Gynodioecy

Gynodioecy is a rare breeding system that is found in certain flowering plant species in which female and hermaphroditic plants coexist within a population. Gynodioecy is the evolutionary intermediate stage between being a hermaphrodite (plants that have both female and male parts) and dioecy (having two distinct morphs: male and female). Gynodioecy is the opposite of androdioecy, which is a breeding system consisting of male and hermaphroditic plants in a population. Gynodioecy occurs as a result of a genetic mutation that inhibits a hermaphroditic plant from producing pollen, while keeping the female reproductive parts intact. Gynodioecy is extremely rare, with fewer than 1% of angiosperm species exhibiting the breeding system. Some notable species that exhibit a gynodioecious mating system include Beta vulgaris (wild beet), Lobelia siphilitica, Silene, and Lamiaceae.

Gynodioecy is often referred to as the evolutionary intermediate state between hermaphroditism and dioecy. Gynodioecy has been investigated by biologists dating as far back as to Charles Darwin. Gynodioecy can evolve from hermaphroditism due to certain environmental factors. If enough resources in a population are allocated to the female functions in a hermaphroditic species, gynodioecy will ensue. On the other hand, if more of those resources are divvied up to favor a hermaphrodite’s male functions, androdioecy will result. A high rate of self-pollination in a population facilitates the maintenance of gynodioecy by increasing the inbreeding costs for hermaphrodites. Thus, as the rate of inbreeding increases in a population, the more likely gynodioecy is to occur.

Since hermaphrodites can reproduce on their own, they are referred to as being self-compatible. On the contrary, non-hermaphroditic plants are self-incompatible. Research has shown that a species can be either gynodioecious or self-incompatible, but very rarely is there a co-occurrence between the two. Therefore, gynodioecy and self-incompatibility tend to prevent each other’s maintenance. Self-incompatibility of plants helps maintain androdioecy in plants, since males are in competition with only hermaphrodites to sire ovules. Self-incompatibility leads to a loss in gynodioecy, since neither hermaphrodites nor females have to deal with inbreeding depression.

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