Valorization of fish by-products: rheological,textural and microstructural properties of mackerel skin gelatins

The fish processing industry generates significant amounts of waste which is usually discarded. The present study investigated the recovery of gelatins from Atlantic mackerel (Scomber scombrus) skins after pre-treatment with different environmentally friendly organic acids (acetic, citric, lactic, tartaric or malic acid). The chemical composition, the rheological and the textural properties as well as the microstructural characteristics of the extracted gelatins were analysed and compared to commercial bovine hide gelatin. Although the organic acid used in the pre-treatment step did not affect the extraction yield and the chemical composition of the prepared gelatins, differences were observed in terms of rheology and texture. The highest gel strength (P < 0.05) was observed with gelatins extracted after pre-treatment with acetic, citric and malic acids (71–80 g). From an industrial point of view, gelatin can be extracted using any of these organic acids with similar yield. However, in order to obtain better rheological and textural properties the use of acetic, citric or malic acid in the pre-treatment step is recommended.     

Evaluation of surface water quality using an ecotoxicological approach: a case study of the Alqueva Reservoir (Portugal)

Background, aim, and scope  

Freshwater reservoirs can be impacted by several hazardous substances through inputs from agricultural activity, sewage discharges, and groundwater leaching and runoff. The water quality assessment is very important for implementation of the monitoring and remediation programs to minimize the risk promoted by hazardous substances in aquatic ecosystems. Evaluation of the degree of contamination of aquatic environments must not take in account only its chemical characterization but it must be complemented with biological assays, which determine potential toxic effects and allows an integrated evaluation of its effects in populations and aquatic ecosystem communities. The application of this type of strategy has clear advantages allowing a general evaluation of the effects from all the water components, including those due to unknown substances and synergic, antagonistic, or additive effects. There are only a few studies that reported ecotoxicological acute end points, for the assessment of surface water quality, and the relationship among toxicity results and the anthropogenic pollution sources and the seasonal period. The aim of this study was to assess the ecotoxicological characterization of the surface water from Alqueva reservoir (South of Portugal) and to evaluate the influence of anthropogenic sources of pollution and their seasonal variation in its toxicity. The construction of Alqueva reservoir was recently finished (2002) and, to our knowledge, an ecotoxicological assessment of its surface water has not been performed. Because of that, no information is available on the possible impact of pollutants on the biota. The surface water toxicity was assessed using acute and chronic bioassays. The results are to be used for developing a monitoring program, including biological methods.     

Extractability and mobility of mercury from agricultural soils surrounding industrial and mining contaminated areas

This study focussed on a comparison of the extractability of mercury in soils with two different contamination sources (a chlor-alkali plant and mining activities) and on the evaluation of the influence of specific soil properties on the behaviour of the contaminant. The method applied here did not target the identification of individual species, but instead provided information concerning the mobility of mercury species in soil. Mercury fractions were classified as mobile, semi-mobile and non-mobile. The fractionation study revealed that in all samples mercury was mainly present in the semi-mobile phase (between 63% and 97%). The highest mercury mobility (2.7 mg kg(-1)) was found in soils from the industrial area. Mining soils exhibited higher percentage of non-mobile mercury, up to 35%, due to their elevated sulfur content. Results of factor analysis indicate that the presence of mercury in the mobile phase could be related to manganese and aluminium soil contents. A positive relation between mercury in the semi-mobile fraction and the aluminium content was also observed. By contrary, organic matter and sulfur contents contributed to mercury retention in the soil matrix reducing the mobility of the metal. Despite known limitations of sequential extraction procedures, the methodology applied in this study for the fractionation of mercury in contaminated soil samples provided relevant information on mercury's relative mobility.     

Wheat yield functions for analysis of land-use change in China

CERES-Wheat, a dynamic process crop growth model, is specified and validated for eight sites in the major wheat-growing regions of China. Crop model results are then used to test the Mitscherlich-Baule and the quadratic functional forms for yield response to nitrogen fertilizer, irrigation water, temperature, and precipitation. The resulting functions are designed to be used in a linked biophysical-economic model of land-use and land-cover change in China. While both functions predict yield responses adequately, the Mitscherlich-Baule function is preferable to the quadratic function because its parameters are biologically and physically realistic. Variables explaining a significant proportion of simulated yield variance are nitrogen, irrigation water, and precipitation; temperature was a less significant component of yield variation within the range of observed year-to-year variability at the study sites. Crop model simulations with a generic soil with median characteristics of the eight sites compared to simulations with site-specific soils showed that agricultural soils in China have similar and, in general, low-to-moderate water-holding capacities and organic matter contents. The validated crop model is useful for simulating the range of conditions under which wheat is grown in China, and provides the means to estimate production functions when experimental field data are not available.     

Bioindication of atmospheric trace metals--with special references to megacities

After considering the particular problems of atmospheric pollution in megacities, i.e. agglomerations larger than 5 mio. inhabitants, with urbanization of World's population going on steadily, possibilities of active biomonitoring by means of green plants are discussed. Based on specific definitions of active and passive bioindication the chances of monitoring heavy metals in Sao Paulo megacity were demonstrated (first results published before). This is to show that there is need for increased use of bioindication to tackle the particular problems of megacities concerning environmental "health", the data to be processed according to the Multi-Markered-Bioindication-Concept (MMBC). Comparison to other work shows this approach to be reasonable.     

Use of multiple tools to assess the feeding preference of coastal dolphins

The feeding preferences of the coastal dolphins Pontoporia blainvillei and Sotalia guianensis in south-eastern Brazil (21o18′S–22o25′S) were assessed through the prey’s index of relative importance (IRI), total mercury concentration (Hg_tot), and stable isotopic (δ¹⁵N and δ¹³C) to compare their efficiency in the discrimination of prey contribution to the predators’ diet. The IRI was the best tool to describe the dolphins’ preference, while Hg_tot and δ¹⁵N seemed to be efficient as a trophic marker when the diet is made up of prey of varying sizes, as observed in S. guianensis. Both dolphins presented lighter δ¹⁵N than their prey species, which is an unusual pattern. However, as the sample size to isotope ratios analysis was small, especially to the dolphins, the results should be considered with caution, and further studies are necessary to corroborate these findings. The δ¹³C values characterized a typical coastal food chain, confirming the preferential area of these species.     

Blinkered teaching: tandem running by visually impaired ants

During tandem runs, one ant worker recruits another to an important resource. Here, we begin to investigate how dependent are tandem leaders and followers on visual cues by painting over their compound eyes to impair their vision. There are two ways in which Temnothorax albipennis might use vision during tandem running. First, the follower might track the movements of the leader by keeping it in sight. Our results suggest that the ants do not use vision in this way. For example, in all four classes of tandem run (those with either leader or follower, both, or neither of their participants with visual impairments) progress was most smooth at about 3 mm/s. This suggests that communication between leaders and followers during tandem runs is not based on vision and is purely tactile and pheromonal. Second, the leader and the follower might be using vision to navigate and our results support this possibility but also suggest that these ants have other methods of navigation. Ants with visual impairments were more likely to follow than to lead, but could occupy either role, even though they had many fully sighted nestmates. This might help to explain why the ants did not focus grooming on their most visually impaired nestmates. Wild-type tandem runs, with both participants fully sighted and presumably taking time to learn landmarks, were overall significantly slower, smoother, and a little less tortuous, than the other treatments. All four classes of tandem run significantly increased mean instantaneous speeds and mean absolute changes in instantaneous acceleration over their journeys. Moreover, tandems with sighted followers increased their speed with time more than the other treatments. In general, our findings suggest that eyesight is used for navigation during tandem running but that these ants also probably use other orientation systems during such recruitment and to learn how to get to new nest sites. Our results suggest that the ants’ methods of teaching and learning are very robust and flexible.     

White tail markings are an indicator of quality and affect mate preference in rock sparrows

In birds, colourful and elaborate feathers are important traits in mate choice. Distinct tail white patches are present in many species of birds, but they remain little studied. Tail markings may indeed have a signal function because in many species males spread the tail offering a good view of these markings to females during courtship behaviour. Here, we investigated whether white tail spots in male rock sparrow, Petronia petronia, play a role in mate choice. In a free-living population of rock sparrows, we found a reduction in white tail spots size as the breeding season progressed due to abrasion, which was expected if tail spots act as a reliable quality indicator (i.e. a handicap). The same reduction was found under captive conditions, and males in worse condition (individuals that lost more weight) abraded a bigger part of white. This suggests that white tail markings are an indicator of male quality. In captivity, we measured female preference for males differing in white patch size in a mate choice experiment. The experimental reduction of the size of the males’ white spots resulted in a lower sexual interest by females. During courtship display, male rock sparrow shows a yellow breast patch (a carotenoid-based, sexually selected ornament) together with the white spots in the tail. The sizes of these two traits are positively correlated, but only the abraded white area in the tail correlates with a surrogate of individual quality (lost of weight). In conclusion, we can assert that the size of the white spots is preferred by female rock sparrows and it is a part of a multiple signal system.     

Global distribution of a key trophic guild contrasts with common latitudinal diversity patterns

Most hypotheses explaining the general gradient of higher diversity toward the equator are implicit or explicit about greater species packing in the tropics. However, global patterns of diversity within guilds, including trophic guilds (i.e., groups of organisms that use similar food resources), are poorly known. We explored global diversity patterns of a key trophic guild in stream ecosystems, the detritivore shredders. This was motivated by the fundamental ecological role of shredders as decomposers of leaf litter and by some records pointing to low shredder diversity and abundance in the tropics, which contrasts with diversity patterns of most major taxa for which broad-scale latitudinal patterns haven been examined. Given this evidence, we hypothesized that shredders are more abundant and diverse in temperate than in tropical streams, and that this pattern is related to the higher temperatures and lower availability of high-quality leaf litter in the tropics. Our comprehensive global survey (129 stream sites from 14 regions on six continents) corroborated the expected latitudinal pattern and showed that shredder distribution (abundance, diversity and assemblage composition) was explained by a combination of factors, including water temperature (some taxa were restricted to cool waters) and biogeography (some taxa were more diverse in particular biogeographic realms). In contrast to our hypothesis, shredder diversity was unrelated to leaf toughness, but it was inversely related to litter diversity. Our findings markedly contrast with global trends of diversity for most taxa, and with the general rule of higher consumer diversity at higher levels of resource diversity. Moreover, they highlight the emerging role of temperature in understanding global patterns of diversity, which is of great relevance in the face of projected global warming.