Cytomorbhological Studies on Gynacantha Milliardi Fraser of the Family Aeschnidae (Anisoptera: Odonata)

Cytomorbhological Studies on Gynacantha milliardi Fraser of the family Aeschnidae (Anisoptera: Odonata)

Gurinder Kaur Walia*

Department of Zoology, Punjabi University, Patiala–147 002 (Punjab), India

Received November 13, 2006; accepted November 28, 2006

Summary Male germ cell complement of Gynacantha milliardi belonging to family Aeschnidae has been investigated. Specimens were collected from Karnataka (Mangalore) state of South India. Chromosome analysis shows 2 types of spermatogenetic cycles viz., 2n?27m; n?14m and 2n?25; n?13 with XO sex determining mechanism. Karyotypic evolution of m chromosomes has been observed in the species. Meiotic behaviour of autosomes and sex chromosome has also been studied. Gynacantha milliardi is described for the ﬁrst time in odonate cytotaxonomy.

Key words Gynacantha milliardi, Aeschnidae, Odonata, Chromosome number, m chromosomes.

The family Aeschnidae of odonates includes large and robust forms having wide distribution. They are also known as darners. Most of the cytogenetic data pertains to 2 genera namely, Anax and Aeschna because species of these genera are cosmopolitan and few reports are available on Acanthaeschna, Anaciaeschna, Basiaeschna, Boyeria, Castroaeschna, Cephalaeschna, Coryphaeschna, Gynacantha, Hemianax, Oplonaeschna and Planaeschna genera (Lefevre and McGill 1908, Makalovskaja 1940, Oksala 1943, 1944, Omura 1957, Seshachar and Bagga 1962, Cumming 1964, Cruden 1968, Kiauta 1968f, 1969a, 1970c, Hung 1971, Kiauta 1972, 1975, 1979, Ferriera et al. 1979, Tyagi 1978a,b, 1982, Tyagi and Sangal 1982, Thomas and Prasad 1986, Mola and Papeschi 1994, Sandhu and Malhotra 1994, Mola 1995, Walia and Sandhu 1999). So far, 86 species of Gynacantha genus are known taxonomically, while only 3 species are reported cytologi- cally. These are Gynacantha japonica, n?14m (Omura 1957, Kiauta 1972), Gynacantha interioris, 2n?26, n?13m, neo-XY (Ferriera et al. 1979) and Gynacantha hyalina, n/14m, XO and n/14, 13, 12, 11, 10 etc. (Tyagi 1978a,b, 1982, 1986). All the species of Gynacantha genus possess variation in chromosome numbers because during the course of karyotypic evolution in the family, chromosome number varies from 2n14 to 27. Reduction in chromosome number is due to the fusion of autosomes with autosomes or autosomes with sex chromosome. Present study on Gy- nacantha milliardi also shows variable chromosome numbers that is, 2n?27m; n?14m and 2n?25; n?13 with XO sex determination.

Material and methods Male individuals were collected from the Mangalore city present at Karnataka state of South India during the pre-monsoon season. Gynacantha milliardi is very beautiful, large in size having bluish green head and thorax with long black abdomen. This dragonfly is mostly flying or reposing under shady areas. Specimens were dissected in the saline water and testes were fixed in Carnoy’s fixative (3 absolute alcohol: 1 glacial acetic acid). Chromosomal preparations were made in the field by air-drying method (Sandhu and Walia 1995). Relative meiotic stages were micro pho-

* Corresponding author, e-mail: [email protected] 58 G. K. Walia Cytologia 72(1) tographed for further karyological investigations. Meiotic behaviour of X and m chromosome has also been studied.

Results Two types of spermatogonial prometaphase plates were observed. One plate shows 27 elements; out of these 26 are autosomes and 1 sex chromosome. Autosomes also include a strickingly small pair of m chromosomes (Fig. 1). Other plate possesses 25 elements, which include 24 autosomes (without m chromosomes) and 1 X chromosome (Fig. 20). In both the plates X chromosome is univalent and smallest in the whole complement, which depicts XO type sex determination. At pachytene, the X chromosome is positively heteropycnotic and present in the network of chromatin material (Fig. 2). In the diplotene, autosomal bivalents show cross or ‘V’ shape structures because of the chiasma formation (Fig. 3). During diakinesis 2 types of plates are present, one plate shows 14 elements, out of these 13 are autosomal bivalents and one X univalent. Autosomal bivalents also have thin, long and negatively heteropycnotic m bivalent (Figs. 4–6). It is small and lightly stained in some plates (Figs. 9–11), while thin and very dim just like impression in others (Figs. 14–16). Second type of plate possesses 13 elements, which include 12 autosomal bivalents and 1 X univalent. m bivalent is absent (Figs. 21–23). All the bivalents have only 1 chiasma at medial or terminal position. At metaphase-I, 2 plates having n14m and n13 are present. All the bivalents including m bivalent are rod shaped having constriction in the center, which give dumbbell shape appearance. m bivalent shows variation in size and shape. It is thin, long and dumbbell shape (Figs. 7, 8); small and lightly stained (Figs. 12, 13), very dim just like impression (Figs. 17–19) and absent (Fig. 24). X is oval shaped and mostly occupies peripheral position on the plate.

Discussion Cytological data available to the family Aeschnidae shows chromosome number 2n27 (26XO) as the modal number. Most of the species belonging to genera Anax and Aeschna and few species of Acanthaeschna, Anaciaeschna, Basiaeschna, Boyeria, Castroaeschna, Cephalaeschna, Coryphaeschna, Gynacantha, Hemianax, Oplonaeschna and Planaeschna possess this number (Lefevre and McGill 1908, Makalovskaja 1940, Oksala 1943, 1944, Omura 1957, Cumming 1964, Cruden 1968, Kiauta 1968f, 1970c, Hung 1971, Kiauta 1972, 1975, 1979, Tyagi 1982, Tyagi and Sangal 1982, Thomas and Prasad 1986, Mola and Papeschi 1994, Mola 1995, Walia and Sandhu 1999). During the course of karyotypic evolution in the family, chromosome number varies from 2n14 to 27 and sex determination from XO to neo-XY (Cumming 1964, Seshachar and Bagga 1962, Kiauta 1967e, 1971b, 1975, Ferriera et al. 1979, Tyagi 1978a,b, Kiauta and Kiauta 1982, Tyagi 1982, 1986, Mola and Papeschi 1994, Sandhu and Malhotra 1994, Mola 1995, Walia and Sandhu 1999). Reduction in chromosome number is due to the chromosome fusions rather than chromosome ﬁssions and neo-XY sex determining mechanism is also originated by fusion of autosomes with sex chromosome. Taxonomically, Gynacantha genus includes 86 species, while cytoge- netical data is available only on 3 species viz., Gynacantha japonica, n?14m (Omura 1957, Kiau- ta 1972), Gynacantha interioris, 2n?26, n?13m, neo-XY (Ferriera et al. 1979) and Gynacan- tha hyalina, n/14m, XO and n/14, 13, 12, 11, 10 etc. (Tyagi 1978a,b, 1982, 1986). All the species of the Gynacantha genus possess unstable karyotype and chromosome number varies from n14m to 10. Reduction in number is due to the karyotypic evolution in the family by fusion of autosomes with autosomes or autosomes with sex chromosome. Chromosome analysis of Gynacantha milliardi has been studied for the ﬁrst time during present investigation. It also shows variable chromosome numbers that is, 2n?27m; n?14m and 2n?25; n?13 with XO sex determination. Variation in chromosome number is due to the presence or absence of m chromosomes observed 2007 Cytomorphological studies on Gynacantha milliardi Fraser 59

Figs. 1–12. Fig. 1: Spermatogonial metaphase (2n27m). Fig. 2: Pachytene. Fig. 3: Diplotene. m bivalent is thin, long and negatively heteropycnotic; Figs. 4–6: Diakinesis. Figs. 7, 8: Metaphase-I. m bivalent is small and lightly stained; Figs. 9–11: Diakinesis. Fig. 12: Metaphase-I. (10X100X). 60 G. K. Walia Cytologia 72(1)

Figs. 13–24. Fig. 13: Metaphase-I. m bivalent is thin and very dim just like impression;. Figs. 14–16: Di- akinesis. Figs. 17–19: Metaphase-I. m bivalent is absent; Fig. 20: Spermatogonial metaphase (2n25). Figs. 21–23. Diakinesis. Fig. 24: Metaphase-I. (10X100X). 2007 Cytomorphological studies on Gynacantha milliardi Fraser 61 during diakinesis and metaphase-I. m bivalent is thin, long and negatively heteropycnotic in 25% plates, dot like and lightly stained in 10% plates, thin and very dim just like impression in 40% plates and absent in 25% plates. These observations show m chromosomes are in process of karyotypic evolution in the species because they are present in some cells and absent in other cells of the same individual. In family Aeschnidae most of the species possess variable chromosome numbers because chromosome fusions frequently occurred for the adaptation of the species to the changed environmental conditions.

Acknowledgement The author is thankful to DST New Delhi for ﬁnancial assistance and Dr. A. R. Lahiri, Z. S. I. Kolkata for identiﬁcation of specimens.

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