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Physiological diversification of diatoms in a highly structured marine phytoplankton ecosystem shows no phylogenetic constraint

A positive correlation between phylogenetic distance and physiological diversification is the base for ecological analyses based on higher taxonomic levels. Such a correlation however complicates the observation of high sympatric and syngeneric diversity in planktonic ecosystems. We used the northern Adriatic as a model marine ecosystem that is characterized by steep spatiotemporal ecological gradients and high phytoplankton diversity. We analyzed the distribution of key species (diatoms) along those gradients in situ. Subsequently, we isolated monoclonal cultures of these species and exposed them to different nutrient regimes to record physiological responses (growth rate ; activity, localization, and characterization of alkaline phosphatase ; phosphate uptake rates ; morphometrics ; ultrastructure ; cell cycle control). Our results indicate a distinct uncoupling or even negative correlation between phylogenetic distance and physiological similarity or life strategy adaptations in the highly structured phytoplankton ecosystem of the northern Adriatic. These observations have implications on the concept of evolution of phytoplankton diversity as well as on the application of higher taxonomic levels in ecosystem analysis.

phytoplankton ; Adriatic Sea ; diatoms ; APA ; P LIMITATION

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