Lima-Mendez, Faust, Henry et al.
Plankton interactome determined – major role for parasites
The oceans are full of microscopic life influencing the structure and dynamics of the oceanic ecosystem. These ocean communities form the basis of all ocean life and present a bewildering diversity but the functioning of this ecosystem is poorly known. It is still a black box, despite its importance. The planktonic microbes (bacteria, viruses, and other plankton) interact with each other in different ways – they compete, collaborate, infect and eat each other; they form huge food webs that are also influenced by the environment and affect major processes such as carbon sequestration and photosynthesis. But all these interactions were mostly unknown – until now.
The researchers studied biotic (interactions between species: grazing, pathogenicity and parasitism) and abiotic (environmental conditions and nutrient availability) factors shaping ocean plankton communities, and constructed an interactome that described the network of interactions among plankton groups in the photic zone. They developed and applied novel computer programs to predict interactions between the planktonic microbes (symbiosis leading to mutual advantages, competition, parasitism…). Through advanced microscopy on the samples they confirmed that the computer-predicted interactions were actually occurring in nature.
Analysis of the network showed that the interactions between species were non-randomly distributed and suggested that abiotic factors have a more limited effect on community structure than previously assumed. The results emphasize the role of top-down biotic interactions in the epipelagic zone and especially of parasitism. Parasitic interactions are the most abundant pattern present in the network, which is also eminent by repeated microscopic observation of parasitic interactions from the Tara samples. The high prevalence of parasitism in the ocean was one of the most important observations of this study and seems to indicate that parasites play a major role in marine plankton ecology.
By unraveling the global ocean plankton interactome this study provides a rich first resource towards understanding the dynamics and structure of the oceanic ecosystem. The interactome reported here spans all three organismal domains and viruses. This data will inform future research to understand how symbionts, pathogens, predators and parasites interact with their target organisms, and ultimately help elucidate the structure of the global food webs that drive nutrient and energy flow in the ocean
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