Coevolution of Partners and Integrity of Symbiotic Systems

摘要

Symbioses are very beneficial models for studying the integrity of biosystems, which characterizes their structure—function orderliness and allows the partners to adequately respond to environmental changes. An analysis of various types of the plant—microbe and animal—microbe symbioses suggests that their integrity qualitatively increases during facultative and ecologically obligatory interactions of the partners, reaching its climax in the case of genetically obligatory interactions. Mathematicalmodels enabled us to demonstrate that the functional integrity of N2-fixing legume—rhizobium symbiosis (concordance of the changes in the geno-typic frequencies of the partners induced by environmental fluctuations) correlates with its ecological efficiency, which is increased by natural selection. The result is the establishment of tight regulatory feedbacks between the partners, leading to their genetic integration, which is referred to as "symbiogenome." The genetic integrity of symbiosis determines its high evolutionary potential based on (a) the epigenetic inheritance of symbiotic characters by the host, implemented as a vertical transfer of either microsymbionts themselves or their genes and (b) interspecific altruism, which is associated withpositive feedbacks between the partners and determines the ecological efficiency of mutualistic interactions. Realization of this potential leads to the deep genetic integration of initially independent partners, including their fusion into novel integral organisms.