_??_ 1995 The Japan Mendel Society Cytologia 60: 369-374 , 1995

Cytogenetic Studies of Two Puffer Species (Sphoeroides,

Tetraodontidae) from Rio de Janeiro Coast, Brazil

Mario Jorge Ignacio Brum1, Carla Carneiro de Oliveira1

and Pedro Manoel Galetti Jr.2

1 Universidade Federal do Rio de Janeiro, Instituto de Biologia, Departamento de Zoologia,

21.941-590, Rio de Janeiro, RJ, Brazil2

Universidade Federal de Sao Carlos, Departamento de Genetica e Evolucao,

13.565-905, Sao Carlos, SP, Brazil

Accepted September 22, 1995

Tetraodontiformes have the smallest amount of DNA/cell among fishes (Hinegardner and

Rosen 1972) and are considered to be the fish group most derived and probably one of the few "post -perciformes" groups (Lauder and Liem 1983). With respect to which group among the

Euteleostei may be their ancestor, most systematists (Johnson and Patterson 1993) do not accept the hypothesis of Rosen (1984) that Tetraodontiformes may be more related to Zeiformes (a "pre-perciforme" group according to Lauder and Liem 1983), but prefer the hypothesis of Tyler (1980), whereby Acanthuroidei, one of the suborders of Perciformes, may be the sister-group of Tetraodontiformes. Of the 329 species of Tetraodontiformes (Nelson 1984), cytogenetic information is availiable only for 48, most of them from Japan, where these fishes, although poisonous, are highly appreciated as food (Halstead 1967). Thus, any effort that may expand this information is important, especially for the species from other seas,

permitting more comprehensive inferences about the karyotypic evolution and the phylogenetic relationships of the group. In the present investigation, we studied the mitotic chromosomes of Sphoeroides greeleyi and Sphoeroides spengleri, tetraodontids that occur in sympatry along the coast of the State of Rio de Janeiro (Brazil). The species S. greeleyi (Gilbert 1900), occurs in coastal waters of tropical Atlantic from Honduras, through the Caribbean, to the litoral of Parana, Brazil (Figueiredo, personal communication). In contrast, S. spengleri (Bloch 1785), is a puffer of wide distribution in the wersten Atlantic, occurring from Massachusetts, USA to Rio de Janeiro, Brazil (Shipp 1978).

Material and methods

A cytogenetic study was conducted on 9 females and 4 males of S. greeleyi and 6 females

and 4 males of S. spengleri, all collected with a line and hook in the Guanabara Bay, RJ (22•K

55•ŒS, 43•K10•ŒW). The specimens have been deposited in the Ichthyological Collection of the

National Museum of the Federal University of Rio de Janeiro. The lots formed by 9 females

and 4 males of S. greeleyi received the numbers MNRJ 12,530 and 13,224-13,230 and the lots

consisting of the S. spengleri specimens received the numbers MNRJ 13,220-13,223.

Mitotic chromosomes were obtained by direct preparation from kidney cells by the

conventional air drying technique, as previously described in Brum et al. (1992). To improve

the quantity and quality of metaphase cells, a yeast suspension was injected into the animals

before the direct preparation (Cavallini and Bertollo 1988). Chromosomes were classified

according to Levan et al. (1964).

370 Mario Jorge Ignacio Brum, Carla Carneiro de Oliveira and Pedro Manoel Galetti Jr. Cytologia 60

Results

Both species present a modal diploid number of 46 chromosomes with no differences

between sexes. Slight differences in the chromosome formulae are observed between the two species, with chromosome complements of S. greeleyi (Fig. 1) and S. spengleri (Fig. 2) showing

great similarity. Unfurtunately, the separation between uniarmed and biarmed chromosomes in each species is difficult. S. greeleyi, for example, seems to have twelve pairs of biarmed chromosomes, the pairs 1, 2, 4, 5, 6, 7, 8, 13, 16, 18, 20 and 23. By the other hand, in S. spengleri, the biarmed chromosomes would be the pairs number 1, 2, 5, 7, 15, 16, 17, 19 and 22, totalizing nine pairs of biarmed chromosomes.

Discussion

Considering, (1) that Tetraodontiformes are a monophyletic Glade with close phylogenetic relationships with Perciformes (Lauder and Liem 1983); and (2) that the karyotype of 2n=48 acrocentrics is considered to be basic to the latter group (Ohno et al. 1968, Cataudella and

Fig. 1. Giemsa karyotype of Sphoeroides greeleyi. The bar equals 5ƒÊm.

1995 Cytogenetic Studies of Two Puffer Species 371

Fig. 2. Giemsa karyotype of Sphoeroides spengleri. The bar equals 5ƒÊm.

Capanna 1973, Alvarez et al. 1986, among others), we may infer that the karyotype observed in the species of Triacanthidae (2n=48, FN=48) represents the karyotypic basis also for Tetraodontiformes (Table 1). The karyotypes of Balistidae, Tetraodontidae and Diodontidae

species, which have diploid numbers ranging from 28 to 46, may represent derivations from the Triacanthidae karyotype. This inference may be supported by the occurrence of biarmed chromosomes in these groups, as observed in S. greeleyi and S. spengleri, which might be arisen through centric fusions and pericentric inversions. Thus, the phylogenetic and karyotypic data available for Tetraodontiformes suggest that there may be two major chromosome evolution

pathways in this group: (1) the Triacanthidae line, which has been considered one of the most

primitive groups among Tetraodontiformes, where 2n=48 appears to be a commom feature among the species (Choudhury et al. 1982); and (2) a more specialized Glade, formed by balistids, ostraciids, tetraodontids and diodontids, where 2n=46 might be considered the

plesiomorphic condition (Arai and Nagaiwa 1976). In tetraodontids this value has been reported for the first time in the Sphoeroides species here studied, genus considered the most

primitive of the family Tetraodontidae (Arai 1983). As suggested in Arai and Nagaiwa (1976) the 2n<46 values observed in Balistidae, Ostraciidae and Tetraodontidae are probably resulted of centric fusions, while the 2n>46, as the two ostraciids species with 2n=50, might be

372 Mario Jorge Ignacio Brum, Carla Carneiro de Oliveira and Pedro Manoel Galetti Jr. Cytologia 60

Table 1. Summary of karyotypic data of the Tetraodontiformes

1995 Cytogenetic Studies of Two Puffer Species 373

evidences of centric fissions among these fishes .With respect to which group among the Euteleostei may have given origin to the

Tetraodontiformes, the contribution of cytogenetics may be considered modest . Only three of the 36 species of Zeiformes has been karyotyped thus far: Allocyttus verrucosus , with 2n and NF=42 (Suzuki and Tonosaki 1993); Capros aper , with 2n=42, 44 and 46 and NF=50 (Vitturi and Lafargue 1992); and Zeus Faber, with 2n=42 and 44 and NF=44 (Vitturi et al. 1991). While these complements of zeiform species do not corrobore the hypothesis of a larger relationship of this group with the Tetraodontiformes , the karyotype 2n=48 acrocentrics presented by the only two species of Acanthuroidei studied thus far, Acanthurus triostegus and Prionurus microlepidotus (Arai and Inoue 1976), can reinforce the assumption that the latter

group share an ancestral form with the Tetraodontiformes.

Summary

The value of 2n=46, which has been considered ancestral for Balistidae, Ostraciidae , Tetraodontidae and Diodontidae, and not detected previously in any representative of the

family Tetraodontidae, is the diploid number presented by S. greeleyi and S. spengleri, tetraodontids that occur in sympatry along the Brazilian coast.

Acknowledgment

The authors are grateful to FUJB, UFRJ and UFSCar for financial support, to J. L.

Figueiredo and to P. R. D. Lopes for specimens identification and to S. L. Machado for helping

in the graphic confection of the table present in this work.

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