Fernandez, C., Valle, C., Saravia, F., & Allende, H. (2012). Behavior analysis of neural network ensemble algorithm on a virtual machine cluster. Neural Comput. Appl., 21(3), 535–542.
Abstract: Ensemble learning has gained considerable attention in different learning tasks including regression, classification, and clustering problems. One of the drawbacks of the ensemble is the high computational cost of training stages. Resampling local negative correlation (RLNC) is a technique that combines two well-known methods to generate ensemble diversity-resampling and error negative correlation-and a fine-grain parallel approach that allows us to achieve a satisfactory balance between accuracy and efficiency. In this paper, we introduce a structure of the virtual machine aimed to test diverse selection strategies of parameters in neural ensemble designs, such as RLNC. We assess the parallel performance of this approach on a virtual machine cluster based on the full virtualization paradigm, using speedup and efficiency as performance metrics, for different numbers of processors and training data sizes.
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Labra, F. A., San Martin, V. A., Jahnsen-Guzman, N., Fernandez, C., Zapata, J., Garcia-Huidobro, M. R., et al. (2022). Metabolic rate allometry in intertidal mussels across environmental gradients: The role of coastal carbonate system parameters in mediating the effects of latitude and temperature. Mar. Pollut. Bull., 184, 114149.
Abstract: We assess the role of direct and indirect effects of coastal environmental drivers (including the parameters of the carbonate system) on energy expenditure (MR) and body mass (M) of the intertidal mussel, Perumytilus pur-puratus, across 10 populations distributed over 2800 km along the Southern Eastern Pacific (SEP) coast. We find biogeographic and local variation in carbonate system variables mediates the effects of latitude and temperature on metabolic rate allometry along the SEP coast. Also, the fitted Piecewise Structural Equation models (PSEM) have greater predictive ability (conditional R2 = 0.95) relative to the allometric scaling model (R2 = 0.35). The largest standardized coefficients for MR and M were determined by the influence of temperature and latitude, followed by pCO2, pH, total alkalinity, and salinity. Thus, physiological diversity of P. purpuratus along the SEP coast emerges as the result of direct and indirect effects of biogeographic and local environmental variables.
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Martel, S. I., Fernandez, C., Lagos, N. A., Labra, F. A., Duarte, C., Vivanco, J. F., et al. (2022). Acidification and high-temperature impacts on energetics and shell production of the edible clam Ameghinomya antiqua. Front. Mar. Sci., 9, 972135.
Abstract: Warming and ocean acidification are currently critical global change drivers for marine ecosystems due to their complex and irreversible effects on the ecology and evolution of marine communities. Changes in the chemistry and the temperature of the ocean impact the biological performance of marine resources by affecting their energy budget and thus imposing energetic restrictions and trade-offs on their survival, growth, and reproduction. In this study, we evaluated the interplaying effects of increased pCO(2) levels and temperature on the economically relevant clam Ameghinomya antiqua, an infaunal bivalve inhabiting a wide distributional range along the coast of Chile. Juvenile clams collected from southern Chile were exposed to a 90-day experimental set-up emulating the current and a future scenario projeced to the end of the current century for both high pCO(2)/low-pH and temperature (10 and 15 degrees C) projected for the Chilean coast. Clams showed physiological plasticity to different projected environmental scenarios without mortality. In addition, our results showed that the specimens under low-pH conditions were not able to meet the energetic requirements when increased temperature imposed high maintenance costs, consequently showing metabolic depression. Indeed, although the calcification rate was negative in the high-pCO(2) scenario, it was the temperature that determined the amount of shell loss. These results indicate that the studied clam can face environmental changes for short-term periods modifying energetic allocation on maintenance and growth processes, but with possible long-term population costs, endangering the sustainability of an important benthic artisanal fisheries resource.
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Mora-Ruiz, M. D., Cifuentes, A., Font-Verdera, F., Perez-Fernandez, C., Farias, M. E., Gonzalez, B., et al. (2018). Biogeographical patterns of bacterial and archaeal communities from distant hypersaline environments. Syst. Appl. Microbiol., 41(2), 139–150.
Abstract: Microorganisms are globally distributed but new evidence shows that the microbial structure of their communities can vary due to geographical location and environmental parameters. In this study, 50 samples including brines and sediments from Europe, Spanish-Atlantic and South America were analysed by applying the operational phylogenetic unit (OPU) approach in order to understand whether microbial community structures in hypersaline environments exhibited biogeographical patterns. The fine-tuned identification of approximately 1000 OPUs (almost equivalent to “species”) using multivariate analysis revealed regionally distinct taxa compositions. This segregation was more diffuse at the genus level and pointed to a phylogenetic and metabolic redundancy at the higher taxa level, where their different species acquired distinct advantages related to the regional physicochemical idiosyncrasies. The presence of previously undescribed groups was also shown in these environments, such as Parcubacteria, or members of Nanohaloarchaeota in anaerobic hypersaline sediments. Finally, an important OPU overlap was observed between anoxic sediments and their overlaying brines, indicating versatile metabolism for the pelagic organisms. (C) 2017 Elsevier GmbH. All rights reserved.
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Ramajo, L., Fernandez, C., Nunez, Y., Caballero, P., Lardies, M. A., & Poupin, M. J. (2019). Physiological responses of juvenile Chilean scallops (Argopecten purpuratus) to isolated and combined environmental drivers of coastal upwelling. ICES J. Mar. Sci., 76(6), 1836–1849.
Abstract: Coastal biota is exposed to continuous environmental variability as a consequence of natural and anthropogenic processes. Responding to heterogeneous conditions requires the presence of physiological strategies to cope with the environment. Ecosystems influenced by upwelling endure naturally cold, acidic and hypoxic conditions, nevertheless they sustain major fisheries worldwide. This suggests that species inhabiting upwelling habitats possess physiological adaptations to handle high environmental variability. Here, we assessed the impact of the main upwelling drivers (temperature, pH and oxygen) in isolation and combined on eco-physiological responses of Chilean scallop Argopecten purpuratus. A. purpuratus responded to hypoxia by increasing their metabolic performance to maintain growth and calcification. Calcification was only affected by pH and increased under acidic conditions. Further, A. purpuratus juveniles prioritized calcification at the expense of growth under upwelling conditions. Increasing temperature had a significant impact by enhancing the physiological performance of A. purpuratus juveniles independently of oxygen and pH conditions, but this was associated with earlier and higher mortalities. Our results suggest that A. purpuratus is acclimated to short-term colder, acidic and hypoxic conditions, and provide important information of how this species responds to the heterogeneous environment of upwelling, which is significantly relevant in the climatic context of upwelling intensification.
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