Key Features of Intertidal Food Webs That Support Migratory Shorebirds

The migratory shorebirds of the East Atlantic flyway land in huge numbers during a migratory stopover or wintering on the French Atlantic coast. The Brouage bare mudflat (Marennes-Oléron Bay, NE Atlantic) is one of the major stopover sites in France. The particular structure and function of a food web affects the efficiency of carbon transfer. The structure and functioning of the Brouage food web is crucial for the conservation of species landing within this area because it provides sufficient food, which allows shorebirds to reach the north of Europe where they nest. The aim of this study was to describe and understand which food web characteristics support nutritional needs of birds. Two food-web models were constructed, based on in situ measurements that were made in February 2008 (the presence of birds) and July 2008 (absence of birds). To complete the models, allometric relationships and additional data from the literature were used. The missing flow values of the food web models were estimated by Monte Carlo Markov Chain – Linear Inverse Modelling. The flow solutions obtained were used to calculate the ecological network analysis indices, which estimate the emergent properties of the functioning of a food-web.The total activities of the Brouage ecosystem in February and July are significantly different. The specialisation of the trophic links within the ecosystem does not appear to differ between the two models. In spite of a large export of carbon from the primary producer and detritus in winter, the higher recycling leads to a similar retention of carbon for the two seasons. It can be concluded that in February, the higher activity of the ecosystem coupled with a higher cycling and a mean internal organization, ensure the sufficient feeding of the migratory shorebirds.     

Importance of the large copepod Paraeuchaeta antarctica (Giesbrecht, 1902) in coastal waters and the diet of seabirds at Kerguelen, Southern Ocean

The importance of the euchaetid copepod Paraeuchaeta antarcticain the subantarctic pelagic ecosystem was quantified in thecoastal waters of the Golfe du Morbihan at Kerguelen Islandsby comparing food samples from two diving seabirds with concurrentnet samples taken within the predator foraging area. Paraeuchaetaantarctica occurred in very high densities (up to 30 individualsm^-3 and 96 mg dry weight m^-3) in the water column, being moreabundant in the deepest part of the gulf than in shallow watersor at the more offshore shelf stations. The common diving petrelfeeds almost exclusively on crustaceans, its diet being dominatedby the amphipod Themisto gaudichaudii (52% by number and 84%by reconstituted mass) and P. antarctica (33% and 16%, respectively).Rockhopper penguins preyed upon crustaceans and fish, with fourtaxa being important, namely T. gaudichaudii (37% and 23%, respectively),Euphausia vallentini (24% and 41%), postlarval fish (10% and24%), and P. antarctica (13% and 3%). Paraeuchaeta antarcticadominated numerically in 21% of the diving-petrel food samplesand in 12% of penguin samples. The two bird species segregatedby preying upon different developmental stages of P. antarctica,diving petrels fed equally on CV of both sexes and CVI, whilepenguins fed on CVI only. Comparison of P. antarctica foundin net and food samples indicated no prey selection by commondiving petrels that caught the different copepod stages in proportionto their availability in the water column. On the other hand,the diving performance of penguins, which is better than thatof the petrels (mean maximum dive depths 69 m for penguins versus32 m in petrels), allows them to catch CVI in deeper waters,probably near the bottom. Our study shows that P. antarcticais a major component of the coastal macrozooplankton communityand a significant prey for two species of diving seabirds inhabitingKerguelen. This is also the first record of a copepod speciesas a prey for penguin, and the first to highlight P. antarcticain the food of austral seabirds.     

Reproductive conflicts affect labor and immune defense in the queenless ant Diacamma sp. "nilgiri"

In many species of social Hymenoptera, totipotency of workers induces potential conflicts over reproduction. However, actual conflicts remain rare despite the existence of a high reproductive skew. One of the current hypotheses assumes that conflicts are costly and thus selected against. We studied the costs of conflicts in 20 colonies of the queenless ant Diacamma sp. "nilgiri" by testing the effects of conflicts on labor and worker immunocompetence, two parameters closely linked to the indirect fitness of workers. In this species, the dominant female is the only mated worker (gamergate) and monopolizes reproduction. We experimentally induced conflicts by splitting each colony into two groups, a control group containing the gamergate and an orphaned group displaying aggressions until a new dominant worker arises. Immunocompetence was assessed by the clearance of Escherichia coli bacteria that we injected into the ants. Time budget analysis revealed a lower rate of labor and especially brood care in orphaned groups, supporting the existence of a cost of conflicts on labor. Fifteen days after splitting, a lower immunocompetence was also found in orphaned groups, which concerned workers involved and not involved in conflicts. We propose that this immunosuppression induced by conflicts could stem from stress and not directly from aggression.     

Anaerobic digestion of secondary residuals from an anaerobic bioreactor at a brewery to enhance bioenergy generation

Many beer breweries use high-rate anaerobic digestion (AD) systems to treat their soluble high-strength wastewater. Biogas from these AD systems is used to offset nonrenewable energy utilization in the brewery. With increasing nonrenewable energy costs, interest has mounted to also digest secondary residuals from the high-rate digester effluent, which consists of yeast cells, bacteria, methanogens, and small (hemi)cellulosic particles. Mesophilic (37 °C) and thermophilic (55 °C) lab-scale, low-rate continuously-stirred anaerobic digestion (CSAD) bioreactors were operated for 258 days by feeding secondary residuals at a volatile solids (VS) concentration of ∼40 g l⁻¹. At a hydraulic retention time (HRT) of 15 days and a VS loading rate of 2.7 g VS l⁻¹ day⁻¹, the mesophilic bioreactor showed an average specific volumetric biogas production rate of 0.88 l CH₄ l⁻¹ day⁻¹ and an effluent VS concentration of 22.2 g VS l⁻¹ (43.0% VS removal efficiency) while the thermophilic bioreactor displayed similar performances. The overall methane yield for both systems was 0.21 l CH₄ g⁻¹ VS fed and 0.47–0.48 l CH₄ g⁻¹ VS removed. A primary limitation of thermophilic digestion of this protein-rich waste is the inhibition of methanogens due to higher nondissociated (free) ammonia (NH₃) concentrations under similar total ammonium (NH₄ ⁺) concentrations at equilibrium. Since thermophilic AD did not result in advantageous methane production rates or yields, mesophilic AD was, therefore, superior in treating secondary residuals from high-rate AD effluent. An additional digester to convert secondary residuals to methane may increase the total biogas generation at the brewery by 8% compared to just conventional high-rate digestion of brewery wastewater alone. JIMB-2008: BioEnergy—Special issue.     

Influence of the diet on the bioaccumulation of heavy metals in zooplankton-eating petrels at Kerguelen archipelago,Southern Indian Ocean

Concentrations of cadmium, mercury, copper and zinc were measured in muscle, kidney and liver tissues and in the main prey of five species of zooplankton-eating petrels: blue petrel (Halobaena caerulea), thin-billed (Pachyptila belcheri) and Antarctic (P. desolata) prions, and South Georgian (Pelecanoides georgicus) and common (Pelecanoides urinatrix) diving petrels. Since some of these species are closely related species with respect to body size, timing of moult and life span, their diet has been examined to evaluate its influence on heavy-metal bioaccumulation. Inter-specific differences were significant for Hg concentrations in the liver and for Zn concentrations in both liver and kidney tissues. Blue petrels exhibited the highest Hg concentrations in the liver (3.9±2.02 µg.g^–1 wet weight). No significant differences were found in Cd concentrations between species. Exposure to heavy metals through the most important prey species in the diet during the breeding period was evaluated. The most evident result was the influence of fish prey on Hg levels. Although crustacean species exhibit different cadmium concentrations, the diet composition does not appear to be discriminant for Cd bioaccumulation within the small petrel community at Kerguelen.     

The two variants of oxysterol binding protein-related protein-1 display different tissue expression patterns,have different intracellular localization,and are functionally distinct

Oxysterol binding protein (OSBP) homologs comprise a family of 12 proteins in humans (Jaworski et al., 2001; Lehto et al., 2001). Two variants of OSBP-related protein (ORP) 1 have been identified: a short one that consists of the carboxy-terminal ligand binding domain only (ORP1S, 437 aa) and a longer N-terminally extended form (ORP1L, 950 aa) encompassing three ankyrin repeats and a pleckstrin homology domain (PHD). We now report that the two mRNAs show marked differences in tissue expression. ORP1S predominates in skeletal muscle and heart, whereas ORP1L is the most abundant form in brain and lung. On differentiation of primary human monocytes into macrophages, both ORP1S and ORP1L mRNAs were induced, the up-regulation of ORP1L being >100-fold. The intracellular localization of the two ORP1 variants was found to be different. Whereas ORP1S is largely cytosolic, the ORP1L variant localizes to late endosomes. A significant amount of ORP1S but only little ORP1L was found in the nucleus. The ORP1L ankyrin repeat region (aa 1-237) was found to localize to late endosomes such as the full-length protein. This localization was even more pronounced for a fragment that additionally includes the PHD (aa 1-408). The amino-terminal region of ORP1L consisting of the ankyrin repeat and PHDs is therefore likely to be responsible for the targeting of ORP1L to late endosomes. Interestingly, overexpression of ORP1L was found to enhance the LXRalpha-mediated transactivation of a reporter gene, whereas ORP1S failed to influence this process. The results suggest that the two forms of ORP1 are functionally distinct and that ORP1L is involved in control of cellular lipid metabolism.     

Phenotypic plasticity of immune defence linked with foraging activity in the ant Cataglyphis velox

Because immune defences are costly, life-history theories predict a modulation of immune investment according to its potential benefits. Social insects provide interesting models since infection risk may vary among individuals within a colony. In particular, the foraging workers, that have to leave the nest, suffer a higher infection risk and can contaminate their nest, which may favour high immune investments. However, evolutionary theories of aging predict that foragers should reduce their immune investment when they suffer high extrinsic mortality. To test these two predictions, we investigated the levels of phenoloxidase (PO) and prophenoloxidase, two important enzymes of the insect immune system, in workers of the ant Cataglyphis velox. We found a higher PO activity in foragers than in intra-nidal workers. This could result from an adaptive upregulation of the harmful PO (an enzyme potentially leading to autoimmune reactions) only when the risk of infection and wounding is high.