The Asymmetric Response Concept explains ecological consequences of multiple stressor exposure and release.

Our capacity to predict trajectories of ecosystem degradation and recovery is limited, especially when impairments are caused by multiple stressors. Recovery may be fast or slow and either complete or partial, sometimes result in novel ecosystem states or even fail completely. Here, we introduce the Asymmetric Response Concept (ARC) that provides a basis for exploring and predicting the pace and magnitude of ecological responses to, and release from, multiple stressors. The ARC holds that three key mechanisms govern population, community and ecosystem trajectories. Stress tolerance is the main mechanism determining responses to increasing stressor intensity, whereas dispersal and biotic interactions predominantly govern responses to the release from stressors. The shifting importance of these mechanisms creates asymmetries between the ecological trajectories that follow increasing and decreasing stressor intensities. This recognition helps to understand multiple stressor impacts and to predict which measures will restore communities that are resistant to restoration.

A new technique to study nutrient flow in host-parasite systems by carbon stable isotope analysis of amino acids and glucose.

Stable isotope analysis of individual compounds is emerging as a powerful tool to study nutrient origin and conversion in host-parasite systems. We measured the carbon isotope composition of amino acids and glucose in the cestode Schistocephalus solidus and in liver and muscle tissues of its second intermediate host, the three-spined stickleback (Gasterosteus aculeatus), over the course of 90 days in a controlled infection experiment. Similar linear regressions of δ13C values over time and low trophic fractionation of essential amino acids indicate that the parasite assimilates nutrients from sources closely connected to the liver metabolism of its host. Biosynthesis of glucose in the parasite might occur from the glucogenic precursors alanine, asparagine and glutamine and with an isotope fractionation of - 2 to - 3 ‰ from enzymatic reactions, while trophic fractionation of glycine, serine and threonine could be interpreted as extensive nutrient conversion to fuel parasitic growth through one-carbon metabolism. Trophic fractionation of amino acids between sticklebacks and their diets was slightly increased in infected compared to uninfected individuals, which could be caused by increased (immune-) metabolic activities due to parasitic infection. Our results show that compound-specific stable isotope analysis has unique opportunities to study host and parasite physiology.

Insights into amino acid fractionation and incorporation by compound-specific carbon isotope analysis of three-spined sticklebacks.

Interpretation of stable isotope data is of upmost importance in ecology to build sound models for the study of animal diets, migration patterns and physiology. However, our understanding of stable isotope fractionation and incorporation into consumer tissues is still limited. We therefore measured the δ13C values of individual amino acids over time from muscle and liver tissue of three-spined sticklebacks (Gasterosteus aculeatus) on a high protein diet. The δ13C values of amino acids in the liver quickly responded to small shifts of under ± 2.0‰ in dietary stable isotope compositions on 30-day intervals. We found on average no trophic fractionation in pooled essential (muscle, liver) and non-essential (muscle) amino acids. Negative Δδ13C values of - 0.7 ± 1.3‰ were observed for pooled non-essential (liver) amino acids and might indicate biosynthesis from small amounts of dietary lipids. Trophic fractionation of individual amino acids is reported and discussed, including unusual Δδ13C values of over + 4.9 ± 1.4‰ for histidine. Arginine and lysine showed the lowest trophic fractionation on individual sampling days and might be useful proxies for dietary sources on short time scales. We suggest further investigations using isotopically enriched materials to facilitate the correct interpretation of ecological field data.

Injectable biopolymer based hydrogels for drug delivery applications.

Biopolymer based pH-sensitive hydrogels were prepared using chitosan (CS) with polyethylene glycol (PEG) of different molecular weights in the presence of silane crosslinker. The incorporated components remain undissolved in different swelling media as they are connected by siloxane linkage which was confirmed by Fourier transform infrared spectroscopy. The swelling in water was enhanced by the addition of higher molecular weight PEG. The swelling behaviour of the hydrogels against pH showed high swelling in acidic and basic pH, whereas, low swelling was examined at pH 6 and 7. This characteristic pH responsive behaviour at neutral pH made them suitable for injectable controlled drug delivery. The controlled release analysis of Cefixime (CFX) (model drug) loaded CS/PEG hydrogel exhibited that the entire drug was released in 30 min in simulated gastric fluid (SGF) while in simulated intestinal fluid (SIF), 85% of drug was released in controlled manner within 80 min. This inferred that the developed hydrogels can be an attractive biomaterial for injectable drug delivery with physiological pH and other biomedical applications.