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In behavioral ecology, polyandry is a class of mating system where one female mates with several males in a breeding season. Polyandry is often compared to the polygyny system based on the cost and benefits incurred by members of each sex. Polygyny is where one male mates with several females in a breeding season (Mating Systems, p. 255) (e.g., lions, deer, some primates, and many systems where there is an alpha male).〔Evolutionary anthropology of the human family; In C. A. Salmon and T. K. Shackelford (Eds.), ''The Oxford Handbook of Evolutionary Family Psychology''. New York: Oxford University Press.〕 A common example of polyandrous mating can be found in the Field Cricket, Gryllus bimaculatus, of the invertebrate order Orthoptera (containing crickets, grasshoppers, and groundhoppers). Polyandry also occurs in some primates such as marmosets, mammal groups, the marsupial genus' ''Antechinus'' and bandicoots, whales,〔"Blue Whale". Discovery Channel Blue Ocean.〕 around 1% of all bird species, such as jacanas and dunnocks, insects such as honeybees, and fish such as pipefish. ==Benefits and Cost of Mating for Females== The adaptive significance of polyandry in animals is controversial. Polyandry has direct benefits for females allowing fertilization assurance, provision of resources, and parental care for their offspring.〔 House mice (''Mus musculus musculus'') have shown indirect, genetic benefits, where females have increased offspring survival through multiple mating, showing that practicing polyandry mating results in an increase in offspring viability.〔Firman, R. C., & Simmons, L. W. (2008). Polyandry, sperm competition, and reproductive success in mice. Behavioral Ecology, 19(4), 695–702.〕 In a meta analysis, including 10 different orders of insects, polyandry increased the production of eggs by females specifically in Lepidopterans and Orthopterans.〔Arnqvist, G., & Nilsson, T. (2000). The evolution of polyandry: multiple mating and female fitness in insects. Animal Behaviour, 60(2), 145–164.〕 Indirect benefits of mating for females can be gained through sperm competition to attain “good genes”, cryptic female choice, increased genetic quality, and genetic diversity.〔Simmons, L. W. (2005). THE EVOLUTION OF POLYANDRY: Sperm Competition, Sperm Selection, and Offspring Viability. Annual Review of Ecology, Evolution, and Systematics.〕 Females spiders (''Pisaura mirabilis'') store more sperm from gift-giving males suggesting that sperm storage is under female control through cryptic sperm choice.〔"Albo, M. J., Bilde, T., & Uhl, G. (2013). Sperm storage mediated by cryptic female choice for nuptial gifts. Proceedings of the Royal Society B: Biological Sciences, 280(1772)">〕 The increase in sperm storage from the gift giving males might allow females to produce “sexy sons” that also give gifts and increase the fitness of offspring. Sperm storage and fertilization success increased with copulation duration, suggesting an advantage in sperm competition.〔 Many reptile species also demonstrate polyandry, especially among members of the tortoise family (''Testudinidae''). Through polyandry and long-term sperm storage, recent studies have found evidence for the ability of female tortoises to produce clutches of eggs that demonstrate multiple paternity.〔Johnston, E., Rand, M., and Zweifel, S. 2006. Detection of multiple paternity and sperm storage in a captive colony of the central Asian tortoise, Testudo horsfieldii. Canadian Journal of Zoology 84:520-526.〕〔Davy C., Edwards T., Lathrop A., Bratton M., Hagan M., Henen B., Nagy K., Stone J., Hillard L., and Murphy R. 2011. Polyandry and multiple paternities in the threatened Agassiz’s desert tortoise, Gopherus agassizii. Conservation Genetics 12:1313-1322.〕 Predictably, these hatchlings showed an increase in genetic variability compared to those sired by a single male.〔 Potential for multiple paternity within a clutch is primarily a result of sperm storage across reproductive cycles, since studies have confirmed the presence of multiple males’ sperm in the female tortoise reproductive tract simultaneously.〔 As a result of clutches with greater variation in paternal genes and increased sperm competition, females can maximize both the genetic quality and number of offspring.〔Moon J., McCoy E., Mushinsky H., and Karl S. 2006. Multiple paternity and breeding system in the gopher tortoise, Gopherus polyphemus. The Journal of Heredity 97:150–157.〕 Multiple paternities within a single clutch is therefore considered an effective strategy to increase the reproductive success and fitness of female tortoises.〔 Acorn woodpeckers provide substantial information on breeding systems because they practice monogamy, polyandry, and polygyny. In polyandry the presence of more male breeders in acorn woodpeckers has shown that females reproduce the optimal clutch size and that with paternity sharing between males it is behaviorally more stable increasing male and female fitness.〔"Chao, L. (1997). Evolution of polyandry in a communal breeding system. Behavioral Ecology, 8(6), 668–674.">〕 As opposed to polygyny, where it has been observed that polygynous females that lay a large number of eggs exceeding the optimal clutch size reduces the fitness of the group.〔 Polygynous trios compared to polyandrous trios showed that having more eggs lowered the group fitness. Chao (1997) studies using Acorn Woodpeckers suggest that other mating systems are practiced at a lower rate when compared to polyandry because it is polyandry that can maximize the fitness of males and females when obtaining optimal clutch size. In polyandrous mating, optimal clutch size is obtained because there is only one female and it becomes more stable when all members remain together.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Polyandry in nature」の詳細全文を読む スポンサード リンク
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