Summary1. Parental effects can have profound consequences on offspring phenotype. Still, little is known about the relative influence of prenatal versus postnatal parental effects of parasite exposure of parents on offspring traits. 2. In this study, we investigated the respective role of a prenatal and a postnatal immune challenge of parent feral pigeons (Columba livia) on offspring humoral immunity, growth and survival. We used a cross-fostering design and antigen injections in biological and foster parents. Feral pigeons are particularly suitable for studying the effects of parental immune challenges because they can affect the phenotype of their young through the transmission of prenatal antibodies in the egg and postnatal antibodies in the 'crop milk', a substance produced in the crop of both parents. 3. Results show that a prenatal immune challenge of biological parents with keyhole limpet haemocyanin (KLH) antigen decreased the humoral response against KLH of nestlings injected at 14 days of age. In contrast, a postnatal immune challenge of foster parents with KLH enhanced the humoral response of 1-year-old juveniles exposed to a second KLH injection, but only when these juveniles had received their first injection at 3 days of age. 4. No effect on nestling and juvenile response to another antigen (NDV) was observed, indicating that the changes in humoral responses were specific to the KLH injected in parents. In addition to this, prenatal and postnatal parental immune challenges had an interaction effect on fledging body mass, but no effect on juvenile survival. 5. This study shows that pre-and postnatal exposure to antigens in parents has contrasted effects on offspring humoral response and growth. Moreover, it shows that the timing of an early exposure to antigens in nestlings has important effects on their specific humoral response. 6. This study thus suggests that pre-and postnatal parental effects have distinct roles in shaping the phenotype of the offspring on different time scales and calls for further investigations on the potential adaptive role of combined parental effects. Moreover, it suggests that pigeon milk has positive effects on offspring humoral immunity and thus could potentially have a similar immune role as mammalian milk.
To compare environmental and culture-derived microbial communities, we performed 16S metabarcoding of uncultured samples and their culture-derived bacterial lawns. Microbial communities were obtained from freshwater river samples representative of an anthropization gradient along a river stream. Their culture-derived bacterial lawns were obtained by growing aliquots of the samples on a broad range medium and on two different semi-selective media. The V3–V4 16S rRNA region was amplified and sequenced. The bacterial diversity of water samples decreased from the upper to lower stream sampling sites and, as expected, these differences were mostly suppressed by the culture step. Overall, the diversity of cultured-derived bacterial communities reflected selectivity of each tested medium. Comparison of treatments indicated that the culture selected both detected and rare undetected environmental species. Accurate detection of rare environmental bacteria of the Pectobacterium genus by 16S metabarcoding of the culture lawn was demonstrated. Interestingly, for abundant taxa, such as those of the Pseudomonas genus, the culture/environment ratio varied between sampled sites, indicating the difficulty of comparing cultured-derived taxa abundance between environmental sites. Finally, our study also highlighted media specificity and complementarity: bacterial communities grown on the two selective media, while selecting a small set of specific species, were mostly a subset of the bacterial community observed on the broad range medium.
1. We examined the effects of wind-induced mixing and particle resuspension on the pelagic food web in eutrophic shallow lakes. These processes are known to have a major impact on a variety of biological, physical or chemical parameters such as the underwater light climate, the nutrient availability in the water column and the abundance and composition of the phytoplankton community. However, little is known about the effects of these processes on other compartments of the freshwater food web.2. We conducted a 9-week experiment comprising a manipulation of mixing intensity in 15 m 3 mesocosms equipped with wavemakers in order to explore the impact of two mixing regimes on water chemistry as well as viral, bacterial, phytoplankton and zooplankton communities.3. The turbidity level in mixed mesocosms (compared to calm conditions) was higher on average, especially at the bottom, indicating a successful resuspension of the sediment bed. Mixing increased chlorophyll a concentration without any clear increase in algal abundance, measured as cell counts by flow cytometry, which pointed to a change in species composition or a physiological adaptation to mixing. pH increased strongly in mixed mesocosms, suggesting enhanced primary productivity in perturbed conditions. Zooplankton responses to mixing were neutral for cladocerans and negative for copepods, which potentially mediated top-down controls on the rotifer population.4. Bacterial and viral abundances were not significantly changed by the mixing regimes; however, peaks of viral lysis of heterotrophic bacteria were seen in each mixed mesocosm, while none were observed in calm mesocosms. These results suggest that viral lysis is enhanced by the water column mixing.5. Our experiment demonstrates that mixing is likely to influence shallow lake functioning through a complex combination of direct and indirect effects on the underwater light climate and water chemistry, phytoplankton physiology and productivity, zooplankton growth and possibly virus-host interactions. These complex effects could play a major role in structuring pelagic and benthic communities in shallow lakes
The production of reactive oxygen species (ROS) is one of the first defense reactions induced in Arabidopsis in response to infection by the pectinolytic enterobacterium Dickeya dadantii. Previous results also suggest that abscisic acid (ABA) favors D. dadantii multiplication and spread into its hosts. Here, we confirm this hypothesis using ABA-deficient and ABA-overproducer Arabidopsis plants. We investigated the relationships between ABA status and ROS production in Arabidopsis after D. dadantii infection and showed that ABA status modulates the capacity of the plant to produce ROS in response to infection by decreasing the production of class III peroxidases. This mechanism takes place independently of the well-described oxidative stress related to the RBOHD NADPH oxidase. In addition to this weakening of plant defense, ABA content in the plant correlates positively with the production of some bacterial virulence factors during the first stages of infection. Both processes should enhance disease progression in presence of high ABA content. Given that infection increases transcript abundance for the ABA biosynthesis genes AAO3 and ABA3 and triggers ABA accumulation in leaves, we propose that D. dadantii manipulates ABA homeostasis as part of its virulence strategy.
To better understand the interaction between wind waves and the biological properties of freshwater ecosystems, it is highly desirable to reproduce coherent water motions generated by wind. This paper presents new 15 m3 mesocosms with wavemakers, also known as wave flumes, which are designed to emulate the effects of surface waves on the biological processes in shallow lakes. First, we succinctly review existing approaches to modify mixing of the water column in ecological studies: most mixing devices that have been used to date generate turbulence, but do not create the coherent water motions generated by surface waves. This justifies the development of mesocosms that seek to reproduce these coherent water motions. Tanks with wave generators are common devices in fluid mechanics, and we adapted them for aquatic ecology. Second, we describe the effects of waves on the water column, provide some theoretical background on wavemakers, and detail the choices adopted for the design of our device. Our system is able to generate waves with a wavelength of 0.1–5 m and amplitude of 1–5 cm in a 10 m long tank with a 1 m water column, which allows to choose mixing intensity from superficial to complete mixing of the water column. Experimental results show effects of mixing regime on water chemistry and plankton abundance. We finally discuss challenging research questions on the ecological role of surface waves in shallow lakes that can be addressed with mesocosms with wavemakers.
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