Linking local to global properties in branching modular networks: gorgonian coral colonies
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Branching growth is present both in plants and animals, either marine or terrestrial. Although cellular and other modular levels of organization in plants and animals have evolved through different molecular and physiological mechanisms, several aspects of their branching modular system and morphology are similar. We studied vessel organization and colony integration, in order to comprehend underlying relationships between different structural components in a gorgonian coral network. The theoretical formalism was validated in the gorgonian coral Eunicea mammosa (Plexauridae, Octocorallia) in Belize. As in vascular plants, these colonial animals create a complex network of connections among modular branches integrated in stem canals downstream toward the base. A new formalism is proposed for describing gorgonian branching. A global property of a colony is for instance the size of its base or its weight whereas a local property is the size of branch in a particular place of the colony. However, a global property is not the simple addition of local modular properties, as the case of stem canals in the colony base. Theoretically, the process of branching is tightly intertwined with the internal network organization. The colony network centralization is driven by a linear relationship between the total number of branches and the stem canals at the base of the colony. If stem canals play important roles in the transport of nutrients throughout the colony and the biomechanical support from the base up to the tips, we can assume that there is an underlying association between the number of stem canals at the base and the number of for example, terminal branches. These associations may provide new findings that extend our understanding of the functional organization of tree-like networks in octocorals and their vascular systems. The idea that the external components of a tree-like plant network are directly correlated and connected down to the main trunk seems to be analogous in an animal system.
KeywordsTree-like networks Animal branching colonies Gorgonian coral Modular organisms Pipe-model theory Stem canals
We want to thank our sponsors, Vicerrectoría de Investigaciones (Proyecto interfacultades), Facultad de Ingeniería, Facultad de Ciencias and Department of Biological Sciences (Universidad de los Andes, Bogotá, Colombia), COLCIENCIAS (Grant # 1204-09-177774, J.A. Sánchez), and Smithsonian Institution. Special thanks to H. R. Lasker (U. Buffalo), whom ideas and discussions were of great influence to develop this study. We are also grateful to the Smithsonian Institution Marine Science Network (K. Ruetzler and M. Lang) for their field support (NMNH-CCRE contribution No. 874), and to M. Orkisz (CREATIS Laboratory, Lyon, France) and J. Adrien (MATEIS Laboratory, Lyon, France) for their contribution in acquiring the high-resolution computed tomography images of corals. Comments from T. Goulet and three anonymous reviewers greatly improved the manuscript.
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