Fighting parasites and predators: How to deal with multiple threats?

ABSTRACT: BACKGROUND: Although inducible defences have been studied extensively, only little is known about how the presence of parasites might interfere with these anti-predator adaptations. Both parasites and predators are important factors shaping community structure and species composition of ecosystems. Here, we simultaneously exposed Daphnia magna to predator cues (released by the tadpole shrimp, Triops, or by a fish) and spores of the yeast parasite Metschnikowia sp. to determine how life history and morphological inducible defences against these two contrasting types of predators are affected by infection. RESULTS: The parasite suppressed some Triops-induced defences: Daphnia lost the ability to produce a greater number of larger offspring, a life-history adaptation to Triops predation. In contrast, the parasite did not suppress inducible defences against fish: induction (resulting in smaller body length of the mothers as well as of their offspring) and infection acted additively on the measured traits. Thus, fish-induced defences may be less costly than inducible defences against small invertebrate predators like Triops; the latter defences could no longer be expressed when the host had already invested in fighting off the parasite. CONCLUSIONS: In summary, our study suggests that as specific inducible defences differ in their costs, some might be suppressed if a target prey is additionally infected. Therefore, adding parasite pressure to predator-prey systems can help to elucidate the costs of inducible defences.     

Postmortem Metabolic,Physicochemical, and Lipid Composition Changes in Litopenaeus vannamei in Response to Harvest Procedures

Ante-mortem stress is recognized as one of the factors that could reduce shelf life in fish, although this topic has been scarcely addressed in crustaceans, particularly in cultivated penaeid shrimp where common harvest practices involves stressful conditions such as chasing, emersion, and confinement. This study analyzes indices of freshness in shrimp in response to such practices before storage in ice for six days. During ice storage, several indicators follow the typical postmortem pattern, although most of them (hypoxanthine, change in pH, and color) did not reach critical levels at day 6. Adenosine-5’-triphosphate (ATP) and degradation products (adenosine monophosphate, AMP, and inosine monophosphate, IMP), as well as several indicators of freshness (pH, expressible water, hardness, color, and the overall fatty acid composition) were not significantly affected by harvest. Other variables such as lower springiness, higher hypoxanthine, lipid hydroperoxides, and 20:4n-6/20:5n-3 ratio were observed in shrimp subjected to common harvest practices. However, under the current conditions of harvesting, these effects were marginal and probably do not substantially affect meat quality for human consumption, but care should be taken at higher environmental temperatures (e.g. harvest in summer) and for a duration of ice-storage over 6 days.     

Thermal characteristics of soil organic matter measured by DSC: A hint on a glass transition

Glass transitions have been reported for purified humic acids only. In this study, a glass transition was detected in a sample of a sandy forest soil by Differential Scanning Calorimetry (DSC). The glass transition temperature was 79°C for air‐dried samples and 77°C for pre‐moistened samples. In addition to the glass transition, an exothermic process around 30°C was detected in pre‐moistened samples. This could be due to water loss of soil organic matter. However, the nature of this process is not yet understood. This study showed that the macromolecular behaviour of SOM, as indicated by DSC, reacts to the moisture state of soil organic matter.     

Detection and characterisation of bovine rotavirus in Ireland from 2006–2008

Background

Worldwide, Group A bovine rotavirus (RVA boRV) is one of the main causes of neonatal calf diarrhoea. Currently, limited epidemiological and sequence data exists on the RVA disease in bovines in Southern Ireland only. The aim of the study was to generate epidemiological and sequence data of RVA boRV distributed over a wide geographical area in Ireland.

Findings

272 stool samples were obtained from symptomatic calves and analysed to identify the prevalent G and P genotypes. Viral type combinations including G6P[5], G6P[11] and G10P[11] genotype were the most frequently identified. The G6P[5] combination was predominant throughtout the study, accounting for 70% (n = 191). Sequence analysis of the VP7 gene revealed that Irish G6 strains fell within Lineage IV, similiar to previous reports in Ireland.

Conclusion

The detection of unusual G and P combinations may have an impact on rotavirus control programmes and current vaccines may need to incorporate new strains, as the current vaccine available may not offer protection against all of these circulating types.     

Ecotoxicological assessment of road runoff residues for aquatic surface ecosystems in a scenario of reuse

Purpose  

Road runoff residues are often reused in road and civil works building. Although the physicochemical and ecotoxicological characteristics of these materials are known, no extensive ecotoxicological studies have been carried out on the leachates obtained from these residues once they have been spread and exposed to rainfall. This study was aimed at assessing the ecotoxicological risks for lentic aquatic ecosystems receiving the leachates of road runoff residues, either raw or treated, through granulometric sieving.     

Comparison of susceptibility to antimicrobials of bacterial isolates from companion animals in a veterinary diagnostic laboratory in Canada between 2 time points 10 years apart

The susceptibility to antimicrobials of bacterial species most frequently isolated from companion animals in a veterinary teaching diagnostic laboratory was evaluated retrospectively. A significant decrease between 1990-1992 and 2002-2003 was noted in the susceptibility of dog isolates to the following antimicrobials: Escherichia coli to cephalothin (86% to 61%, P < 0.001); E. coli to ampicillin (85% to 67%, P < 0.001); Proteus spp. to ampicillin (92% to 71%, P < 0.01); coagulase-positive staphylococci (Staphylococcus aureus and Staphylococcus intermedius) to enrofloxacin (99% to 95%, P < 0.01). Significantly increased susceptibilities were also noted as follows: coagulase-positive staphylococci to erythromycin (78% to 90%, P < 0.001) and tetracycline (61% to 77%, P < 0.001). Despite a limited number of results available for cats, a significant increase in susceptibility was noted for Pseudomonas spp. to gentamicin (40% to 100%, P < 0.05) and for E. coli to tetracycline (59% to 80%, P < 0.05). Regular updates on the resistance to antimicrobials used in veterinary medicine are required.     

Fitness trade-offs and environmentally induced mutation buffering in isogenic C. elegans

Mutations often have consequences that vary across individuals. Here, we show that the stimulation of a stress response can reduce mutation penetrance in Caenorhabditis elegans. Moreover, this induced mutation buffering varies across isogenic individuals because of interindividual differences in stress signaling. This variation has important consequences in wild-type animals, producing some individuals with higher stress resistance but lower reproductive fitness and other individuals with lower stress resistance and higher reproductive fitness. This may be beneficial in an unpredictable environment, acting as a "bet-hedging" strategy to diversify risk. These results illustrate how transient environmental stimuli can induce protection against mutations, how environmental responses can underlie variable mutation buffering, and how a fitness trade-off may make variation in stress signaling advantageous.     

Long-term dynamic of nestedness in bird assemblages inhabiting fragmented landscapes

Landscape Ecology - Nestedness is a common pattern of species assemblages in fragmented landscapes. The spatial pattern and ecological drivers of nested communities have been widely explored, but...