Natural triploidy in Leporinus cf. elongatus bearing sex chromosomes

Abstract

Although several cases of natural triploidy in fish have already been described, spontaneous polyploidy in species with differentiated sex chromosomes are rare. We report the occurrence of a triploid fish (3n = 81) Leporinus cf. elongatus, a species characterized by a highly differentiated ZZ/ZW sex chromosome system, from the São Francisco river. The occurrence of a ZZZ triploid adult indicates the viability of this chromosome constitution in this fish.Key words: polyploidy, triploid fish, ZW chromosomes, sex chromosomes, Anostomidae. The family Anostomidae is composed of 12 genera, constituting a group relatively rich in species, distributed from South to Central America (Garavello, 1979). Eight species from this group, all from the genus Leporinus, exhibit a ZZ/ZW sex chromosome system with marked structural modifications between the sex chromosomes (Galetti et al., 1995;Venere et al., 2004; Molina and Galetti, 2006). The ZW chromosomes of these species point a monophyletic origin, apparently differentiated through processes of heterochromatinization (Galetti and Foresti, 1986;1987). Leporinus is one of the more complexes groups among Characiformes and the largest in number of species, with 87 already described. Several attempts to subdivide it into additional genera and subgenera have failed (Garavello and Britski, 2003).A diploid number of 2n = 54 is common among Leporinus species (Galetti et al., 1995) and no chromosome number variation has been reported in this genus thus far, despite of several reports of natural triploidy in different neotropical fish families (Characidae, Morelli et al., 1983;Fauaz et al., 1994;Centofante et al. 2001; Sternopygidae, Almeida-Toledo et al., 1985; Curimatidae, Venere and Galetti, 1985; Erythrinidae, Giuliano-Caetano and Bertollo, 1990; Thricomycteridae, Borin et al., 2002).This study reports a case of spontaneous natural triploidy in Leporinus cf. elongatus with a highly differentiated ZZ/ZW sex chromosome system. A total of 28 specimens of Leporinus cf. elongatus (12 males and 16 females) collected in the São Francisco river (Três Marias municipality; Brazil) were cytogenetically analyzed through the air-drying technique (Bertollo et al., 1978;Gold et al., 1990). the chromosome preparations were submitted to Ag-NOR (Howell and Black, 1980) and mithramycin staining (Schweizer, 1980). Our results confirmed the previously reported 2n = 54 with a highly differentiated ZZ/ZW sex chromosome system, characterized by a large subtelocentric W chromosome and a submetacentric Z (Molina et al., 1998).A young triploid male with 2n = 3x = 81 and presenting three copies of the Z chromosome was detected ( Figure 1a, b). A previously reported conspicuous mithramycin positive heterochromatic block on the long arm of the Z chromosomes (Molina et al., 1998) was evident in the three Z chromosomes of the triploid complement (Figure 1c). No morphological differences were observed between the triploid and the diploid specimens.The nucleolus organizer regions (NORs) were located near ...

Occurrence of natural triploidy in Rhamdia quelen (Siluriformes, Heptapteridae)

“…AgNORs were detected in the terminal portion of the short arm of 3 submetacentric chromosomes of the triploid individual (Figure 2b), confirming triploidy and suggesting that there is no genetic inactivation of the triploid ribosomal cistrons, a hypothesis also supported by Maistro et al (1994), Fernandes-Matioli et al (1998), Borin et al (2002, Garcia et al (2003), and Molina et al (2007). CMA 3 fluorochrome staining produced fluorescent bands coincident with AgNORs, in the triploid as well as the diploid individuals (Figure 2c and d, respectively), showing that the DNA sequences of ribosomal genes are GC-base rich in both karyotypes.…”

“…Triploidy in Characidium gomesi (Centofante et al, 2001) and in Leporinus cf. elongatus (Molina et al, 2007) was even more interesting, since these species have differentiated sex chromosomes. In the first species, the triploid individual was a female with one W and two Z chromosomes, while in the second the triploid was a male with 3 Z chromosomes.…”

The key role of repeated DNAs in sex chromosome evolution in two fish species with ZW sex chromosome system

“…Leporinus (Anostomidae, Characiformes) represents a frequently investigated genus that shows a conserved chromosome number (2n = 54) with a conspicuous ZW sex chromosome system shared by several species. The typical W chromosome is always the largest one in the karyotype, almost fully heterochromatic and much bigger than the Z chromosome, representing a model of well-differentiated ZW sex systems without degeneration of the sex-specific chromosome [ 15 - 20 ]. On the other hand, Triportheus (Characidae, Characiformes) is also a well investigated genus, in which all species present 2n = 52 chromosomes and a ZW sex chromosome system The size of W chromosome in Triportheus is reduced compared to the Z chromosome, representing a distinct model of a well-differentiated ZW system with degeneration of the sex-specific chromosome [ 21 - 24 ].…”

Triploidy in tambaqui Colossoma macropomum identified by chromosomes of fish larvae

“…zebra (Characiformes, Crenuchidae), Hoplerythrinus unitaeniatus (Characiformes, Erythrinidae), Gymnotus carapo (Gymnotiformes, Gymnotidae), Trichomycterus davisi (Siluriformes, Trichomycteridae), among others. [31][32][33][34][35][36] In aquaculture, fish triploid induction for Neotropical species have been developed for jundiá Rhamdia quelen. [37][38][39] In these experiments, the protocols allow obtaining 100% of triploids.…”