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Female sperm storage is a biological process and often a type of sexual selection in which sperm cells transferred to a female during mating are temporarily retained within a specific part of the reproductive tract before the oocyte, or egg, is fertilized. The site of storage is variable among different animal taxa and ranges from structures that appear to function solely for sperm retention, such as insect spermatheca〔Klowden MJ. 2003. Spermatheca. In Resh VH and Cardé RT (eds.): Encyclopedia of Insects. San Diego, CA: Academic Press. 1266.〕 and bird sperm storage tubules (bird anatomy),〔Liem KL, Bemis WE, Walker WF & Grande L. 2001. Functional Anatomy of the Vertebrates, an Evolutionary Perspective 3rd ed. Belmont, CA: Brooks/Cole – Thomson Learning. Pp703.〕〔Birkhead TR. 1998. Sperm Competition in Birds: mechanisms and function. In Birkhead TR & Møller AP (eds.) 1998. Sperm Competition and Sexual Selection. San Diego, CA: Academic Press. Pp. 826.〕 to more general regions of the reproductive tract enriched with receptors to which sperm associate before fertilization, such as the caudal portion of the cow oviduct containing sperm-associating annexins.〔Ignotz GG, Cho MY & Suarez SS. 2007. Annexins are candidate oviductal receptors for bovine sperm surface proteins and thus may serve to hold bovine sperm in the oviductal reservoir. Biology of Reproduction 77:906–913.〕 Female sperm storage is an integral stage in the reproductive process for many animals with internal fertilization. It has several documented biological functions including: * Supporting the sperm by: a.) enabling sperm to undergo biochemical transitions, called capacitation and motility hyperactivation, in which they become physiologically capable of fertilizing an oocyte (e.g. mammals)〔Suarez SS. 2002. Formation of a reservoir of sperm in the oviduct. Reproduction in Domestic Animals 37:140–143.〕〔Suarez SS. 2008. Control of hyperactivation in sperm. Human Reproduction Update 14(6):647–657.〕 and b.) maintaining sperm viability until an oocyte is ovulated (e.g. insects and mammals).〔〔Allen AK & Spradling AC. 2008. The Sf1-related nuclear hormone receptor Hr39 regulates Drosophila female reproductive tract development and function. Development. 135(2): 311–321.〕 * Decreasing the incidence of polyspermy (e.g. some mammals such as pigs).〔〔Hunter RHF & Léglise PC. 1971. Polyspermic fertilization following tubal surgery in pigs, with particular reference to the role of the isthmus. Journal of Reproduction and Fertility. 24:233–246.〕 * Enabling mating, ovulation and/or fertilization to occur at different times or in different environments (e.g. many insects and some amphibians, reptiles, birds and mammals).〔Kardong KV. 2009. Vertebrates: Comparative Anatomy, Function, Evolution. 5th ed. Boston, MA: McGraw Hill. Pp 779.〕〔Birkhead TR & Møller AP. 1993. Sexual selection and the temporal separation of reproductive events: sperm storage data from reptiles, birds and mammals. Biological Journal of the Linnean Society. 50:295–311.〕 〔 Holt W. 2011. Mechanisms of sperm storage in the female reproductive tract: an interspecies comparison. Reproduction in Domestic Animals 46:68-74. 〕 * Supporting prolonged and sustained female fertility (e.g. some insects).〔Ridley M. 1988. Mating frequency and fecundity in insects. Biological Reviews. 63:509–549.〕〔Den Boer SPA, Baer B, Dreier S, Aron S, Nash DR, Boomsma JJ. 2009. Prudent sperm use by leaf-cutter ant queens. Proceedings of the Royal Society B. 276: 3945–3953.〕 * Having a role influencing offspring sex ratios among some insects possessing a haplodiploid sex-determination system (e.g. ants, bees, wasps and thrips as well as some true bugs and some beetles).〔Antolin MF & Henk AD. 2003. Sex Determination. In Resh VH and Cardé RT (eds.): Encyclopedia of Insects. San Diego, CA: Academic Press. 1266.〕〔Werren JH. 1980. Sex ratio adaptations to local mate competition in a parasitic wasp. Science 208:1157–1159.〕〔King PE. 1961. A possible method of sex ratio determination in the parasitic hymenopteran Nasonia vitripennis. Nature 189:330–331.〕 * Serving as an arena in which sperm from different mating males compete for access to oocytes, a process called sperm competition, and in which females may preferentially utilize sperm from some males over those of others, called female sperm preference or cryptic female choice (e.g. many invertebrate animals, birds and reptiles).〔Birkhead TR & Møller AP (eds.) 1998. Sperm Competition and Sexual Selection. San Diego, CA: Academic Press. Pp. 826.〕〔Eberhard WG. 1996. Female Control: Sexual Selection and Cryptic Female Choice. Princeton, NJ: Princeton University Press. Pp 501.〕 〔Leonard J. & Cordoba-Aguilar A. 2010. The Evolution of Primary Sexual Characters in Animals (pp. 1–52). Oxford: Oxford University Press. 〕 ==Increased diversity of offspring == One important advantage female insects that store sperm gain is increased genetic diversity in their offspring. There are many ways that females can alter offspring genetics to increase their success and diversity. An example of how this can be accomplished is in female Scathophaga that preferentially fertilize eggs to survive in different environments. Since many environments require different traits for success, females are somehow able to match sperm (acquired from multiple mates) that have the best genes for whichever environment in which they will develop.〔Ward,P. 2000. Cryptic Female Choice in the Yellow Dung Fly ''Scathophaga stercoraria'' (L.) Evolution. 54(5):1680–1686〕 Many of the different properties of the environment, including temperature and thermal properties affect the female's sperm choice.〔Ward P, VonWil J, Scholte E, Knop E. 2002. Field experiments on the distributions of eggs of different phosphoglucomutase(PGM) genotypes in the yellow dung fly ''Scathophaga stercoraria'' (L.). Molecular Ecology. 11:1781–1785〕 Studies have also shown that ovipositing is nonrandom and females lay eggs with varying PGM(phosphoglucomutase) genotypes in different environments in order to optimize offspring success. Females are acutely aware to their environment and manipulate the genetic diversity of their offspring in appropriate ways to ensure their success. Another way sperm-storing females can alter the diversity of their offspring is controlling the relatedness to the males that provide them with sperm. Inbreeding depression can have a deleterious impact on populations of organisms and is due to mating of closely related individuals. To combat this effect, female insects appear to be able to sort out the sperm of relatives from the sperm of non-relatives to choose the best option to fertilize their eggs. Female crickets are able to preferentially store sperm of multiple unrelated males to that of their siblings; this results in more of the offspring having unrelated parentage. Being able to choose between sperm after coupling might be advantageous to females because choosing between mates precopulation may be more costly, or it may just be too difficult to tell males apart before mating.〔Bretman A, Newcombe D, Tregenza T. 2009. Promiscuous females avoid inbreeding by controlling sperm storage. Molecular Ecology. 18:3340–3345〕 Females possess remarkable abilities to select sperm to store and to fertilize their eggs that will make their offspring diverse. Though it has been shown that a majority of female insect species can store sperm, specific examples that have been studied could include field crickets,〔 dung flies 〔 and Mediterranean fruit flies.〔Taylor PW, Yuval B. 1999. Postcopulatory sexual selection in Mediterranean fruit flies: advantages for large and protein-fed males. Animal Behaviour. 58:247–254.〕 Females largely benefit from this mechanism, but males often can experience low fitness because their paternity is not secure. 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「Female sperm storage」の詳細全文を読む スポンサード リンク
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