Symbiosis—Evolution’s Co-Author

Abstract

Symbiotic integration is a primary contributor to the centerpiece of evolution, genetic novelty. Acquisition of foreign organisms or parts thereof, and potential subsequent assimilation and often internalization of one or several different genomes into another different entity are the foundational expressions upon which natural selection acts, particularly in eukaryotic organisms. Thus, the entire landscape of life—from cells to biomes—is substantially an evolving collection of chimeric communities. Competition may be pronounced and successful in evolution in large part because the competing organisms do not function as, and indeed are not, individuals. Moreover, growing evidence indicates symbiosis to be on a flexible continuum of physiological expression, often with real plasticity in the organisms’ integrating life cycles. Therefore, so-called “mutualism”, “parasitism”, and “commensalism” as symbiotic reference points and analyses may be outdated and perhaps of dubious use. For example, fundamental ecological principles show us that “parasitism” among two different organisms is often of significant advantage to not only the “parasite” but its “host.” Symbiosis system examples are here reviewed and redefined on a more meaningful evolutionary context; namely, symbiosis is the acquisition of one organism(s) by another different organism(s), and through subsequent long-term integration, new structures and metabolism emerge.

Glossary

Arbuscular

Branching tree like hyphae of mycorrhizal fungi within, but not entirely enclosed, plant root cells

Actinobacteria

Filamentous bacteria commonly found in soils and featuring an array of antibiotic chemistry

Archaeans

Microscopic organisms that thrive in “extreme” temperature or saline conditions. They have many biochemical and genetic features that are closer to eukaryotes than prokaryotes

Ascomycete

Small craterlike features on the surface of fungi and lichens, from which spores are emitted

Bacteriocytes

Specialized intracellular regions of many insects that house symbiotic bacteria which are transmitted via the insect egg and often grouping during the life cycle to form functional organs known as bacteriomes

Bioaugmentation

Any intervention by humans that seeks to promote the viability and fitness of a holobiont (organism) living in non-anthropogenic nature

Chimera

In the context of a holobiont, it is a collection of different genomes interacting as one entity

Coccoliths

The plates of calcium carbonate (limestone) surrounding holobionts known as coccolithophores. These algae in the group haptophta build these structures as part of their outer covering

Endemic

A species that is characteristic of a biogeographical region over a significant period of geologic time

Extant

In the context of biology and evolution, organisms or conditions from more ancient geological time that have persisted to the present

Endophytes

Bacteria or fungi that live symbiotically in between or within plant cells

Epibiotic

An organism lives on the surface of another different organism. It may or may not be symbiotic

Facultative

An organism that functions with clear options such as being to live in either aerobic or anaerobic conditions

Gnotobiology

The study of organisms living in an artificially created environment, namely in conditions where no other living organisms are present

Heamatophagous

The ability of certain animals to penetrate body parts of other organisms and feed on blood

Hermatypic

Coral–dino holobionts that build exoskeletons known commonly as reefs, as opposed to many corals which do not extrude limestone and thus known as a hermatypic

Holobiont

Any living entity (all eukaryotes and rarely some prokaryotes) made of two or more different symbionts—minimally a so-called host species and different symbiont species

Horizontal transmission

The passing of a symbiont to following generations through one symbiont acquiring the other symbiont from the environment

Karst

Geological formations usually created by the dissolution of carbonate rocks such as limestone

Lithosphere

The outermost section of the solid earth, frequently referred to as “crust” but encompassing as well somewhat deeper layers, such as the upper region of the mantle. Much of the lithosphere can be considered part of the region where life can be found, known as the biosphere

Metagenomic

The collection of genomes from different organisms as collected directly from the natural environment as opposed to laboratory cultures

Microbiogenic

Geological structures and features which are the result of living microbial processes and depositions

Nucleomorph

A genetic fraction or remnant of a previously complete nucleus from an alga and now embedded in a new alga with its own nucleus

Pedosphere

The outermost layer of the solid earth composed of the soil and rock eroding regions

Peptidoglycan

A chemical compound made up of sugars and amino acids that forms a mesh-like cell layer known as the bacterial cell wall. It is the defining characteristic of eubacteria, for it is not found in the microbial domain, Archaea

Phagocytosis

The process whereby a cell, usually a eukaryotic one, or an organism envelopes and then internalizes materials or other organisms from the surrounding environs

Rhizosphere

The soil regions among the roots of plants, including the organisms and all their interactions

Rumen

The specialized first section of the alimentary canal of many hooved animals, wherein fermenting, cellulose-producing microbes are housed

Stromatolites

Lithified structures built by the trapping, binding, processing, and then deposition of sediment by cyanobacteria. They are prominent in the fossil record and serve as evidence that our oxygenated atmosphere was substantially the result of cyanobacterial metabolism

Syconium

The section of the Ficus (fig) tree that becomes a fruit, but initially is a completely enclosed structure with numerous internal flowers. Only its holobiont specific partners, certain fig wasps can gain entry and promote the necessary pollination

Symbiosome

A specialized membrane usually substantially formed by the “host” member of a holobiont which completely encloses the entering or captured symbiont

Syntrophy

One species lives off the products of another organism

Thallus

The living structure built by the algal–fungal lichen symbiosis. It bears little or no resemblance to the morphology of either the fungus or the alga. Some lichens have a cyanobacterial holobiont partner which also contributes to its development

Trophosome

A specialized symbiosis-created food-processing organ which houses sulfur oxidizing and other bacteria, in deep sea vent tube worms

Vertical transmission

The persistence from generation to generation of a symbiont(s) through direct transfer via the “host,” often through incorporation within or attachment to an egg

Viviparous

Animals which produce live young emerging from the body as opposed to the deposition externally of eggs