Energy flow in Foraminifera: from empirical to theoretical models

Foraminifers as organisms are open systems with a dissipative structure. We review crucial aspects of energy exchange between individual foraminifers and their microhabitats. Understanding the energy flow between the foraminiferal system and the environment is essential to unravel its complexity and adaptability to environmental changes. Energetic efficiency of individuals critically depends on their size and shape determined by development and controlled by dynamic changes in gene expression. Most foraminiferal cells are relatively large in comparison to other eukaryotic cells and often reach the size of smaller metazoans. In consequence, foraminifera face the same supplyproblem as multicellular organisms due to their low surface-to-volume ratio. The solution to this limitation was a major evolutionary innovation in metabolic design based on space-filling fractal networks, such as respiratory, circulatory systems in animals or vascular systems in plants. Foraminifera as unicellular organisms could not build multicellular veins, nevertheless, their cytoskeleton organization evolved into granuloreticulopodia. This special anastomosing fractal network highly enhances the surface/volume ratio and allows flexible regulation of ion exchange between the cell and its microenvironment. This gives us the unique opportunity to establish the group of foraminifera as model organisms for metabolic energy fluxes. We discuss metabolic adaptations of foraminifera associated with feeding, dispersal, and life history strategies. This empirical knowledge is used for the construction and development of mathematical and simulation models of organisms to test energetic, behavioural and evolutionary patterns. The research received support from the Polish National Science Centre (DEC-2013/09/B/ST10/01734).