Meiotic Studies in Seven Heteropteran Species

© 2012 The Japan Mendel Society Cytologia 77(3): 311–322 Meiotic Studies in Seven Heteropteran Species Vikas Suman and Harbhajan Kaur Department of Zoology and Environmental Sciences, Punjabi University, Patiala-147 002, Punjab, India Received March 1, 2012; accepted May 22, 2012 Summary In the present study, 5 species of Lygaeidae and 1 each of Berytidae and Malcidae have been cytologically investigated for the first time; the diploid numbers in them vary from 12 to 20. Out of the 5 lygaeids, male diploid number is 12=8A+2m+XY in Dieuches leucoceras and Polycrates nexus while being 14=10A+2m+XY in Aphanus orientalis, Lanchnophorus sp. and Mizaldus sp. A pair of extremely large autosomes is found in both the species with 2n=12 while it may or may not present in species with 2n=14. One species each of Berytidae (Metacanthus pulchellus) and Malcidae (Malcus flavidipes) show 2n=20=18A+XY and 2n=16=12A+2m+XY respec- tively, and both lack an extremely large pair of autosomes. Microchromosomes are present in Lygaeidae (Rhyparochrominae) and Malcidae but absent in Berytidae. The sex determining mecha- nism in all the species of 3 families is XY/XX (♂/♀). Fragmentations seem to have played a piv- otal role in the origin of new species irrespective of family. Key words Lygaeidae, Berytidae, Malcidae, Chromosomes, Meiosis. In organisms with holocentric chromosomes, such as those of suborder Heteroptera, simple fusions and fragmentations readily lead to decreases and increases in chromosome number as the re- sulting chromosome elements retain the kinetic activity and thus can persist during dividing cycles (Heizer 1950, La Chance et al. 1970). Precisely for this reason, fragmentations and fusions have been considered to play the key role in evolution of heteropteran species (Ueshima and Ashlock 1980, Grozeva 1995). Members of Heteroptera are evolutionarily very successful because of their great array of feeding types and preferences which cover the entire range varying from phytophagous to zoopha- gous to hematophagous. Most of the heteropterans are herbivorous, piercing and sucking nutrients from plants, and thus are serious pests. Members of Lygaeidae (seed bugs) and Berytidae feed on reproductive parts such as flowers, ovules and seeds of a wide variety of plants while members of Malcidae are found on wild vines. Lygaeidae, a large and diverse family, is paraphyletic with some of its subfamilies taken as sister taxons to members of other Heteropteran families such as Berytidae, Colobathristidae and Malcidae (Southwood and Leston 1959, Stys 1967). Thus, the taxonomic characterization of this family is difficult and the complex relationship among its members is far from being established. Cytologically, Lygaeidae constitutes a heterogeneous group differing in chromosome number and types. The most common diploid chromosome number is 14 (Ueshima 1979, Ueshima and Ashlock 1980, Grozeva and Kuznetsova 1993, Souza et al. 2007, Kaur and Suman 2009). Berytidae is a small family comprising about 40 genera and more than 170 species grouped in 2 subfamilies, namely Metacanthinae and Berytinae. In this family, 2n=16 is the most common diploid chromosomal complement (Grozeva 1995). Malcidae consists of 2 subfamilies namely Malcinae and * Corresponding author, e-mail: [email protected] DOI: 10.1508/cytologia.77.311 312 V. Suman and H. Kaur Cytologia 77(3) Table 1. Chromosomal complements of 7 studied species. Species Location 2n EL Lygaeidae Dieuches leucoceras Walker Punjab 12 8A+2m+XY + Polycrates nexus Stal* Punjab 12 8A+2m+XY + Aphanus orientalis Distant Punjab 14 10A+2m+XY － Lachnophorus sp. Reuter Punjab 14 10A+2m+XY + Mizaldus sp. Distant* Punjab 14 10A+2m+XY － Berytidae Metacanthus pulchellus Stal Punjab, Himachal Pradesh 20 18A+XY － Malcidae Malcus flavidipes Stal* Punjab, Himachal Pradesh 16 12A+2m+XY － * First ever cytological report of the genus. EL=extremely large chromosome pair. Chauliopinae, with modal number still not distinctly known. In the present study, 5 species of Lygaeidae (Rhyparochrominae) and 1 species each of Berytidae (Metacanthinae) and Malcidae (Malcinae) from India have been cytologically investigated for the first time to describe their chromosomal complements and course of meiosis. Materials and methods Adult male specimens of Dieuches leucoceras, Polycrates nexus, Aphanus orientalis, Lachnophorus sp., Mizaldus sp. (Lygaeidae), Metacanthus pulchellus (Berytidae) and Malcus fal- vidipes (Malcidae) were collected from different regions of Punjab and Himachal Pradesh, India (Table 1). Testes were dissected out in 0.67% saline water and were fixed in freshly prepared Carnoyʼs fixative (3:1, absolute alcohol: glacial acetic acid) for 15 min followed by a second change of fresh Carnoyʼs fixative. The fixed material was tapped on clean slides and air dried slides were 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. Results Dieuches leucoceras Walker The spermatogonial metaphase plate reveals 2n=12=8A+2m+XY (Fig. 1) One of the autosomal pairs is distinctly larger in size while the rest are almost identical in size. X is larger than Y. Microchromosomes are the smallest and lightest elements of the complement. The diffuse stage shows 2 heteropycnotic bipartite bodies, representing X and Y lying well apart against diffuse chromatin (Fig. 2). At early diplotene, 4 autosomal bivalents, 2 darkly stained unequal sex chromosomes, X and Y and 2 faintly stained m-chromosomes are observed. During late diplotene, autosomal bivalents show single terminal or sub-terminal chiasma. Micro- chromosomes come close to forming a bivalent (Figs. 3 and 4). At metaphase-I, autosomal bivalents along with sex chromosomes and m-chromosomes roughly form a circle (Fig. 5). During anaphase-I, m-bivalent and autosomal bivalents divide reductionally while sex chromosomes X and Y 2012 Meiosis in Heteropteran Species 313 Figs. 1–8. Dieuches leucoceras. (1) Spermatogonial plate along with karyotype, (2) diffuse stage, (3 and 4) diplotene, (5) Metaphase-I, (6) Anaphase-I, (7) Metaphase-II, (8) Telophase-II. Bar: 0.01 mm. divide equationally so that each pole receives 4 autosomes, 1 m-chromosome and 2 sex chromosomes, X and Y (Fig. 6). At metaphase-II, autosomes roughly form a circle while X and Y come close to forming a pseudobivalent that, along with the m-chromosome, lies inside the circle (Fig. 7). Metaphase-II is reductional for sex chromosomes and equational for autosomes and m-chromosome as a result of which, 2 types of telophase nuclei are formed, one with 4A+m+X and the other with 4A+m+Y (Fig. 8). Polycrates nexus Stal It is the first species of the genus to be examined kayrologically. The diploid chromosomal complement is 2n=12=8A+2m+XY (Fig. 9). One of the autosomal pairs is distinctly larger while the rest of the 3 autosomal pairs are almost identical in size. Sex chromosomes are smaller than autosomes, X being larger than Y. Microchromosomes are the smallest elements. At the diffuse stage, 2 elongated bipartite heteropycnotic bodies representing X and Y are observed (Fig. 10). At diplotene, single terminal/sub-terminal chiasma are seen in 3 of the autosomal 314 V. Suman and H. Kaur Cytologia 77(3) Figs. 9–14. Polycrates nexus. (9) Spermatogonial plate along with karyotype, (10) Diffuse stage, (11) diplotene, (12) Metaphase-I, (13) Anaphase-I, (14) Metaphase-II. Bar: 0.01 mm. bivalents while 1 bivalent shows 2 terminal chiasmata. Autosomes are isopycnotic with X chromosome while Y is negatively heteropycnotic (Fig. 11). The metaphase-I plate shows one of the autosomal bivalents lying in the centre of the ring formed by rest of the chromosomes (Fig. 12). During anaphase-I, sex chromosomes divide equationally while autosomes and m-chromosomes divide reductionally so that each pole receives 4 autosomes, 2 sex chromosomes, X and Y and 1 m-chromosome (Fig. 13). The metaphase-II plate shows 4 autosomes, XY pseudobivalent and faint m-chromosome (Fig. 14). Aphanus orientalis Distant The chromosomal complement is 2n=14=10+2m+XY. At the diffuse stage, 2 unequal elements representing X and Y associated with the nucleolar cloud are seen (Fig. 15). At the diplotene stage, 4 autosomal bivalents show single terminal/ sub-terminal chiasma each while 1 bivalent shows 2 terminal chiasmata (Figs. 16 and 17). At metaphase-I, autosomal bivalents roughly form a ring while the m-bivalent (very faint) and sex chromosomes arrange themselves in the centre (Fig. 18). At metaphase-II, X and Y come close to forming a pseudobivalent (Fig. 19). At telophase-II, 2 types of nuclei are formed, 1 with n=5A+m+X and the other with n=5A+m+Y (Fig. 20). Lachnophorus sp. Reuter The chromosomal complement is 2n=10A+2m+XY (Fig. 21). One pair of autosomes is distinctly larger in size while remaining 4 pairs show gradation in size. X is bigger than Y. Microchromosomes are the smallest elements in the complement. At the diffuse stage, unequal X and Y appear as well separated bipartite heteropycnotic bodies 2012 Meiosis in Heteropteran Species 315 Figs. 15–20. Aphanus orientalis. (15) Diffuse stage, (16 and 17) diplotene stages, (18) Metaphase-I, (19) Mataphase-II, (20) Telophase-II (arrowheads show m-chromosomes). Bar: 0.01 mm. (Fig. 22). At diplotene, all the autosomal bivalents show single terminal or sub-terminal chiasma each. Sex chromosomes lie well separated and 2 very faintly stained m-chromosomes lie close to each other (Fig. 23). At metaphase-I, autosomal bivalents roughly form a ring and X and Y along with the m-bivalent, lie in the centre of the ring (Fig. 24). During anaphase-I, autosomes along with m-chromosomes divide reductionally while sex chromosomes X and Y divide equationally (Fig.

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