Geographic Variation of Chromosomal Polymorphism in Nine Populations of Ctenomys Azarae, Tuco-Tucos of the Ctenomys Mendocinus Group (Rodentia: Octodontidae)

Abstract

Previous studies of Ctenomys species from Central and Western Argentina, referred to as the mendocinus‐group, which included a single C. azarae specimen, showed that they share a similar karyotype of 2n = 47–48, a complex chromosomal polymorphism and heterochromatic short arms in most of biarmed autosomes. In this study karyotypes of 46 specimens of C. azarae from nine local populations from La Pampa and Cordoba Provinces (Argentina) were analyzed. Diploid numbers ranged from 2n=46 to 2n=48 and the G‐banding pattern was identical to the other species of the mendocinus‐group. As in C. mendocinus and C. porteousi, heterochromatin was highly variable, exhibiting a large number of polymorphisms that involved C‐positive blocks. Our data also revealed that the same polymorphism displayed in pair A1, was present in five C. azarae populations. Another significant finding was the presence of the homomozygous karyotype (2n = 46), which was absent in 106 previously studied specimens of C. porteousi and C. mendocinus, in two C. azarae populations. Cytogenetic, morphometric, and sperm morphology studies of the mendocinus‐group suggest recent allopatric speciation events, in which chromosomal rearrangements did not play a central role.

Cytogenetics Status of Four Ctenomys Species in the South of Brazil

“…Although there is a large inter-specific chromosomal variation, intraspecific variation also occurs in many species (Reig & Kiblisky, 1969;Kiblisky et al, 1977;Freitas & Lessa, 1984;Novello & Lessa, 1986;Massarini et al, 1991;Freitas, 1997;Gimenez, Contreras & Bidau, 1997;Massarini, Dyzenchauz & Tiranti, 1998;Garcia et al, 2000a, b;Freygang, Marinho & Freitas, 2004). Figure 1 shows the geographic distribution of five species of Ctenomys in the south of Brazil: C. torquatus, C. flamarioni, C. lami, C. minutus and Ctenomys sp.…”

Intra- and interspecific skull variation in two sister species of the subterranean rodent genusCtenomys(Rodentia, Ctenomyidae): coupling geometric morphometrics and chromosomal polymorphism

“…The systematics within the genus Ctenomys can be fairly simple, as some species posses a unique karyotype and distinct skull size or other morphological characteristics. In contrast, other species show extensive intraspecific karyotypic variation (Ortells, Contreras & Reig, 1990; Gallardo, 1991; Massarini et al ., 1991; Ortells, 1995; Giménez, Contreras & Bidau, 1997; Freitas, 1997; Massarini, Dyzenchauz & Tiranti, 1998; Garcia et al ., 2000a, b; Freitas, 2001; Freygang, Marinho & Freitas, 2004), or variation in pelage colour, within populations (Reig, Contreras & Piantanida, 1966; Langguth & Abella, 1970; D’Elia, Lessa & Cook, 1998). In these cases, species delimitation can be an especially important issue for the conservation of tuco‐tucos, as many habitats of species are being destroyed (Altuna et al ., 1999; Fernández‐Stolz, Stolz & Freitas, 2007).…”

Evolutionary and systematic relationships among tuco-tucos of the Ctenomys pundti complex (Rodentia: Octodontidae): a cytogenetic and morphological approach

“…The fossorial rodents of the genus Ctenomys, commonly known as tuco-tucos, are characterized by an extensive karyotypic heterogeneity, ranging from 2n = 10 in C. steinbachi to 2n = 70 in C. pearsoni and C. dorbignyi (Reig & Kibliski 1969;Anderson et al 1987;Cook et al 1990;Ortells et al 1990;Reig et al, 1990;Gallardo 1991;Ortells 1995). However, some species from western and central Argentina, referred to as the C. mendocinus group (Massarini et al 1991;Freitas 1994;D'Elía et al 1999), show a similar karyotype of 2n = 47 to 48, and recently has been described de 2n = 46 karyomorph for two population of C. azarae (Massarini et al 1998). Moreover, some species exhibit a wide array of chromosomal polymorphisms, and interpopulation variation (Massarini et al 1991;Freitas 1995;Massarini et al 1998).…”

“…However, some species from western and central Argentina, referred to as the C. mendocinus group (Massarini et al 1991;Freitas 1994;D'Elía et al 1999), show a similar karyotype of 2n = 47 to 48, and recently has been described de 2n = 46 karyomorph for two population of C. azarae (Massarini et al 1998). Moreover, some species exhibit a wide array of chromosomal polymorphisms, and interpopulation variation (Massarini et al 1991;Freitas 1995;Massarini et al 1998). The significance of this extensive intra and interspecific chromosomal variation has been the subject of considerable debate (Baker et al 1983;Reig 1989;Nevo 1991;Ortells & Barrantes 1994;Freitas 1994;Freitas 1997).…”