Trioecy is a sexual system characterized by the coexistence of males, females, and hermaphrodites. It has been found in both plants and animals.[1][2] Trioecy, androdioecy and gynodioecy may be described as mixed mating systems.[3]
Terminology
Trioecy is also called tridioecy, subdioecy,[4] or triecy.
Evolution of trioecy
Trioecy may be an unstable transient state[6] associated with evolutionary transitioning from gynodioecy to dioecy.[7][6] In brachiopod species, trioecy usually breaks into androdioecy or gynodioecy.[8] Other studies show that trioecious populations originated from gonochoristic ancestors which were invaded by a mutant selfing hermaphrodite, creating a trioecious population.[1] It has been suggested that chromosomal duplication plays an important part in the evolution of trioecy.[9]
But one study found that trioecy can be stable under nucleocytoplasmic sex determination.[10] Another theoretical analysis indicates that trioecy could be evolutionary stable in plant species if a large amount of pollinators vary geographically.[11]
Occurrence
Trioecy is a relatively common sexual system in plants,[12] estimated to occur in about 3.6% of flowering plant species,[10] although most reports of trioecy could be misinterpretations of gynodioecy.[13] It is rare as well as poorly understood in animals.[12]
Species that exhibit trioecy
The following species have been observed to exhibit a trioecious breeding system.
Plants
- Buddleja sessiliflora
- Buddleja americana
- Coccoloba cereifera[14]
- Garcinia indica[15]
- Fragaria virginiana[16]
- Fraxinus excelsior[3]
- Fuchsia procumbens[17]
- Mercurialis annua[18]
- Opuntia robusta[4]
- Pachycereus pringlei[4][19]
- Pleodorina starrii[20]
Animals
- Aiptasia diaphana[21]
- Auanema rhodensis[1][6]
- Auanema freiburgensis[6]
- Hydra viridissima[22]
- Thor manningi [3]
- Semimytilus algosus Pacific mussel[12]