Allogamy

Allogamy is a mode of sexual reproduction in which fertilization occurs between gametes from different individuals of the same species. In flowering plants, it commonly refers to cross-pollination, where pollen from one plant fertilizes the ovules of another plant. In animals, allogamy describes mating between distinct individuals that produces fertilized gametes.

Allogamy contrasts with autogamy, or self-fertilization, where fertilization occurs within the same individual. By combining genetic material from separate individuals, allogamy generally increases genetic diversity among offspring and reduces the likelihood of deleterious homozygosity, which can enhance population adaptability in changing environments.

In plants, mechanisms often promote allogamy. These include self-incompatibility systems that prevent self-pollen from fertilizing the ovules, dioecy with separate male and female individuals, and floral traits that promote cross-pollination, such as dichogamy (temporal separation of male and female function) and herkogamy (physical separation of anthers and stigma). Pollination agents—insects, birds, or wind—facilitate pollen transfer between individuals. While allogamy is common, many species still experience occasional selfing, depending on ecological conditions and population structure.

From an evolutionary perspective, allogamy favors genetic recombination and can help populations respond to environmental change. However, it typically requires reliable pollination or mates, which can impose costs if pollination services are unreliable or mate availability is limited.

See also: autogamy, geitonogamy, xenogamy, outcrossing.