Research Article Reaction Network Modeling of Complex Ecological Interactions: Endosymbiosis and Multilevel Regulation Tomas Veloz 1,2,3 and Daniela Flores 1,4 1 Fundaci´ on para el Desarrollo Interdisciplinario de la Ciencia, la Tecnolog´ ıa y Las Artes, Arturo Prat 249, Santiago, Chile 2 Universidad Andres Bello, Departamento Ciencias Biologicas, Facultad Ciencias de la Vida, Santiago 8370146, Chile 3 Centre Leo Apostel, Vrije Universiteit Brussel, Rue de la Strategie 33, 1060, Brussels, Belgium 4 Universidad de Chile, Departamento de Biolog´ ıa, Facultad de Ciencias, Ñuñoa, Santiago, Chile Correspondence should be addressed to Tomas Veloz; tveloz@gmail.com Received 10 July 2020; Accepted 29 July 2021; Published 9 August 2021 Academic Editor: Abdellatif Ben Makhlouf Copyright © 2021 Tomas Veloz and Daniela Flores. is is an open access article distributed under the Creative Commons AttributionLicense,whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkis properly cited. Endosymbiosisisatypeofsymbiosiswhereonespeciesofmicroscopicscaleinhabitsthecellofanotherspeciesofalargerscale, suchthattheexchangeofmetabolicbyproductsproducesmutualbenefit.esebenefitscanoccuratdifferentbiologicallevels.For example,endosymbiosispromotesefficiencyofthecellmetabolism,cellreplication,andthegenerationofamacroscopiclayerthat protects the organism from its predators. erefore, modeling endosymbiosis requires a complex-systems and multilevel ap- proach.Weproposeamodelofendosymbiosisbasedonreactionnetworks,wherespeciesofthereactionnetworkrepresenteither ecological species, resources, or conditions for the ecological interactions to happen, and the endosymbiotic interaction mechanismsarerepresentedbydifferentsequencesofreactions(processes)inthereactionnetwork.Asanexample,wedevelopa toy model of the coral endosymbiotic interaction. e model considers two reaction networks, representing biochemical traffic and cellular proliferation levels, respectively. In addition, the model incorporates top-down and bottom-up regulation mech- anisms that stabilizes the endosymbiotic interaction. 1. Introduction Endosymbiosis is a particular kind of symbiosis which oc- curswhenanorganism(endosymbiont)liveswithinanother (host)inamutualisticrelationship.isrelationshipisgiven by the coupling of the host’s and endosymbiont’s metabo- lisms through exchange of useful metabolites [1, 2]. e endosymbiotic concept was proposed by Lynn Margulis, whodeveloped Serial Endosymbiosis eory (SET)toexplain the origin of plastids and mitochondria as organelles in the eukaryotic cell, promoting the emergence of eukaryotic cell complexity[3].Endosymbiosisisrecognizedasawidespread mechanism in nature and is taking relevance as an evolu- tionary mechanism in different lineages [4]. Symbiotic in- teractions allow alternative ways of evolution, for example, through natural selection, in evolving complexity for a population of individuals. Endosymbiosis implies the cou- pling of two or more species in an intimate relationship. Such relation leads to an increase of phenotypic complexity at the genomic, physiological, and morphological levels. erefore, endosymbiosis enables ecological expansion into different and new niches. As Darwin said in his book e Origin of Species: “Natural Selection cannot possibly produce any modification in a species exclusively for the good of another species; although throughout nature one species in- cessantly takes advantage of, and profits by, the structures of other” [5]. One of the examples of endosymbiosis corresponds to the relationship between corals (Cnidaria, Anthozoa) and a photosynthetic algae of the genus Symbiodinium or Zoo- xanthellae [6], in which the latter lives within the gastro- dermis coral cells. is relationship is typical when the environmental food is scarce [7, 8], and they (the Symbio- dinium and the coral) can feed back through their metab- olisms,bythenutrientacquisitionviathecyclingoforganic compounds which supplies extra energy to both Hindawi Complexity Volume 2021, Article ID 8760937, 12 pages https://doi.org/10.1155/2021/8760937