© 2011 The Japan Mendel Society Cytologia 76(2): 119–123, 2011
Karyotypes of 2 Species, Meretrix lusoria and M. petechialis, of Veneridae in Korea
Gab-Man Park1*, Yong-Min Kim2 and Ee-Yung Chung3
1 Department of Environmental Medical Biology, Kwandong University College of Medicine, Gangneung 210–701, Korea 2 Korea National Parks Service, Park Conservation Team, #129 Mapo-ro (Gongdeok-dong), Mapo-gu, Seoul 121–717, Korea 3 Korea Marine Environment & Ecosystem Research Institute, Dive Korea, Bucheon 420–857, Korea
Received September 1, 2010; accepted February 23, 2011
Summary The karyotypes of Meretrix lusoria and M. petechialis in the family Veneridae in Korea were studied in order to analyse their genetic relationships. The 2 species showed a diploid chromosome number of 2n 38, with 5 metacentric, 10 submetacentric, 2 subtelocentric, and 2 telocentric chromosome pairs for Meretrix lusoria, and 5 metacentric, 9 submetacentric, 3 subtelocentric, and 2 telocentric for M. petechialis. The karyotypes of these 2 species are clearly different in the same genus.
Key words Karyotype, Veneridae, Meretrix lusoria, Meretrix petechialis, Korea.
Meretrix species (Bivalvia: Veneridae), an important economic species, is naturally distributed along the costal waters of China, Japan and Korea. To date, only 3 species of Meretrix, M. lisoria, M. petechialis and M. lamarkii, have been reported in Korea (Kwon et al. 1993). The genus Meretrix has a wide distribution on the south and west coasts of Korea and also reveals closely similar species from taxonomic point of view. In particular, M. lusoria and M. petechialis have various morphological patterns within the same species. Additionally, high variations in shell morphology at the same place in the intertidal and subtidal zones on the west coast of Korea have been found. Meretrex lusoria is without V-character (v-spot or pattern) on the shell and showing the ventral region of the shell is somewhat straight line. While, M. petechialis is containing a number of V spots (v-characters) on the shell, and the ventral region of the shell is somewhat slightly round as well as a regular triangle in shape on the whole. However, commonly we have understood that M. lusoria and M. petechialis are the same species because of external morphological characters showing a very similar pattern. For that reason, it is important to study some differences of cytogenetic characteristics of inter-species. To date, there have been many previous studies on the morphology (Kwon et al. 1993, Park et al. 2002), reproduction (Chung et al. 2005, Chung 2006, 2007, Kim 2006), genetic relationships (Jung et al. 2004), ecology (Ryu et al. 2006), and the second intermediate host of Himasthla kusasigi (Kim and Chun 1984). In recent years, through a considerable number of works, a large amount of information has been accumulated on the chromosomes of the mollusks. Cytogenetic studies of mollusks have been important in aspects of phylogenetics and cytogenetic relationships among the species (Patterson 1969, Nakamura 1986, Borsa and Thiriot-Quiévreux 1990). Little information is available on karyotypes of the genus Meretrix. Therefore, it is important to clarify cytogenetic information of 2 Meretrix spp. The purpose of the present study is to determine and analyze the karyotypes of M.
* Corresponding author, e-mail: [email protected] 120 G.-M. Park et al. Cytologia 76(2) lusoria and M. petechialis for the future comparative study of bivalvia karyology.
Materials and methods The specimens of 2 species used in this study were collected in Simpo, Kimje-gun, Jollabuk- do and Hadong, Gyeongsangnam-do, Korea, from April 2008 to March 2009, and examined shortly after collection (Fig. 1). Sixteen specimens of Meretrix lusoria were collected in the brackish water of Sumjin River, Hadong-gun, Gyeongsangnam-do, and 20 specimens of Meretrix petechialis Lamarck (1818) in Simpo, Jeollabuk-do, Korea (Fig. 2). The chromosome preparations were made on gonad of the specimens by the usual air-dry method (Park et al. 1996). The prepared slides were observed under an Olympus BX-51 microscope. Nomenclature of chromosome morphological types follows Levan et al. (1964). To estimate the NF (Nombre Fondamental or Fundamental Number) value, metacentric and submetacentric chromosomes were scored as bi-armed and the chromosomes of acrocentric as uni-armed. Voucher specimens of the 2 species used in this investigation have been placed in the Department of Environmental Medical Biology, Kwandong University College of Medicine, Korea.
Fig. 1. Map showing the sampling area in the brackish water of of Sumjin River, Hadong-gun, Gyeongsangnam-do and in the coastal waters of the Simpo, Kimje-gun, Jeollabuk-do, Korea
Fig. 3. Metaphase chromosomes of Meretrix lusoria (A) Fig. 2. Morphology of Meretrix lusoria (A) and and karyotype constructed from A (B). Scale bar Meretrix petechialis (B). indicates 6 mm. 2011 Karyotypes of 2 Species of Veneridae in Korea 121
Table 1. Relative lengths and total lengths (mm) of chromosomes of Meretrix lusoria and Meretrix petechialis
Meretrix lusoria Meretrix petechialis
Chromosome RL SE TL SE Type Chromosome RL SE TL SE Type
1 5.88 0.41 5.55 0.20 M 1 5.89 0.14 5.35 0.21 M 2 5.74 0.20 5.42 0.21 M 2 5.63 0.21 5.12 0.12 M 3 5.67 0.14 5.35 0.33 M 3 5.45 0.10 4.95 0.34 M 4 5.56 0.16 5.25 0.20 M 4 5.34 0.06 4.85 0.25 M 5 4.71 0.13 4.45 0.13 M 5 4.51 0.16 4.10 0.16 M 6 5.77 0.13 5.45 0.21 SM 6 6.11 0.23 5.55 0.22 SM 7 5.67 0.23 5.35 0.33 SM 7 5.89 0.20 5.35 0.31 SM 8 5.45 0.16 5.15 0.12 SM 8 5.61 0.16 5.10 0.12 SM 9 5.4.5 0.32 5.15 0.12 SM 9 5.56 0.34 5.05 0.10 SM 10 5.36 0.31 5.06 0.11 SM 10 5.38 0.31 4.89 0.11 SM 11 5.30 0.12 5.00 0.22 SM 11 5.17 0.22 4.70 0.23 SM 12 5.03 0.25 4.75 0.31 SM 12 4.90 0.45 4.45 0.34 SM 13 4.98 0.13 4.70 0.32 SM 13 4.73 0.35 4.30 0.32 SM 14 4.92 0.31 4.65 0.26 SM 14 4.51 0.41 4.10 0.46 SM 15 4.34 0.15 4.10 0.11 SM 15 5.50 0.10 5.00 0.31 ST 16 5.66 0.09 5.34 0.14 ST 16 5.32 0.07 4.84 0.11 ST 17 5.56 0.06 5.25 0.40 ST 17 4.43 0.06 4.03 0.20 ST 18 4.61 0.12 4.35 0.12 T 18 5.30 0.12 4.82 0.11 T 19 4.34 0.11 4.10 0.34 T 19 4.79 0.11 4.35 0.34 T
* Based on measurements from 6 sets from M. lusoria and M. petechialis of karyotyped cells. M, metacentric; RL, relative length; SE, standard error; SM, submetacentric; ST, subtelocentric; T, telocentric; TL, total length
Results Meretrix lusoria The diploid chromosome number of this species was 38 (NF 34) and consisted of 19 pairs of chromosomes (Fig. 3). Table 1 shows the mean lengths and relative lengths of each chromosome as examined in 6 set cells. Observed chromosomes ranged from 4.10 to 5.55 mm. The mean total chromosome length based on the measurements of 3 cells was 94.42 3.21 mm. Figure 3B is the karyotype constructed from the chromosomes shown in Fig. 3A, which was one of the most elongated complements. The chromosomes were arranged by size. The karyotype consisted of 5 pairs of metacentric, 10 pairs of submetacentric, 2 pairs of subtelocentric, and 2 pairs of telocentric chromosomes.
Meretrix petechialis This species had 38 (NF 34) diploid chromosomes consisting of 19 pairs of chromosomes (Fig. 4). Observed chromosomes ranged from 4.03 to 5.55 mm (Table 1). The mean total chromosome length based on the measurements of 3 cells was 90.9 2.11 mm. Figure 4B is the karyotype constructed from the chromosomes shown in Fig. 4A, which was one of the most elongated complements. The karyotype consisted of 5 pairs of metacentric, 9 pairs of submetacentric, 3 pairs of subtelocentric, and 2 pairs of telocentric chromosomes.
Discussion The venerid clams are commercially important because all of them belonging to this family are edible. Additionally, high variations in morphology have been found to exist in wild population. 122 G.-M. Park et al. Cytologia 76(2)
In the venerid, the chromosomes and karyotypes have been reported that 18 species in 13 genera have ranging from n 14 to n 19 (Park et al. 1996). Tapes philippinarum have the chromosome number n 14 (Nishigawa and Hisatomi 1959), Venus gallina n 15 (Rosotto et al. 1981), and all other species have n 19. Also, in this study, Meretrix lusoria and M. petechialis have n 19. Although having the same diploid numbers, the karyotype formulae and their sizes differ a little in the 2 species. The morphology of mitotic chromosomes has long been recognized to be species-specific and useful as a taxonomic character in many animals. The present species is first reported in Korea. The karyotypes of these 2 species are different from other species in Veneridae. The karyotypes in 5 species (Circe scripta, Paphia vernicosa, Irus mitis, Venerupis aurea, Ruditapes philippinarum) of Veneridae investigated and all species has characteristically metacentric and submetacentric chromosomes (Ieyama 1980, Corni and Trentini 1990). However, M. lusoria and M. petechialis have different karyotypes. Meretrix lusoria has metacentric, Fig. 4. Metaphase chromosomes of Meretrix petechialis (A) and karyotype constructed from A (B). Scale submetacentric, subtelocentric, and telocentric bar indicates 6 mm. chromosomes. Also, M. petechialis has metacentric, submetacentric, subtelocentric, and telocentric chromosomes. The results obtained showed a marked chromosomal conservation with the presence of 2n 38 chromosomes in the genus Meretrix. Detailed studies of chromosome morphology and population cytology of the Veneridae are very little. In fact modern cytogenetic techniques have only recently been adopted for studies of Bivalvia. Also, we did not find any sexual dimorphism of chromosomes in this study. Further study will need various analyses for the investigation of the karyo-systematically evolution in the family Veneridae.
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