Genetica (2007) 130:99–103 DOI 10.1007/s10709-006-0023-4 BRIEF REPORT The karyotypes of the thorny catfishes Wertheimeria maculata Steindachner, 1877 and Hassar wilderi Kindle, 1895 (Siluriformes: Doradidae) and their relevance in doradids chromosomal evolution Eduardo S. Eler Æ Jorge A. Dergam Æ Paulo C. Veˆnere Æ Lı´lian C. Paiva Æ Gabriela A. Miranda Æ Alessandro A. Oliveira Received: 13 March 2006 / Accepted: 24 May 2006 / Published online: 8 August 2006 Ó Springer Science+Business Media B.V. 2006 Abstract We studied the karyotypes of two doradids, chromosome numbers, chromosomal evolution in do- the rare and endangered Wertheimeria maculata and a radids has involved pericentric inversions and an in- derived Amazonian species, Hassar wilderi. Cytoge- crease of heterochromatic blocks. netic characterization was assessed using conventional staining (Giemsa), C-banding, and NOR banding. Both Keywords Brazilian coastal basins Æ Conservation species had 2n = 58 chromosomes but differed in their genetics Æ Cytotaxonomy Æ South American biodiversity chromosome formulae, 24 m + 14sm + 8st + 12a for W. maculata and 32 m + 16sm + 10st for H. wilderi.In W. maculata heterochromatin was mainly telomeric, Introduction and three chromosomes had a fully heterochromatic arm; in H. wilderi heterochromatin was also predomi- Although the Neotropical fish fauna of freshwater nantly telomeric and evident in many more chromo- fishes is the richest in the planet, studies of the evolu- somes. Hassar wilderi also presented one pair of tion of its ostariophysan (Characiformes + Silurifor- homologues with a fully heterochromatic arm. In both mes) groups have barely started (De Pinna 1998). species, nucleolar organizer regions were restricted to Whereas characiforms are usually diurnal, small-sized one pair of subtelocentric chromosomes. Assuming a and silvery, siluriforms are dark-colored, usually basal position for W. maculata, we hypothesized that nocturnal and have undergone a wide ecological underlying conserved diploid and NOR-bearing adaptation in the Neotropics, ranging from the tiny (0.025–0.06 m) vampire fish, parasitic Vandellia spp. to large species, such as Brachyplatystoma filamentosum (3.6 m) (Lundberg and Littmann 2003). To date, 1649 E. S. Eler species of siluriforms have been described, 1000 only in Gene´tica, Conservac¸a˜o e Biologia Evolutiva – Instituto the last century (Ferraris and Reis 2005 and references Nacional de Pesquisas da Amazoˆ nia, Av. Andre´ Arau´ jo, therein). Among the currently 15 Neotropical catfish 2936, Petro´ polis, 69083-000 Manaus, AM, Brazil families, the family Doradidae encompasses 30 extant J. A. Dergam (&) Æ L. C. Paiva Æ G. A. Miranda Æ genera and 72 valid species (Sabaj and Ferraris 2003) A. A. Oliveira diagnosed by several osteological synapomorphies and Departamento de Biologia Animal, Universidade Federal by the presence (albeit modified in Wertheimeria and a de Vic¸osa, Avenida P.H. Rolfs s/n, Campus Universita´rio, few other species) of ossified tubules of the lateral-line 36570-000 Vic¸osa, AM, Brazil e-mail: [email protected] system, arranged on a lateral row. Size variation within doradids is also remarkable, ranging from 3.5 cm P. C. Veˆnere standard length in Physopyxis lira Cope 1871 to 120 cm Departamento de Cieˆncias Biolo´ gicas e da Sau´ de, Instituto fork length and 20 kg in Oxydoras niger (Valenciennes, de Cieˆncias e Letras do Me´dio Araguaia, Universidade Federal de Mato Grosso, Rodovia MT 100, Km 3,5, 78698- 1821)(Sabaj and Ferraris 2003). Doradids occur in most 000 Pontal do Araguaia, MT, Brazil South American basins, though they are absent from 123 100 Genetica (2007) 130:99–103 the Pacific Coast drainages and from coastal drainages Cell division was stimulated in vivo with 2 daily south of the La Plata River (Sabaj and Ferraris 2003). applications of MunolanÒ, a commercially available Geographic distribution of the group is also uneven: antigen lysate (1 pill ground and suspended in 0.5 ml of 70% of the valid species occur in the Amazon basin. water per 100 g body weight). Metaphases were The Orinoco basin harbors ca. 22 species and ranks obtained from cephalic kidney, using a protocol mod- second in species richness. Contrasting with these ified from Egozcue (1971). C-banding and NOR pro- drainages, only two species of doradids have been tocols followed Sumner (1972) and Howell and Black described from Brazilian eastern coastal basins: Wert- (1980). Chromosome measures were obtained digitally heimeria maculata from the Jequitinhonha and Pardo from scanned plates using Image Pro-PlusÒ and mor- rivers and Kalyptodoras bahiensis Higuchi, Britski & phology was determined on the basis of arm ratio as Garavello, 1990 from the Paraguac¸u River. Within its proposed by Levan et al. (1964). Chromosomes were restricted range, W. maculata faces strong human classified as metacentrics (m), submetacentrics (sm), habitat disturbances such as siltation, habitat frag- subtelocentrics (st), and acrocentrics (a). NF (chro- mentation, pollution and introduction of exotic species. mosome arm number) was determined considering all Previous systematic studies placed this thorny catfish as chromosome classes as bi-armed, except for acrocen- a member of the family Auchenipteridae, but it was trics, which were counted as being formed by one arm. recognized as a doradid by Miranda-Ribeiro (1911). Based on morphological analysis, Higuchi (1992) placed it as the sister taxon of all other doradids and Results therefore its karyological characters are especially re- levant for the comprehension of the chromosomal The karyotype of W. maculata was 2n = 58 and had 24 evolution of this family. Although chromosome dif- metacentrics, 14 submetacentrics, 8 subtelocentrics, and ferences among related species are well known (White 12 acrocentrics and NF = 104; NORs were telomeric 1978; King 1993), homology assessment on fish chro- and restricted to one pair of homologues (Fig. 2). In H. mosomes is hampered by lack of arm differentiation wilderi, diploid number was also 2n = 58, differing from and therefore, chromosome data are unsuitable for the former species in chromosome morphology, with 32 formulating phylogenetic hypotheses. Instead, we have metacentrics, 16 submetacentrics and 10 subtelocentrics overlapped karyological data on molecular and mor- and NF = 116 (Fig. 2). As in W. maculata, only one phologic hypotheses and explored the information pair of homologues bore NORs in telomeric position, content of karyotypes within a putatively more re- corresponding to a secondary constriction visible in pair stricted monophyletic group. Therefore, the objective 27 in the Giemsa-stained karyotype. Both species pre- of the present paper was to compare some cytogenetic sented also one pair of homologues with a fully het- characters of W. maculata to a phylogenetically derived erochromatic arm (Fig. 3). In W. maculata, species, Hassar wilderi, a member of the Doradinae heterochromatin was mainly telomeric and restricted to (Higuchi 1992). We interpreted these results within the the shorter arms, and heterochromatic blocks were not context of current phylogenetic hypotheses on the evident in 24 chromosomes. One pair of submetacen- evolution of doradids. trics also showed a completely heterochromatic arm, and another pair was characterized by the presence of two interstitial blocks of heterochromatin. Hetero- Material and methods chromatic blocks were apparently more frequent in H. wilderi, which had only six chromosomes without C- Three juvenile specimens of W. maculata were col- bands. The NOR-bearing chromosome pair appeared lected in Berizal (GPS 15°38¢ S–41° 44¢W), State of associated in the C-banding metaphase. Minas Gerais, in the Pardo River, and four females of H. wilderi were collected in Araguaia River (GPS 15°53¢30¢¢ S–52°15¢00¢¢ W) (Fig. 1). Voucher W. mac- Discussion ulata and H. wilderi specimens were deposited in the fish collection of the Museu de Zoologia Joa˜o Moojen Karyotypical data on 13 species of doradids indicate de Oliveira, Universidade Federal de Vic¸osa, Vic¸osa, variable diploid numbers, ranging from 2n = 56 (two MG, Brazil, and in the fish collection of the Instituto de species) (Fenocchio et al. 2003; Oliveira and Gosztonyi Cieˆncias e Letras do Me´dio Araguaia, UFMT, Uni- 2000), 2n = 58 (ten species) (Oliveira and Gosztonyi versidade Federal do Mato Grosso, Pontal do Ara- 2000 and present work), and 2n =66 in Doras guaia, MT, Brazil. eigenmanni (Troy and Miyazawa 2000). Assuming 123 Genetica (2007) 130:99–103 101 Fig. 1 Collecting locales in South America. Left lower inset, H. wilderi collecting locale; right top inset, W. maculata collecting locale Higuchi’s (1992) hypothesis regarding Wertheimeria,a independent evolution involving gains of heterochro- reduction of diploid number would have occurred matin in at least nine pairs of homologues. Although independently in Anadoras and Trachydoras (Oliveira our results are the first published C-banding patterns and Gosztonyi 2000), two taxa distantly related in morphological (Higuchi 1992) and molecular (Moyer et al. 2004) data-based hypotheses. Within doradids, number of arms was also informative: W. maculata and H. wilderi’s differences fitted nicely in a putative pericentric inversion process of chromosomal evolu- tion and a consequent change of character state of acrocentrics to the other chromosome classes. How- ever, the family’s diversity is more complex, and even within H. wilderi’s Doradina group, Doras sp. under- went an increase of diploid number