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McKenzie, D. J., Vergnet, A., Chatain, B., Vandeputte, M., Desmarais, E., Steffensen, J. F., et al. (2014). Physiological mechanisms underlying individual variation in tolerance of food deprivation in juvenile European sea bass, Dicentrarchus labrax. Journal of Experimental Biology, 217(18), 3283–3292.
Résumé: Although food deprivation is a major ecological pressure in fishes, there is wide individual variation in tolerance of fasting, whose mechanistic bases are poorly understood. Two thousand individually tagged juvenile European sea bass were submitted to two ‘fasting/feeding’ cycles each comprising 3 weeks of food deprivation followed by 3 weeks of ad libitum feeding at 25°C. Rates of mass loss during the two fasting periods were averaged for each individual to calculate a population mean. Extreme fasting tolerant (FT) and sensitive (FS) phenotypes were identified that were at least one and a half standard deviations, on opposing sides, from this mean. Respirometry was used to investigate two main hypotheses: (1) tolerance of food deprivation reflects lower mass-corrected routine metabolic rate (RMR) in FT phenotypes when fasting, and (2) tolerance reflects differences in substrate utilisation; FT phenotypes use relatively less proteins as metabolic fuels during fasting, measured as their ammonia quotient (AQ), the simultaneous ratio of ammonia excretion to RMR. There was no difference in mean RMR between FT and FS over 7 days fasting, being 6.70±0.24 mmol h−1 fish−1 (mean ± s.e.m., N=18) versus 6.76±0.22 mmol h−1 fish−1 (N=17), respectively, when corrected to a body mass of 130 g. For any given RMR, however, the FT lost mass at a significantly lower rate than FS, overall 7-day average being 0.72±0.05 versus 0.90±0.05 g day−1 fish−1, respectively (P<0.01, t-test). At 20 h after receiving a ration equivalent to 2% body mass as food pellets, ammonia excretion and simultaneous RMR were elevated and similar in FT and FS, with AQs of 0.105±0.009 and 0.089±0.007, respectively. At the end of the period of fasting, ammonia excretion and RMR had fallen in both phenotypes, but AQ was significantly lower in FT than FS, being 0.038±0.004 versus 0.061±0.005, respectively (P<0.001, t-test). There was a direct linear relationship between individual fasted AQ and rate of mass loss, with FT and FS individuals distributed at opposing lower and upper extremities, respectively. Thus the difference between the phenotypes in their tolerance of food deprivation did not depend upon their routine energy use when fasting. Rather, it depended upon their relative use of tissue proteins as metabolic fuels when fasting, which was significantly lower in FT phenotypes.
Torres-Irineo, E., Amandè, M. J., Gaertner, D., Delgado de Molina, A., Murua, H., Chavance, P., et al. (2014). Bycatch species composition over time by tuna purse-seine fishery in the eastern tropical Atlantic Ocean. Biodiversity and Conservation, 23(5), 1157–1173.
Résumé: Within the Ecosystem-based fisheries management framework, we evaluated
the changes over time in bycatch species of the European tuna purse-seine fishery operating
in the eastern Atlantic Ocean. Bycatch data was collected during two scientific
observer programs conducted in the late 1990s and in the late 2000s. Over these two time
periods, we compared the temporal trends in bycatch species composition, the probability
of occurrence of functional groups per fishing set, the spatio-temporal species richness and
the potential impact on several species listed in the red list of the International Union for
Conservation of Nature (IUCN). The analyses were performed separately on the two main
fishing modes of the fleet, i.e. sets on free-swimming school sets and on fish aggregating
devices (FADs). Owing data quality constraints, we did not estimate bycatch rates. Ours
results showed that the species composition of sharks caught on FADs decreased over time.
The total species richness was higher for FAD sets than for free-swimming school sets (87
vs. 61 species respectively), such difference is common between fishing modes worldwide.
Boudour-Boucheker, N., Boulo, V., Charmantier-Daures, M., Grousset, E., Anger, K., Charmantier, G., et al. (2014). Differential distribution of V-type H+-ATPase and Na+/K+-ATPase in the branchial chamber of the palaemonid shrimp Macrobrachium amazonicum. Cell and Tissue Research, 357(1), 195–206.
Résumé: V-H+-ATPase and Na+/K+-ATPase were localized in the gills and branchiostegites of M. amazonicum and the effects of salinity on the branchial chamber ultrastructure and on the localization of transporters were investigated. Gills present septal and pillar cells. In freshwater (FW), the apical surface of pillar cells is amplified by extensive evaginations associated with mitochondria. V-H+-ATPase immunofluorescence was localized in the membranes of the apical evaginations and in clustered subapical areas of pillar cells, suggesting labeling of intracellular vesicle membranes. Na+/K+-ATPase labeling was restricted to the septal cells. No difference in immunostaining was recorded for both proteins according to salinity (FW vs. 25 PSU). In the branchiostegite, both V-H+-ATPase and Na+/K+-ATPase immunofluorescence were localized in the same cells of the internal epithelium. Immunogold revealed that V-H+-ATPase was localized in apical evaginations and in electron-dense areas throughout the inner epithelium, while Na+/K+-ATPase occurred densely along the basal infoldings of the cytoplasmic membrane. Our results suggest that morphologically different cell types within the gill lamellae may also be functionally specialized. We propose that, in FW, pillar cells expressing V-H+-ATPase absorb ions (Cl-, Na+) that are transported either directly to the hemolymph space or through a junctional complex to the septal cells, which may be responsible for active Na+ delivery to the hemolymph through Na+/K+-ATPase. This suggests a functional link between septal and pillar cells in osmoregulation. When shrimps are transferred to FW, gill and branchiostegite epithelia undergo ultrastructural changes, most probably resulting from their involvement in osmoregulatory processes.
Merbt, S. N., Auguet, J. C., Blesa, A., Marti, E., & Casamayor, E. O. (2014). Wastewater Treatment Plant Effluents Change Abundance and Composition of Ammonia-Oxidizing Microorganisms in Mediterranean Urban Stream Biofilms. Microb Ecol, .
Pellissier, L., Leprieur, F., Parravicini, V., Cowman, P. F., Kulbicki, M., Litsios, G., et al. (2014). Quaternary coral reef refugia preserved fish diversity. Science, 344(6187), 1016–1019.
Résumé: The most prominent pattern in global marine biogeography is the biodiversity peak in the Indo-Australian Archipelago. Yet the processes that underpin this pattern are still actively debated. By reconstructing global marine paleoenvironments over the past 3 million years on the basis of sediment cores, we assessed the extent to which Quaternary climate fluctuations can explain global variation in current reef fish richness. Comparing global historical coral reef habitat availability with the present-day distribution of 6316 reef fish species, we find that distance from stable coral reef habitats during historical periods of habitat loss explains 62% of the variation in fish richness, outweighing present-day environmental factors. Our results highlight the importance of habitat persistence during periods of climate change for preserving marine biodiversity.