No abstract

We present new cytogenetic, morphometric, and sperm morphology data of eight populations belonging to the C. pundti complex from Southern Córdoba and Eastern La Pampa Provinces in Argentina. The diploid numbers ranged from 2n = 44 to 2n = 50, and C- bands revealed a pattern of centromeric and pericentromeric heterochromatin. Comparisons of G-banded karyotypes revealed that the 2n = 44 (Holmberg, Santa Catalina, Sampacho), 2n = 46 (Realicó), 2n = 48 (El Guanaco, Guatraché), 2n = 46-48 (Vicuña Mackenna), and 2n = 50 (Puente Olmos) karyotypes, are closely related. In addition, these karyotypes show a high degree of homology (95%) with C. talarum talarum, despite the fact that five chromosomal rearrangements differentiate both taxa. Discriminant Function Analysis of morphometric data allows to distinguish three clusters: i) the C. mendocinus species group, ii) C. t. talarum, and iii) populations of the C. pundti complex proposed herein. The close phylogenetic relationship between C. talarum and the C. pundti complex, which undoubtedly belong to the same evolutionary lineage, is well supported by two different kinds of evidence: the extensive chromosomal homology and the same symmetric type of sperm. The morphological and chromosomal differences show that these two forms have diverged recently.

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.