We are all lichens: the systems biology of holobionts

30 September 2016

Scott Gilbert
Department of Biology
Swarthmore College


Each organism functions and develops as a consortium of several different species. Symbiotic interactions of animals and plants with microorganisms are now seen to be the rule, not the exception, in these disciplines. As multilineage organisms, "holobionts," our metabolism and developmental signaling is shared between species. Microbes are not only necessary for normal mammalian and insect development, they can also constitute a second mode of genetic inheritance, providing selectable genetic variation for natural selection. This creates a new set of questions for system biology, since the organism has become to be seen as a collection of ecosystems. How are these communities inherited? What is the function of the immune system, when over half the cells of our bodies are microbial and when microbes help induce the formation of immune tissues? How do symbionts and diet interact to generate different states of health and illness? Can the holobiont be considered as a unit of evolutionary selection? Did major evolutionary change come about from new interactions between symbionts and their hosts? Can the holobiont be considered in terms of of niche construction? Recognizing the holobiont as a critically important unit of anatomy, development, physiology, immunology, and evolution opens up new investigative avenues and conceptually challenges the ways in which the biological sub-disciplines have heretofore characterized living entities.

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