Effects of Etching on Zircon Grains and Its Implications for the Fission Track Method

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Studies of zircon grains using optical microscopy, micro-Raman spectroscopy, and scanning electron microscopy (SEM) have been carried out to characterize the surface of natural zircon as a function of etching time. According to the surface characteristics observed using an optical microscope after etching, the zircon grains were classified as: (i) homogeneous; (ii) anomalous, and (iii) hybrid. Micro-Raman results showed that, as etching time increases, the crystal lattice is slightly altered for homogeneous grains, it is completely damaged for anomalous grains, and it is altered in some areas for hybrid grains. The SEM (energy dispersive X-ray spectroscopy, EDS) results indicated that, independent of the grain types, where the crystallinity remains after etching, the chemical composition of zircon is approximately 33% SiO2:65% ZrO2 (standard natural zircon), and for areas where the grain does not have a crystalline structure, there are variations of ZrO2 and, mainly, SiO2. In addition, it is possible to observe a uniform surface density of fission tracks in grain areas where the determined crystal lattice and chemical composition are those of zircon. Regarding hybrid grains, we discuss whether the areas slightly altered by the chemical etching can be analyzed by the fission track method (FM) or not. Results of zircon fission track and U-Ph dating show that hybrid and homogeneous grains can be used for dating, and not only homogeneous grains. More than 50 sedimentary samples from the Bauru Basin (southeast Brazil) were analyzed and show that only a small amount of grains are homogeneous (10%), questioning the validity of the rest of the grains for thermo-chronological evolution studies using zircon FTM dating.665545551Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Circumstellar disks and planets. Science cases for next-generation optical/infrared long-baseline interferometers

We present a review of the interplay between the evolution of circumstellar disks and the formation of planets, both from the perspective of theoretical models and dedicated observations. Based on this, we identify and discuss fundamental questions concerning the formation and evolution of circumstellar disks and planets which can be addressed in the near future with optical and infrared long-baseline interferometers. Furthermore, the importance of complementary observations with long-baseline (sub)millimeter interferometers and high-sensitivity infrared observatories is outlined.Comment: 83 pages; Accepted for publication in "Astronomy and Astrophysics Review"; The final publication is available at http://www.springerlink.co

Lutzomyia umbratilis, the Main Vector of Leishmania guyanensis, Represents a Novel Species Complex?

BACKGROUND: Lutzomyia umbratilis is an important Leishmania guyanensis vector in South America. Previous studies have suggested differences in the vector competence between L. umbratilis populations situated on opposite banks of the Amazonas and Negro Rivers in the central Amazonian Brazil region, likely indicating a species complex. However, few studies have been performed on these populations and the taxonomic status of L. umbratilis remains unclear. METHODOLOGY/PRINCIPAL FINDINGS: Phylogeographic structure was estimated for six L. umbratilis samples from the central Amazonian region in Brazil by analyzing mtDNA using 1181 bp of the COI gene to assess whether the populations on opposite banks of these rivers consist of incipient or distinct species. The genetic diversity was fairly high and the results revealed two distinct clades ( = lineages) with 1% sequence divergence. Clade I consisted of four samples from the left bank of the Amazonas and Negro Rivers, whereas clade II comprised two samples from the right bank of Negro River. No haplotypes were shared between samples of two clades. Samples within clades exhibited low to moderate genetic differentiation (F(ST) = -0.0390-0.1841), whereas samples between clades exhibited very high differentiation (F(ST) = 0.7100-0.8497) and fixed differences. These lineages have diverged approximately 0.22 Mya in the middle Pleistocene. Demographic expansion was detected for the lineages I and II approximately 30,448 and 15,859 years ago, respectively, in the late Pleistocene. CONCLUSIONS/SIGNIFICANCE: The two genetic lineages may represent an advanced speciation stage suggestive of incipient or distinct species within L. umbratilis. These findings suggest that the Amazonas and Negro Rivers may be acting as effective barriers, thus preventing gene flow between populations on opposite sides. Such findings have important implications for epidemiological studies, especially those related to vector competence and anthropophily, and for vector control strategies. In addition, L. umbratilis represents an interesting example in speciation studies