D4.2. Report on compared biogeographic relationships in various species sampled according to standarized scheme and in similar geographic localities

 This deliverable is a report on the application of network methods to characterize and analyze the genetic relationships between biological populations geographically separated. This was one of the main objectives of the EDEN project, and a successful methodology has been developed to identify population structure, central populations, recent and ancient gene flow and its direction, robust identification of biogeographical provinces, and many other properties. This report shows the power and versatility of the techniques developed by combining two papers by EDEN partners, which consider rather different species and contexts: the first one analyzes data from the seagrass Posidonia oceanica in the Mediterranean, and the second one hydrothermal vent organisms across the globe.

Network analysis identifies weak and strong links in a metapopulation system. By A.F. Rozenfeld, S. Arnaud-Haond, E. Hernández-García, V.M. Eguíluz, E.A. Serrăo and C.M. Duarte. Proceedings of the National Academy of Sciences of the USA (PNAS) 105, 18824-18829 (2008).  http://dx.doi.org/10.1073/pnas.0805571105

 The identification of key populations for conservation or eradication is a major challenge in population ecology, particularly when dealing threatened, invasive, and pathogenic species. Network theory was applied to map the genetic structure in a metapopulation system using microsatellite data from populations of the threatened seagrass Posidonia oceanica, as a model, sampled across its whole geographical range. This approach allowed the characterization of hierarchical population structure, and the identification of populations acting as hubs critical for relaying gene flow and sustaining the metapopulation system. This development opens major perspectives in a broad range of applications of molecular ecology and evolution such as conservation biology and epidemiology, where targeting specific populations is crucial.

Biogeography revisited with network theory: retracing the history of hydrothermal vents community. By Y. Moalic, S. Arnaud-Haond, C.M. Duarte, A.F. Rozenfeld, Ch. Bachraty, D. Desbruyčres. Submitted to Systematic Biology, 2009.

 Hydrothermal vents were the first ecosystems based on chemosynthesis to be discovered, thirty years ago, allowing exuberant biological production sustaining oases of life in the darkness of deep oceans. Here, we used the network theory on the most complete database of fauna distribution available thus far, in order to infer the processes driving the world-wide biogeography of those fragmented and unstable oceanic ecosystems. This holistic approach, newly adapted here to biogeographic questions and data, allowed a global revision of the various biogeographical scenarii proposed in previous studies. Besides the genuine identification of robust provinces, the topology of the network allowed pointing out preferential pathways hitherto overlooked, in agreement with a predominant influence of plates tectonic and ridges history on the evolution and connectivity of communities associated to hydrothermal vents. These findings support an ancient dispersal initiation in the early Mesozoic and a possible origin in the Western Pacific.

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