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Lessa, E. P., J. A. Cook, & J. L. Patton. 2003. Genetic footprints of demographic expansion in North America, but not Amazonia, during the Late Quaternary. Proceedings of the National Academy of Sciences, USA 100:10331-10334.

D'Elía, G. 2003. Phylogenetics of Sigmodontinae (Rodentia, Muroidea, Cricetidae), with special reference to the akodont group, and with additional comments on historical biogeography. Cladistics, 19:307-323.

Wlasiuk, G., J. C. Garza, & E. P. Lessa. 2003. Genetic and geographic differentiation in the Río Negro tuco-tuco (Ctenomys rionegrensis): inferring the roles of migration and drift from multiple genetic markers. Evolution, 57:913-926.

Hoffmann, F., E. P. Lessa, & M. F. Smith. 2002. A new species of long-nosed mouse of the genus Oxymycterus (Rodentia: Sigmodontinae) from Uruguay. Journal of Mammalogy 83:408-420.

Tomasco, I., G. Wlasiuk, & E. P. Lessa. 2002. Evaluation of polymorphism in ten microsatellite loci in Uruguayan sheep flocks. Genetics and Molecular Biology, 25:37-41.

Lessa, E. P. 2001. The adaptationist program goes underground (Review of: E. Nevo, 1999, Mosaic evolution of subterranean mammals: regression, progresion and global convergence, Oxford Univ. Press, New York). Evolution 55:2139-2141.

Slamovits, C. H., J. A. Cook, E. P.Lessa, and M. S. Rossi. 2001. Recurrent amplifications and deletions of satellite DNA accompanied chromosomal diversification in South American tuco-tucos (genus Ctenomys, Rodentia: Octodontidae): a phylogenetic approach. Molecular Biology and Evolution, 18:1708-1719.

Cortinas, M. N.,and E. P. Lessa. 2001.Molecular evolution of aldolase A pseudogenes in mice: multiple origins, subsequent duplications, and heterogeneity of evolutionary rate. Molecular Biology and Evolution, 18:1643-1653.

D'Elía, G. 2000. Comments on recent advances in understanding sigmodontine phylogeny and evolution. Mastozoología Neotropical, 7:5-12.

García, G.,G. Wlasiuk, and E. P.Lessa. 2000. High levels of mitochondrial cytochrome b divergence and phylogenetic relationships in the annual killifishes ofthe genus Cynolebias (Cyprinodontiformes, Rivulidae). Zoological Journal of the Linnean Society,129: 93-110.

Tomasco, I., G. Wlasiuk,and E. P.Lessa. 2000. Análisis de parentesco en ovinos mediante microsatélites. Producción Ovina ,13: 117-125.

D´Elía, G., E. P. Lessa, and J. A. Cook. 1999. Molecular phylogeny of tuco-tucos, genus Ctenomys (Rodentia: Octodontidae): evaluation of the mendocinus species group and the evolution of asymmetric sperm. Journal of Mammalian Evolution, 6:19-38.

Joseph, L.G., E.P. Lessa, and C.Christidis. 1999. A phylogenetic and biogeographical approach to the study of the evolution of migration. Journal of Biogeography, 26:329-342.

Lessa, E. P., andJ. A. Cook. 1998. The molecular phylogenetics of tuco-tucos (genus Ctenomys, Rodentia: Octodontidae) suggests an early burst of speciation. Molecular Phylogenetics and Evolution, 9:88-99. Resumen

Molecular Phylogenetics and Evolution, 9: 88-99 (1998)

Variation in the nucleotide sequence of the entire mitochondrial cytochrome b gene (1140 pb) was examined for 27 individuals representing 13 species of South American rodents of the genera Ctenomys, Octodontomys, Tympanoctomys and Spalacopus. Representatives of the family Echimydae, Euryzygomatomys and Mesomys were used as outgroups to test the monophyly of the Octodontinae and Ctenominae. Relationships among species of tuco-tucos (genus Ctenomys) were also examined including representatives of the three described subgenera and the two sperm morphs. Reciprocal monophyly of the Octodontinae and Ctenominae is strongly supported. Several basal relationships among species of the genus Ctenomys are poorly resolved, suggesting the possibility of a hard polytomy due to a rapid and potentially simultaneous radiation early in the history of the genus. In other cases, clades within the Ctenominae previously identified on the basis of allozymes, chromosomes, parasites, or skull morphology were supported. Calibrations based on the fossil record suggest that the mitochondrial cytochrome b of these caviomorphs has evolved at a rapid rate, comparable to those proposed for Mus-Rattus,and three to four time higher than ungulate rates.

D'Elía, G., E. P. Lessa and J. A. Cook. 1998. Geographic structure, gene flow and maintenance of melanism in Ctenomys rionegrensis (Rodentia: Octodontidae). Zeitschrift für Säugetierkunde, 63:285-296. Resumen

Zeitschrift Fur Saugetierkunde
(International Journal of Mammalian Biology), 63: 285-296 (1998)

Ctenomys rionegrensis has three coat color morphs (melanic, agouti, and dark backed) within its total distribution of 50 x 60 km area of Uruguay. The presence of two populations fixed for the melanic form is remarkable because this coat color contrasts markedly with the surrounding substrate. Starch gel electrophoresis was used to analyze variation in 20 allozyme loci assayed in 100 individuals from seven populations of C. rionegrensis to test the hypothesis that melanism was fixed by genetic drift in small, isolated populations. Seven loci were monomorphic (95% criterion) and no alleles correlated exclusively with a particular coat color. Average heterozygosity was H=0.038 (range 0.022-0.058). Using pairwise comparisons of all populations, the mean number of migrants (M) was 6.342 for all pairs except those involving the population at Los Arrayanes (agouti), for which the average value was 1.532. Our results indicate that gene flow in C. rionegrensis is sufficiently high to prevent fixation of alternative alleles exclusively by drift. The absence of a pattern of genetic variation due to isolation by distance suggests that the current distribution resulted from a recent range expansion.

Cook, J. A., and E. P. Lessa. 1998. Are rates of diversification in subterraneanSouthAmerican tuco-tucos (genus Ctenomys, Rodentia: Octodontidae) unusually high? Evolution, 52:1521-1527. Resumen

Evolution, 52: 1521-1527 (1998)

Subterranean rodents have been used frequentely as examples of explosive speciation in mammals. We tested for differential rates of diversification by using information from molecular phylogenies to focus primarily on tuco-tucos (Rodentia: Octodontidae), the most speciose linage of subterranean rodents. Tuco-tucos were not significantly more diverse than their sister taxon (octodontines); however, a linage-through-time analysis suggests an increase in diversification at the base of the tuco-tuco clade.

Lessa, E. P., B.Van Valkenburgh, and R. A. Fariña. 1997. Testing hypotheses of differential mammalian extinction subsequent to the great American biotic interchange. Palaeogeography, Palaeoclimatology, Palaeoecology, 135:157-162. Resumen

Palaeogeography, Palaeoclimatology, Palaeoecology,135: 157-162 (1997).

A predominant viewpoint on the dynamics of the Plio-Pleistocene exchange of mammalian taxa between the Americas invokes competitive displacement, i.e., the notion that North American stocks outcompeted their South American counterparts by virtue of greater resilience to extintion and higher rates of colonization and diversification. A recent statistical test (Lessa and Fariña, 1996) based on South American late Pleistocene mammalian genera failed to demonstrate any significant differences in extinction rates between South and North American stocks, but showed that body mass was the primary factor statistically associated with the probability of extinction. Here we povide additional tests of differential extinction in relation to body mass, origin, and trophic niche, using data of North American late Pleistocene mammals, alone and combined with those of the previous study. Tests were carried out using genera as units and, when possible, also at the species level. The overall results corroborate the not ion that body mass is the only factor to show a strong association with the probability of extinction, althought there was an additional weak association with trophic niche.

Lessa, E. P., andR. A. Fariña. 1996. Reassessment of extinction patterns among late Pleistocene mammals of South America. Palaeontology, 39:651-662. Resumen

Palaeontology, 39: 651-662 (1996)

After the formation of the Isthmus of Panama, about 2.5 Ma, a massive interchange between the previously separated mammalian faunas of South and North America took place. Afterwards, during the Late Pleistocene (Lujanian Land Mammam Age)-Holocene transition (less than 10 000 years BP), many of the taxa originally present in South America became extinct. Here, we report results of a statistical assessment of the relative importance of factors potentially associated with extinctions. Several factors (namely trophic niche, origin and body size) were tested for their association with the probability of extinctions (P < 0.0001). The reduction in deviance with the inclusion of body mass was 55.7 per cent. The fate of 85.6 per cent. of the 120 Late Pleistocene mammalian genera included in the analyses was in accordance with the predictions of a logistic regression model based only on body mass. Trophic niche and origin was also considered, but tured out not to be satistically significant. We propose that the greater resilience against extintion of North American Mammalian contingent played no role in the dynamics of the interchange. Also, the analysis demonstrated that marsupials did not go extinct more that placentals. Mammals of North America origin were successful invaders of the South American subcontinent because of their higher speciation rates, and not because of their lower extinction rates.

Novello, A., M. N.Cortinas, M. Suárez, and H. Musto. 1996. Cytogenetic and molecular analysis of the satellite DNA of the genus Ctenomys (Rodentia Octodontidae) from Uruguay. Chromosome Research, 4: 335-339. Resumen

Chromosome Research, 4: 335-339 (1996)

The genus of subterranean rodents Ctenomys, presents the widest range of variability in diploid number among mammals (from 2n=10 to 2n=70). In Uruguay, this variability is observed in karyotypes with 2n=44, 50 or 58 and two geographically isolated populations with 70 chromosomes but different karyotypic structure. The last three populations were analyzed in the present study. They present a satellite DNA, which was isolated from genomic DNA after AluI digestion. In situ hybridization showed that this satellite DNA is located in the centromeric region of a few chromosomes, coincident with Hoechst 33258 staining and C-banding patterns. A similar satellite DNA was detected in Argentinian species of this genus. We established that, in spite of differences in number of positive heterochromatic blocks per karyotype, the C value is the same in the three populations studied. The nature and possible evolutionary path of this repeated DNA is discussed.

Alvarez, F., M. N.Cortinas, and Musto. 1996. The analysis of protein coding genes suggests monophyly of Trypanosoma. Molecular Phylogenetics and Evolution, 5: 333-343. Resumen

Molecular Phylogenetics and Evolution, 5: 333-343 (1996)

We analyze evolutionary relationshipsamong members of the family Trypanosomatidae, with particular emphasis on whether protein coding genes support paraphyly of the genus Trypanosoma. Phylogenetic reconstruction based on three different protein coding genes (glyceraldehyde-3-phosphate dehydrogenase, trypanothione reductase and alpha-tubulin) suggests that Trypanosoma is monophyletic. Moreover, pairwise comparisons of other protein coding genes show that the distances between Trypanosoma cruzi and T. brucei are significantly smaller than are the distances between each Trypanosoma species and Crithidia or Leishmania. These results contradict recent published phylogenies based on nuclear rRNA genes which suggest that T. cruzi is more closely related to Leishmania and Crithidia than to T. brucei.

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Contacto: Enrique P. Lessa