(C) 2012 Anderson Luis Alves. This is an open access article distributed under the terms of the Creative Commons Attribution License 3.0 (CC-BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
For reference, use of the paginated PDF or printed version of this article is recommended.
The family Loricariidae with 813 nominal species is one of the largest fish families of the world. Hypostominae, its more complex subfamily, was recently divided into five tribes. The tribe Hypostomini is composed of a single genus, Hypostomus Lacépède, 1803, which exhibits the largest karyotypic diversity in the family Loricariidae. With the main objective of contributing to a better understanding of the relationship and the patterns of evolution among the karyotypes of Hypostomus species, cytogenetic studies were conducted in six species of the genus from Brazil and Venezuela. The results show a great chromosome variety with diploid numbers ranging from 2n=68 to 2n=76, with a clear predominance of acrocentric chromosomes. The Ag-NORs are located in terminal position in all species analyzed. Three species have single Ag-NORs (Hypostomus albopunctatus (Regan, 1908), Hypostomus prope plecostomus (Linnaeus, 1758), and Hypostomus prope paulinus (Ihering, 1905)) and three have multiple Ag-NORs (Hypostomus ancistroides (Ihering, 1911), Hypostomus prope iheringi (Regan, 1908), and Hypostomus strigaticeps (Regan, 1908)). In the process of karyotype evolution of the group, the main type of chromosome rearrangements was possibly centric fissions, which may have been facilitated by the putative tetraploid origin of Hypostomus species. The relationship between the karyotype changes and the evolution in the genus is discussed.
Armoured-catfish, Loricariidae, Hypostomus, karyotype evolution, Ag-NORs, centric fission, polyploidy
The subfamily Hypostominae with about 386 species (
Phylogeny of the family Loricariidae proposed by
The genus Hypostomus is the most representative in the family (
Recent studies suggested that the genus Hypostomus might be composed of some monophyletic groups (
A summary of the cytogenetic data available for the genus Hypostomus. 2n = diploid number; M = metacentric; SM = submetacentric; ST = subtelocentric; A = acrocentric.
Species | Locality | 2n | Karyotypic formulae | References |
---|---|---|---|---|
Hypostomus affinis (Steindachner, 1877) | Paraitinga River, São Paulo, Brazil | 66 | 14M, 14SM, 12ST, 26A |
|
Jacuí stream (SP) | 66 | 14M, 14SM, 12ST, 26A |
|
|
Hypostomus albopunctalus (Regan, 1908) | Mogi-Guaçu River, São Paulo, Brazil | 74 | 10M, 20SM, 44ST/A |
|
Corumbataí River, São Paulo, Brazil | 74 | 10M, 20M, 16ST, 28A | Present study | |
Hypostomus ancistroides (Ihering, 1911) | -- | 68 | 10M, 28SM, 30ST/A |
|
Araquá River, São Paulo, Brazil | 68 | 18M, 10SM, 12ST, 28A |
|
|
Corumbataí River, São Paulo, Brazil | 68 | 16M, 4SM, 16ST, 32A | Present study | |
Mogi-Guaçu River, São Paulo, Brazil | 68 | 16M, 18SM, 34ST/A |
|
|
Paranapanema River, São Paulo, Brazil | 68 | 10M, 26SM, 32ST/A |
|
|
Hypostomus prope auroguttatus (Kner, 1854) | Mogi-Guaçu River, São Paulo, Brazil | 76 | 8M, 30SM, 38ST/A |
|
Hypostomus cochliodon (Kner, 1854) | Salobra river and Salobrinha stream (MS) | 64 | 16M, 20SM, 28ST-A (male)/ 16M, 19SM, 27ST-A (female) | Cereali (2006) |
Hypostomus emarginatus (Valenciennes, 1840) | Araguaia River, Mato Grosso, Brazil | 52 | 16M, 30SM, 6ST |
|
Hypostomus goyazensis (Regan, 1908) | Vermelho River, Goiás, Brazil | 72 | 10M, 16SM, 10ST, 36A |
|
Hypostomus prope iheringi (Regan, 1908) | Corumbataí River, São Paulo, Brazil | 74 | 10M, 14M, 20ST, 30A | Present study |
Hypostomus macrops (Eigenmann & Eigenmann, 1888) | -- | 68 | 10M, 14SM, 44ST/A |
|
Hypostomus nigromaculatus (Schubart, 1964) | Tibagi River, Paraná, Brazil. | 76 | 6M, 20SM, 50ST/A |
|
Mogi-Guaçu River, São Paulo, Brazil | 76 | 8M, 20SM, 48ST/A |
|
|
Hypostomus paulinus (Ihering, 1905) | -- | 74 | 10M, 20SM, 44ST/A |
|
Hypostomus prope paulinus (Ihering, 1905) | Corumbataí River, São Paulo, Brazil | 76 | 6M, 18M, 12ST, 40A | Present study |
Hypostomus prope paulinus (Ihering, 1905) | Corumbataí River, São Paulo, Brazil | 76 | 6M, 18M, 12ST, 40A | Present study |
Hypostomus plecostomus (Linnaeus, 1758) | -- | 54 | 24M/SM, 12ST, 18A | Muramoto et al. (1968) |
Hypostomus prope plecostomus (Linnaeus, 1758) | Orinoco River, Bolivar, Venezuela | 68 | 12M, 16M, 12ST, 28A | Present study |
Hypostomus regani (Ihering, 1905) | Mogi-Guaçu River, São Paulo, Brazil | 72 | 10M, 20SM, 42ST/A |
|
Paranapanema River, São Paulo, Brazil | 72 | 10M, 18SM, 44ST/A |
|
|
Araguá River, São Paulo, Brazil | 72 | 12M, 18SM, 26ST, 16A |
|
|
Hypostomus strigaticeps (Regan, 1908) | Corumbataí River, São Paulo, Brazil | 74 | 10M, 14M, 14ST, 36A | Present study |
Mogi-Guaçu River, São Paulo, Brazil | 74 | 8M, 4SM, 62ST/A |
|
|
Paranapanema River, São Paulo, Brazil | 72 | 10M, 16SM, 46ST/A |
|
|
Hypostomus sp. 2 | Salobrinha stream, Mato Grosso do Sul, Brazil | 84 | 6M, 16SM, 62ST/A |
|
Hypostomus sp. 3 | Perdido River, Mato Grosso do Sul, Brazil | 82–84 | 6M, 16SM, 64ST/A - 6M, 12SM, 66ST/A |
|
Hypostomus sp. A | Rincão Stream, São Paulo, Brazil | 70 | 18M, 14SM, 38ST/A |
|
Hypostomus sp. B | Mogi-Guaçu River, São Paulo, Brazil | 72 | 12M, 18SM, 42ST/A |
|
Hypostomus sp. C | Mogi-Guaçu River, São Paulo, Brazil | 68 | 10M, 18SM, 40ST/A |
|
Hypostomus sp. D1 | Mogi-Guaçu River, São Paulo, Brazil | 72 | 10M, 26SM, 36ST/A |
|
Hypostomus sp. D2 | Mogi-Guaçu River, São Paulo, Brazil | 72 | 14M, 20SM, 38ST/A |
|
Hypostomus sp. E | Mogi-Guaçu River, São Paulo, Brazil | 80 | 8M, 16SM, 56ST/A |
|
Hypostomus sp. F | São Francisco River, Minas Gerais, Brazil | 76 | 10M, 16SM, 50ST/A |
|
Hypostomus sp. G | Araguaia River, Mato Grosso, Brazil | 64 | 14M, 24SM, 26ST/A |
|
Hypostomus sp. Xingu-1 | Xingu River, Pará, Brazil | 64 | 32M/SM, 32ST/A |
|
Hypostomus sp. Xingu-2 | Xingu River, Pará, Brazil | 66 | 32M/SM, 34ST/A |
|
Hypostomus sp. Xingu-3 | Xingu River, Pará, Brazil | 65 | 38M/SM, 26ST/A, 1b |
|
Cytogenetic studies in Hypostomus are relatively well documented (Table 1). In a review of genus cytogenetic data by
Cytogenetic analyses were performed on chromosomal preparations obtained from six species. Five species were collected in the Corumbataí River, São Paulo, Brazil: Hypostomus ancistroides (Ihering, 1911) (6 males and 4 females) (LBP 2544), Hypostomus albopunctatus (Regan, 1908) (5 males and 6 females) (LBP 2547), Hypostomus strigaticeps (Regan, 1908) (6 males and 7 females) (LBP 2545), Hypostomus prope iheringi (Regan, 1908) (5 males and 4 females) (LBP 1674), and Hypostomus prope paulinus (Ihering, 1905) (5 males and 6 females) (LBP 2548). One species of Hypostomus prope plecostomus (Linnaeus, 1758) (3 males and 2 females) (LBP 2198) was collected in the Orinoco River, Bolivar, Venezuela. Vouchers were deposited in the fish collection of Laboratório de Biologia e Genética de Peixes (LBP), UNESP, Botucatu, São Paulo, Brazil.
Chromosome preparations were obtained from kidney tissues using the technique described by
Hypostomus ancistroides has karyotype with 2n=68 (16M, 4SM, 16ST, 32A) and terminal Ag-NORs on the short arm of the chromosome pair 1 (M) and pair 10 (SM) (Fig. 2a).
Giemsa stained karyotypes of Hypostomus a Hypostomus ancistroides, 2n=68 b Hypostomus albopunctatus, 2n=74. Ag-NOR-bearing chromosome pairs in the insets. Bar = 10µm.
Hypostomus albopunctatus has 2n=74 (10M, 20SM, 16ST, 28A) and terminal Ag-NORs on the short arm of the chromosome pair 15 (SM) (Fig. 2b).
Hypostomus prope iheringi has 2n=74 (10M, 14SM, 20ST, 30A) and terminal Ag-NORs on the long arms of the chromosome pairs 23, 24, 25, 30 (A) (Fig. 3a).
Giemsa stained karyotypes of Hypostomus a Hypostomus prope iheringi, 2n=74 b Hypostomus strigaticeps, 2n=74. Ag-NOR-bearing chromosome pairs in the insets. Bar = 10µm.
Hypostomus prope paulinus has 2n=76 (6M, 18SM, 12ST, 40A) and terminal Ag-NORs on the long arm of the chromosome pair 20 (A) (Fig. 4b).
Giemsa stained karyotypes of Hypostomus a Hypostomus prope plecostomus, 2n=68 b Hypostomus prope paulinus, 2n=76. Ag-NOR-bearing chromosome pairs in the insets. Bar = 10µm.
Hypostomus prope plecostomus has 2n=68 (12M, 16SM, 12ST, 28A) and terminal Ag-NORs on the short arm of the chromosome pair 16 (ST) (Fig. 4a).
Hypostomus strigaticeps has 2n=74 (10M, 14SM, 14ST, 36A) and terminal Ag-NORs on the short arm of the chromosome pair 14 (ST) and on the long arm of the chromosome pairs 21, 22 e 24 (A) (Fig. 3b).
The genus Hypostomus seems to be the karyotypically most derived genus in Loricariidae (
Three species had single Ag-NORs (Hypostomus albopunctatus, Hypostomus prope plecostomus, and Hypostomus prope paulinus); and the three others had multiple Ag-NORs (Hypostomus ancistroides, Hypostomus prope iheringi, and Hypostomus strigaticeps). All species presented terminal Ag-NORs, a marked characteristic of the species of this genus. The occurrence of multiple Ag-NORs is the most common characteristic among the Hypostomini, however, this phenotype is considered a derived characteristic among siluriforms (
Differences in the karyotype formulae or in the number and position of Ag-NORs are common in species that do not present extensive migration behaviour, since isolated populations are more commonly involved in inbreeding processes, which makes the fixation of chromosome rearrangements easier (
Thus, in the ancestor of Hypostomini an extensive process of chromosome fusions should have occurred changing a putative original karyotype with 2n=108 chromosomes into a karyotype with 2n=54 chromosomes. The alternative hypothesis that species of Hypostomus with high diploid numbers are the most primitive, suggesting that new chromosome fusions are reducing the diploid numbers in the genus, is not corroborated by the phylogenies available for the genus (
The authors are grateful to Renato Devidé for his technical assistance and to C.H. Zawadzki for the taxonomic identification of the species. This research was supported by the Brazilian agencies FAPESP (Fundação de Apoio à Pesquisa do Estado de São Paulo) and CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico).