Comparative post-hatching ontogeny of Pseudoplatystoma reticulatum (Eigenmann & Eigenmann 1889) and Leiarius marmoratus (Gill, 1870) and their hybrid

Ontogenetic studies of the eggs and larvae of fish can provide information on the initial life history and biology of a species, are important for taxonomic and evolutionary studies, and for cultivation in captivity. The aim of this study was to analyze and describe the main morphological differences in the larval ontogeny of Pseudoplatystoma reticulatum, Leiarius marmoratus, and its hybrid (♀ P. reticulatum × ♂ L. marmoratus), as well as to identify characteristics that can identify the species and their hybrid at the larvae and juvenile stages. 205 L. marmoratus, 210 P. reticulatum, and 205 hybrid specimens were analyzed, all of which were obtained through induced reproduction. Analyses were performed from hatching to 30 days post-hatching. 19 morphometric and 5 meristic characteristics were evaluated, in addition to chromatophore shape and distribution. The specimens were classified into two life periods: Larval (stages: yolk sac, pre-flexion, flexion, and post-flexion) and Juvenile. Newly hatched larvae were transparent, poorly developed, and had a scarcity of chromatophores. During the early stages of larval development, the three groups showed similarities in appearance and proportional dimensions. However, at both the end of the post-flexion stage and at the juvenile period when individuals were approximately 2 cm long, it was possible to differentiate between hybrids and their parental species by their morphometric, meristic, and pigment characteristics. The hybrid, despite occupying an intermediate position in relationship to its parents, exhibited a shape and size more similar to P. reticulatum, its maternal parent.     

A trait-based approach predicting community assembly and dominance of microbial invasive species

Understanding the mechanisms underlying community assembly helps to define success and susceptibility to biological invasions. Here, we explored phytoplankton community assembly following niche and neutral paradigms and using a trait-based approach. Under the hypothesis that the morphology-based functional groups (MBFG) clusters species with similar niche, we analysed how trait-related differences in fitness influence dominance of an invasive species. This was based on literature review, field data and model simulations. We predict that invading species can be dominant if: 1) do not belong to the local MBFG but use unexploited areas of the niche, or 2) belong to the resident MBFG but exhibit a higher fitness due to a particular combination of traits. The invasive dinoflagellate Ceratium furcoides was used as the model species to evaluate these hypotheses, its morphological (e.g. volume) and physiological (e.g. growth rates) traits were compared with species from the same (V: photosynthetic flagellates) and different (VII: colonial cyanobacteria) MBFG. Fitness was estimated using models parametrized with MBFG rates (R*, ability to draw down phosphate) under different environmental conditions (i.e. flushing). Results contributed to support both hypotheses. First, the alternation of C. furcoides and cyanobacteria dominance was explained by the use of different niches. Secondly, species from MBFG V were dominant under similar environments. Within this group V C. furcoides showed higher fitness under low flushing and high predation, advantage provided by a distinctive combination of traits. The application of trait-based approaches to represent the niche and estimate fitness along environmental gradients was useful to evaluate community assembly and can be used to predict the dominance of microbial species invasions.     

A Permian nurse log and evidence for facilitation in high‐latitude Glossopteris forests

The biology of trees that grew in high‐latitude forests during warmer geological periods is of major interest in understanding past and future ecosystem dynamics. As we study the different plants that composed these forests, it becomes possible to make comparisons with ecosystem processes that occur today. Here we describe a silicified late Permian (Lopingian) glossopterid (seed fern) trunk from Skaar Ridge, central Transantarctic Mountains, Antarctica, with evidence of glossopterid rootlets growing into its wood. The specimen is interpreted as a nurse log similar to those seen in some extant forests. Together with evidence of glossopterid roots growing within the lacunae of older roots, this new specimen suggests the existence of facilitative interactions among the glossopterid trees that dominated the high‐latitude forests of Gondwana during the late Permian. More generally, the existence of self‐facilitation might have favoured the expansion of glossopterids within various environments, especially those at high palaeolatitudes, during the Permian icehouse to greenhouse transition.     

Evaluation of Antioxidant,Antibacterial and Enhancement of Antibiotic Action by Punica granatum Leaves Crude Extract and Enriched Fraction against Multidrug-Resistant Bacteria

The aim of this study was to evaluate the phytochemical composition, antioxidant, and antimicrobial potential of crude extract and fractions of Punica granatum leaves. The extract was produced by turbo extraction, after which hexanic, ethyl acetate, and aqueous fractions were obtained by partitioning. The chemical analyses were performed by thin layer chromatography and high-performance liquid chromatography, and the antioxidant activities were assayed by DPPH^. and ABTS^.+. Minimal inhibitory and bactericidal concentrations (MIC/MBC) were applied to twenty-two bacteria. Most strains susceptible to extract/fractions and resistant to antibiotics were selected, and ampicillin, azithromycin, ciprofloxacin, and gentamicin were associated with the ethyl acetate fraction (EAF) against multidrug-resistant strains in modulatory and checkboard models. The data from chromatographic analyses showed flavonoids and tannins in the extract, as well as the enrichment of EAF in phenols, mainly flavonoids. The flavonoids were connected to the electron transfer activity demonstrated in the DPPH^. and ABTS^.+ assays. Gram-positive strains are more susceptible to EAF. The subinhibitory concentrations of P. granatum enhanced the antimicrobial activity of the agents and reduced the EAF individual MIC, and the combination of EAF and antibiotics demonstrated a synergistic effect. These results present a promising approach for developing a therapy in which antioxidant extracts and fractions can be used in combination with antibiotics.     

The relative importance of spatial and environmental processes in the assembly of larval Chironomidae (Insecta,Diptera) communities along a transition landscape in southern Brazilian streams

Limnology - Metacommunity structure of stream invertebrates is contingent on complex interplays between species dispersal ability, spatial extent and watershed environmental specificities. Previous...     

Vie di ossidazione della frazione extramitocondriale dei coenzimi piridinici: I. - Sull'Efficienza In Vivo del sistema ascorbato/deidroascorbato

Abstract

OXIDATION PATHWAYS OF EXTRAMITOCHONDRIAL PIRIDINE COENZYMES. I. - ON THE « IN VIVO » EFFICIENCY OF THE ASCORBATE-DEYHDROASCORBATE SYSTEM. — An evaluation of the efficiency in vivo of the AA-DHA couple as an electron carrier system has been attempted, by measuring after short time of anaerobiosis the rate of the increase of AA and of the dicrease of DHA in etiolated pea internode segments and in potato tuber disks. The changes of reduced glutathione (GSH) contents as induced by anaerobiosis or by the addition of DHA to the incubation medium were also followed.

In the pea segments anaerobiosis induced a significant increase of AA and a corresponding decrease of DHA. These changes were almost completed after 10 minutes from starting anaerobiosis. The value (extrapolated to 0 time) of the initial rate of DHA desappearance under anaerobiosis was taken as representing the rate of DHA reduction to AA « in vivo », under aerobic conditions. As this rate — in a steady state situation — corresponds to that of the inverse process of oxidation of AA to DHA, this value should give and indication on the « in vivo » efficiency of the AA-DHA system as an electron carrier in respiration. As some AA was probably reoxidized to DHA in the very short period required to kill the tissue, the value of the AA DHA turnover thus calculated is probably somewhat lower than the real one.

According to the present work, the oxidative turnover of the AA-DHA system would results of 0,7 micromoles/g. fr. weght/h. for the pea internode tissues and of 0,9 micromoles/g. fr. weght^?h for the potato tuber (aged disks). These values would account for 5% of total oxygen uptake, in the former, and for 3% in the latter material.

The very high AA/DHA ratio usually prevailing in living cells suggests that the contents in DHA (and thus the activity of the AA oxidizing systems) is a limiting factor for the efficiency of the AA-DHA system as an electron carrier. This view is supported also by experiments in which DHA (at pH 5) was fed to pea internode segments and to potato tuber disks : as the presence of DHA into the medium induced — under anaerobiotic conditions — a rapid increase of the level of AA in both types of materials. In aerobiosis uptake and reduction of DHA to AA was evident in the potato tuber tissue, while it appeared very scarce in the pea internodes. As an interpretation of this behaviour it is suggested that, in aerobiosis, the very active and probably surface localized ascorbic acid oxidase of the pea tissue re-oxidises the AA formed from reduction of the DHA fed; an accumulation of DHA into the cells would follow, and this excess of DHA would inhibit the enzyme GSH-DHA reductase. This enzyme, in fact, appears, from « in vitro » experiments, to be strongly inhibited by DHA when the DHA/GSH ratio becomes higher than 1. On the other hand, the same hypothesis is also supported by the finding that the addition of DHA to the medium induces a significant drop in the GSH level (probably due to its oxidation to GSSG) only under those conditions in which DHA is absorbed and reduced to AA; that is, in the pea internodes, under anaerobiosis, and in the potato disks, under both anaerobiosis and aerobiosis. These results are also taken as confirming the indication from the enzymatic data that GSH is acting, in vivo as a reducing agent for DHA. The results of this investigation are thus interpred as showing that a comparatively small, but by no means negligeable fraction of respiration is mediated, in higher plant tissues such as those of the pea stem and the potato tuber, by and electron transfer system including glutathione and the ascorbate-dehydroascorbate couple. The efficiency of this system in the materials investigated appears to account for 3–5% of the total 0₂ uptake (minimum value). As enzyme systems transferring electrons from TPNH to ox. glutathione are widely distributed and generally very active in higher plant tissues, it is suggested that the sequence TPNH-GSH-AA/DHA - O₂ is probably of considerable importance in mediating the reoxidation of extramitochondrial trophosphoridine nucleotide and thus in permitting the operation of the TPN requiring pentose phosphate pathway of respiration.