© Comparative Cytogenetics, 2009 . Vol. 3, No. 2, P. 125-130. ISSN 1993-0771 (Print), ISSN 1993-078X (Online) Chiasmate male meiosis in six species of water bugs from infraorders Nepomorpha and Gerromorpha (Insecta: Heteroptera) S. Grozeva1, S. Nokkala2, N. Simov3 1Institute of Zoology, BAS, Sofi a, Bulgaria, 2Laboratory of Genetics, Department of Biology, University of Turku, Finland, 3National Museum of Natural History, BAS, Sofi a, Bulgaria. E-mails: [email protected], 2sepnok@utu.fi , [email protected] Abstract. The type of male meiosis is a stable character at the family level in the order Heteroptera and provides additional information on the relationships between taxa. The most common pattern, probably ancestral in the order is chiasmate mei- osis; however achiasmate meiosis has been described in fi ve families of terrestrial Heteroptera, all belonging to the infraorder Cimicomorpha (Anthocoridae, Micro- physidae, Cimicidae, Miridae, Nabidae). Among water bugs, achiasmate meiosis is reported in the families Saldidae (Leptopodomorpha) and Мicronectidae (Nepomor- pha). Regarding the third infraorder of water bugs, Gerromorpha, data on meiotic patterns are absent, except for the Limnogonus aduncus Drake, Harris, 1933 (Ger- ridae) possessing chiasmate meiosis. In this paper, the male meiotic pattern of six water bugs species from infraorders Nepomorpha (Plea minutissima minnutissima Leach, 1817) and Gerromorpha (Mesovelia furcata Mulsant, Ray, 1852, Microv- elia reticulata (Burmeister, 1835), Gerris costae fi eberi Stichel, 1938, Hydrometra gracilenta Horváth, 1899, Velia pelagonensis Hoberlandt, 1941) is studied, and the karyotypes of the last two species are described for the fi rst time. In the species exam- ined, bivalents are chiasmate, so all these species possess chiasmate meiosis in males. Key words: water Heteroptera, holokinetic chromosomes, chiasmate/achiasmate male meiosis. INTRODUCTION trial Heteroptera, belonging to the infraorder One of the unique cytogenetic characters Cimicomorpha (Anthocoridae, Microphysi- of the true bugs (the order Heteroptera) along dae, Cimicidae, Miridae, Nabidae) (Nokkala, with the holokinetic chromosomes is the type Nokkala, 1984, 1986a, b; Nokkala, Grozeva, of male meiosis, which is chiasmate in some 2000; Grozeva, Nokkala, 2002; Kuznetsova et while achiasmate in other groups. The meiotic al., 2007). Several hundred species studied in pattern is stable at the family level and provides other terrestrial infraorders, Dipsocoromorpha additional information on the relationships be- and Pentatomomorpha, have been shown to tween higher taxa. The most common pattern, possess chiasmate meiosis in males (Ueshima, probably ancestral for the Heteroptera, is the 1979; Grozeva, Nokkala 1996). Among the chiasmate type. However, achiasmate meio- water (heteropteran) bugs achiasmate meiosis sis has been found in fi ve families of terres- has been (earlier) described in the infraorder http://pensoftonline.net/compcytogen Comparative Cytogenetics doi: 10.3897/compcytogen.v3i2.19 126 S. Grozeva et al. Figs 1-15. Male meiotic karyotypes of fi ve species of Heteroptera. 1-3. Plea minutissima minutissima, 2n=20+2m+X. 1, a, b - prometaphase, the largest bivalent with two (a) or one (b) chiasmata. 2 - metaphase I. 3 - metaphase II. 4-5 - Mesovelia furcata, 2n=30+X1X2X3X4Y. 4 - diakinensis. 5 - metaphase I. 6-7 - Hydrometra gracilenta, 2n=18+X. 6 – spermatogonial metaphase. 7 – metaphase I. 8-9. Microvelia reticulata, 2n= 20+X. 8 - metaphase I. 9 - metaphase II. 10-12 - Velia (Plesiovelia) pelagonensis, 2n=24+X. 10 - prometaphase I. 11 - metaphase I. 12 - telophase II. 13-15 - Gerris costae fi eberi, 2n=20+X. 13 - diakinesis. 14 - metaphase I. 15 - metaphase II. Bar = 10 μm. Comparative Cytogenetics Comp. Cytogenet., 2009 3(2) Chiasmate male meiosis in the water Heteroptera 127 Table. Material used for chromosome analysis. Number of Family/Species Place and date of collection specimens studied Pleidae Bulgaria, Schkorpilovtsi, Fandaklijska 1. Plea minutissima minutissima Leach, river, 6.07.2008 1W 1817, 2n=20+2m+X0 Mesoveliidae Bulgaria, Schkorpilovtsi, Fandaklijska 2. Mesovelia furcata Mulsant et Ray, 1852 river, 6.07.2008 14W Hydrometridae 3. Finland, vicinity of Turku, July 2008 Hydrometra gracilenta Horváth, 1899 5W Veliidae (Microveliinae) 4. Finland, vicinity of Turku, July 2008 Microvelia reticulata (Burmeister, 1835) 18W, 4 larvae Veliidae (Veliinae) Bulgaria, Slavianka Mt., Petrovska river, 5. Velia (Plesiovelia) pelagonensis 550m, 2.07.2008 11W Hoberlandt, 1941 Bulgaria, Osogovo Mt., Gerridae 6. in a pool under Ruen peak, 1600m, Gerris costae fieberi Stichel, 1938 3W 22.06.2008 Leptopodomorpha (Saldidae) (Nokkala, Nok- study are presented in the Table. The insects kala, 1983), and recently it has also been re- were fi xed alive in 3:1 fi xative (96% ethanol ported in the infraorder Nepomorpha in the - glacial acetic acid mixture). The abdomen family Micronectidae (Ituarte, Papeschi, 2004; was dissected in 45% acetic acid and the inter- Grozeva et al., 2008). In the infraorder Gerro- nal reproductive system was analyzed under a morpha there are no observations available on stereomicroscope. The gonads were squashed species with achiasmate meiosis. in a small drop of 45% acetic acid. The cover In this paper, the male meiotic pattern of slips were removed by a dry ice technique. six water bug species from the infraorders Slides were dehydrated in fresh fi xative (3:1) Nepomorpha (Plea minutissima minnutissima and air dried. To study the number and the Leach, 1817) and Gerromorpha (Mesovelia behavior of the chromosomes the prepara- furcata Mulsant, Ray, 1852, Microvelia re- tions were stained by Schiff-Giemsa method ticulata (Burmeister, 1835), Gerris costae after Grozeva, Nokkala (1996). Chromosome fi eberi Stichel, 1938, Hydrometra gracilenta spreads were analyzed using a Laborlux 12 Horváth, 1899, Velia pelagonensis Hober- (Leitz, Wetzlar, Germany) and Olympus BХ landt, 1941) is studied, and the karyotypes of 51 microscopes and documented by digital the last two species are described for the fi rst photo camera Moticam 2000. The preparations time. Bivalents in spermatogenesis of all spe- are preserved in the collection of the Labora- cies examined are chiasmate. tory “Cytotaxonomy and evolution”, Institute of Zoology BAS, Sofi a. MATERIAL AND METHODS The data on the insects used in the present Comparative Comp. Cytogenet., 2009 3(2) Cytogenetics 128 S. Grozeva et al. RESULTS The karyotype of this species is described Nepomorpha for the fi rst time. In Fig. 6, a spermatogoni- al metaphase displays 18 autosomes and the Pleidae very large X chromosome, which is the largest Plea minutissima minutissima Leach, chromosome of the set. The autosomes gradu- 1817, 2n=20+2m+X. ally decrease in size. In МІ, there are 9 biva- In the present study, the chromosome for- lents with terminal chiasmata and a univalent mula reported earlier for this species by Jande X chromosome (Fig. 7). The chromatids of the (1959, 1961) was confi rmed. At prometaphase X lie in parallel to the equator and are oriented plates (PMI), most bivalents display one ter- to different poles minal chiasma, while the largest bivalent more often has two terminal chiasmata resulting in Veliidae a ring (Fig. 1, a), or one subterminal chiasma Microvelia reticulata (Burmeister, 1835), (Fig. 1, b). Аt metaphase I (MI), 10 autoso- 2n=20+X. mal bivalents gradually decreasing in size, a Cobben (1968) interpreted the karyotype pair of comparatively large m-chromosomes of M. reticulata as 21 (XO). In the present and the univalent X chromosome as large as study we confi rmed this chromosome formu- the largest autosome can be seen (Fig. 2). The la, as both MI and MII (Figs 8 and 9) show fi rst division is reductional for the autosomes, 11 chromosome elements. It is not possible to whereas the sex chromosome undergoes equa- identify the X chromosome reliably. At МІ, all tional separation (post-reduction). As a result, bivalents displayed terminal chiasmata (Fig. at metaphase II (MII) daughter cells each con- 8). tain 12 elements (10 autosomes, m-chromosome Velia (Plesiovelia) pelagonensis Hober- and the daughter X chromosome) (Fig. 3). landt, 1941, 2n=24+X. The karyotype of this species is studied for Gerromorpha the fi rst time. Fig. 10 shows prometaphase І with 12 bivalents, every bivalent possessing a Mesoveliidae terminal or subterminal chiasma. At MI (Fig. Mesovelia furcata Mulsant, Ray, 1852, 11), the autosomal bivalents gradually de- 2n=30+X X X X Y. 1 2 3 4 crease in size, and the Х chromosome is one In this species, the testes were examined. of the smallest in the set. The fi rst division, re- Every testis consists of one elliptic orange fol- ductional for the autosomes but equational for licle. Our study confi rmed the chromosome the X chromosome, results in two kinds of TII formula of this species published by Ekbolm cells: one with 12 autosomes and the daughter (1941). At diakinensis, 15 bivalents each with X, and the other with 12 autosomes only (Fig. one terminal or subterminal chiasma and fi ve 12). univalent sex chromosomes can be seen (Fig. 4). At МІ, four Х and one Y sex chromosomes Gerridae are placed inside the circle formed by the au- Gerris costae fi eberi Stichel, 1938, tosomal bivalents (Fig. 5). 2n=20+X. Our observations confi rm the chromo- Hydrometridae some formula 2n=20+X earlier reported for Hydrometra gracilenta Horváth, 1899, this species by Sоuthwood and Leston (1959). 2n=18+X. At diakinesis (Fig. 13), autosomal bivalents Comparative