst time, and is described in the present paper.

Materials and methods

Adult males of Homoeocerus signatus Walker and Petillopsis patulicollis (Walker) were col- lected from the Dehradun and Jammu regions of India. Testes were dissected out in 0.67% saline water and were fixed in freshly prepared Carnoy’s fixative (3 : 1, absolute alcohol : glacial acetic acid) for 15 min followed by a second change of the fixative. The fixed material was tapped on clean slides, air dried and stained with carbol-fuschin stain for 4 h followed by differentiation in N-butanol. The slides were allowed to dry and were finally mounted in DPX (Carr and Walker 1961).

Results

Homoeocerus signatus Walker Diploid chromosome number of male H. signatus Walker is 21 comprising 9 pairs of autosomes, 2 microchromosomes and an X chromosome. One pair of autosomes is distinctly large, 4 pairs are medium sized while 4 pairs are small sized. The X chromosome is equal to small the sized autosomes (Fig. 1A). During the diffuse stage, the darkly stained heteropycnotic X chromosome lies at the periphery of the decondensed autosomes (Fig. 1B). At diplotene, autosomes show single terminal, sub-terminal or interstitial chiasma per bivalent. The X chromosome appears distinctly bipartite and microchromosomes remain far apart from each other and remain so upto diakinesis (Fig. 1C, D). At metaphase I, all 9 autosomal bivalents are arranged in a ring, and microchromosomes come close to forming a pseudobivalent that lies in the centre of the ring with X lying outside the ring (Fig. 1E). During anaphase I, autosomes and microchromosomes divide equationally while the X-chromosome divides reductionally (Fig. 1F). At metaphase II, autosomes and microchromosome form a compact ring while the X lies away from the ring (Fig. 1G). During anaphase II, autosomes and microchromosomes divide equationally while the X chromosome divides reductionally and adds to one of the poles as a laggard (Fig. 1H). Two types of telophase II nuclei are formed, one with n=9A+m+X and the other with n=9A+m+0.

Petillopsis patulicollis (Walker) The male diploid chromosome number of P. patulicollis (Walker) is 28 which includes 24 autosomes, 2 microchromosomes and 2 unequal sex chromosomes, X1 and X2. Three autosomal pairs are distinctly smaller as compared to the rest of the 9 pairs which show slight gradation of size (Fig.

2A). The diffuse stage reveals darkly stained fused X1 and X2 lying on the periphery of decondensed autosomes (Fig. 2B). During diplotene, 2 to 3 bivalents show 2 chiasmata while the rest show a single chiasma per bivalent which may be terminal, sub-terminal or interstitial.

Microchromosomes lie far apart and X1 and X2 still appear fused (Fig. 2C). By diakinesis, microchromosomes come close and 2 unequal sex chromosomes become distinct (Fig. 2D). At metaphase I, 2 types of plates are observed. In one, all the autosomal bivalents form a ring and X1 and X2 lie outside the ring (90%) while in the other, 1 or 2 autosomal bivalents lie within the ring formed by the rest of the bivalents and X1 and X2 lie outside the ring (10%) (Fig. 2E, F). During anaphase I, microchromosomes and autosomal bivalents divide reductionally while X1 and X2 divide equationally so that each pole receives 12 autosomes, 1 microchromosome and 2 sex chromosomes, X1 and X2 (Fig. 2G). At metaphase II, 11 autosomes and microchromosome form a ring while 1 autosome lies within the ring and fused X1X2 lie outside the ring (Fig. 2H). During anaphase II, X1 and X2 are added to one of the poles. 2012 Meiosis in Coreinae 375

Fig. 1. Homoeocerus signatus Walker (2n=21=18A+2m+X0): (A) Spermatogonial metaphase with karyotype; (B) Diffuse stage showing darkly stained X chromosome and decondensed autosomes; (C, D) Diplotene showing autosomal bivalents with a single chiasma, distinctly bipartite X chromosome and far placed microchromosomes; (E) Metaphase I showing m-pseudobivalent in the centre and X outside the ring formed by autosomal bivalents; (F) Anaphase I showing equational division of X chromosome; (G) Metaphase II showing X lying away from the compact ring formed by autosomes and microchromosomes; (H) Anaphase II showing X as a laggard. Arrowheads represent X chromosome. Arrows represent microchromosomes. Bar=10 µm.

Discussion

The male diploid number of the subfamily Coreinae ranges from 15 to 29 with a mode of 21 which is present in 52 out of 118 species cytogenetically analyzed so far. The dominant sex mechanism is X0 reported in 82 species while X1X20 is represented in 29 species. A pair of microchromosomes is reported in 91 species (Ueshima 1979, Papeschi and Bressa 2006, Kaur and Bansal 2012). The diploid chromosome number of Homoeocerus signatus Walker (Homoeocerini) is 21 (Parshad 1957a). It possesses 18 autosomes, a pair of microchromosomes and a X0 sex mechanism. So far, 15 species of Homoeocerus have been cytogenetically investigated (including the present 1). 376 H. Kaur and N. Bansal Cytologia 77(3)

Fig. 2. Petillopsis patulicollis (Walker) (2n=28=24A+2m+X1X20): (A) Spermatogonial metaphase with karyotype; (B) Diffuse stage showing fused X1 and X2; (C) Diplotene showing 2 to 3 autosomal bivalents with 2 chiasmata and the rest with single chiasma; (D) Diakinesis showing microchromosomes lying close to each other and 2 distinct unequal sex chromosomes; (E) Metaphase I showing all the autosomal bivalents forming a ring; (F) Metaphase I showing 1 autosomal bivalent within the ring; (G) Anaphase I showing equational division of X chromosome; (H) Metaphase II showing

X1X2 lying away from autosomes. Arrowheads represent X1X2. Arrows represent microchromosomes. Bar=10 µm.

The diploid number varies from 18 to 22 with 21 as the most common number (10 species). Deviations are observed with respect to autosomes, microchromosomes as well as the sex mechanism. Out of 15 studied species, the complement is dominated by an autosome number of 18 (present in 13 species), the presence of microchromosomes (present in 12 species) and X0 sex mechanism (present in 11 species) (Table 1). So far, the chromosome number of 3 species of Petascelini have been given, speciﬁcally Petillopsis patulicollis (Walker), Petillopsis calcar (Dallas) and Trematocoris notatipes Walker (Manna 1951, Parshad 1957b, Dey and Wangdi 1988 respectively). All these species were studied 2012 Meiosis in Coreinae 377

Table 1. Chromosome complements of species of Homoeocerus and Petillopsis.

S. Chromosome Species 2n References No. complement

Homoeocerini 1. Homoeocerus signatus Walker 21 18A+2m+X0 Parshad (1957a) Present work 2. Homoeocerus prominulus (Dallas) 21 18A+2m+X0 Parshad (1957b) 3. Homoeocerus borealis Distant 21 18A+2m+X0 Parshad (1957b) 4. Homoeocerus indus Distant 21 18A+2m+X0 Parshad (1957b) 5. Homoeocerus simidus 21 18A+2m+X0 Parshad (1957a) 6. Homoeocerus lacertorsis Distant 21 18A+2m+X0 Parshad (1957b) 7. Homoeocerus sp. 21 18A+2m+X0 Parshad (1957b), Manna and Deb Mallick (1981) 8. Homoeocerus (Omanocoris) variabilis (Dallas) 21 18A+2m+X0 Dutt (1957) 9. Homoeocerus dilatus Horvath 21 18A+2m+X0 Toshioka (1934) 10. Homoeocerus dilatatus Horvath 21 18A+2m+X0 Takenouchi and Muramoto (1967)

11. Homoeocerus serrifer (Westwood) 18 16A+X1X20 Sands (1982) 12. Homoeocerus unipunctatus (Thunberg) 19 16A+2m+X0 Toshioka (1935)

13. Homoeocerus limbatipennis (Stal) 20 18A+X1X20 Sands (1982) 14. Homoeocerus angulatus Westwood 22 18A+2m+X1X20 Sands (1982) 15. Homoeocerus pallidulus Blote N.M. N.M. Muramoto (1978) Petascelini

1. Petillopsis patulicollis (Walker) (as Petillia 28 24A+2m+X1X20 Dey and Wangdi (1988) patulicollis Walker) Present work

2. Trematocoris notatipes Walker (as Petillia 28 24A+2m+X1X20 Manna (1951) notatipes Walker)

3. Petillopsis calcar (Dallas) (as Petillia calcar 28 24A+2m+X1X20 Parshad (1957b) Dallas)

under the genus Petillia and possess 28 chromosomes with 24 autosomes, a pair of microchromosomes and an X1X20 sex mechanism (Table 1). The meiotic behavior of chromosomes in Homoeocerus signatus Walker and Petillopsis patulicollis (Walker) has been described for the ﬁrst time in the present paper and characteristic features are discussed here. The diffuse stage has been a common meiotic feature in heteropteran species where autosomes are decondensed, sex chromosomes are condensed and cell size increases which is recorded in both P. patulicollis (Walker) and H. signatus Walker. Parshad (1957b) reported 2 chiasmata in 1 or 2 bivalents of the complement in 5 species of Homoeocerus. However, H. signatus Walker has been observed to differ in having a single chiasma per bivalent which is the pre- dominant trend in Coreidae (Sands 1982, Papeschi and Mola 1990, Cattani et al. 2004, Cattani and Papeschi 2004, Bressa et al. 2005, Franco et al. 2006). In P. patulicollis (Walker), 2 chiasmata are seen in 2 to 3 autosomal bivalents as is observed in its other species (Manna 1951, Parshad 1957b). In Coreidae, a regular arrangement of chromosomes is observed during metaphase I by which all the autosomal bivalents form a ring with an m-pseudobivalent lying inside and sex chromosomes lying outside the ring (Manna 1951, Dutt 1957, Parshad 1957b, Sands 1982, Papeschi et al. 2003, Cattani and Papeschi 2004, Cattani et al. 2004, Bressa et al. 2005, 2008, Franco et al. 2006, Souza et al. 2007, 2009). Similar arrangements are observed in H. signatus Walker and P. patulicollis (Walker). In P. patulicollis (Walker), occasionally (10%) 1 or 2 autosomal bivalents are seen lying inside the ring which is recorded in Trematocoris notatipes Walker also (Manna 1951). At metaphase II, in P. patullicolis (Walker), autosomes and microchromosomes form a ring while 1 autosome lies within the ring and sex chromosomes lie away from the ring. In H. signatus Walker, the arrangement pattern is same but the ring is compact. Parshad (1957b) and Sands (1982) failed to observe a deﬁnite pattern in other species of Homoeocerus and Petillopsis. In both the species, 378 H. Kaur and N. Bansal Cytologia 77(3) sex chromosomes act as laggards and are passively added to one of the poles during anaphase II, as observed in other coreids (Manna 1951, Dutt 1957, Parshad 1957b, Sands 1982, Papeschi and Mola 1990, Bressa et al. 2005, 2008, Kaur et al. 2006, Souza et al. 2009).

Acknowledgements

The authors are thankful to the Department of Zoology and Environmental Sciences, Punjabi University, Patiala, Punjab, India for providing laboratory facilities.

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