Presence of males and hermaphrodites in a population
Androdioecy is a reproductive system characterized by the coexistence of males and hermaphrodites. Androdioecy is rare in comparison with the other major reproductive systems: dioecy, gynodioecy and hermaphroditism.[1] In animals, androdioecy has been considered a stepping stone in the transition from dioecy to hermaphroditism, and vice versa.[2]
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.[5][6] Particularly, males and hermaphrodites have to have the same fitness, in other words produce 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.[7][8]
Androdioecy can evolve either from hermaphroditic ancestors through the invasion of males or from dioecious ancestors through the invasion of hermaphrodites. The ancestral state is important because conditions under which androdioecy can evolve differ significantly.[citation needed]
In roundworms, clam shrimp, tadpole shrimp and cancrid shrimps, androdioecy has evolved from dioecy. In these systems, hermaphrodites can only fertilize their own eggs (self-fertilize) and do not mate with other hermaphrodites. Males are the only means of outcrossing. Hermaphrodites may be beneficial in colonizing new habitats, because a single hermaphrodite can generate many other individuals.[9]
In the well-studied roundwormCaenorhabditis elegans, males are very rare and only occur in populations that are in bad condition or stressed.[10]InCaenorhabditis elegans androdioecy is thought to have evolved from dioecy, through a trioecous intermediate.[11]
In barnacles, androdioecy evolved from hermaphroditism.[3] Many plants self-fertilize, and males may be sustained in a population when inbreeding depression is severe because males guarantee outcrossing.[citation needed]
The most common form of androdioecy in animals involves hermaphrodites that can reproduce by autogamyorallogamy through ovum with males. However, this type does not involve outcrossing with sperm. This type of androdioecy generally occurs in predominantly gonochoric taxonomy groups.[12]: 21
One type of androdioecy contains outcrossing hermaphrodites which is present in some angiosperms.[12]: 21
Another type of androdioecy has males and simultaneous hermaphrodites in a population due to developmental or conditional sex allocation. Like in some fish species small individuals are hermaphrodites and under circumstances of high density, large individuals become male.[12]: 21
^ abWeeks, SC (2012). "The role of androdioecy and gynodioecy in mediating evolutionary transitions between dioecy and hermaphroditism in the Animalia". Evolution. 66 (12): 3670–3686. doi:10.1111/j.1558-5646.2012.01714.x. PMID23206127. S2CID3198554.
^Charlesworth, D (1984). "Androdioecy and the evolution of dioecy". Biological Journal of the Linnean Society. 22 (4): 333–348. doi:10.1111/j.1095-8312.1984.tb01683.x.
^Darwin C. 1877. The different forms of flowers and plants of the same species. New York: Appleton.
^Lloyd, DG (1975). "The maintenance of gynodioecy and androdioecy in angiosperms". Genetica. 45 (3): 325–339. doi:10.1007/bf01508307. S2CID20410507.
^Charlesworth, B; Charlesworth, D (1978). "A Model for the Evolution of Dioecy and Gynodioecy". The American Naturalist. 112 (988): 975–997. doi:10.1086/283342. S2CID83907227.
^Pannell, J (2000). "A hypothesis for the evolution of androdioecy: the joint influence of reproductive assurance and local mate competition in a metapopulation". Evolutionary Ecology. 14 (3): 195–211. doi:10.1023/A:1011082827809. S2CID38050756.
^Fürst von Lieven A (2008). "Koerneria sudhausi n. sp. (Nematoda: Diplogastridae); a hermaphroditic diplogastrid with an egg shell formed by zygote and uterine components". Nematology. 10 (1): 27–45. doi:10.1163/156854108783360087.
^Kiontke K, Manegold A, Sudhaus W (2001). "Redescription of Diplogasteroides nasuensis Takaki, 1941 and D. magnus Völk, 1950 (Nematoda: Diplogastrina) associated with Scarabaeidae (Coleoptera)". Nematology. 3 (8): 817–832. doi:10.1163/156854101753625317.
^Ragsdale EJ, Kanzaki N, Sommer RJ (2014). "Levipalatum texanum n. gen., n. sp. (Nematoda: Diplogastridae), an androdioecious species from the south-eastern USA". Nematology. 16 (6): 695–709. doi:10.1163/15685411-00002798. S2CID17802237.
^Potts FA (1908). "Sexual phenomena in the free-living nematodes". Proceedings of the Cambridge Philosophical Society. 14: 373–375.
^Ragsdale EJ, Kanzaki N, Röseler W, Herrmann M, Sommer RJ (2013). "Three new species of Pristionchus (Nematoda: Diplogastridae) show morphological divergence through evolutionary intermediates of a novel feeding-structure polymorphism". Zoological Journal of the Linnean Society. 168 (4): 671–698. doi:10.1111/zoj.12041. S2CID4484091.
^ abHermmann M, Ragsdale EJ, Kanzaki N, Sommer RJ (2013). "Sudhausia aristotokia n. gen., n. sp. and S. crassa n. gen., n. sp. (Nematoda: Diplogastridae): viviparous new species with precocious gonad development". Nematology. 15 (8): 1001–1020. doi:10.1163/15685411-00002738. S2CID4505014.
^Vicky G. Hollenbeck; Stephen C. Weeks; William R. Gould; Naida Zucker (2002). "Maintenance of androdioecy in the freshwater shrimp Eulimnadia texana: sexual encounter rates and outcrossing success". Behavioral Ecology. 13 (4): 561–570. doi:10.1093/beheco/13.4.561.
^ abcMcLaughlin, PA; Henry, DP (1972). "Comparative Morphology of Complemental Males in Four Species of Balanus (Cirripedia Thoracica)". Crustaceana. 22 (1): 13–30. doi:10.1163/156854072x00642.
^Henry, DP; McLaughlin, PA (1967). "A Revision of the Subgenus Solidobalanus Hoek (Cirripedia Thoracica) including a Description of a New Species with Complemental Males". Crustaceana. 12 (1): 43–58. doi:10.1163/156854067x00693.
^Yusa, Y; Takemura, M; Miyazaki, K; Watanabe, T; Yamato, S (2010). "Dwarf Males of Octolasmis warwickii (Cirripedia: Thoracica): The First Example of Coexistence of Males and Hermaphrodites in the Suborder Lepadomorpha". The Biological Bulletin. 218 (3): 259–265. doi:10.1086/bblv218n3p259. PMID20570849. S2CID23908199.
^Valiente-Banuet, A; Rojas-Martínez, A; Del Coro, Arizmendi M; Dávila, P (1997). "Pollination biology of two columnar Cacti (Neobuxbaumia mezcalaensis and Neobuxbaumia macrocephala) in the Tehuacan Valley, central Mexico". American Journal of Botany. 84 (4): 452–455. doi:10.2307/2446020. JSTOR2446020.
^Thomson JD, Shivanna KR, Kenrick J and Knox RB. 1989" American Journal of Botany 76 (7):1048-1059
^Muenchow, G (1998). "Subandrodioecy and male fitness in Sagittaria lancifolia subsp. lancifolia (Alismataceae)". American Journal of Botany. 85 (4): 513–520. doi:10.2307/2446435. JSTOR2446435. PMID21684934.
Ishida, Kiyoshi; Hiura, Tsutom (1998). "Pollen Fertility and Flowering Phenology in an Androdioecious Tree, Fraxinus lanuginosa (Oleaceae), in Hokkaido, Japan". International Journal of Plant Sciences. 159 (6): 941–947. doi:10.1086/314088. S2CID84228081.
