Trioecy , also spelled triecy, is a sexual system characterized by the coexistence of males, females, and

hermaphrodite A hermaphrodite () is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are either male or female are gonochoric, which is the opposite of hermaphroditic. The individuals of many ...

s. It has been found in both

plants Plants are the eukaryotes that form the kingdom Plantae; they are predominantly photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with cyanobacteria to produce sugars f ...

and

animal Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...

s. Like androdioecy and gynodioecy, trioecy is a mixed mating systems.

Terminology

Trioecy is also called tridioecy and subdioecy . The term trioecy comes from the

Neo-Latin Neo-LatinSidwell, Keith ''Classical Latin-Medieval Latin-Neo Latin'' in ; others, throughout. (also known as New Latin and Modern Latin) is the style of written Latin used in original literary, scholarly, and scientific works, first in Italy d ...

word '' Trioecia'', a former order of trioecious plants.

Evolution of trioecy

Trioecy may be an unstable transient state associated with evolutionary transitioning from gynodioecy to dioecy. In

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...

species, trioecy usually breaks into androdioecy or gynodioecy. Other studies show that trioecious populations originated from gonochoristic ancestors which were invaded by a mutant selfing hermaphrodite, creating a trioecious population. It has been suggested that chromosomal duplication plays an important part in the evolution of trioecy. But one study found that trioecy can be stable under nucleocytoplasmic sex determination. Another theoretical analysis indicates that trioecy could be evolutionary stable in plant species if a large amount of

pollinator A pollinator is an animal that moves pollen from the male anther of a flower to the female carpel, stigma of a flower. This helps to bring about fertilization of the ovules in the flower by the male gametes from the pollen grains. Insects are ...

s vary geographically.

Occurrence

Trioecy is a relatively common sexual system in plants, estimated to occur in about 3.6% of

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

species, although most reports of trioecy could be misinterpretations of gynodioecy. It is rare as well as poorly understood in animals.

Species that exhibit trioecy

The following species have been observed to exhibit a trioecious breeding system.

Plants

* '' Buddleja sessiliflora'' * '' Buddleja americana'' *'' Coccoloba cereifera'' *'' Garcinia indica'' *'' Fragaria virginiana'' *'' Fraxinus excelsior'' *'' Fuchsia procumbens''Godley, E. J. (1955)
"Breeding Systems in New Zealand Plants: I. ''Fuchsia''."
Annals of botany, 19(4), 549-559. * '' Mercurialis annua'' * '' Opuntia robusta'' * '' Pachycereus pringlei'' * '' Pleodorina starrii''

Animals

* '' Aiptasia diaphana'' *'' Auanema rhodensis'' *'' Auanema freiburgensis'' *'' Hydra viridissima'' *'' Thor manningi'' *'' Semimytilus algosus'' Pacific mussel

References

{{Reflist Reproductive system Fertility Sex Sexual system