Colony (biology)

Colonies can form in various shapes and ways depending on the organism involved. For instance, the bacterial colony is a cluster of identical cells (clones). These colonies often form and grow on the surface of (or within) a solid medium, usually derived from a single parent cell.

Colonies, in the context of development, may be composed of two or more unitary (or solitary) organisms or be modular organisms. Unitary organisms have determinate development (set life stages) from zygote to adult form and individuals or groups of individuals (colonies) are visually distinct. Modular organisms have indeterminate growth forms (life stages not set) through repeated iteration of genetically identical modules (or individuals), and it can be difficult to distinguish between the colony as a whole and the modules within. In the latter case, modules may have specific functions within the colony.

In contrast, solitary organisms – such as jaguars – do not associate with colonies; they are ones in which all individuals live independently and have all of the functions needed to survive and reproduce.

Some organisms are primarily independent and form facultative colonies in reply to environmental conditions while others must live in a colony to survive (obligate). For example, some carpenter bees will form colonies when a dominant hierarchy is formed between two or more nest foundresses (facultative colony), while corals are animals that are physically connected by living tissue (the coenosarc) that contains a shared gastrovascular cavity.

Types

Social colonies

Unicellular and multicellular unitary organisms may aggregate to form colonies. For example,

• Protists such as slime molds are many unicellular organisms that aggregate to form colonies when food resources are hard to come by, as together they are more reactive to chemical cues released by preferred prey.
• Eusocial insects like ants and honey bees are multicellular animals that live in colonies with a highly organized social structure. Colonies of some social insects may be deemed superorganisms.
• Some animals, including various species of birds and mammals, form breeding or nesting colonies, potentially for more successful mating and to better protect offspring.
  • The Bracken Cave is the summer home to a colony of around 20 million Mexican free-tailed bats, making it the largest known concentration of mammals.

Modular organisms

Modular organisms are those in which a genet (or genetic individual formed from a sexually-produced zygote) asexually reproduces to form genetically identical clones called ramets.

Clonal colony

A clonal colony a group of ramets from one genet that live in close proximity or are physically connected. Ramets may have all of the functions needed to survive on their own or be interdependent on other ramets. For example, some sea anemones go through the process of pedal laceration in which a genetically identical individual is asexually produced from tissue broken off from the anemone's pedal disc. In plants, clonal colonies are created through the propagation of genetically identical individuals by stolons or rhizomes.

Colonial organisms

Colonial organisms are clonal colonies composed of many physically connected, interdependent individuals. The subunits of colonial organisms can be unicellular, as in the alga Volvox (a coenobium), or multicellular, as in the phylum Bryozoa. Colonial organisms may have been the first evolutionary step toward multicellular organisms. Individuals within a multicellular colonial organism may be called ramets, modules, or zooids. Structural and functional variation (polymorphism), when present, designates ramet responsibilities such as feeding, reproduction, and defense. To that end, being physically connected allows the colonial organism to distribute nutrients and energy obtained by feeding zooids throughout the colony. The hydrozoan Portuguese man o' war is a classic example of a colonial organism, one of many in the taxonomic class.

Microbial colonies

A microbial colony is defined as a visible cluster of microorganisms growing on the surface of or within a solid medium, presumably cultured from a single cell. Because the colony is clonal, with all organisms in it descending from a single ancestor (assuming no contamination), they are genetically identical, except for any mutations (which occur at low frequencies). Obtaining such genetically identical organisms (or pure strains) can be useful; this is done by spreading organisms on a culture plate and starting a new stock from a single resulting colony.

A biofilm is a colony of microorganisms often comprising several species, with properties and capabilities greater than the aggregate of capabilities of the individual organisms.