Colonial organism

In biology, a colony is composed of two or more conspecific individuals living in close association with, or connected to, one another, usually for mutual benefit such as stronger defense or the ability to attack bigger prey. In contrast, a solitary organism is one in which all individuals live independently and have all of the functions needed to survive and reproduce.

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 as a whole.

Some organisms are primarily independent and form facultative colonies in response to environmental conditions while others must live in a colony to survive (obligate). For example, some carpenter bees will form colonies when a dominance 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.

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

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.

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