Alicia Massarini

The population genetic structure of Ctenomys porteousi (Rodentia: Octodontidae)

Abstract Several aspects of the population biology and the population genetic structure of Ctenomys porteousi were studied. Chromosomal and allozyme polymorphisms in two local populations separated by 10 km were used to infer genetic structure. Heterochromatic addition/deletion rearrangements for six autosomal pairs were employed as genetic markers. Allozyme variants were analysed by the study of thirty-one presumptive loci. Thirteen loci (43%) were polymorphic, average observed heterozygosity per locus was 10%, and mean number of alleles per locus was 1.57. Chromosomal and allozyme frequencies were homogeneous across populations. The estimated F st values were very low, 0.009 and 0.022 for chromosomal and allozyme data respectively. Gene flow was indirectly estimated by the method of Wright, Nm values (mean number of migrants per generation per deme) was very high (27.2 and 11.3 for chromosomal and allozyme data respectively). The F is values suggest a significant defect of heterozygotes that could be explained by the Wahlund effect. The ecological data indicate the occurrence of sharp changes in density and in distribution pattern in short time. The genetic and ecological data suggest that the population structure of C. porteousi differs from that found in other species of Ctenomys affected by chromosomal mechanisms of speciation.

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

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.

Contemporary Controversies Within the Framework of the Evolutionary Theory

The Evolutionary Theory is, without a doubt, the paradigm that structures and makes up modern biology. Ever since Darwin proposed in 1859 the process of natural selection as the causal mechanism of the biological evolution, the theory has been enriched by several contributions of different branches of biology. Nevertheless, the development of this theory has not been unidirectional, because in the last 150 years the original Darwinism has gone through moments of intense crisis. The objective of this work is to present a review of the main discussions raised in the last three decades between different trends of evolutionary biology.