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androdioecy
Androdioecy is a reproductive system characterized by the coexistence of males and hermaphrodites. Androdioecy is rare in comparison to the other major reproductive systems dioecy and hermaphroditism. In animals, androdioecy has been considered an important stepping stone in the transition from dioecy to hermaphroditism, and vice versa.
==Evolution of androdioecy==
The fitness requirements for androdioecy to arise and sustain itself are theoretically so improbable that it was long considered that such systems do not exist.〔Darwin C. 1877. The different forms of flowers and plants of the same species. New York: Appleton.〕 Particularly, males and hermaphrodites have to have the same fitness, in other words the same number of offspring, in order to be maintained. However, males only have offspring by fertilizing eggs or ovules of hermaphrodites, while hermaphrodites have offspring both through fertilizing eggs or ovules of other hermaphrodites and their own ovules. This means that all else being equal, males have to fertilize twice as many eggs or ovules as hermaphrodites to make up for the lack of female reproduction.
Androdioecy can evolve either from dioecious ancestors through the invasion of hermaphrodites or from hermaphroditic ancestors through the invasion of males. The ancestral state is important because conditions under which androdioecy can evolve differ significantly.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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