title: Mixotrophy everywhere on land and in water: the grand écart hypothesis.
abstract: There is increasing awareness that many terrestrial and aquatic organisms are not strictly heterotrophic or autotrophic but rather mixotrophic. Mixotrophy is an intermediate nutritional strategy, merging autotrophy and heterotrophy to acquire organic carbon and/or other elements, mainly N, P or Fe. We show that both terrestrial and aquatic mixotrophs fall into three categories, namely necrotrophic (where autotrophs prey on other organisms), biotrophic (where heterotrophs gain autotrophy by symbiosis) and absorbotrophic (where autotrophs take up environmental organic molecules). Here we discuss their physiological and ecological relevance since mixotrophy is found in virtually every ecosystem and occurs across the whole eukaryotic phylogeny, suggesting an evolutionary pressure towards mixotrophy. Ecosystem dynamics tend to separate light from non-carbon nutrients (N and P resources): the biological pump and water stratification in aquatic ecosystems deplete non-carbon nutrients from the photic zone, while terrestrial plant successions create a canopy layer with light but devoid of non-carbon soil nutrients. In both aquatic and terrestrial environments organisms face a grand écart (dancer's splits, i.e., the need to reconcile two opposing needs) between optimal conditions for photosynthesis vs. gain of non-carbon elements. We suggest that mixotrophy allows adaptation of organisms to such ubiquist environmental gradients, ultimately explaining why mixotrophic strategies are widespread.
authors.affiliation: Institut de Systématique, Évolution, Biodiversité (ISYEB - UMR 7205 - CNRS, MNHN, UPMC, EPHE), Muséum national d'Histoire naturelle, Sorbonne Universités, 57 rue Cuvier, CP50, 75005, Paris, France.|Department of Plant Taxonomy and Nature Conservation, University of Gdansk, Wita Stwosza 59, 80-308, Gdansk, Poland.
authors.forename: Marc-André
authors.initials: MA
authors.lastname: Selosse
authors.affiliation: Université Blaise Pascal, Clermont-Ferrand, CNRS Laboratoire micro-organismes: Génome et Environnement, UMR 6023, 1 Impasse Amélie Murat, 63178, Aubière, France.
authors.forename: Marie
authors.initials: M
authors.lastname: Charpin
authors.affiliation: Sorbonne Universités, UPMC Université Paris 06, CNRS, Laboratoire Adaptation et Diversité en Milieu Marin UMR7144, Station Biologique de Roscoff, 29680, Roscoff, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Not
mesh_terms: D052818:Autotrophic Processes; D005075:Biological Evolution; D050260:Carbohydrate Metabolism; D056890:Eukaryota / Q000502:physiology*; D052836:Heterotrophic Processes; D010802:Phylogeny
keywords: Biological pump; carnivorous plants; hemiparasitism; kleptoplastidy; mycoheterotrophy; mycorrhiza; osmotrophy; phagotrophy; photosymbiosis; protists