Neotropical Ichthyology, 4(1):93-97, 2006 Copyright © 2006 Sociedade Brasileira de Ictiologia Karyotype description of three species of Loricariidae (Siluriformes) and occurrence of the ZZ/ZW sexual system in Hemiancistrus spilomma Cardoso & Lucinda, 2003 Renildo Ribeiro de Oliveira*, Issakar Lima Souza**, and Paulo Cesar Venere** The neotropical freshwater systems have a high number of catfish species (Siluriformes), and many of those are denominated “cascudos” in Brazil. Cytogenetic data about three “cascudos” species fished in the rio Araguaia are described in the present study. The Pterygoplichthys joselimaianus showed 2n=52, with 28 metacentrics (M) chromosomes, 16 submetacentrics (SM) and 8 subtelocentrics/acrocentrics (ST/A) in both sexes. Hemiancistrus spinosissimus showed 2n=52, with karyotype formulae 26M+22SM+4ST, in both sexes. Hemiancistrus spilomma also showed 2n=52, but in this species a ZZ/ZW sex chromosome system (25M+21SM+6ST in females and 24M+22SM+6ST in males) was observed. The cells from H. spinosissimus and P. joselimaianus showed one chromosome pair bearing Ag-NORs, while in the H. spilomma three chromosome pairs bearing AgNORs were detected. The data showed in this work reveal particular chromosomal characteristics, important for a good recognition of both Hemincistrus species, and also show the importance of the insertion of cytogenetic data on taxonomic phylogenetic studies. Os sistemas de água doce neotropicais possuem um alto número de espécies de peixes Siluriformes, muitas das quais popularmente conhecidas como cascudos no Brasil. Dados citogenéticos sobre três espécies de cascudos, capturadas na bacia do rio Araguaia são descritos no presente trabalho. Pterygoplichthys joselimaianus possui 2n=52, com 28 cromossomos metacêntricos (M), 16 submetacêntricos (SM) e 8 subtelecêntricos/acrocêntricos (ST/A) em ambos os sexos. Hemiancistrus spinosissimus revelou 2n=52, com fórmula cariotípica 26M+22SM+4ST, nos dois sexos. H. spilomma também possui 2n=52, porém, nesta espécie foi observado um sistema de cromossomos sexuais do tipo ZZ/ZW (25M+21SM+6ST para fêmeas e 24M+22SM+6ST para machos). As células de H. spinosissimus e P. joselimaianus mostraram um par de cromossomos portadores de Ag-RONs. Em H. spilomma, três pares de cromossomos portadores de Ag-RONs foram observados. Os dados apresentados neste trabalho revelam características cromossômicas particulares, importantes para um bom reconhecimento de ambas as espécies de Hemiancistrus e mostram a importância da inserção dos dados citogenéticos nos estudos taxonômicos e filogenéticos. Key words: Ancistrinae, cytogenetic, sexual chromosomes, Araguaia. Introduction and Gosztonyi (2000) only 56 loricariid species have been investigated at the cytogenetic level, and a range of diploid number among 2n=36 in Rineloricaria latirostris (Loricariinae) (GiulianoCaetano, 1998) and 2n=80 in Hypostomus sp. (Hypostominae) has been reported (Artoni & Bertollo, 1996). Andreata et al. (1992, 1993) described a XX/XY sexual chromosome determination in Pseudotocinclus tietensis and a ZZ/ZW in Microlepidogaster leucofrenatus, respectively. Structural chromosome polymorphisms in several other species of Hypoptopomatinae (Loricariidae) related to NORs position and C-banding pattern at both species and popula- The Siluriformes is the most diverse and widely distributed of ostariophysan groups, with approximately 30 families, 412 genera and over 2400 species (Nelson, 1994). Except for the families Ariidae and Plotosidae, is limited to the tropical freshwater systems (Burgess, 1989). The Loricariidae, regionally called “cascudos” or “acarís” is endemic to the Neotropical region and is the largest family of catfishes, with 646 species currently considered valid (Isbrucker, 1980; Armbruster, 2004). Nevertheless, the Loricariidae is not a very studied group. According to Oliveira *Instituto Nacional de Pesquisas da Amazônia – INPA, Manaus, AM, Brasil. **Departamento de Ciências Biológicas e da Saúde, Instituto de Ciências e Letras do Médio Araguaia da Universidade Federal de Mato Grosso, 78698-000, Pontal do Araguaia, MT, Brazil. e-mail: pvenere@uol.com.br 93 Karyotype description of three species of Loricariidae 94 tion levels was detected (Andreata et al., 1994). A ZZ/ZW system was also observed in Loricariichthyis platymetopon (Scavone & Júlio Jr. 1995), Hypostomus sp. from the Rio Araguaia (Artoni et al., 1998), and Ancistrus cf. dubius (Mariotto et al., 2004). Ancistrinae has been recognized as a well-defined monophyletic group (Schaefer, 1987), but a recent study showed that the species of this group are more related to those of the tribe Pterygoplichthini and were grouped in the tribe Ancistrini (Armbruster, 2004). Both these tribes now belong to the subfamily Hypostominae (Armbruster, 2004). Chromosome data from Ancistrini are showed in Table 1. Except for Ancistrus n.sp.1 from the rio São Francisco (Acre, Brazil), with 2n=38 (Alves et al., 2003), Ancistrus sp. from the rio Iguaçu (Paraná, Brazil) with 2n=48 (Lara, 1998), and Ancistrus cf. dubius from the rio Paraguai basin (MT), with 2n=44 (Mariotto et al., 2004) all other species have a diploid number of 2n=52. The only species of Pterygoplichthini karyotyped, Liposarcus anisitsi, also has 2n=52 chromosomes (Artoni & Bertollo, 1996). In the present work, the karyotypes and active rDNA nucleolar location of the three species of Loricariidae are presented, as well as the description of ZZ/ZW sexual chromosome system in Hemiancistrus spilomma. Material and methods In the present study, the taxonomy proposed by Armbruster (2004) who considers the genus Glyptoperichthys as synonyms with Pterygoplichthys was applied. In this way, P. joselimaianus (Weber, 1991) (three females, four males and one unidentified sex) were sampled in the lago Quatro Bocas (15º23’20.1’’S, 51º42’45.9’’W), near the city of Araguaiana, Mato Grosso, Brazil. Voucher specimens were deposited in the fish collection of the Instituto de Ciências e Letras do Médio Araguaia, Universidade Federal de Mato Grosso, Brazil (ICLMA434). Hemiancistrus spinosissimus Cardoso & Lucinda, 2003 (two female and two males) and H. spilomma Cardoso & Lucinda, 2003 (eight females and two males) were catched in the rio Araguaia (15o50’15"S - 051o58’43"W), near the city of Pontal do Araguaia, Mato Grosso, Brazil. Voucher specimens were deposited in the Museu de Ciências e Tecnologia of Pontifícia Universidade Católica do Rio Grande do Sul (MCP36689, MCP36686, MCP36685). Chromosomal preparations were obtained either from kidney cells after in vivo colchicine treatment (Bertollo et al., 1978), or from short-term cell culture (Fenocchio et al., 1991). These were Giemsa stained for conventional analysis. The active rDNA nucleolar cistrons (Ag-NORs) were detected using AgNO3 staining (Howell and Black, 1980). The chromosomes were classified as metacentric (M), submetacentric (SM), subtelocentric (ST), and acrocentric (A), according to the arm ratio criteria adopted by Levan et al. (1964). Results In both sexes of Pterygoplichthys joselimaianus, the diploid number was 2n=52 and the karyotypic formulae 28M+16SM+8ST/A (Figure 1). In both sexes of Hemiancistrus spinosissimus the diploid number was 2n=52 and the karyotypic formulae 26M+22SM+4ST (Figure 2a). H. spilomma also showed 2n=52 but, a ZZ/ZW sex chromosome mechanism was observed, with a karyotypic formulae of 25M+21SM+6ST in females and 24M+22SM+6ST in males (Figure 2b). The ZZ chromosomes are represented by the first submetacentric pair whereas the W chromosome is morphologically similar to the third metacentric pair. In the present study, it was observed that P. joselimaianus and H. spinosissimus cells showed one Ag-NOR-bearing chromosome pair (inset of Figure 1 and 2a, respectively). The AgNOR signals were subterminally located on the short arm of pair 9 in P. joselimaianus (Figure 1, inset) and terminally on the long arm of the pair 17 in H. spinosissimus (Figure 2a, inset). Three Ag-NOR-bearing pairs were detected in H. spilomma, one located in the terminal regions of the long arm in pairs 2 and 18 and other at the terminal end of the short arm of pair 3 (Figure 2b, inset). Discussion In Ancistrini, pericentric and paracentric inversions probably were the most important chromosome rearrangements Table 1. Cytogenetic data from the species of Ancistrini. References: 1. Lara (1998), 2. Alves et al. (2003), 3. Mariotto et al. (2004), 4. Artoni & Bertollo (2001), 5. Souza et al. 2004, 6. present study. Species Ancistrus sp. Ancistrus n.sp.1 Ancistrus n.sp.2 Ancistrus cf. dubius Ancistrus multispinnis Hemiancistrus sp. Hemiancistrus spinosissimus Hemiancistrus spilomma Rivers / Brazilian states Iguaçu / Paraná São Francisco / Acre Betari / São Paulo Pantanal / Mato Grosso Itapocu / Santa Catarina Araguaia / Mato Grosso Araguaia / Mato Grosso Araguaia / Mato Grosso 2n 48 38 52 44 52 52 52 52 Karyotype formulae 18M+14SM+12ST+4A 30M/SM+8ST 32M/SM+20ST/A 18M+10SM+8ST+8A (ZZ/ZW) 28M/SM+24ST/A 20M+20SM+8ST+4A 26M+22SM+4ST Female 25M+21SM+6ST(ZW) Megalancistrus aculeatus Panaque cf. nigrolineatus Baryancistrus aff. niveatus Paraná / Paraná Araguaia / Mato Grosso Xingu / Pará 52 52 52 Male 24M+22SM+6ST(ZZ) 26M+26SM 26M+20SM+6ST 16M+32SM+4A Ag-NOR locations (ST)p, terminal (M)5p, interstitial (ST)24p, terminal (SM)13p, intertitial (ST)17p, terminal (SM)q, terminal (SM)17q, terminal (M)2q, terminal; (SM)18q, terminal; (M)3p, terminal Ref 1 2 2 3 2 4 6 6 (SM)p, interstitial (A)p terminal (M) 3p, interstitial 1 4 5 R. R. de Oliveira, I. L. Souza & P. C. Venere 95 Fig. 1. Karyotypes of female and male of Pterygoplichthys joselimaianus with conventional Giemsa staining. The chromosome pair bearing Ag-NORs are in the inset. that occurred in the karyotypic evolution of the group (Alves et al., 2003). The present data reinforce this hypothesis since all species analyzed also have 2n=52 chromosomes. These rearrangements keep the diploid number equal to 2n=52 chromosomes, metacentric and submetacentric, in most of the studied species (Table 1). Ancistrini has a lower diploid number when compared with Loricariinae (Alves et al., 2003), Hypostominae (Artoni & Bertollo, 1996), and Hypoptopomatinae (Andreata et al., 1994). However, these conclusions are preliminary because Ancistrini is a very specious subfamily and these data are only related to a few species from five genera. The species P. joselimaianus also has 2n=52, the same diploid number found in Liposarcus anisitsi (Artoni & Bertollo, 1996), other species of the tribe Pterygoplichthini. According to Armbruster (2004), the tribes Ancistrini and Pterygoplichthini are sister groups and compose a derived clade of the Hypostominae. The present cytogenetic data reinforce the putative relationship between these tribes suggesting that 2n=52 could be a primitive diploid number for them. A few years ago the presence of a sexual differentiation at a chromosome level was considered an uncommon occurrence in fishes. Advances in the studies of Neotropical fishes, however, have shown a great number of new occurrences in different species and families. Among those species with dif- ferentiated sex chromosomes, 64% showed female heterogamety and 36% male heterogamety. Eighty percent of the sex chromosomes corresponds to simple systems (77% ZZ/ZW and 23% XX/XY) and twenty percent correspond to multiple sex chromosome mechanisms (Centofante et al., 2002). The presence of a ZZ/ZW sex chromosome system in H. spilomma (present study) and in Ancistrus cf. dubius (Mariotto et al., 2004) suggest that this system may has a wide distribution in Ancistrini. Some fish groups have a predominance of one chromosome pair in their karyotype bearing just one active NOR, as some species of Pimelodidae (Dias & Foresti, 1993) and Loricariidae (Alves et al., 2003). On the other hand, occurrence of multiple NORs can be observed in some species of Hypostominae (Artoni & Bertollo, 1996). Among the species examined, Hemiancistrus spilomma is the only species thus far to show multiple NORs, as described in Table 1 and confirmed by the nucleolus analysis (Figure 2b). It is early to draw conclusions on the significance of the ZZ/ZW occurrence associated with the multiplicity of AgNORs in Hemiancistrus spilomma, as well the maintenance of 2n=52 and single Ag-NOR in the majority of the Ancistrini species because this tribe is very specious (Fisch-Muller, 2003), and only a few species from five genus have been studied. 96 Karyotype description of three species of Loricariidae Fig. 2. Karyotypes of female and male of Hemiancistrus spinosissimus (a) and Hemiancistrus spilomma (b), with conventional Giemsa staining. The chromosome pair bearing Ag-NORs are in the inset. R. R. de Oliveira, I. L. Souza & P. C. Venere Nevertheless, our research contributes to new karyological information that can aid in understanding of the evolutionary history of this group of fish. Hemiancistrus spilomma and Hemiancistrus spinosissimus are morphologically very similar and can easily be confused. 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