In This Article Expand or collapse the "in this article" section Endosymbiosis

  • Introduction
  • Using Endosymbiont Products in Medicine and Pest Control

Evolutionary Biology Endosymbiosis
Nancy A. Moran, Rebecca A. Chong
  • LAST REVIEWED: 12 August 2022
  • LAST MODIFIED: 25 September 2018
  • DOI: 10.1093/obo/9780199941728-0114


Without endosymbiosis, life on Earth would be vastly different. Endosymbiosis has been key to the diversification of eukaryotes as a whole, all plants, large clades of insects and other invertebrates, and diverse protozoan groups. Many life forms and lifestyles would not exist without it. Endosymbiosis was once considered a sideshow of eukaryotic evolution, with nuclear genomes providing the main stage. But we now know that endosymbiosis has played a massive and ongoing role in evolution. The “endosymbiotic theory,” the proposal that mitochondria and chloroplasts each evolved from bacterial ancestors that invaded ancestral unicellular eukaryotes, was verified over forty years ago, but this verification left many questions unresolved. Mainly due to molecular data, we now have a vastly expanded appreciation of the centrality of endosymbiosis in evolution. Endosymbiosis has enabled bursts of species diversification by enabling eukaryotic lineages to invent new ecological niches. It affords new sources of needed nutrients and new weaponry for defending against parasites and predators. In some cases, endosymbionts enable host organisms to live in harsh environments that would be otherwise inaccessible, due to extreme temperatures or aridity. The endosymbiotic lifestyle often leads to massive evolutionary changes in the genomes of endosymbionts themselves, and, as a consequence, potentially leads to extinctions of lineages. It has also provided a source of novel genes, taken up by nuclear genomes of hosts and conferring new capabilities. The literature on endosymbiosis and its role in evolution is enormous, with thousands of publications on this subject in the last two decades. We include the most critical themes under this broad topic and emphasize those pertaining to evolutionary processes or evolutionary history. The scientific literature and community pertaining to endosymbiosis are fragmented. For example, those studying organelle origins, symbioses in insects, and symbioses in plants typically publish in different journals, attend different conferences, and rarely cite one another. Publications on endosymbiosis appear in journals within microbiology, botany, entomology, mycology, cell biology, genetics, evolution, ecology, and other subdisciplines, with many in generalist biology journals. Despite this fragmentation, the same biological processes and questions span these different groups of organisms. One aim with this bibliography is to make these subfields more accessible to one another. Finally, endosymbiosis research is itself fast-evolving. This bibliography includes both recent papers and papers from the last twenty years that represent major advances or good overviews of knowledge at critical stages in the past.

General Overviews

Endosymbiosis research entered a new era when molecular technologies enabled sequencing of endosymbiont and host genes and, later, genomes. Many endosymbionts cannot be cultured in the lab, so the earlier work relied largely on microscopy, and researchers were largely unable to confirm hypotheses about the history and function of endosymbioses that they observed. The following sections include both original works from the early, nonmolecular research on symbiosis; works describing endosymbiosis research from a historical perspective; a few of the major accounts of more modern endosymbiosis research; and popular accounts of examples of current endosymbiosis research.

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