Neotropical Ichthyology, 6(1):101-108, 2008 ISSN 1679-6225 (Print Edition) Copyright © 2008 Sociedade Brasileira de Ictiologia ISSN 1982-0224 (Online Edition) Cytogenetic studies in three species of Lutjanus (Perciformes: Lutjanidae: Lutjaninae) from the Isla Margarita, Venezuela Mauro Nirchio1, Rodolfo Rondón1, Claudio Oliveira2, Irani A. Ferreira2, Cesar Martins2, Julio Pérez3, Luciana Sola4 and Anna Rita Rossi4 In the present study, three species of Lutjaninae, Lutjanus analis, L. griseus and L. synagris, were analyzed by conventional Giemsa staining, C-banding and silver staining, to reveal active Nucleolus Organizer Regions (NORs). Fluorescent in situ hybridization (FISH) was also applied to establish the number and location of the ribosomal gene clusters (18S and 5S rRNA genes). Counts of diploid metaphasic cells revealed a diploid modal chromosome complement composed of 48 acrocentric chromosomes in both L. analis and L. griseus. Two cytotypes were observed in L. synagris: cytotype I, with 2n=48 acrocentric chromosomes, found in 19 specimens, and cytotype II, with 46 acrocentric chromosomes and one large metacentric, found in two specimens. The large metacentric, which possibly originated from a Robertsonian rearrangement, was not found to be sex- related. In the three species, constitutive heterochromatin is located in the centromeres of all chromosomes. NORs were detected on the short arms of a single chromosome pair, number 24 in L. analis and number 6 in both cytotypes of L. synagris. In L. griseus, a polymorphism of the NORs number was detected, by both Ag-staining and FISH, as females show a maximum of three NORs, and males a maximum of six NORs. In all species, minor ribosomal genes were found located on a single chromosome pair. The obtained data, along with those previously reported for other five Lutjanidae species, show that a general chromosome homogeneity occurs within the family, but that derived karyotypes based on Robertsonian rearrange- ments as well as multiple and variable NORs sites can also be found. No presente estudo três espécies de Lutjaninae, Lutjanus analis, L. griseus e L. synagris foram analisadas através da coloração convencional com Giemsa, banda C e coloração com nitrato de prata para identificar as Regiões Organizadoras de Nucléolo (NORs) ativas. Hibridação fluorescente in situ (FISH) foi também aplicada para estabelecimento do número e localização dos agrupamentos de genes ribossômicos (18S e 5S rRNA). A contagem de células metafásicas revelou um número diplóide modal de 48 cromossomos acrocêntricos em L. analis e L. griseus. Dois citótipos foram observados em L. synagris: citótipo I com 2n=48 cromossomos acrocêntricos, encontrado em 19 espécimes, e citótipo II com 46 cromossomos acrocêntricos e um grande metacêntrico, encontrado em dois espécimes. O grande metacêntrico, que possivelmente se originou por um rearranjo Robertsoniano, não está relacionado com o sexo. Nas três espécies a heterocromatina constitutiva está localizada nas regiões centroméricas de todos os cromossomos. NORs foram detectadas no braço curto de um único par cromossômico, número 24 em L. analis e número 6 em ambos os citótipos de L. synagris. Em L. griseus, um polimorfismo de número de NORs foi observado, após coloração com prata e por FISH, as fêmeas apresentaram um máximo de três NORs e os machos um máximo de seis NORs. Em todas as espécies os genes ribossômicos 5S foram encontrados em um único par cromossômico. Os dados obtidos, somados aos demais previamente publicados para cinco outras espécies de Lutjanidae, mostram que na família há uma homogeneidade cromossômica, porém também são encontrados cariótipos derivados, originados por rearranjos Robertsonianos, assim como pela ocorrência de sítios múltiplos e variados de NORs. Key words: Karyotype, Ribosomal genes, NOR polymorphism, C-banding, Robertsonian rearrangement. 1Escuela de Ciencias Aplicadas del Mar, Universidad de Oriente, Apartado Postal 147, Porlamar, Venezuela. [email protected] 2Departamento de Morfologia, Instituto de Biociências Universidade Estadual Paulista, 18618-000 Botucatu, São Paulo, Brazil. 3Instituto Oceanográfico de Venezuela, Universidad de Oriente, Cumaná, Venezuela. 4Department of Human and Animal Biology, University of Rome “La Sapienza”, via Borelli 50, 00161 Rome, Italy. 101 102 Cytogenetic studies in three species of Lutjanus Introduction fishes were injected intramuscularly with a yeast glucose solution (Lee & Elder, 1980) for mitosis stimulation. Chromo- The Lutjanidae (snappers) is a group composed of 17 gen- somes were obtained from kidney cells according to Foresti era and 105 species of mostly reef-associated marine fishes, et al. (1993). C-bands were obtained according to the method which are distributed in all the tropical and subtropical seas described by Sumner (1972), modified by testing different of the world (Nelson, 2006). The family is divided in four time of exposition to barium hydroxide, from 1 to 180 sec- subfamilies. Three smaller subfamilies include the onds, in order to enhance the contrast of constitutive hetero- Paradichthyinae, with two monotypic genera (Symphorus and chromatin on chromosomes. For detection of the active Symphorichthys), the Etelinae, with five genera (Aphareus, Nucleolus Organizer Regions (NORs), slides were stained with Aprion, Etelis, Pristipomoides and Rhandallichthys) and 19 silver nitrate using the method of Howell & Black (1980). species, and the Apsilinae, with four genera (Apsilus, The 5S and 18S rDNA sites were identified by FISH ac- Lipocheilus, Paracesio and Parapristipomoides) and 12 spe- cording to the method of Pinkel et al. (1986). A sequence of cies (Nelson, 2006). The subfamily Lutjaninae is the largest, 1800 base pairs of the 18S rRNA gene of Oreochromis with three monotypic genera (Hoplopagrus, Ocyurus and niloticus (Nile tilapia), cloned in pGEM-T plasmid, was used Rhomboplites), the genera Macolor and Pinjalo with two as a probe to localize sites for 45S rDNA. PCR products con- species each, and the genus Lutjanus, which is the most taining 5S rDNA repeats from each species were used as speciose, with 64 species. In Venezuela, Cervigón (1993) rec- probes for the chromosome mapping of 5S rDNA. DNA was ognizes six genera of Lutjanidae (Etelis, Pristipomoides, extracted from muscle (Sambrook & Russel, 2001) and the 5S Apsilus, Ocyurus, Rhomboplites and Lutjanus ) including 15 rDNA repeats were generated by Polymerase Chain Reaction species, 10 of which belong to the genus Lutjanus (L. analis, (PCR) with the primers 5SA (5’TAC GCC CGA TCT CGT CCG L. apodus, L. aya, L. bucanella, L. cyanopterus, L. griseus, L. ATC3’) and 5SB (5’CAG GCT GGT ATG GCC GTA AGC3’) jocu, L. mahogoni, L. purpureus, L. synagris and L. vivanus). according to Martins & Galetti (1999). In spite of their high number and their ecological and eco- The 18S rDNA and 5S rDNA probes were labeled by nick nomic importance, cytogenetic studies on Lutjanidae are translation with biotin-14-dATP, following the manufacturer’s scarce. In fact, among the 105 recognized species of (BionickTM Labelling System-Gibco.BRL) instructions. Signals Lutjanidae, barely five species have been karyotyped to date: were detected and amplified by a three-round application of Lutjanus argentimaculatus (Raghunath & Prasad, 1980), L. Avidin-FITC/biotinilated Anti-avidin. Chromosomes were kasmira (Choudhury et al., 1979; Ueno & Takai, 2008), L. counter-stained with Propidium Iodide (50µg/ml) diluted in sanguineus (Rishi, 1973), L. russelli (Ueno & Ojima 1992), Antifade. and L. quinquelineatus (Ueno & Takai, 2008). For most of The mitotic figures were photographed using a Motic B400 them, only the chromosome number and morphology have microscope equipped with a Moticam 5000C digital camera. been reported and there is no data regarding the chromo- The fundamental number (NF) of arms was determined con- somal distribution and composition of the constitutive het- sidering acrocentrics (A) as having one chromosome arm and erochromatin or numbers and locations of the major and mi- metacentrics (M) as having two chromosome arms. FISH nor ribosomal genes, which have proved to be useful markers metaphases were photographed with a Olympus BX61 pho- in the investigation of the phylogenetic relationships among tomicroscope equipped with a DP70 digital camera. fish species within a family (Sola et al., 2007). In the present study, three species of Lutjaninae, Lutjanus Results analis, L. griseus and L. synagris were analyzed by conven- tional Giemsa staining and C-banding, and by Fluorescent in The counts of diploid metaphasic cells (Table 1) revealed situ hybridization with 18S rDNA and 5S rDNA, in order to a modal chromosome complement composed of 2n=48 acro- obtain a fine karyotype characterization, and, thus, chromo- centric chromosomes (NF=48) in both L. analis and L. griseus some markers which can provide useful information concern- and in 19 out of the 21 examined specimens of L. synagris ing relationships within the family. (cytotype I). The two remaining specimens, one male and one unsexed, of L. synagris show a modal count of 2n=47 (NF=48), Materials and Methods made up of one large metacentric and 46 acrocentric chromo- somes. This karyomorph was named cytotype II. The karyo- Eight sexually immature (unsexed) specimens of L. analis, types obtained by arranging the chromosomes in order of seven specimens of L. griseus (3 males, 3 females, 1 unsexed) decreasing size are shown in Fig. 1. The negligible differ- and 21 specimens of L.