Limnological changes in a sub‐tropical shallow hypertrophic lake during its restoration: two years of a whole‐lake experiment

1. Lake Rodó is a turbid system, a condition attributed to algal biomass. The proximal source of the eutrophication was stormwater discharges from an ill‐defined urban area. This paper describes an attempt to restore the water quality of Lake Rodó, the first time this has been done in Uruguay. In spring 1996 it was drained, sediments were removed and stream inputs were diverted. Groundwater was used to re‐fill the lake. Due to its high nutrient concentration a re‐circulation system was designed, pumping water from associated pools covered with free‐floating plants. 2. After the lake was refilled, the system was characterized by oxygen saturation or over‐saturation, neutral to basic pH, and high phosphorus, nitrogen and silicate concentrations. Ratios of total nitrogen (TN):total phosphorus (TP) and chlorophyll a (Chl a):TP indicated that phosphorus was the primary limiting nutrient during the period of groundwater supply. Once groundwater pumping had ceased, there was a decrease in TN:TP and Chl a:TP ratios, suggesting N‐limiting conditions prevailed in some periods. 3. Before restoration, the phytoplankton community was dominated year‐round by Planktothrix agardhii; since restoration the community has been more diverse. This change has favoured grazing by mesozooplankton, and the onset of clear‐water phases in spring. 4. Abundant populations of small omnivorous fish maintained a high predation pressure on zooplankton, restricting the abundance of large‐bodied herbivores, which, in turn, allowed an increase in phytoplanton biomass and a decrease in water transparency. Based on this observation, together with the phosphorus concentration and the low abundance of filamentous cyanobacteria compared with previous studies, we suggest that top‐down control has played a key role in increasing transparency in Lake Rodó. 5. A nutrient reduction programme, by the mechanical harvest of floating plants, and a removal of small omnivorous fishes and stocking strictly with piscivores, could be key factors in the achievement of a stable clear‐water phase. However, if blooms of Microcystis or other similar genera occur in summer, additional measures (e.g. reduction of the hydraulic residence time) will be needed to improve water transparency. Copyright © 2001 John Wiley & Sons, Ltd.     

Hybridization barriers between diploid Solanum tuberosum and wild Solanum raphanifolium

Wild potato germplasm represents a unique, diverse and accessible resource for disease and pest resistance, along with useful agronomic traits that may be introgressed into the cultivated potato (Solanum tuberosum L.). Hybridization of diploid wild Solanum species with haploids (2×) of cultivated potato (4×) is generally an effective technique for introducing genetic diversity and desirable traits into potato. However, in this study, hybridization barriers were found in crosses between S. tuberosum haploids and the wild species S. raphanifolium. Male sterility, likely due to nuclear-cytoplasmic interactions, was observed in some haploid tbr?×?S. raphanifolium hybrids. In addition, pollen-pistil incompatibilities were observed in backcross, F2, and reciprocal cross hybridization attempts that failed to produce seed. More crosses were successful when F1 clones were crossed as females to wild clones than to cultivated clones. When crosses were made in the other direction, with F1 hybrids used as male parents, seeds were almost never produced.     

SMEDWI-2 is a PIWI-like protein that regulates planarian stem cells

We have identified two genes, smedwi-1 and smedwi-2, expressed in the dividing adult stem cells (neoblasts) of the planarian Schmidtea mediterranea. Both genes encode proteins that belong to the Argonaute/PIWI protein family and that share highest homology with those proteins defined by Drosophila PIWI. RNA interference (RNAi) of smedwi-2 blocks regeneration, even though neoblasts are present, irradiation-sensitive, and capable of proliferating in response to wounding; smedwi-2(RNAi) neoblast progeny migrate to sites of cell turnover but, unlike normal cells, fail at replacing aged tissue. We suggest that SMEDWI-2 functions within dividing neoblasts to support the generation of cells that promote regeneration and homeostasis.     

Identification of bovine viral diarrhea virus type 1 in yaks (Bos poephagus grunniens) in the Himalayan region

Since cattle are widely infected by bovine viral diarrhea virus (BVDV) in India, we searched for pestivirus infection in yaks. Of 71 pure and crossbred yaks from Himalayan region, pestivirus antigen was detected by Ag-ELISA in three animals. Pestivirus in leukocyte and cell culture isolated virus samples originating from positive yaks was also confirmed by RT-PCR using panpestivirus specific primers selected from 5'-untranslated region (5' UTR). The 5' UTR, N(pro) and E2 regions were sequenced and used for genetic typing. Phylogenetic analysis revealed that pestiviruses detected in three Himalayan yaks were similar genetically, belonging to BVDV-1. Antigenic characterisation of yak pestivirus also confirmed the typing as BVDV-1. This is the first report on the identification of BVDV type 1 in yaks.     

Adenosine A2A receptor agonists inhibit lipopolysaccharide-induced production of tumor necrosis factor-alpha by equine monocytes

Adenosine is an endogenous nucleoside that regulates many physiological processes by activating one or more adenosine receptor subtypes, namely A1, A2A, A2B and A3. The results of previous studies indicate that adenosine analogues inhibit lipopolysaccharide (LPS)-induced production of reactive oxygen species (ROS) by equine neutrophils primarily through activation of A2A receptors. Because peripheral blood monocytes produce cytokines that are responsible for many of the deleterious effects of LPS, the current study was performed to evaluate the effects of an array of novel adenosine receptor agonists on LPS-induced production of tumor necrosis factor-alpha (TNF-alpha), and to assess the selectively of these agonists for equine adenosine A2A over the A1 receptor. Radioligand binding studies performed with equine tissues expressing adenosine A1 and A2A receptor subtypes yielded a rank order of affinity for the equine A2A receptor of ATL307>ATL309 approximately ATL310 approximately ATL313>ATL202 approximately ATL361 approximately ATL376>ATL372>CGS21680>NECA. Co-incubation of equine peripheral blood monocytes with LPS and these agonists resulted in inhibition of TNF-alpha production with a rank order of potency that strongly correlated with their binding affinities for equine adenosine A2A receptors. Results of experiments performed with one of the adenosine receptor agonists (ATL313) and selective adenosine receptor antagonists confirmed that inhibition of LPS-induced production of TNF-alpha occurred via stimulation of A2A receptors. Although incubation of monocytes with IB-MECA, a compound purported to act as an adenosine A3 receptor agonist, reduced LPS-induced TNF-alpha production, this effect of IB-MECA was inhibited by the A2A selective antagonist ZM241385 but not by the A3 receptor antagonist MRS1220. These results indicate that the adenosine receptor subtype responsible for regulation of LPS-induced cytokine production by equine monocytes is the A2A receptor. To address the signal transduction mechanism responsible for the anti-inflammatory effects of ATL313 in equine monocytes, production of cAMP was compared in the presence and absence of either the adenosine A2A receptor antagonist ZM241385 or the adenosine A2B receptor antagonist MRS1706. In the absence of the antagonists, ATL313 increased production of cAMP; ZM241385 inhibited this effect of ATL313, whereas MRS1706 did not. Furthermore, incubation of monocytes with either the stable analogue of cAMP, dibutyryl cAMP, or forskolin, an activator of adenylyl cyclase, also inhibited LPS-induced production of TNF-alpha production by equine monocytes. Collectively, the results of the current study indicate that adenosine analogues inhibit LPS-induced production of TNF-alpha by equine monocytes primarily via activation of adenosine A2A receptors and do so in a cAMP-dependent manner. The results of this study indicate that stable adenosine analogues that are selective for adenosine A2A receptors may be suitable for development as anti-inflammatory drugs in horses.     

Seroepidemiology of infection with Toxoplasma gondii in waste pickers and waste workers in Durango, Mexico

Municipal waste is a potential source of infection for Toxoplasma gondii as it may contain contaminated meat with parasite tissue cysts and cat excrement with parasite oocysts. Therefore, we sought to determine the prevalence of T. gondii infection and associated characteristics in two populations exposed to municipal solid waste in Durango, Mexico. Ninety waste pickers and 83 waste workers of Durango City, Mexico were examined for T. gondii infection. They were tested for anti-T. gondii IgG and IgM antibodies using enzyme-linked immunoassays. In addition, socio-demographic and behavioural characteristics from each participant were obtained. Nineteen (21.1%) of the 90 waste pickers and seven (8.4%) of the 83 waste workers were positive for anti-T. gondii IgG antibodies. The difference in prevalence among the groups was statistically significant (P =0.03). Waste pickers aged 31-50 years showed a significantly higher prevalence (40.9%) than waste workers of the same age group (2.9%, P < 0.001). Anti-T. gondii IgM antibodies were found in two (2.2%) of the waste pickers but in none of the waste workers. The seroprevalence of T. gondii was significantly higher in workers of the waste transfer station (25.0%) than in drivers or helpers of waste vehicles (2.5%) (P =0.03). Multivariate analysis showed that T. gondii infection was associated with consuming food found in the garbage [adjusted odds ratio (OR) = 4.4; 95% confidence interval (CI) 1.6-11.8] and with lack of education (adjusted OR = 3.2; 95% CI 1.1-8.8). From this study, we conclude: (i) waste pickers may represent a risk group for T. gondii infection; (ii) lack of education might be a contributing factor for T. gondii infection; (iii) the higher the exposure to garbage, the higher the seroprevalence of T. gondii infection; (iv) Eating food products from the garbage may represent an important route for T. gondii infection.     

Selected Aspects of Advanced Porcine Reproductive Technology

In vitro fertilization (IVF) of in vitro matured (IVM) oocytes in pigs has become the most popular method of studying gametogenesis and embryogenesis in this species. Furthermore, because of recent advances in in vitro culture (IVC) of IVM–IVF embryos, in vitro production (IVP) of embryos now enables us to generate viable embryos as successfully as for in vivo -derived embryos and with less cost and in less time. These technologies contribute not only to developments in reproductive physiology and agriculture but also to the conservation of porcine genetic resources and the production of cloned or genetically modified pigs. However, in IVP, there still remains the problem of abnormal ploidy, which is caused by performing procedures under non-physiological conditions. In recent years, unique technologies such as intracytoplasmic sperm injection (ICSI) or xenografting of gonadal tissue into immunodeficient experimental animals have been developed to help conserve gamete resources. These technologies combined with IVP are expected to be useful for the conservation of gametes from important genetic resources. Here, we discuss the developmental ability and normality of porcine IVP embryos and also the utilization of ICSI and xenografting in advancing biotechnology in pigs.