The species complex Astyanax fasciatus Cuvier (Teleostei, Characiformes) - a multidisciplinary approach

Cytogenetic data have provided important clues that the Astyanax fasciatus populations from the Upper Parana River basin could be a part of a more diverse fish group, usually included on the same taxa. Samples collected in Cachoeira de Emas, SP, in Mogi-Guacu River basin, show two major cytotypes presenting 2n = 46 and 2n = 48 chromosomes, with distinct karyotypic formula, despite the fact that the molecular data suggested some degree of gene flow between these cytotypes. Cytogenetic and morphometric analyses were performed in this species, aiming to contribute to the understanding of the natural history from such fish group. Two allopatric populations with distinct standard cytotypes were analysed, and the data obtained suggest the separation into two groups. (c) 2008 The Authors Journal compilation (c) 2008 The Fisheries Society of the British Isles.

The spider genus Chrysometa (Araneae, Tetragnathidae) from the Pico da Neblina and Serra do Tapirapeco mountains (Amazonas, Brazil): new species, new records, diversity and distribution along two altitudinal gradients

Eight new species of the spider genus Chrysometa Simon, 1894 (Araneae, Tetragnathidae) are described and illustrated. Chrysometa nubigena n. sp., C. waikoxi n. sp., C. petrasierwaldae n. sp., C. santosi n. sp., C. yanomami n. sp., C. candianii n. sp., C. lomanhungae n. sp., and C. saci n. sp. Those species were collected in a study on the diversity of spider communities along altitudinal gradients in Brazilian Amazonia. C. saci was captured at the Serra do Tapirapeco (Barcelos), while all the other species are from the Pico da Neblina (Sao Gabriel da Cachoeira), the highest mountain in Brazil. We provide new records for C. boraceia, C. flava, C. guttata, C. minuta and C. opulenta, and we describe the male of C. minuta for the first time. We also present the first results on the diversity and altitudinal distribution of the species of Chrysometa at the Pico da Neblina and Serra do Tapirapeco. We sampled the first locality at six different elevations, and obtained 336 specimens distributed in 12 species. Richness and abundance, as well as relative importance peaked at the highest sites sampled (2,000 and 2,400 m). The three most abundant species showed a segregated distribution, being dominant or exclusively distributed in different altitudes. At the Serra do Tapirapeco, sampling at four different elevations up to 1200 m, we only obtained 40 individuals divided in four species, and there was no clear relation to altitude. Most of the new species were found at mid and high altitude sites, while species from lower altitude sites represented widespread species. The comparison with other neotropical spiders inventories highlights the high diversity recorded at Pico da Neblina, which could be assigned to the large environmental variation covered in this work and to the sampling of high-altitude environments. Inventories in the Andean region and other information in the literature also seem to support the association of Chrysometa with high altitude environments.

Spin-density functional for exchange anisotropic Heisenberg model

Ground-state energies for anti ferromagnetic Heisenberg models with exchange anisotropy are estimated by means of a local-spin approximation made in the context of the density functional theory. Correlation energy is obtained using the non-linear spin-wave theory for homogeneous systems from which the spin functional is built. Although applicable to chains of any size, the results are shown for small number of sites, to exhibit finite-size effects and allow comparison with exact-numerical data from direct diagonalization of small chains. (C) 2009 Elsevier B.V. All rights reserved.