Do aquatic macrophytes co-occur randomly? An analysis of null models in a tropical floodplain

One of the main issues in community ecology is the detection of structure and the identification of its related causes. In this study, co-occurrence null models were used to identify possible spatio-temporal patterns in the assemblage of aquatic macrophytes in the Upper Paraná River floodplain. The samples were obtained through the Long Term Ecological Research (LTER) Program at two different grains: (1) a coarser spatial grain in January and August 2001 (entire floodplain lagoons); (2) and a finer spatial grain in November 2006 (1 m² quadrats). The study was conducted in 36 lagoons, both connected and disconnected to the main river channel, located in the sub-basins of the Baía, Ivinheima and Paraná rivers. Two null models of species co-occurrence, the C-Score and Checkerboard indices, were used to test the null hypothesis of random structure of the aquatic macrophyte assemblages. The null models showed that the aquatic macrophyte assemblages were spatially structured in the distinct spatial grains. However, despite this general pattern, macrophyte assemblages are organized differently depending on the degree of connectivity, seasonal period and, at a finer grain, depth. Species co-occurrences were random in the disconnected lagoons during flood periods, in deep zones of the lagoons of the Baía River and in the shallow littoral zone in the lagoons of the Paraná River. Analysis of the patterns of co-occurrence indicated that competition and/or habitat preferences are probably important influences on the nonrandom structure of assemblages. However, we suppose that at least three important factors (disturbances by water level fluctuation, dispersion and facilitation) counteract potential effects of competition in specific situations, leading macrophyte assemblages to assume random structure.     

Morphologic and morphometric analysis of Hepatozoon spp. (Apicomplexa,Hepatozoidae) of snakes

Hepatozoon species are the most abundant hemoparasites of snakes. Its identification has been based mainly on the morphologic characterization of the gamonts in the peripheral blood of the vertebrate host and also of the cysts found in the internal organs of the vertebrate and invertebrate hosts. Using a computerized image analysis system, we studied five species of Hepatozoon from recently captured snakes in Botucatu, State of S o Paulo, Brazil, to evaluate the importance of the morphology and morphometry of the gamonts for the characterization of Hepatozoon species and to analyze the morphologic changes induced in the erythrocytes by the parasite. The studied species were H. terzii of Boa constrictor amarali, Hepatozoon sp. of Crotalus durissusterrificus, H. philodryasi of Philodryas patagoniensis, and H. migonei and H. cyclagrasi of Hydrodynastes gigas. We observed three different groups, one of them including the species H. terzii, H. philodryasi and Hepatozoon sp. of C. durissus terrificus; and the other two consisting of H. migonei and H. cyclagrasi. Degree of alterations in the erythrocytes was variable and it may be useful for characterization of Hepatozoon species.     

Stability of immobilized laccase on Luffa Cylindrica fibers and assessment of synthetic hormone degradation

In this work were studied the pH, thermal, and storage stability of free and immobilized laccases. Enzymes were produced by Pleurotus ostreatus on potato dextrose (PD) broth and potato dextrose modified (PDM) broth, and immobilized using Luffa cylindrica fibers as support. Both free and immobilized enzymes were assessed on their respective enzymatic activities and for 17α-ethinylestradiol (EE2) degradation. The optimum pH conditions concerning laccase activity ranged from 3.6 to 4.6, while temperature ranged between 30?°C and 50?°C for both free and immobilized enzyme. Laccase produced using PD broth presented greater storage stability and thermal stability than that of PDM. Best EE2 removals were of 79.22% and 75.00% for the free and immobilized enzymes, respectively. Removal rates were assessed during 8?h at pH 5. The removal of 17α-ethinylestradiol was stabilized in the fourth cycle of use. Results imply that immobilization promoted stability towards pH and temperature variations, although media played a decisive role in the enzymatic activity. Both free and immobilized laccases of P. ostreatus were able to degrade EE2, whereas immobilized laccase in PDM medium presented possible reuse applicability, albeit removal was not optimal when compared to other reports.     

Phytochemical and antinociceptive properties of Matayba elaeagnoides Radlk. barks

A mixture of triterpenes named lupeol (1), alpha-amyrin (2), beta-amyrin (3), and beta-sitosterol (4) has been isolated from the hexane fraction of Matayba elaeagnoides. In addition, scopoletin (5), umbelliferone (6), 3beta-O-D-glycopyranosyl-sitosterol (7) and betulin (8) were isolated from the chloroform fraction. All the structures were identified by spectroscopic techniques in accordance with literature data. The extracts (hydroalcoholic and methanolic) and some fractions (hexane, chloroform, ethyl acetate and butanol) exerted promising antinociceptive effects in mice. In addition, we have tested the pure compound betulin (8). When analyzed against induced pain using the writhing test (3-10 mg kg(-1), i.p.), betulin showed a dose-dependent effect with a calculated ID50 value of 7.74 (6.53-9.17) mg kg(-1) [17.5 (14.7-20.7) micromol kg(-1)] and a maximal inhibition (MI) of 58.3% in relation to the control group. When evaluated in the formalin test (3-10 mg kg(-1), i.p.), this compound inhibited both phases of pain (neurogenic and inflammatory pain), with calculated ID50 values of 18.3 (17.7-18.9) and 8.3 (7.7-8.9) mg kg(-1) [41.5 (38.4-42.7) and 18.8 (17.6-19.9) micromol kg(-1)] and maximal inhibition of 40.8 and 64.39% for the first and second phases, respectively. Using the same models, this compound was several times more active than two clinically used drugs, namely aspirin and paracetamol, suggesting that its main active principle is related to the antinociceptive effect found for the chloroform fraction of M. elaeagnoids barks.     

Response of native Egeria najas Planch. and invasive Hydrilla verticillata (L.f.) Royle to altered hydroecological regime in a subtropical river

Egeria najas Planch. is the dominant native submersed macrophyte of the Upper Paraná River in Brazil, while Hydrilla verticillata (L.f.) Royle has recently invaded this area. From January 2006 to December 2007, comprising two annual flood cycles, we conducted monthly surveys at two river stations and two lakes connected to the river within this stretch of the Paraná River, aiming to understand how the hydrological regime influences the distribution and abundance of these native and invasive Hydrocharitaceae species. Hydrilla did not develop in the lakes, possibly due to the elevated proportion of organic matter in the sediment (∼10% DW). However, the exotic species dominated the river sites apparently suppressing E. najas. In the lakes E. najas reached a maximum biomass of 628 ± 82 g DW m⁻² but did not surpass 333 ± 83 g DW m⁻² in the river, where H. verticillata peaked at 1415 ± 255 g DW m⁻². Macrophyte biomass development was greatest during low-water periods, with transparent water and high temperatures. Floods probably affected submersed macrophytes (especially in 2007, when an extreme flood caused by an El Niño Southern Oscillation (ENSO) event occurred) via sediment movement and plant scouring (uprooting) effects, coupled with reduced water transparency. Macrophyte recovery started soon after the (less intense) 2006 flood but was delayed in 2007. In the river recovery started five months after the major flood, but in the lakes no significant plant regeneration was found even nine months after the disturbance. E. najas and H. verticillata started regeneration practically at the same time but H. verticillata had much higher rates of biomass increase.