Corresponding author: Maria José de J. Silva (
Academic editor: A. Barabanov
Rodents constitute one of the most diversified mammalian orders. Due to the morphological similarity in many of the groups, their taxonomy is controversial. Karyotype information proved to be an important tool for distinguishing some species because some of them are species-specific. Additionally, rodents can be an excellent model for chromosome evolution studies since many rearrangements have been described in this group.This work brings a review of cytogenetic data of Brazilian rodents, with information about diploid and fundamental numbers, polymorphisms, and geographical distribution. We point out that, even with the recent efforts on cytogenetic studies in this group, many species lack karyotypic data. Moreover, we describe for the first time the karyotype of
Di-Nizo CB, Banci KRS, Sato-Kuwabara Y, Silva MJJ (2017) Advances in cytogenetics of Brazilian rodents: cytotaxonomy, chromosome evolution and new karyotypic data. Comparative Cytogenetics 11(4): 833–892.
More than three decades after the last revision of cytogenetics of Brazilian rodents (
Cytogenetic information on Brazilian rodents was firstly described by
Throughout the following decades, several Master dissertations and PhD theses have addressed cytogenetic studies on Brazilian rodents. It became evident that karyotypic data could contribute to accurate taxonomic information, since different names were applied to groups that shared the same karyotype, and very distinct karyotypes were attributed to a single species. Additionally, major fieldwork efforts in Brazil (especially in unexplored areas) have led to the discovery of many new species.
The increasing number of cytogenetic studies on rodents resulted in the characterization of banding patterns, recognition of sex chromosomes, identification of supernumerary chromosomes, pericentric inversions and Robertsonian rearrangements, variations in the amount and localization of constitutive heterochromatin, and recognition of species (cytotaxonomy). These discoveries have led researchers to consider that rodents have undergone a “karyotypic explosion” process and that they stand out as an excellent group for chromosomal evolution studies, since they present many examples of chromosome rearrangements. These rearrangements may have played an important role in karyotype diversification and speciation, with the reduction of gene flow due to meiotic problems (
Previously, chromosome evolution studies were essentially based on the comparison of banding patterns (Yonenaga-Yassuda et al. 1975,
More recently, probes from entire chromosomes were obtained by microdissection or flow sorting, representing a breakthrough in evolutionary studies. The first Brazilian study employing this technique was published by
More than one decade later,
After the tribe
The role of cytogenetics in species recognition (cytotaxonomy) has been know for a while, considering that many rodents’ species are morphologically similar (
Therefore, the aim of this review is to compile all the cytogenetic data available for Brazilian rodents, presenting not only the diploid and fundamental numbers, but also the chromosomal polymorphisms, synonyms, and geographic distribution. In addition, we describe for the first time the karyotype of the monotypic species
This review was done after an extensive revision of the literature, including Master’s and Ph.D. theses, when available (Table
Compilation of cytogenetic data of Brazilian rodents, with the respective synonyms, diploid number (2n) and fundamental number (
Species | Synonyms | 2n |
|
Karyotypic Variations | Distribution | References | ||
---|---|---|---|---|---|---|---|---|
|
- | 64 | 116, 124 | - | ||||
- | 64 | 124 | - | Eastern Brazil, between |
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|
62 | 108 | - | Endemic from |
||||
- | 62; 64 | 102; 124 | Pericentric inversions; addition and deletion of constitutive hetechromatin; Robertsonian rearrangement | |||||
- | 64* | 100-102 | Polymorphism in chromosome 1 | All Brazilian States | ||||
- | N/A | N/A | - | Northwestern |
|
|||
- | 64 | 118 | - | |||||
- | 66 | 102 | - | All Brazilian States, except |
||||
- | 52 | 92 | - | Northeastern |
||||
- | 52 | 92, 94 | Pericentric inversion | From |
||||
|
|
- | 37-38 | 40-44 | Variation in the Y morphology; deletion of the X long arm | Southern Brazil | ||
|
14-16 | 18-26 | Pericentric inversions in pairs 2, 4 and 6; centric fusion and pericentric inversion in pairs 1 and 3; trisomy of the pair 7; |
Atlantic Forest formations in Eastern Brazil from |
||||
42 | 42 |
|
Cerrado habitat, Central and Southeastern Brazil | |||||
23; 24-26; 24/25; 23/24 | 40; 42; 44 | X monosomy; 1 or 2 B chromosomes; mosaicism; reciprocal translocation (1, 6); sex chromosome heteromorphism | Southeastern Brazil, from |
|||||
|
|
- | 42, 44 | 42 | - | Pico da Bandeira, in the border of |
||
|
44 | 44 | Non-disjunction of the sex chromosomes (2n = 43 and 45) | Eastern |
|
|||
- | 44 | 44 | - | Southernmost Brazil ( |
|
|||
- | N/A | N/A | - | Serra do Mar, Southeastern Brazil |
|
|||
- | 9; 10 | 14-16 | X monosomy; pericentric inversion in pair 3; |
Only known from its type locality, |
|
|||
|
40*; 42-43* | 40*; 44* | Karyotype of specimens from Paraguay | Southwestern |
||||
- | 70 | 80 | - | Northern |
||||
- | 28; 31 (29+2Bs); 34; 37 (36 + 1B); 43 (39 + 4Bs); 45 (44 + 1B); 52; 52 (50 + 2Bs) | 48, 50; 50; 50; 50; 50; 50, 51; 50; 50 | B chromosomes; Robertsonian rearrangement; |
Atlantic Forest regions of Southeastern Brazil (from |
||||
- | 52 | 52, 53 | Pericentric inversion in pair 2 | Eastern |
||||
- | N/A | N/A | - | Southeastern |
||||
|
52 | 52 | - | Southern Brazil | ||||
- | 52 | 52 | - | Eastern |
||||
46 | 46 |
|
Atlantic Forest from Southeastern |
|||||
- | 34 | 34 | - | Only known from its type locality, São Francisco de Paula/ |
|
|||
- | 35-38 | 38 | Centric fusion/fission; multiple sex determination system. | Eastern |
||||
|
|
- | 40 | 40 | - | Esmeralda ( |
|
|
|
N/A | N/A | - | Lagoa Santa ( |
||||
|
N/A | N/A | - | Westcentral Brazil |
|
|||
- | N/A | N/A | - |
|
|
|||
- | 44 | 42 | - | Westcentral Brazil | ||||
34, 33, 33/34 | 34 | Robertsonian rearrangement; centric fusion, X polymorphism; mosaicism (XX/X0) | Southern Amazon River, Brazil | |||||
- | 18 | 30 | - | Northern Brazil | Reig et al. 1986, |
|||
- | 54 | N/A | - | Lower Amazon Basin, Southern Amazon River, between Tocantins and Madeira Rivers, Central Brazil, Northwestern |
||||
- | 54 | 64 | - | Eastern |
||||
54 | 64 | - | Atlantic and interior forest of Eastern Brazil ( |
|||||
54 | 62 | - | Southcentral Brazil | |||||
- | 54 | N/A | - | Acre | ||||
- | 54 | 64 | - | Eastern |
||||
|
54 | N/A | - | Eastern Brazil, from |
||||
- | 54 | 66 | - | Southeastern |
|
|||
- | 16 | 26 | - |
|
||||
|
|
- | 32 | 40 | - | Westernmost |
|
|
34, 36 | 40 | Centric fusion | Southern Brazil | |||||
- | 24 | 40 | - | Southernmost Brazil ( |
||||
- | 36 | 34 | - | Cerrado of Central Brazil | ||||
|
37, 38 | 38 | Centric fusion/fission; heterochromatin variation in an autosomal pair | Cerrado of Central Brazil |
|
|||
|
52 | 52 | - | Southeastern Brazil, |
||||
- | 50 | 48 |
|
Only known from its type locality - |
|
|||
|
- | 92 | 98 | - | Amazonian lowland of |
|
||
- | N/A | N/A | - | Amazonian of Northern Brazil ( |
|
|||
|
- | 60 | 74 | - |
|
|
||
- | 54 | 62, 63, 66 | Different interpretation of morphology of small pairs and pericentric inversion in small chromosome | Northeastern littoral of |
||||
46, 48, 49, 50 | 56 | Centric fusion/ fission; Y polymorphism; |
||||||
- | 56 | 58 | - | Central |
||||
- | 56 | 54 | - | |||||
|
58 | 70-72 | Pericentric inversion in small chromosome pair; X and Y polymorphisms | |||||
|
|
- | 54; 55; 56 | 62; 63; 64 | Robertsonian rearrangement; pericentric inversion in pair 5; X and Y polymorphisms; |
|||
|
50 | 62, 63 | Pericentric inversion; |
|||||
- | 62 | 62 |
|
Atlantic Forest of |
||||
|
80 | 86 | - | Centraleastern |
||||
- | 58; 60, 64 | 82, 84; 84 | One name with different karyotypes associated | Western |
||||
|
64; 58 | 70; 90 | One name with different karyotypes associated | Northern Brazil | ||||
|
80 | 86 | - | |||||
80; 80/81 | 86 | Dissociation of the X chromosome; X and Y polymorphisms | Southeastern Brazil from |
|||||
- | 76 | 86 | - | Only known from its type locality - |
|
|||
- | 55; 56-58 | 56 | Centric fusion; 0 to 2 B chromosomes | Southern and Southeastern Brazil | ||||
- | 48-56* | 56-60* | Centric fusion, inversion and B chromosomes | Western |
||||
|
55-56 | 56 | Centric fusion and heteromorphism in pair 1 | Northern, Northeastern and Central Brazil | ||||
|
40 | 56 | - | Western |
||||
48 | 60 | - | Eastern Atlantic Forest, from |
|
||||
|
|
54 | 62 | - | Northern and Central Brazil | |||
|
52 | 62 | - | Northern Rio São Francisco, in |
||||
|
52 | 62 | - | Western Brazil | ||||
48 | 60 | - | Southern Rio São Francisco, from |
|
||||
|
52-60 | 62-67 | Chromosome polymorphisms within and between western and eastern population | Northern Brazil | ||||
|
52 | 58 | Variation in the X chromosome | Central |
||||
- | 38 | 46 | - |
|
||||
|
64 | 68 | - | Northwestern Brazil | ||||
- | 62, 64 | 68 | Robertsonian rearrangement | Northern |
||||
- | 56 | N/A | - | Northern Brazil | ||||
- | 35-36 | 40 | Robertsonian rearrangement | Southwestern |
||||
- | 34 | 64-68 | Pericentric inversion | Westernmost |
||||
- | 56 | 62, 66 | Pericentric inversion | Northernmost Brazil | ||||
- | 58 | 64, 66, 70 | Differences in amount of heterochromatin, pericentric inversion | |||||
- | 42 | 40 | - | Westernmost Brazil, |
||||
52-55 | 52, 54, 56 | B chromosomes; X and Y polymorphisms | Northern, Northeastern and Central Brazil | |||||
|
|
- | 56-59; 55; 56/57 | 56-58; 60; 62 | B chromosomes; fusion/fission of autosomes; X monossomy; X and Y polymorphisms | Southeastern Brazil from |
||
- | 64; 66; 72 | 110; 114; 80 | One name with different karyotypes associated | Northern |
||||
|
60 | 62 | - | |||||
- | 80 | 140; 142 | - | Northern and Central Brazil |
|
|||
- | 60 | 62; 64 | - | Atlantic forest from |
||||
- | 80; 82 | 124, 134, 140, 142; 116 | One name with different karyotypes associated | |||||
|
60 | 62 | - | Northwestern Brazil | ||||
- | 72 | 90 | - | Pantanal | ||||
- | N/A | N/A | - | Westcentral Brazil | ||||
- | 68; 70 | 72; 72, 74, 76 | One name with different karyotypes associated | Central Brazil, Southern Amazon River | ||||
- | 62 | 80 | - | Northern Amazon Rio ( |
||||
- | 80; 82 | 114; 106 | - | Amazon region of |
||||
- | 54 | 82, 90 | - | Eastern |
||||
- | 80 | 108 | - | Western |
|
|||
- | 58 | 96 | - | Northern |
|
|||
- | 86 | 98 | - |
|
||||
|
80 | 124 | - |
|
||||
- | 54 | 54 | - |
|
|
|||
|
|
- | 60 | 62 | - | Aripuanã ( |
|
|
- | 60 | 62 | - | São Joaquim da Barra ( |
|
|||
- | 62 | 62 | - | Vila Rica ( |
|
|||
- | 58 | 74 | - | Centraleastern Brazil | ||||
- | 64-68 | 66-72 | 1 to 4 B chromosomes; sex chromosome polymorphisms | Eastern Brazil, from |
||||
62 | 64-66 | Pericentric inversion in small acrocentric pair | ||||||
- | 66 | 74 | - | Northern Brazil ( |
||||
- | 64 | 64, 66 | Pericentric inversion in pair 1; X polymorphism | Amazon Basin of Brazil | Aniskin and Voloboeuv 1999, |
|||
70 | 72, 74, 76 | Pericentric inversion in small acrocentric pairs; sex chromosome polymorphisms | Southern |
|||||
61, 62 | 78-82 | Pericentric inversions in pairs 2, 3, 4 and 8; Sex chromosome polymorphism; mosaicism (XX/X0) | ||||||
46 | 52 | - | high altitudes in |
|||||
- | 52 | 68-70 | Pericentric inversion in one small acrocentric pair | Cerrado ( |
||||
|
72 | 76 | - |
|
||||
|
56 | 58 | - |
|
||||
- | 44; 45 | 52; 53 | Mosaicism of a small acrocentric pair; X chromosome polymorphisms | Only known from its type locality (Serra do Cipó, |
|
|||
- | 56 | 54; 55 | Addition of constitutive heterochromatin in pair 17 | Central Brazil ( |
||||
|
50 | 68 | - | Westernmost Brazil ( |
||||
|
|
- | 57-60 | 60-64 | 0-2 B chromosomes | Southeastern Brazil, from |
||
- | 86; 84; 82 | 96-100; 96-98; 94 | One name with different karyotypes associated | Northernmost Brazil ( |
||||
|
- | 62 | 116 | - | Only known in three localities in Central |
|
||
|
- | 64 | 66 | - |
|
|
||
- | 48 | 66 | - | Western Brazil ( |
||||
- | 50 | 66 | - | Western |
||||
- | 36; 38 | 66 | Centric Fusion | |||||
- | 66 | 68 | - | Caatinga and Cerrado formations from |
||||
- | 64 | 68 | - | Southermost |
||||
- | 64; 66 | 64; 66 | One name with different karyotypes associated | Atlantic Forest region and habitats bordering the Cerrado, Southeastern Brazil ( |
||||
46 | 66 | - | Cerrado habitats |
|||||
|
- | 28 | 40 | - | Boundary between |
|||
|
- | 78, 80, 82* | N/A | Robertsonian polymorphisms; Karyotype of specimens from Venezuela | Northernmost Brazil ( |
|||
|
- | 36 | 50 | - | ||||
|
|
|
44 | 48, 50 | ||||
- | 44 | 46, 52, 64 | Pericentric inversion | Eastern |
||||
- | 44 | 50 | - | Northwestern |
||||
- | N/A | N/A | - | Endemic to the Araguaia-Tocantins basin | ||||
- | 44 | 48-50 | Pericentric inversion |
|
||||
- | 44 | 46, 48, 52 | Pericentric inversion | Northwestern Brazil ( |
||||
- | 44* | 50* | Karyotype of specimens from Venezuela | |||||
- | 44 | 48-52 | Pericentric inversion | Cerrado and Caatinga biomes, from |
||||
- | 44 | 70, 74, 76, 80 | Pericentric inversion | Atlantic Forest region, from |
||||
48; 50 | 68; 71, 72 | Pericentric inversion in pair 8, addition and deletion of constitutive hetechromatin | Northcentral Brazil ( |
|||||
- | 44 | 50 | - | Serra do Caraça, Southern |
||||
- | N/A | N/A | - | Northern Brazil | ||||
|
- | 60 | 88 | - | Only known from its type locality (Southwestern |
|
||
- | 62 | 86, 90, 104 | Pericentric inversion in the smallest pairs | Southern |
||||
|
|
- | 58 | N/A | - | |||
- | 82 | 86 | - | Disjunction distribution in Itatiaia ( |
Gonçalves and Oliveira 2014 | |||
82 | 80 | - | Atlantic Forest of Southeastern Brazil, from |
|||||
- | 72 | 90 | - | Atlantic Forest of Southeastern Brazil, from |
||||
- | 20 | 36 | - | Southern |
||||
|
36 | 34 | - | Southeastern Brazil, from |
||||
- | 20 | 34 | - | High altitudes at Serra da Mantiqueira, in |
||||
- | 32 | 48 | - | Aparados da Serra National Park, |
|
|||
- | 78 | 114 | - | Restricted areas from Serra do Mar, in |
||||
- | N/A | N/A | - | Southern Brazil and Southeastern |
|
|||
|
- | 40 | 64 | - |
|
|
||
- | 48 | 50-78 | Variation in the amount of constitutive heterochromatin | Eastern |
||||
- | 50 | 68 | - | Western |
|
|||
- | 54-58 | 74-82; 84 | Centric fusion/ fission in pairs 1 and 2; pericentric inversion | |||||
- | 42, 43, 44; 45; 46-51; 49-51; 48-51; 51; 52 | 74; 75/76; 77; 78; 78, 80; 79 | Robertsonian rearrengements and tandem fusions | Eastern |
||||
|
36 | 64 | - | Southwestern |
||||
- | N/A | N/A | - |
|
||||
|
- | 40, 42, 44, 46 | 72 | Robertsonian fusion; Variation in the amount of constitutive heterochromatin; secondary constricton | Southeastern |
|||
|
- | 74 | 98 | - | All Brazilian States | |||
|
|
64 | 122 | - | Southcentral Brazil, |
|||
- | N/A | N/A | - | Northeastern |
||||
- | 64; 65 | 116; 122 | B chromosome | |||||
|
64 | 122 | - | Littoral zone in |
||||
- | 64, 65 | 122-124 | B chromosome | Northermost Brazil ( |
||||
|
64, 65 | 122 | B chromosome | Northeastern Brazil, and Northern |
||||
- | N/A | N/A | - | Southeastern Brazil | ||||
- | 64* | 124 | - | Western Brazil |
|
|||
- | 64, 65 | 124 | B chromosome | unknown distribution |
|
|||
- | 62 | 118 | - | |||||
- | N/A | N/A | - | |||||
|
- | 64 | 98 | - | ||||
|
- | 42 | 76 | - | Southeastern |
|||
- | 66 | N/A | Secondary constriction in the forth largest pair | |||||
|
|
34; 32 | 58, 60, 62; 54 | Pericentric inversion; Robertsonian rearrangement; secondary constriction in pair 1; addition of constitutive heterochromatin | ||||
- | 118 | 168 | - |
|
||||
- | 94 | 144 | - | |||||
- | N/A | N/A | - | Southern |
|
|||
- | N/A | N/A | - | Central-Easternmost |
|
|||
- | 46 | 82 | - | Eastern |
||||
- | 60 | 116 | - | Northern |
||||
- | 60 | 112 | - | Northern |
||||
- | 22 | 38 | - | Northeastern |
||||
- | 98 | 126 | - | Eastern Brazil, from |
||||
- | N/A | N/A | - | Eastern |
|
|||
- | 66 | 106 | Secondary constriction in pair 11 | |||||
- | N/A | N/A | - |
|
||||
- | N/A | N/A | - | Eastern |
|
|||
- | 60 | 116 | - | Northern Brazil, and Northwestern |
||||
- | 42 | 54 | Secondary constriction in the smallest biarmed pair | Central |
||||
- | 60 | 116 | - | Eastern |
||||
- | 42 | 76 | - |
|
González and Brum-Zorilla 1995, |
|||
|
- | 50 | 88, 94-96 | Pericentric inversion | ||||
- | N/A | N/A | - | Central |
|
|||
- | 72 | 108 | - | Southern |
||||
- | N/A | N/A | - | Ubatuba ( |
|
|||
- | 56 | 102 | - | Eastern Brazil, from |
||||
- | N/A | N/A | - | Southern |
|
|||
- | N/A | N/A | - | Serra da Mantiqueira ( |
|
|||
- | 96 | 108 | - | From |
Sbalqueiro et al. 1989, |
|||
- | 84, 85 | N/A | Secondary constriction in one acrocentric pair | Coast from |
||||
- | 72; 76; 80 | 114; 148; 100, 108, 112 | Pericentric inversion; centric fusion/ fission | From |
||||
- | 92 | 102 | - | Southern Brazil, from |
||||
- | N/A | N/A | - | Ilha de São Sebastião ( |
||||
- | N/A | N/A | - | Southernmost |
||||
- | 28 | 48-50 | Variations in |
|||||
- | 28 | 46-48 | Differences in the number of subtelocentrics and acrocentrics | Northern Brazil | ||||
- | 32 | 60 | - | Northwestern |
||||
- | 40 | 54, 56 | Pericentric inversion; secondary constriction in the smallest submetacentric pair | Southern |
||||
- | 24 | 44 | - | Easternmost |
||||
|
- | 15 | 16 | - |
|
|
||
|
- | 38, 44 | 52 | One name with different karyotypes associated | Northeastern |
|||
- | N/A | N/A | - | Northernmost |
|
|||
- | 34 | 52 | - | Southeastern |
||||
- | 28 | 48-50 | Pericentric inversion of pairs 3 and 11; addition/deletion of constitutive heterochromatin |
|
||||
|
- | 16, 17 | 14 | Robertsonian rearrangement between X and the largest acrocentric chromosome; Multiple sex chromosome system (XX, XY1Y2) |
|
|
||
- | 40 | 56 | - | Western |
||||
- | 28 | 42 | - | Northcentral |
||||
- | 30 | 54-56 | Pericentric inversion of pairs 13 and 14 | Eastern |
||||
|
32 | 56-58 | Pericentric inversion; secondary constriction in pair 8 of the karyotype with NF=56 | |||||
- | 24 | 40-42 | Pericentric inversion in pair 3 (smallest metacentric), with homo or heterozigous chromosomes | |||||
|
30 | 52 | - | Rio Jamari, |
||||
|
38 | 52 | - | Rio Negro-Rio Aracá, |
|
|||
- | 46 | 50 | - | |||||
- | 28 | 50, 52 | Secondary constriction in pair 2 | |||||
- | 26 | 48 | Secondary constriction in pair 2 | |||||
- | 30 | 54 | Secondary constriction in pair 1 | Northeastern Brazil, except |
||||
|
|
- | 30 | 56 | Secondary constriction in pair 1 | Central Brazil | ||
- | 34 | 64 | Secondary constriction in pair 2 | Southern |
||||
- | 60 | 116 | Secondary constriction in pair 10 | |||||
- | 60 | 116 | Secondary constriction in pair 10 | |||||
- | 38 | 112 | Secondary constriction in pair 10 |
|
||||
|
56 | 108 | Secondary constriction in pair 10 | Southcentral |
||||
|
60-65 | 116 | 1 to 5 B chromosomes; secondary constriction in pair 7 | Coast from Southern |
||||
- | N/A | N/A | - |
|
||||
- | 56 | 106 | - | Only known from the type locality ( |
||||
- | 58 | 112 | Secondary constriction in long arm of a median size autosome | South-central |
||||
56 | 108, 104 | NFs refer to each subspecies, respectively | Eastern Brazil, from |
|||||
- | 54 | 104 | Secondary constriction in pair 10 | |||||
- | N/A | N/A | - | Eastern |
|
|||
|
- | 52 | 76 | - | ||||
|
62 | 76 | - | Eastern Brazil, from |
||||
|
72 | 76 | - | Northernmost Brazil ( |
||||
- | N/A | N/A | - | Easternmost |
||||
- | 74 | 82 | - | From Northern to Southeastern Brazil | ||||
|
N/A | N/A | - | Centraleastern |
||||
|
- | N/A | N/A | - | Eastern |
|||
42 | 76 | - | Southern Brazil, Southeastern |
|||||
|
- | 40 | 38 | - | All Brazilian States | |||
- | 38 | 58-59 | Pericentric inversion in pair 8 | All Brazilian States | ||||
- | 42 | 64 | - | All Brazilian States | ||||
|
N/A | N/A | - | |||||
40 | 74, 76 | Pericentric inversions | Disjunct distribution of Amazonian, Caatinga, and Coastal Brazil | |||||
|
N/A | N/A | - | Northern Brazil, Southern Amazon River | ||||
N/A | N/A | - | Western Brazilian Amazonia |
|
||||
|
40 | 76 | - | Central to Southern |
||||
- | N/A | N/A | - | Northern Amazon River, Brazil |
|
|||
|
N/A | N/A | - | Northwestern |
|
|||
- | N/A | N/A | - | Eastern |
|
Abbreviations: Brazilian states
The single female of
Regarding
Chromosome preparations of
DNA was extracted from the liver or muscle with Chelex 5% (Bio-Rad) (
PCR was performed in a thermal cycler (Eppendorf Mastercycler ep Gradient, Model 5341) using primers MVZ05 (5-CGA AGC TTG ATA TGA AAA ACC ATC GTT G-3) and MVZ16 (5-AAA TAG GAA RTA TCA YTC TGG TTT RAT-3) (
Models of nucleotide substitution were selected using Bayesian Information Criterion (
The current review encompasses all rodent species which up to the present have been reported in Brazil, comprising 271 species from 10 families (
Many species show chromosome rearrangements leading to variation in diploid and fundamental numbers. Also, more than one diploid number was associated with one single species, suggesting that they could represent species’ complexes. Additionally, new karyotypes were assigned to 22 species highlighting them as candidate species, which have not been formally described yet.
All comments below refer to the data compiled and presented in Table
From a total of ten species, cytogenetic data is lacking for only one:
This is the second most diverse tribe in the subfamily
In this tribe, the diploid number varied from 2n = 9, 10 in
Sex chromosome variation is also common, occurring in six species. It is also remarkable that
Cytogenetic studies have proved to be a useful tool in the recognition of species, mainly in the case of the cryptic and sympatric species as
Two species of
Comprising 73 species up to now, this tribe alone comprises about 47% of the
Pericentric inversion (n = 13) and Robertsonian rearrangements (n = 8) are common rearrangements, as well as sex chromosomes variations, that were described in 12 species and correlated to addition/deletion of constitutive heterochromatin and pericentric inversions.
Besides,
Karyotype information proved to be important in this tribe, since many species present species-specific karyotypes. For example, species of the genus
Chromosome data also show evidence that distinctive karyotypes are being attributed to the same name, for instance
Additionally, some species could not be identified by chromosome data alone, because they share the same karyotype. This is the case of
Just as in all hierarchical levels of rodents’ taxonomy, cytogenetic diversity is underestimated in this tribe. For instance, recently,
Herein, we describe the same diploid (2n = 58), but with a different fundamental number (66) to
Karyotype of a male of
For phylogenetic analyses, the best model selected for the mitochondrial gene (cyt-
Bayesian phylogenetic hypothesis of
In Brazil, this tribe was initially composed only of the genus
In Brazil, the only representative of this tribe is
Only one species of this tribe can be found in Brazil,
This tribe is represented by only two genera in Brazil:
This tribe is composed of two species:
This group comprises the genera
This family comprises a single genus,
This family is represented by a single species,
This family comprises two genera:
This family possesses only one species,
Even being the second largest Brazilian rodent family, a remarkable gap regarding cytogenetic data of this family still remains, with 14 species out of 68 lacking such information. This represents about 37% of all the unknown karyotypic information of all Brazilian rodents.
Diploid numbers varied from 2n = 15 in
Within this family, there are also cases in which different diploid numbers are assigned to the same name. In the case of
In this work, the karyotype of
Karyotype of a female of
Within the
Three out of eight species lack cytogenetic information. The diploid number varied from 42 in
This family (represented by the genera
Little is known about the cytogenetics of the
Karyotype after C-banding of a male of
For the black rat
Cytogenetic data is unknown for almost the entire family. For the two species to which chromosome information is known, diploid number is 2n = 40, and pericentric inversion has been described for one of them,
The last cytogenetic revision on Brazilian rodents, published in 1984, described the karyotype of 62 species, mainly from South and Southeast Brazil (
Since then, new cytotypes have been attributed to already known species. For instance, new diploid numbers were described for
Since 1984, many species’ names have been redescribed or validated (e.g.
Technological advances with fluorescent
In this paper, we provide a new fundamental number for an undescribed species of
Karyotype information was the first to point out that this specimen may represent a new species, since 2n = 58,
In fact,
The description of the karyotype of
We also show the picture of the karyotype of the exotic species
During the beginning of the 1970s (although banding techniques had already been described), karyotypes of Brazilian rodents were studied mainly through conventional staining and the description was limited to diploid and fundamental numbers. Even so, the idea of a wide chromosomal variability already existed. From the 1980s until now, comparative cytogenetics with chromosome banding persists and contributed for elucidating these variations, being that G and C-banding and Ag-NORs are the commonest and cheapest banding techniques.
In fact, the distribution of constitutive heterochromatin and Ag-NORs can be markers in some species. For example, large blocks of constitutive heterochromatin were detected in
Extensive chromosomal rearrangements such as Robertsonian,
The advent of chromosome painting made it possible to compare not only related species but also distant ones, something which is difficult to achieve with banding patterns.
Despite the ‘modern cytogenetics era’, chromosome banding is still an important tool for animal cytogenetic studies, not only because
Rodents proved to be a good model for chromosome evolution studies. Cytogenetics associated with molecular or morphological phylogenetic reconstruction broke cytogeneticist paradigms that fusion rearrangement is more common than fission, and that the reduction in 2n is the expected pattern (e.g.
Chromosomal rearrangement could possibly be the cause of reproductive isolation in many Brazilian rodents’ species, leading to speciation. The main rearrangements that lead to species formation are Robertsonian,
For a long time, it was thought that chromosomal structural rearrangements promoted speciation by generating gametes with duplications and deficiencies, therefore, causing less adaptability of the heterozygotes, but this model was rejected because it lacked theoretical support (
In fact, normal meiotic behavior with suppression of crossing over in inverted segments of heteromorphic chromosomes caused by pericentric inversions of
A remarkable chromosome variation can be found in the semi- and fossorial Brazilian rodents
For example, a very well-known case of chromosome speciation due to population adaptation to climatic stress and ecological unpredictability was described in the subterranean rodent
Cytotaxonomy is the use of chromosome data as the first clue in the identification of species. Since many Brazilian rodent species present species-specific karyotype and show morphological similarities, chromosome information showed to be useful in the diagnosis of species.
The present revision showed that the delimitation of species based on chromosome data (cytotaxonomy) is essential for recognizing some species of the genera
On the other hand, since rates of karyotype evolution differ in distinct branches of the rodents’ phylogeny, some species present identical diploid and fundamental numbers, and they cannot be identified solely through chromosome data. This is the case of the following species: (i)
Furthermore, some unrelated species, that belong to different tribes, or even families, present the same diploid and fundamental number, suggesting a homoplastic character: (i)
Since the beginning of the cytogenetic studies in Brazilian rodents, there have been cases in which different karyotypes were assigned to one species or the same karyotype was referred to in different species. In fact, many of these cases were solved after the integration of different disciplines. For instance, for many years cytogenetic information indicated that the previous “
The opposite occurred in the genus
Some of these cases persist until today, for instance, more than one karyotype was described for
Remarkably, such examples can also be found in the family
Interdisciplinary approaches, including cytogenetic, molecular phylogeny, morphology and geographic distribution are essential for accessing the limits of Brazilian rodents’ species. One of the best-known examples was the old genera
Within the Family
Despite the new technological approaches, chromosome characterization with conventional staining and banding pattern is still important, mainly because 38 species lack any karyotype information (Table
Concerning the family
The future of molecular biology is promising, with next-generation sequencing (NGS) technology and mitogenomics hopefully providing more robust phylogenetic studies. This new approach was performed with the Family
However, it is important to reiterate the heterogeneity of characters since DNA, chromosomes, morphology, and behavior are not evolving at the same rate. This particularity may imply in different taxonomic interpretations, with a population being identified as a unique species by one character and two or more species by another, especially in the cases of recent or ongoing speciation. The consequences can be taxonomic inflation or underestimation of the biodiversity, and that is why interdisciplinary approaches are crucial to better understand the biological diversity of rodents.
The authors would like to thank Dr. Ana Paula Carmignotto, Pedro Luís B. da Rocha, Leonora P. Costa, and Miguel T. Rodrigues for collecting samples and donating tissues, and Yatiyo Yonenaga-Yassuda for infrastructure and for reading the first version of the manuscript. CAPES and FAPESP (2014/02885-2 for MJJS) supported this work.
Table S1
molecular data
Sequences analysed for phylogenetic reconstruction (Maximum likelihood and Bayesian Inference) of
N/A means that the information is not available. *Cytogenetic data analysed in this work. In bold, sequences obtained in this work. Coordinates for