A ZZ/ZW sex chromosome system in a new species

Vol. 55, no. 2: 139-150, 2002
CARYOLOGIA
A ZZ/ZW sex chromosome system in a new species
of the genus Parodon (Pisces, Parodontidae)
LIANO CENTOFANTE*, LUIZ ANTONIO CARLOS BERTOLLO and ORLANDO MOREIRA-FILHO
Departamento de Genética e Evolução, Universidade Federal de São Carlos, Rodovia Washington Luis, Km 235, C.P.676, CEP
13565-905 São Carlos, SP, Brazil.
Abstract - A chromosome analysis was carried out in two sympatric fish species
of the genus Parodon, Parodon sp. and P. tortuosus, from the Paraná basin, São
Paulo State, Brazil. Although both species showed the same diploid number
(2n=54), an interspecific diversity was detected concerning their karyotypic formulas and banding patterns, besides a ZZ/ZW sex chromosome system detected in Parodon sp., which was caracterized as a new species for this genus. No heteromorphic sex chromosomes were found in P. tortuosus. These data are discussed concerning the characterization of the regional ictiofauna and its evolutionary aspects.
Key words: Biological diversity, Parodon fish, sex chromosomes.
INTRODUCTION
Research on sex chromosomes in neotropical
fish has increased in the last years, with the description of several systems in diverse species/populations (MOREIRA-FILHO et al. 1993). One of
the first indications about a probable male heterogamety in fish was reported by NOGUSA (1955,
1960) in the Gobiidae, Mogrunda obscura (In:
OHNO 1974). Early cytogenetic studies were carried out especially through histological sectioning or squash of tissues/organs. As these methods
in general difficult a detailed chromosomal analysis, the first descriptions enhanced some more
easily detectable characteristics, such as the different haploid and/or diploid numbers among
males and females bearing multiple sex chromosomes (UYENO and MILLER 1971; 1972), or the
differentiated chromosomal size in some simple
systems (XX/XY or ZZ/ZW).
In the 1970’s, cell suspension methods – originally employed for chromosomal studies in higher vertebrates – were adapted to fish study. As a
result, good mitotic chromosomes could be ob-
* Corresponding author: e-mail: [email protected]
tained, advancing progress in fish cytogenetics.
In the same period, SUMNER (1972) described the
C-banding method, which was also later applied
to fish chromosomal analyses. This methodology
soon led to new findings on fish sex chromosome
systems, as well as the confirmation/invalidation
of some former descriptions. In the last decades,
the development and improvement of new cytogenetics methods, such as the use of base pairs
(GC or AT) specific fluorochromes and the differentiation of multiple bands on the chromosomes, became fundamental to demonstrating the
chromosomal rearrangements related to the origin of the sex chromosome systems. More recently, the use of fluorescent in situ hybridization
(FISH), with satellite DNA probes, has improved
these studies.
Although this work not deals with a detailed
revision of fish sex chromosome systems, we have
prepared a list (Table 1), in order to show the diversity of systems found in different neotropical
fish families, genera and species, in contrast to
other vertebrate groups, such as mammals and
birds, where an XX/XY or ZZ/ZW sex chromosome system is predominant, respectively. Fiftyfive occurrences of heteromorphic sex chromosomes have been characterized so far in neotrop-
140
CENTOFANTE, BERTOLLO
and MOREIRA-FILHO
Table 1 – Sex chromosome systems described in neotropical fish species.
Order/Family/species
CHARACIFORMES
Anostomidae
Leporinus elongatus
Leporinus obtusidens
Leporinus reinhardti
Leporinus macrocephalus
Leporinus trifasciatus
Leporinus conirostris
Leporinus cf. elongatus
Leporinus cf. brunneus
Characidae
Triportheus albus
Triportheus signatus
Triportheus elongatus
Triportheus cf. elongatus
Triportheus guentheri
Triportheus flavus
Triportheus paranense (MT)
Triportheus paranense (MS)
Triportheus paranense (Argentina)
Gasteropelecidae
Thoracocharax cf. stellatus
Crenuchidae
Characidium cf. fasciatum
Characidium gomesi
Erythrinidae
Erythrinus erythrinus
Hoplias cf. lacerdae (rio Pardo)
Hoplias cf. malabaricus (Vale R. Doce)
Hoplias cf. malabaricus (rio Ribeira)
Hoplias cf. malabaricus (Alto Paraná)
Hoplias cf. malabaricus (rio Aripuanã)
Parodontidae
Apareiodon affinis
Parodon hilarii
Parodon sp.
Curimatidae
Potamorhina squamoralevis
Prochilodontidae
Semaprochilodus taeniurus
Cheirodontidae
Cheirodon notomelas
Cheirodon sp.
Odontostilbe cf. microcephala
SILURIFORMES
Loricariidae
Hypostomus ancistroides
Hypostomus sp.
Hypostomus macrops
Microlepdogaster leucofrenatus
Microlepdogaster sp.
Pseudotocinclus tietensis
Loricariichthys platymetopon
Doradidae
Opsodoras sp.
Pimelodidae
Pimelodella sp.
GYMNOTIFORMES
Sternopygidae
Eigenmannia virescens
Eigenmannia virescens
Eigenmannia sp.
Brachyhypopomus pinnicaudatus
Hypopomus sp.
m
chromosome
systems
type of
analysis
Ref.
f
2n
54
54
54
54
54
54
54
54
54
54
54
54
54
54
54
54
ZZ/ZW
ZZ/ZW
ZZ/ ZW
ZZ/ZW
ZZ/ZW
ZZ/ZW
ZZ/ZW
ZZ/ZW
G,C,F
G,C,F
G,C,F
G,C
G,C,F
G,C
G,C,F
G,C,F
14,15
14,15
14,15
15
32,43
43
14
32
52
52
52
52
52
52
52
52
52
52
52
52
52
52
52
52
52
52
ZZ/ZW
ZZ/ZW
ZZ/ZW
ZZ/ZW
ZZ/ZW
ZZ/ZW
ZZ/ZW
ZZ/ZW
ZZ/ZW
G,C
G,C
G,C
G,C,H,F
G,C,H,F
G,C
G,C,H,F
G,C,H,F
G,C
11
11
11
29,44
5,29,44
11
29,44
29,44
42
52
52
ZZ-ZW
G,C
40
50
50
50
50
ZZ/ZW
ZZ/ZW
G,C
G,C
25
39
52
50
42
42
40
40
51
50
42
42
39
41
X1X1X2X2/X1X2Y
XX/XY
XX/XY
XX/XY
X1X1X2X2/X1X2Y
XX/XY1Y2
G,M,C
G,C
G,C,M,H,F,B
G,M
G,C,M,B
G,M
50,51
6
7,46
7
8,9,45
8
55
54
54
54
54
54
ZZ/ZW1W2
ZZ/ZW
ZZ-ZW
G,C,F
G,C,H,F,B
G,C,H
17,48
18,47
41
102
102
ZZ/ZW
G,C
34
54
54
ZZ/ZW
G,C
12
52
52
52
52
52
52
ZZ/ZW
ZZ/ZW
ZZ/ZW
G
G
G
33
33
38
68
64
68
54
54
54
54
68
64
68
54
54
54
54
XX/XY
ZZ/ZW
XX/XY
ZZ/ZW
ZZ/ZW
XX/XY
ZZ/ZW
G
G,C
G
G,C
G,C
G,C
G,C
16
26
16
4
37
3
27
58
58
ZZ/ZW
G,C,F
31,32
46
46
XX/XY
G
10
38
32
42
38
31
41
XX/XY
ZZ/ZW
X1X1X2X2/X1X2Y
X1X1X2X2/X1X2Y
X1X1X2X2/X1X2Y
G,C
G,C
G,C,M,F
G,C,H,F
G,C
2
13
1,49
36
28
141
SEX CHROMOSOMES AND A NEW PARODON SPECIES
Order/Family/species
CYPRINODONTIFORMES
Cyprinodontidae
Mexican anonymous species
Goodeidae
Mexican anonymous species
Poeciliidae
Poecilia reticulata
Gambusia puncticulata
PERCIFORMES
Gobiidae
Awaous strigatus
Eleotridae
Dormitator maculatus
CLUPEIFORMES
Clupeidae
Brevorita aurea
m
chromosome
systems
type of
analysis
Ref.
f
2n
48
47
X1X1X2X2/X1X2Y
G,M
22
48
47
X1X1X2X2/X1X2Y
G,M
23
46
48
46
48
XX/XY
ZZ/ZW
G,C,H
G,M
19
21
46
45
X1X1X2X2/X1X2Y
G,C
30
48
48
XX/XY
G,M
20
46
45
X1X1X2X2/X1X2Y
G,M
24
G = conventional staining with Giemsa; C = C banding; M = meiosis analysis; H = in situ hybridization; F = fluorochromes; B =
G and/or R banding; m = male; f = female.
References: 1. ALMEIDA-TOLEDO et al. (1984); 2. ALMEIDA-TOLEDO et al. (1988); 3. ANDREATA et al. (1992); 4. ANDREATA et al. (1993);
5. BERTOLLO and CARVALHO (1992); 6. BERTOLLO et al. (1978); 7. BERTOLLO et al. (1979); 8. BERTOLLO et al. (1983); 9. BERTOLLO
et al. 1997); 10. DIAS and FORESTI (1993); 11. FALCÃO (1988); 12. FELDBERG et al. (1987); 13. FORESTI (1987); 14. MOLINA et al.
(1998); 15. GALETTI JR. and FORESTI (1986); 16. MICHELE et al. (1977); 17. MOREIRA-FILHO et al. (1980); 18. MOREIRA-FILHO et al.
(1993); 19. NANDA et al. (1990); 20. OLIVEIRA and ALMEIDA-TOLEDO (1985); 21. RAB (1984); 22. UYENO and MILLER (1971);
23. UYENO and MILLER (1972); 24. BRUM et al. (1992); 25. MAISTRO et al. (1998); 26. ARTONI et al. (1998); 27. SCAVONE and JULIO
JR. (1995); 28. ALMEIDA-TOLEDO et al. (1995); 29. ARTONI et al. (2001); 30. SOUZA et al. (1998); 31. VENERE and GALETTI JR. (1998);
32. VENERE (1998); 33. NISHIYAMA and MARTINS-SANTOS (1996); 34. NAVARRETE and JULIO JR. (1996); 35. MOLINA et al. (1996);
36. ALMEIDA-TOLEDO et al. (1998); 37. ANDREATA et al. (1999); 38. SATO and MARTINS-SANTOS (1999); 39. CENTOFANTE et al. (2001);
40. CARVALHO (2001); 41. Present study; 42. SÁNCHEZ et al. (1999); 43. GALETTI JR. et al. (1995); 44. ARTONI (1999); 45. BERTOLLO
and MESTRINER (1998); 46. BORN and BERTOLLO 2000; 47. VICENTE (2001); 48. JESUS (1996); JESUS et al. (2000); 49. ALMEIDA-TOLEDO
et al. (2000); 50. MOLINA and BERTOLLO (1993); 51. SILVESTRO and MARGARIDO (2001).
ical fish (Table 1), 64% of them showing female
heterogamety and 36% male heterogamety.
Eighty percent of these cases correspond to simple sex chromosome systems, among with 77%
are ZZ/ZW and 23% are XX/XY. The remaining
20% cases correspond to multiple sex chromosome systems, among which 91% and 9% show
male and female heterogamety, respectively.
Besides diversity, variability in the shape and
size of the sex chromosomes may also be observed. Thus, in some species the Z chromosome
has, in general, a meddle size in the karyotype,
whereas the W chromosome is the largest in the
complement, as observed in the Leporinus genus,
Parodon hilarii, Semaprochilodus taenniurus, Microlepidogaster leucofrenatus. In contrast, the Z
chromosome is the largest one in Triportheus,
whereas the W chromosome presents a differential size among the distinct species, although always smaller than the Z chromosome. On the
other hand, in Hypostomus sp. the W corresponds to the small chromosome of the karyotype. Identical occurrences are observed with respect to the XX / XY sex system. Hence, in
Pseudotocinclus tietensis, the Y chromosome is
much larger than the X, with a great amount of
heterochromatin. Contrarily, in Hoplias malabaricus, the X chromosome is larger than the Y,
which is the smallest chromosome in the karyotype, and with little heterochromatin. Other interesting situation may be observed in some genera, such as Hypostomus and Eigenmannia, where
the heterogametic sex are the females (ZZ/ZW)
in some species, or the males (XX/XY), in others. Besides, both simple and multiple sex chromosome systems may be found in different
species of the same genus, as in Hoplias and Eingenmannia (Table 1).
The Parodontidae family is represented by 3
genera: Parodon, Apareiodon and Saccodon. The
first two genus have a broad distribution
throughout the South American continent, except for the western side of the Andes, whereas
Saccodon has a more restrict distribution, only in
the northern regions of the continent. This fish
group presents a small number of species as compared to other neotropical Characiformes, adapted to small brooks and running water.
142
The cytogenetic studies in this family are restricted to seven Apareiodon and four Parodon
species, including the species now analyzed.
Thus, no cytogenetic study has been carried out
so far in Saccodon. Although all the above eleven
species show 2n=54 chromosomes, two distinct
sex chromosome systems have already been described, a ZZ/ZW1W2 system in Apareiodon affinis (MOREIRA-FILHO et al. 1980; JESUS et al. 1999;
JORGE and MOREIRA-FILHO 2000), and a ZZ/ZW
system, in Parodon hilarii (MOREIRA-FILHO et al.
1993; JESUS and MOREIRA-FILHO 2000). The nucleolus organizing regions (NORs) do not vary
concerning their number and chromosomal sites
in most of the Apareiodon species (MOREIRA-FILHO et al. 1984). On the contrary, these regions appears as species-specific in Parodon (JESUS and
MOREIRA-FILHO 2000). Besides, the occurrence
of supernumerary chromosomes has already been
reported in Apareiodon piracicabae (FALCÃO et al.
1984). In general these studies point to the maintenance of the diploid number among the different species of the group, as well as to a karyotypical diversification regarding other chromosomal
characters.
CENTOFANTE, BERTOLLO
and MOREIRA-FILHO
This work describes a ZZ/ZW system in a Parodon species that has not been yet described, including its characterization, probable origin and
evolution.
MATERIALS AND METHODS
Chromosomal studies were carried out in two Parodon species, one of them representing a new species,
not taxonomically described yet and here denominated as Parodon sp., and another one identified as Parodon tortuosus (EIGENMANN and NORRIS 1900). Both
species were collected under sympatric and syntopic
conditions in the Paiol Grande stream (São Bento do
Sapucaí, São Paulo State, Brazil), and were stored in
the Museu de Zoologia, Rio de Janeiro, Brazil (lot:
MNRJ21446).
Three-hundred and forty-eight Parodon sp.
metaphases (12 specimens: 8 females and 4 males) and
780 Parodon tortuosus metaphases (30 specimens: 18
females and 12 males) were analyzed.
Mitotic chromosome preparations followed
BERTOLLO et al. (1978). The detection of constitutive
heterochromatin was done according SUMNER (1972),
and adapted to sequential analyses (conventional
Giemsa/C banding) as suggested by CENTOFANTE
Fig. 1 – (a) Parodon sp., 120 mm SL; (b) Parodon tortuosus, 110mm SL; (MNRJ 21446).
SEX CHROMOSOMES AND A NEW PARODON SPECIES
(2000). The analysis of the nucleolar organizing regions after silver staining (Ag-NORs), followed HOWELL and BLACK (1980). The fluorescent in situ hybridization (FISH) was based on PINKEL et al. (1986),
using: (1) pPh2004 (200pb) satellite DNA probe,
cloned from the DNA genome of Parodon hilarii; (2)
18S rDNA probe, obtained by PCR with NS1 and
NS2 primers (VICENTE 2001); and (3) 5S rDNA
probe, obtained from Leporinus elongatus (MARTINS
and GALETTI Jr. 1999). The chromosome types were
classified according their arm ratio, as proposed by
LEVAN et al. (1964).
RESULTS
Parodon sp. (Fig. 1a) exhibited a diploid number equal to 54 meta-submetacentric chromosomes and a fundamental number (number of
143
chromosome arms) equal to 108, for both sexes.
The chromosomes were organized in a decreasing order of size in the karyotypes. The males
showed 27 meta-submetacentric chromosome
pairs, whereas the females showed 26 meta-submetacentric chromosome pairs plus one large
metacentric and one medium-sized submetacentric chromosomes (Fig. 2). Hence, it occurs a
ZZ/ZW sex chromosomal heteromorphism, the
large metacentric chromosome, which is similar
in size to the first pair of the complement, corresponding to the W chromosome, and the medium-sized submetacentric chromosome (chromosome no. 6), corresponding to the Z chromosome
(Fig. 2).
The Ag-NORs are located on the terminal region of the long arm of the no. 15 submetacentric
chromosome pair (Fig. 2, box). The in situ hy-
Fig. 2 – Karyotype of Parodon sp., female (a, b) and male (c, d) with conventional Giemsa staining (a, c) and C-banding (b,
d). In highlight, n° 15 pair, bearer of the NORs, after silver nitrate staining.
144
bridization (FISH), with 18S rDNA, confirmed
the Ag-NORs results (Fig. 3a). On the other
hand, the hybridization with the 5S rDNA probe
evidenced a medium-sized submetacentric chromosome pair labeled on its short arm (Fig. 3b).
The Z chromosome has a conspicuous terminal heterochromatic region on the long arm, and
a discrete band on the short arm. The W chromosome also evidences a terminal block on the
short arm, while the long arm is totally heterochromatic. However, this is a paler heterochromatin as compared to that present on the
short arm. C-bands also occur in the pericen-
CENTOFANTE, BERTOLLO
and MOREIRA-FILHO
tromeric region of most chromosomes, besides
some more conspicuous bands in pairs 2, 3, 4, 8,
12, 15, 18 and 22. In pair 15, the terminal heterochromatic block on the long arm coincides with
the nucleolus organizing regions (Fig. 2). The in
situ hybridization with the pPh2004 satellite
DNA probe showed that the heterochromatin
found in the terminal region of the long arm of
the Z chromosome, as well as in the terminal region of the short arm of the W chromosome,
comprises this repetitive DNA family, besides
some punctual regions observed in other two
small metacentric pairs (Fig. 3c/d).
a
b
c
d
Fig. 3 – In Situ hybridization (FISH) in Parodon sp. showing (a) 18S rDNA, (b) 5S rDNA, (c) satellite DNA Pph2004 in female
and (d) male.
SEX CHROMOSOMES AND A NEW PARODON SPECIES
Parodon tortuosus (Fig. 1b) also exhibited a
diploid number equal to 2n=54 chromosomes: 48
meta-submetacentric and 6 subtelocentric ones,
with a fundamental number equal to 108. Sex
chromosome heteromorphism was not found in
this species (Fig. 4a).
The nucleolus organizing regions are also of
the simple type, found on the terminal region of
the long arm of the subtelocentric pair no. 25
(Fig. 4, box). The constitutive heterochromatin
occurs on the pericentromeric region of several
pairs of the karyotype, as well as in other more
conspicuous bands in the chromosomes 1, 3, 4,
12, 14, 25, 26 and 27, coinciding with the AgNORs in the 25th pair (Fig. 4b).
DISCUSSION
Sympatry and syntopy among karyotypically divergent but morphologically similar specimens, without the occurrence of hybrid forms,
have already been reported for some neotropical fish groups, such as the Bryconamericus
(WASKO et al., 1996), Hoplias (BERTOLLO et al.
2000) and Synbranchus marmoratus (TORRES
2000) genus. These cases suggest that chromosome differences may have contributed to a re-
145
productive isolation process, allowing the coexistence of the distinct forms in the same environment today.
In the Parodontidae family cases of sympatric
and syntopic species have been described in the
Apareiodon genus (SAZIMA 1980; MOREIRA-FILHO et al. 1985). However, for the Parodon genus,
none occurrence had been reported before the
present work. Morphological differences were
observed between the two species now analyzed,
the most remarkable ones concerning the shape
and color of the longitudinal stripe along the lateral line and the scales right above this line. In
Parodon sp., this longitudinal stripe is dark and
irregular, extending from the operculum to the
distal extremity of the medium caudal-fin rays.
In Parodon tortuosus this longitudinal stripe appears as a zigzag, with oblique projections
(Fig. 1). It is important to remark that P. tortuosus represents the only known species of this
genus in the Alto Paraná river basin.
Although both species have the same diploid
number (2n=54) and the same fundamental
number (FN=108), other karyotypic differences
were also observed. Thus, Parodon sp. presents
only meta- and submetacentric chromosomes in
the karyotype, whereas P. tortuosus presents
meta-, submeta- and subtelocentric chromo-
Fig. 4 – Karyotype of Parodon tortuosus with conventional Giemsa staining (a) and C-banding (b). In highlight, n° 25 pair,
bearer of the NORs, after silver nitrate staining.
146
CENTOFANTE, BERTOLLO
somes. The ribosome sites in Parodon sp. are located in the submetacentric pair no. 15, while in
Parodon tortuosus these sites are located in the
subtelocentric pair no. 25. The C banding pattern also differs, with fewer marked regions in
Parodon sp. as compared to Parodon tortuosus.
However, the most remarkable difference refers
to the ZZ/ZW sex chromosome system present
in Parodon sp. and its absence in P. tortuosus
(Figs. 2 and 4).
The W chromosome differentiation in Parodon sp. may have occurred through a heterochromatization process, beginning from a discrete heterochromatic segment located on the
short arm of an ancestral W chromosome, probably similar to the Z chromosome (pair 6 in
males). The heterochromatization advancement
may have increased this chromosomal arm size
and the resulting differentiation of the long arm
of the actual heterochromatic W chromosome.
In addition, the C-banding pattern and the
FISH results with the satellite DNA probe
(pPh2004) show a clear correspondence between the telomeric bands found on the long
arm of the Z chromosome and on the short arm
of the W chromosome, corroborating the hypothesis of an ancestral W chromosome homologue to the Z chromosome. This hypothesis was
also used by VICENTE (2001) to explain the origin of a same sex chromosome system present in
another species of this genus, P. hilarii. Therefore, we suggest that the heterochromatization
process that originated the ZZ/ZW system in
these two species is the same. On the other
hand, the satellite DNA probe labels only some
specific heterochromatic segments on the W
chromosome, thus demonstrating that distinct
repetitive DNA families occur in this chromosome. Accordingly, the heterochromatin of the
long arm of W chromosome shows a differentiable staining degree, which appears lighter
than the heterochromatic segment present on
the short arm of this same chromosome.
and MOREIRA-FILHO
Previous studies, with other Parodontidae
species (MOREIRA-FILHO et al. 1985; JESUS and
MOREIRA-FILHO 2000; VICENTE 2001) show a
constancy in size of the first chromosome pair in
the karyotype. Thus, this chromosome pair can
be used as a comparative parameter between the
ZZ/ZW sex chromosome systems of Parodon sp.
and P. hilarii. In this last species the W chromosome, a subtelocentric one, shows a 30% larger
size as compared to the 1st chromosome pair of
the karyotype, whereas in Parodon sp. the W
chromosome is metacentric, with a similar size to
that of the 1st karyotypic pair. In addition, P. hilarii exhibits a greater amount of satellite DNA,
i.e., besides the sex chromosomes there are six
other chromosome pairs showing evident hybridization regions (VICENTE 2001). This fact
does not occur in Parodon sp. since only two other chromosome pairs show a punctual hybridization, besides the sex chromosomes. Other karyotypic differences between these species
may be seen in Table 2. On the other hand, the
only similarity observed refers to the number and
localization of the Ag-NORs, which are located
in the same pair of chromosomes.
Among neotropical fish, distinct sex chromosome systems may be found (Table 1), among
species of the same genus, as in Hoplias (BERTOLLO et al. 2000), Eigenmannia (ALMEIDA-TOLEDO
et al. 1984), Characidium (MAISTRO et al. 1998;
CENTOFANTE et al. 2001) or among species of a
same family, as in Parodontidae (MOREIRA-FILHO et al. 1993). Indeed, two distinct sex chromosome systems have already been described
in the Parodontidae fish. The first one, in
Apareiodon affinis, corresponds to a ZZ/ZW1W2
multiple sex chromosome system, with a probable origin from chromosome rearrangements
(MOREIRA-FILHO et al. 1980; JESUS et al. 1999;
JORGE and MOREIRA-FILHO 2000). The second
one corresponds to the ZZ/ZW system, which
may have originated from a heterochromatization process, present in P. hilarii (MOREIRA-FIL-
Table 2 – Parodon species studied and their sites. Brazilian states: MG = Minas Gerais, SP=São Paulo, MT=Mato Grosso;
Chromosomal types: M=metacentric, SM=submetacentric, ST=subtelocentric; CS=sex chromosomes; T=terminal; NOR=nucleolus organizing regions; R=references.
Species
P. hilarii
P. pongoensis
P. tortuosus
Parodon sp.
Karyotype
SC
NOR
Source
R
54 M-SM
50 M-SM+4 ST
48 M-SM+6 ST
54 M-SM
ZZ/ZW
ZZ/ZW
pair 15 (T)
pair 2 (T)
pair 25 (T)
pair 15 (T)
São Francisco - MG
Médio Araguaia - MT
Alto Paraná - SP
Alto Paraná - SP
1-2
2
2-3
4
1 - MOREIRA-FILHO et al. (1993); 2 - JESUS and MOREIRA-FILHO (2000); 3 -MOREIRA-FILHO et al. (1985); 4 - Present study.
147
SEX CHROMOSOMES AND A NEW PARODON SPECIES
HO et al. 1993; JESUS et al. 2000; VICENTE 2001)
and in Parodon sp. (present study). The diversity and origin of the sex chromosome systems in
the neotropical fish have been associated with
the geographic distribution of the species and
the geomorphologic events in the South American continent (MOREIRA-FILHO et al. 1980;
ALMEIDA-TOLEDO et al. 2000; ARTONI et al.
2001; CENTOFANTE et al. 2001).
Some morphological similarities occur between Parodon sp. and P. pongoensis ALLEN, 1942
(type locality: Pongo de Manseriche, Peru). P.
pongoensis (cited as Parodon sp.), from the
Araguaia river (Brazil), has already been karyotyped by JESUS and MOREIRA-FILHO (2000), and
later identified from the taxonomic revision of
the Parodontidae family (PAVANELLI 1999). Nevertheless, besides the similarities between Parodon sp. and P. pongoensis, there are also evident
differences. These morphological analyses are
being carried out together with taxonomy researches, in order to obtain the correct characterization and the specific denomination for Parodon sp. However, the cytogenetic data already
show marked differences between Parodon sp.
and P. pongoensis, concerning the chromosome
structure, location of the nucleolus organizing regions (pair 2 in Parodon pongoensis and pair 15
in Parodon sp.) and occurrence of a ZZ/ZW sex
chromosome system in Parodon sp. and its absence in P. pongoensis (Table 2). In addition, they
also differ in the geographic distribution: Parodon sp. seems to be restricted to the northeastern
Alto Paraná river basin, whereas P. pongoensis,
according to PAVANELLI (1999), occurs in the
tributaries of the Amazon river basin. Thus,
there is a significant geographic isolation between these two species.
The results obtained by this study evidence
exclusive chromosomal characteristics for the
species till now named Parodon sp., in comparison to the remaining Parodon species. These data, as well as its sympatry and syntopy with P. tortuosus at the collection site, without the detection of hybrid forms, suggest that Parodon sp.
corresponds to a new species in this genus, to be
further described following the conventional taxonomy rules, after the end of the current morphological analyses.
Acknowledgments – This study was supported
by FAPESP – Fundação de Amparo à Pesquisa do
Estado de São Paulo (Proc. 01-00713-0).
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Received January 17, 2002; accepted February 25, 2002