Anderson Ferreira

Permeability of riparian forest strips in agricultural, small subtropical watersheds in south-eastern Brazil

If riparian buffer zones are ineffective in preventing C4 plant carbon from upland areas reaching the stream sediment, the composition of stream fauna can be significantly altered. The permeability of riparian forest strips in agricultural, small subtropical watersheds in south-eastern Brazil was measured in nine watersheds categorised according to the predominant land cover of the legally required 30-m buffer riparian zone. Four watersheds with well preserved riparian forest along the 30-m buffer zone were designated as FOREST watersheds; three watersheds, with a predominance of C4 grasses from sugarcane to pasture, mixed with preserved riparian forests, were designated MIXED watersheds; and two watersheds were termed PASTURE-SUGAR because their entire 30-m buffer zone was covered by C4 plants. Stable carbon (δ13C) isotopes were used as tracers of upland C4 carbon in sediments, suspended particulate organic carbon, terrestrial and aquatic invertebrates and two species of neotropical fish. Although the intact 30-m buffer zone of riparian forests did not entirely prevent the input of C4 to the river environment and food web, there was a significant increase in C4 carbon in those watersheds where the buffer zone was not covered by riparian forests. These findings emphasise the importance of riparian forests in mitigating disturbance in streams and support efforts to preserve such riparian corridors.

Diversidade genética de Tibraca limbativentris Stål (Hemiptera: Pentatomidae) de Santa Catarina e do Rio Grande do Sul, usando marcadores RAPD

The work was carried out to test DNA extraction protocols and to characterize populations of Tibraca limbativentris Stål, an important rice insect-pest. Insects were collected in Joinville, Rio do Oeste and Turvo, in Santa Catarina State, and Agudo, Uruguaiana, Pelotas and Palmares do Sul, in Rio Grande do Sul State, and six literature-referenced protocols, besides a new one, were tested. DNA from ten individuals of each population was extracted using the best protocol and RAPD reactions were carried out with ten initiators. The new protocol showed the best results and was used in the PCR reactions, that generated 151 polymorphic bands, allowing to access genetic differences among all the populations; no individuals from one population were clustered with individuals from another. The largest intrapopulacional similarity was found in Uruguaiana (22%), and the smallest in Palmares do Sul (50%), which was also the most divergent population in relation to the others. The Gst was 0.5215, and the Nm was 0.4588; these values reflect the low similarity between the populations. The smallest genic flow was obtained when Palmares do Sul and Pelotas were included in the comparisons, in accordance with the largest divergence of these two populations in relation to the others. There was no significant relation between geographic distance and genetic similarity, which can reflect unknown model of dispersion of T. limbativentris. New studies exploring the species dispersion strategies may help to understand the insect distribution and to unveil the main factors linked to the genetic variability within and between populations.

Colonization of rice and Spodoptera frugiperda J.E. Smith (Lepidoptera: Noctuidae) larvae by genetically modified endophytic Methylobacterium mesophilicum.

The colonization of Spodoptera frugiperda J.E. Smith larvae and rice seedlings by genetically modified endophytic bacterium Methylobacterium mesophilicum, and also the possible transfer of this bacterium to inside the larvas body during seedlings consumption were studied. The data obtained by bacterial reisolation and fluorescence microscopy showed that the bacterium colonized the rice seedlings, the larvas body and that the endophytic bacteria present in seedlings could be acquired by the larvae. In that way, the transference of endophytic bacterium from plants to insect can be a new and important strategy to insect control using engineered microorganisms.

Seletividade de agrotóxicos utilizados na cultura do arroz irrigado ao fungo Metarhizium anisopliae, agente de controle microbiano de Tibraca limbativentris

Searching for integrated control strategies for the insect-pest Tibraca limbativentris, the in vitro compatibility between isolated CG 891 of Metarhizium anisopliae and several pesticides used in the culture of irrigated rice was evaluated. The followings parameters were studied: vegetative growth, sporulation and the germination viability in pre- and post-contact of the fungus for two concentrations of fipronil, thiametoxan, fenitrothion, carbofuran, pyrazosulfuron-ethyl, bentazon, clomazone, glyfosate and quinclorac and one concentration of tricyclazole and azoxystrobin. Significant reductions in the vegetative growth and sporulation of M. anisopliae were observed for fenitrothion, carbofuran and azoxystrobin. The germination in pre-contact was affected by azoxystrobin. The percentage of germination changed the classification of pesticides in relation to its selectivity on the fungus. However, the results show that in vitro, the pesticides fenitrothion, carbofuran, glyfosate and azoxystrobin are harmful to isolated CG 891 of M. anisopliae.

Microsatellite genotyping from faeces of Lontra longicaudis from southern Brazil

A lontra neotropical de rio Lontra longicaudis (Olfers, 1818), cujo estado de conservacao e ainda desconhecido, foi estudada geneticamente na Estacao Ecologica do Taim e nas margens do arroio Vargas, RS, sul do Brasil. Amostras de fezes foram coletadas e o DNA foi extraido por um metodo de silica-guanidina. Cinco locos de microsatelites foram amplificados por PCR utilizando primers heterologos previamente descritos para Lutra lutra (Linnaeus, 1758). Dezesseis amostras de fezes de um total de 29 coletadas no Taim e onze das 14 obtidas no arroio Vargas contiveram DNA suficiente para prosseguir com a analise genetica. Um total de 49 alelos foram obtidos, dos quais 18 foram exclusivos de individuos do Taim e 17 exclusivos dos individuos do arroio Vargas. Em tres locos (Lut715, Lut733 e Lut818) os individuos das duas localidades compartilharam o alelo mais comum. Foi encontrada uma alta diversidade genetica (NeTaim=4,1; HoTaim=0,299; HeTaim=0,681; NeVargas=4,9; HoVargas=0,355; HeVargas=0,724), sendo esta maior no arroio Vargas. Uma alta e significativa deficiencia de heterozigotos foi observada em quase todos os locos de acordo com o teste do χ2. O teste do χ2 de homogeneidade genetica (P<0,001) mostrou diferencas significativas entre as frequencias alelicas das duas localidades. A genotipagem para mais de um loco foi possivel em 81,5% das amostras, sendo que somente em 37% destes foi possivel a genotipagem para mais de tres locos. Foi encontrado um baixo grau de parentesco entre os individuos do Taim (R=0,055±0,310), sendo este ainda menor nos individuos do arroio Vargas (R=-0,285±0,440). O grau significativo de diferenciacao genetica (I=0,890; FST=0,059) entre os individuos do Taim e do arroio Vargas sugere a existencia de mais de uma populacao de lontras no extremo sul do Brasil, que provavelmente estejam associadas aos diferentes corpos de agua existentes nesta regiao: a Lagoa Mirim e o sistema de lagoas Cauiva/Flores/Mangueira. A alta diversidade genetica e o baixo grau de parentesco dos individuos do arroio Vargas nos leva a considerar a possibilidade que o arroio Vargas possa estar atuando como um corredor entre estes corpos de agua para a dispesao das lontras.

Exactly solvable interacting spin-ice vertex model.

A special family of solvable five-vertex model is introduced on a square lattice. In addition to the usual nearest-neighbor interactions, the vertices defining the model also interact along one of the diagonals of the lattice. This family of models includes in a special limit the standard six-vertex model. The exact solution of these models is an application of the matrix product ansatz introduced recently and applied successfully in the solution of quantum chains. The phase diagram and the free energy of the models are calculated in the thermodynamic limit. The models exhibit massless phases, and our analytical and numerical analyses indicate that such phases are governed by a conformal field theory with central charge c=1 and continuously varying critical exponents.

The n-site approximation for the triplet-creation model

The nonequilibrium phase transition of the one-dimensional triplet-creation model is investigated using the n-site approximation scheme. We find that the phase diagram in the space of parameters (γ, D), where γ is the particle decay probability and D is the diffusion probability, exhibits a tricritical point for n ≥ 4. However, the fitting of the tricritical coordinates (γt, Dt) using data for 4 ≤ n ≤ 13 predicts that γt becomes negative for n ≥ 26, indicating thus that the phase transition is always continuous in the limit n → ∞. However, the large discrepancies between the critical parameters obtained in this limit and those obtained by Monte Carlo simulations, as well as a puzzling non-monotonic dependence of these parameters on the order of the approximation n, argue for the inadequacy of the n-site approximation to study the triplet-creation model for computationally feasible values of n.