Early detection of Leishmania (Leishmania) chagasi in draining lymph node after subcutaneous inoculation in hamster

To study the route of migration of Leishmania (Leishmania) chagasi to the viscera from the subcutaneous inoculation site, ultrastructural studies were carried out. These studies on popliteal draining lymph nodes of hamsters inoculated with 10⁷ promastigotes of Leishmania (Leishmania) chagasi in the hind footpad were carried out. Parasites were detected in lymph nodes just 2 h after inoculation. Parasites were either preserved or degenerated in macrophages. In 24 h signs of binary division of the parasites were found in macrophages. This fact suggests that the parasites migrate from skin to the lymph node early in the infection within phagocytes and proliferate in lymph nodes before dissemination to the viscera.     

A bioclimatic classification of Chile: woodland communities in the temperate zone

The results of application of a global bioclimatic classification to Chile are presented. A total of 140 weather stations are assigned to bioclimatic belts on the basis of temperature and rainfall regime. In view of these assignements and of phytosociological data, a zonation of Chile into four major bioclimatic regions (Tropical, Mediterranean, Temperate and Boreal) is proposed. For the Temperate region, we discuss the distribution of the various climax forest communities with respect to bioclimatic belt. It is suggested that increased knowledge of the phytosociology of Chile will improve understanding of the climate of the different parts of the country.Nomenclature: Plant nomenclature follows Marticorena et al. (1985) for Chilean species.     

Artificial endosperm of Cleopatra tangerine zygotic embryos: a model for somatic embryo encapsulation

Synthetic seed technology may be of value in breeding programs and allow the propagation of many elite genotype-derived plants in a short time. In this work, a range of artificial endosperm treatments of Cleopatra tangerine zygotic embryos were evaluated for suitability for encapsulation of somatic embryos. Different complexing ions in the form of alginate capsules, zeolite as an ion exchanger and the relationship between capsule-nutrient gel on germination of zygotic embryos, were evaluated. Artificial endosperm assays showed that abscisic acid (1 μM) and mannitol (0.25 M) delayed germination and conversion of zygotic embryos, whereas amino acid supplements (proline, glutamic acid and arginine) accelerated the conversion process. An artificial endosperm was used to encapsulate somatic and zygotic embryos. After encapsulation, zygotic embryos germinated after four days of culture while somatic embryos germinated asynchronously after 20 days. Somatic embryo-derived plantlets showed greater vigour than zygotic embryo-derived plantlets. Results showed that this artificial endosperm is adequate for Cleopatra tangerine somatic embryo germination and conversion into plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Exonic Sequences in the 5′ Untranslated Region of α-Tubulin mRNA Modulate trans Splicing in Trypanosoma brucei

Previous studies have identified a conserved AG dinucleotide at the 3′ splice site (3′SS) and a polypyrimidine (pPy) tract that are required for trans splicing of polycistronic pre-mRNAs in trypanosomatids. Furthermore, the pPy tract of the Trypanosoma brucei α-tubulin 3′SS region is required to specify accurate 3′-end formation of the upstream β-tubulin gene and trans splicing of the downstream α-tubulin gene. Here, we employed an in vivo cis competition assay to determine whether sequences other than those of the AG dinucleotide and the pPy tract were required for 3′SS identification. Our results indicate that a minimal α-tubulin 3′SS, from the putative branch site region to the AG dinucleotide, is not sufficient for recognition by the trans-splicing machinery and that polyadenylation is strictly dependent on downstream trans splicing. We show that efficient use of the α-tubulin 3′SS is dependent upon the presence of exon sequences. Furthermore, β-tubulin, but not actin exon sequences or unrelated plasmid sequences, can replace α-tubulin exon sequences for accurate trans-splice-site selection. Taken together, these results support a model in which the informational content required for efficient trans splicing of the α-tubulin pre-mRNA includes exon sequences which are involved in modulation of trans-splicing efficiency. Sequences that positively regulate trans splicing might be similar to cis-splicing enhancers described in other systems.     

Assessing the origin of Neotropical mountain dung beetle assemblages (Scarabaeidae: Scarabaeinae): the comparative influence of vertical and horizontal colonization

Aims The fauna of mountains and their surrounding regions are likely to be influenced principally by two biological processes: horizontal colonization along similar altitudinal levels by elements originating from lineages inhabiting higher latitudes; and vertical colonization by lineages from the same latitude, but at lower altitudes. We examine whether the expected patterns derived from the latter process can be observed in mountain dung beetle assemblages. Specifically, we study the variation in species composition and richness with altitude in five regions spanning elevation gradients, analysing whether the altitudinal rates of change in the number of species and genera differ, and whether beta‐diversity scores for adjacent sites in each altitudinal gradient are different for species and genera. Location Eastern Cordillera of the Colombian Andes. Methods Field work was carried out in 1997–99 at 27 sites in five regions with elevation gradients, with 10–32 pitfall traps placed in each site. For each altitudinal level the numbers of species and genera were analysed with respect to altitude, and the slope of the linear regression between these variables was calculated. The slope of the curve of the altitude against the cumulative number of species and genera was also calculated for each altitudinal gradient to describe the compositional change between adjacent sites (beta diversity). Species and generic slopes were compared using analysis of covariance. The turnover of species along each altitudinal gradient was measured using presence/absence data and Cody's beta‐diversity index between adjacent pairs of sites. A cluster analysis was used to detect faunistically homogeneous groups of localities. Results Species richness always decreased with altitude, although the slopes did not differ significantly from zero. The number of genera also decreased with increasing altitude, but generally at a significantly slower rate than for species. Variation in the species beta‐diversity scores between altitudinal levels did not follow a homogeneous pattern in the different regions. Two main altitudinal groups of sites with a boundary c. 1500–1750 m a.s.l. can be detected with respect to faunistic similarity. Low‐ and mid‐altitude sites are inhabited by all of the genera (19) and 80% of all species collected. Eight genera and 61 species (c. 60% of the total) are unable to inhabit high‐altitude sites, and only 20 species appear to be exclusive to these high‐altitude environments (> 2000 m a.s.l.). Main conclusions The dominant processes explaining dung beetle composition in the high north‐eastern Andean mountains are probably those of vertical colonization. The limited role of horizontal colonization processes, or colonization from northern or southern lineages, could be a consequence of the isolation and recent geological origin of these mountains.     

A phylogeographical analysis across three biogeographical provinces of the south-eastern Pacific: the case of the marine gastropod Concholepas concholepas

Aim The present‐day population structure of a species reflects the influence of population history as well as contemporary processes. Little is known about the mechanisms that have shaped the geographical distribution of genetic diversity in marine species present on the south‐eastern Pacific (SEP) coast. Here we provide the first comprehensive phylogeographical study of a species distributed along the SEP coast by analysing the endemic and emblematic muricid gastropod Concholepas concholepas. Location The study localities were distributed along the SEP coast ranging from Matarani (11° S) to Puerto Eden (49° S), crossing three major biogeographical provinces: Peruvian Province, Intermediate Area and Magellanic Province. Methods A total of 337 specimens of C. concholepas were collected from 14 localities in the three biogeographical provinces/areas. Mitochondrial cytochrome oxidase I (COI) gene partial sequences (658 bp) were obtained and analysed using coalescence‐based methods to infer molecular diversity and phylogeographical patterns. Results Across the 337 individuals, we found a large diversity, with a total of 179 haplotypes at the COI gene fragment. Although a slight decrease in gene diversity was observed from north to south, an analysis of molecular variance did not reveal any significant spatial population differentiation from Peru to the tip of Chile, not even across the recognized biogeographical boundaries at 30° S and 42° S. In addition, a star‐like haplotype network suggested the past occurrence of a rapid demographic and geographical expansion over the total range examined. Calculations of the onset of this expansion suggest that it might be due to climatic conditions during the period of the marine isotope stage 11 (MIS 11, 400,000 years ago), the longer and warmer interglacial episode during the Pleistocene epoch. Main conclusions Our phylogeographical analyses indicate that in the recent past C. concholepas mitochondrial DNA lineages underwent a sudden population expansion event. In addition, our data do not support the hypothesis of concordance between biogeographical barriers and phylogeographical breaks along the SEP coast. These two results are in accordance with the paradigm of high larval dispersal ability in marine species with an extended pelagic larval phase.