Mecanismos genéticos y estrategias adaptativas de productores primarios (microalgas y cianobacterias) en un escenario de cambio global.

Resumo

Aquatic ecosystems are under threat from alterations to their environment due to global change. Although there are still numerous uncertainties in relation to the evolution of such changes, evidence is rapidly accumulating that supports the reality of these alterations. Climate change and the release of contaminants to the environment, derived from anthropogenic activities, are fundamental parts of global change. One of the most important consequences of global change is the impact on living organisms, with marine phytoplankton being particularly affected. Cyanobacteria and microalgae play an important ecological role as the primary producers and the base of the trophic web in aquatic ecosystems. They also participate in the control of biochemical cycles, a key factor in preserving the equilibrium of the Planet. Therefore, the capacity for these organisms to respond to the predicted environmental changes is a matter of concern. The studies presented in this thesis aim to improve our knowledge about the mechanisms allowing phytoplankton adaptation to different extreme conditions. To this end, the response of these organisms to different contaminants (formaldehyde, chloramphenicol, crome, simazime and diquat) as well as to different extreme environments (Aguas Agrias, Vulcano, y Agrio Argentino) was studied. The results, by means of the fluctuation analysis, indicate that the phytoplankton can adapt to toxic substances exposure through the selection of resistant mutants that arose randomly prior to the toxic exposure. In the case of the adaptation to extreme environments, mesophilic phytoplankton along environmental gradients showed different strategies of adaptation. We could then explain the variation in the species diversity found in these environments. In addition, by means of Ratchet protocol, we observed that phytoplankton present different capacities to adapt depending on their taxonomic group as well as their preferred habitat. Hence, global change will lead to alterations in the dynamic and structure of populations. But adaptation is not the only force driving evolutionary change. Another components can also contribute to evolutionary process. The study of the evolution of the cyanobacteria Microcystis aeruginosa, under a scenario of increasing temperatura and nutrient concentration, revealed that adaptation was the main component driving growth rate evolution, although chance events also contributed to a lesser extent. However, the evolution of toxin production was mainly determined by historic contingency and chance mechanisms. Finally, we attempted to study the effect of ocean acidification and nutrient availability on Emiliani huxleyi physiology, considering its important role in the regulation of carbon cycle. The results show that calcification process is highly altered with CO2 increase and it response varies as a function of nutrient availability. The capacity for nutrient assimilation is also altered as can be observed by the modification of nitrate reductase and alkaline phosphatase activity.