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CYTOGENETICS OF Aequidens plagiozonatus KULLANDER, 1984 AND Crenicichla

lepidota HECKEL, 1840 (PERCIFORMES: CICHLIDAE) FROM THE UPPER

PARAGUAI BASIN – MT, CENTRAL BRAZIL.

Claudineia Barbosa De Lima1; Anderson Fernandes2; Ilsamar Mendes Soares2; Daniel

Garcia Silva² & Jorge Abdala Dergam1 (1Departamento de Biologia Animal, Universidade

Federal de Viçosa, 36570-000, Viçosa, Brasil, claubarlima@hotmail.com; 2Departamento

de Ciências Biológicas, Universidade do Estado de Mato Grosso, 78300-000, Tangará da

Serra, MT, Brasil, don10@bol.com.br )

Index Terms: fish fauna; C banding; NOR banding; chromosome arm; ichthyology

Introduction

Although the Neotropical freshwater fish fauna is considered the richest in the world

(Schaefer, 1998), the knowledge of the fishes of the Cerrado is still scanty. The Cerrado is

one of the biodiversity hotspots in Brazil and in the last 35 years more than half of its 2

million km2 have been altered for agriculture.

Within the neotropics the Cichlidae are well represented, with 111 and 291 species

in Central America and South America. Cichlids are diurnal and characteristic of lenthic

environments, although some species are adapted to lotic habitats. They are nest builders

and show parental care (Kullander, 2003). The genus Crenicichla is endemic to South

America, and includes 74 valid species (Kullander, 2003). Five species, C. lepidota, C.

haroldoi, C. vittata, C. jupaiensis e C. semifasciata are currently known in the upper

Paraguai basin, and a karyotypic analysis of the former is reported in this study. With 23

species, the genus Aequidens is less speciose than Crenicichla and only one species,

Aequidens plagiozonatus, has been described in the upper rio Paraguai. This taxonomic

paucity contrasts with the occurrence of 14 species of Aequidens described for the Amazon

basin. To date, cytogenetic studies have been carried on in only 28 species of Crenicichla

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and Aequidens (http://www.fihsbase.org.search.cfm). This work aimed to characterize

cytogenetic aspects of populations of C. lepidota and A. plagiozonatus in the upper Paraguai

drainage.

Materials and Methods

Twenty-one specimens of Aequidens plagiozonatus (8 females and 13 males) were

collected in the Bocaiuval Spring and in the Sepotuba River. Fourteen specimens of

Crenicichla lepidota (five females and nine males) were collected in the Piracema locality

(Fig. 1). Renal tissue was processed according to Bertollo et al. (1978), C banding, NOR

banding, and fluorochrome techniques followed Sumner (1972), Howell & Black (1980)

and Schweizer (1980) respectively. Chromosome arm relationships were determined

according to Levan et al. (1964).

Results & Discussion

Both species were 2n=48 (Table 1 and Fig. 1) and sex chromosomes were not

detected. C. lepidota was characterized by 4m+4sm+40 st-t chromosome formula and NF=

56. In this species, a large interstitial secondary constriction was evident in the long arm of

the largest chromosome pair (Fig. 1c); this same region was also NOR+ and DAPI - (Figs 1c

and 2a).

Populations of A. plagiozonatus showed two allopatric cytotypes. In corrego

Bocaiuval, the population was characterized by a 4st+44t chromosome formula and NF=52

(Fig. 1a) and it was named cytotype A. Twenty kilometers away from Bocaiuval, another

cytotype was collected in a lagoon close to the rio Sepotuba; this cytotype had

6sm+12stT+30t and NF=66 (Fig. 1b) and it was named cytotype B. Both cytotypes showed

heterochromatic blocks restricted to a pair of subtelocentrics, which were also associated to

NORs, and DAPI- (Figs 1 and 2b).

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C. lepidota and both cytotypes of A. plagiozonatus showed chromosomes with

heterochromatic regions in the pericentromeric regions, but heterochromatic regions were

more evident in telocentric chromosomes.

Table 1. Locales and cytogenetic data of Aequidens and Crenicichla from the Upper

Paraguai River basin.

Cytotypes Collecting locales

(GPS)

Diploid

chromos

ome

number

Karyotypic

Formula

Fundamen

tal

Number

Crenicichla

lepidota

P1-Piracema

(14º39`03`` S

57º26`14`` O)

48 4m+4sm+40

a 56

A. plagiozonatus

Citótipo A

P1- Córrego São José

(14º37`01`` S

57º20`25`` O)

48 4st+44a 52

A. plagiozonatus

Citótipo B

P2- Córrego

Bocaiuval

(14º32`08`` S

57º37`12`` O)

48 6sm+12st+3

0a 66

Crenicichla species are characterized by a stable diploid number (twenty-eight

species are 2n=48) but their chromosome formulae and fundamental numbers show great

variation among species (http://www.fihsbase.org.search.cfm). The Upper Paraguai

population of C. lepidota species also shows distinctive chromosome formula (Table 1)

differing from other species of the genus. Another more southern C. lepidota population

from the Paraguay River was described by Feldberg & Bertollo (1985a) as having three

pairs of m-sm and 21 pairs of st-t. The karyotypes of both populations differ in many

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respects: there are three pairs of m-sm in Miranda while four pairs of m-sm occurred in

Piracema.

All Cichlidae are characterized by the presence of a single pair of NORs, always

present in the largest chromosome pair (Feldberg et al., 2003). In some cases, a secondary

constriction is also evident in the NOR region. In Crenicichla, this region is interstitial in all

species and it may occur on the short or on the long arm of the first chromosome pair.

Feldberg & Bertollo (1985b) analyzed three species from different Brazilian basins and

found high levels of variation in NOR patterns among species. In C. lacustris and C. vitatta,

the NOR region was interstitial and present on the short arm, while in C. lepidota it was

interstitial and on the long arm. NORs of C.niederleinii from Tibagi River (Upper Paraná)

and Crenicichla sp. from the coastal basin of Itajaí-Açu River were characterized by

Loureiro et al. (2000) as interstitial and located on the short arm.

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Aequidens plagiozonatus from the upper Paraguai showed diploid number of 2n=48,

a conserved character also reported for other species such as A. metae, A. portalegrensis, A.

pulcher, A. tetramerus, A. rivulatus (Marescalchi, 2005). Feldberg et al. (2003) suggest that

diploid number and the presence of a few metacentrics and submetacentrics are due to the

prevalence of pericentric inversions during chromosome evolution.

Both A. plagiozonatus cytotypes showed a single pair of NORs on a subtelocentric

chromosome pair, a chromosome location that is common in cichlids such as Geophagus

brasiliensis, Chaetobranchopsis australe e Cichlasoma facetum (Feldberg & Bertollo,

1985a). Brinn et al. (2004) indicate simple NORs in Cichla monoculus and in Cichla

temensis, although in these two species the NORs were located on telocentric chromosomes.

Fig. 1. a) Cytotype A of A. plagiozonatus; b) Cytotype B of A. plagiozonatus; c) Karyotype of C. lepidota. Insets show A. plagiozonatus and C. lepidota NOR´s. Bar = 5µm.

Fig. 2. C. lepidota (a) of A. plagiozonatus (b) metaphase chromosomes subject to DAPI. Arrows indicate AT- regions. Bar = 5µm.

a

b

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In C. lepidota and A. plagiozonatus, C-banding also included regions near to NOR

sites. Loureiro et al. (2000) also report heterochromatic C+ regions in most chromosomes of

C. niederleinii and Crenicichla sp., and in the secondary constriction regions.

Heterochromatin was pericentromeric in most Oreochromis niloticus chromosomes

(Oliveira & Wright, 1998). Few cichlids have been studied with C-banding techniques;

however, all neotropical species studied (32) have heterochromatin blocks in the

chromosome pericentromeric regions, which were typically associated to NORs (Feldberg

et al., 2003). In C. lepidota and A. plagiozonatus, DAPI/CMA3 showed CG+ regions on the

first pair of metacentrics abutting the heterochromatic block and the NOR. These regions

are also DAPI-, as already reported by Loureiro et al. (2000) for populations of Crenicichla

in the Upper Paraná drainage. The same pattern of CMA+ was observed in Hoplias

malabaricus (Vicari et al., 2005).

Conclusions. Our results underline the fact that the fish populations of the Cerrado

hold high levels of genetic variation and that the Upper Paraguai basin is essential for a

more comprehensive understanding of the ichthyology of the Paraná and the Amazon

drainages.

Acknowledgements

The authors wish to thank the Fundação de Amparo à Pesquisa do Estado do Mato

Grosso and the Universidade Federal de Viçosa for financial support.

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