Abstract Contrary to predictions from classical hybrid sterility models of chromosomal speciation, some organisms display high rates of karyotype variation. Ctenomys are the current mammals with the greatest interspecific and intraspecific chromosomal variation. A large number of species have been studied cytogenetically. The diploid numbers of chromosomes range from 2n = 10 to 2n = 70. Here, we analyzed karyotype evolution in Ctenomys using comparative phylogenetic methods. We found a strong phylogenetic signal with chromosome number. This refutes the chromosomal megaevolution model, which proposes the independent accumulation of multiple chromosomal rearrangements in each closely related species. We found that Brownian motion (BM) described the observed characteristic changes more thoroughly than the Ornstein-Uhlenbeck and Early-Burst models. This suggests that the evolution of chromosome numbers occurs by a random walk along phylogenetic clades. However, our data indicate that the BM model alone does not fully characterize the chromosomal evolution of Ctenomys. speciation variation cytogenetically n 1 70 Here methods (BM OrnsteinUhlenbeck Ornstein Uhlenbeck EarlyBurst Early Burst clades However 7

We describe variation at microsatellite loci and the chromosomal polymorphisms of a hybrid population, and hybridizing populations of Ctenomys minutus (the minor tuco-tuco) from the coastal plain of Rio Grande do Sul, southern Brazil. Cytogenetic analysis and a survey of six microsatellite loci included 101 specimens of C. minutus from the parental populations (2n/AN = 42/74 and 48a/76) and their contact zone. Cytogenetic analysis recorded 26 different karyotypes exhibited by 50 individuals from the hybrid population. Of the 26 karyotypes, only 14% presented a parental-like configuration, and none had the combinations of 2n and AN expected for an F1 hybrid. The remaining karyotypes were alternative hybrid forms, with 2n varying from 42 to 46 and AN from 68 to 80. These results suggest chromosomal rearrangements are only of minor significance in the establishment of reproductive barriers for this species.

In reptiles, dorsal body darkness often varies with substrate color or temperature environment, and is generally presumed to be an adaptation for crypsis or thermoregulation. However, the genetic basis of pigmentation is poorly known in this group. In this study we analyzed the coding region of the melanocortin-1-receptor (MC1R) gene, and therefore its role underlying the dorsal color variation in two sympatric species of sand lizards (Liolaemus) that inhabit the southeastern coast of South America: L. occipitalis and L. arambarensis. The first is light-colored and occupies aeolic pale sand dunes, while the second is brownish and lives in a darker sandy habitat. We sequenced 630 base pairs of MC1R in both species. In total, 12 nucleotide polymorphisms were observed, and four amino acid replacement sites, but none of them could be associated with a color pattern. Comparative analysis indicated that these taxa are monomorphic for amino acid sites that were previously identified as functionally important in other reptiles. Thus, our results indicate that MC1R is not involved in the pigmentation pattern observed in Liolaemus lizards. Therefore, structural differences in other genes, such as ASIP, or variation in regulatory regions of MC1R may be responsible for this variation. Alternatively, the phenotypic differences observed might be a consequence of non-genetic factors, such as thermoregulatory mechanisms.

In this study, the microsatellite technique was used to evaluate the genetic variability in populations of collared and white-lipped peccaries kept in captivity. Six primers developed for domestic pigs were used and amplified in both species. They revealed the presence of five polymorphic loci and one monomorphic locus. The polymorphic loci included 4 of the 16 alleles in collared peccaries, and 3 of the 10 alleles in the white-lipped peccaries. Polymorphic information content (PIC) in both species and all the loci was highly informative. The probability of paternity exclusion (PEC), if one of the parents is known, was almost as high in white-lipped peccaries (95.53%) as in the collared (99,48%). The Fst values for collared (0.042) and white-lipped (0.1387) peccaries showed that both populations are not structured. The Fis values for all loci, except ACTG2 in white-lipped peccaries (-0.0275) and in both species (0.1985 to 0.9284 in collared peccaries and 0.3621 to 0.4754 in the white-lipped), revealed a high level of homozygosis, probably caused by inbreeding. Data on heterologous amplification and genetic variability in collared and white-lipped peccaries are presented for the first time.

A mais importante vantagem do Ensaio Cometa é a possibilidade do seu uso em qualquer organismo e tipo celular. Além de ser barato e rápido, se obtem resultados em poucas horas. Devido a isto é que ele vem sendo recomendado como teste inicial para monitoramento genotóxico ambiental. Neste trabalho investigaram-se adaptações na técnica para trabalhos de campo, com o uso de roedores endêmicos de região de mineração de carvão. O organismo utilizado foi o Ctenomys torquatus, capturado em duas diferentes áreas: Pelotas (região sem mineração de carvão-controle) e Candiota (zona de mineração de carvão). Foi coletado sangue periférico de 18 roedores, que após marcação foram liberados. O sangue foi protegido da luz e mantido sob refrigeração, e processado in loco. As concentrações das agaroses e as condições alcalinas de lise e eletroforese foram modificadas a partir das metodologias sugeridas pelas revisões existentes. As amostras restantes foram mantidas em RPMI 1640 (1:10) (4ºC) e pela nossa experiência podem ser utilizadas por até 4 dias. Foram analisadas 50 células por animal. As células foram classificadas de 0-4, segundo seu grau de lesão, além de serem medidas em unidades arbitrárias. Foi demonstrado aumento significante no nível de dano do DNA no grupo de Candiota (P < 0,05 - teste t), quando comparado com Pelotas. Ainda se demonstrou correlação entre o índice de danos e as medidas celulares. Estes resultados, neste estudo piloto, indicam que o carvão induz efeitos no DNA que são detectáveis através do Ensaio Cometa, o que indica a viabilidade deste teste para o biomonitoramento ambiental.

The main advantages of single-cell gel electrophoresis (SCG) are its applicability to any eukaryotic organism and cell type, its low cost and the short time required to obtain results. These properties make the SCG assay particularly useful in screening for environmental genotoxicity. The present study describes a modified version of this technique for use in field work with native rodents and examines some factors which influence the outcome of the assay. Wild rodents (Ctenomys torquatus, "tuco-tuco") from a region close to a strip coal mine and from a region with no coal mines were used. Animals from the coal mining region had significantly more DNA damage than those from the control area. The use of this SCG technique for direct sampling in the field should facilitate environmental genotoxicity studies with natural populations, without the need to remove the animals from their habitat or to sacrifice them.