319:, with the fast, but transient, electrical block superseded after the first minute or so by a more slowly developing permanent mechanical block. Electrical blocks are helpful in species where a very fast block to polyspermy is needed, due to the presence of many sperm arriving simultaneously at the egg surface, as occurs in animals such as sea urchins. In sea urchins, fertilization occurs externally in the ocean, such that hundreds of sperm can encounter the egg within several seconds.
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339:), and additional mechanisms that are not well understood modify the egg's plasma membrane. The zona pellucida is modified by serine proteases that are released from the cortical granules. The proteases destroy the protein link between the cell membrane and the vitelline envelope, remove any receptors that other sperm have bound to, and help to form the fertilization envelope from the cortical granules.
231:, Dr. Nicola Hemmings, an evolutionary biologist at the University of Sheffield, and one of the study's authors reported that the eggs of zebra finches and chickens require multiple sperm, from 10 to hundreds of sperm, to penetrate the egg to ensure successful fertilization and growth of the bird embryo.
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Physiological polyspermy happens when the egg normally accepts more than one sperm but only one of the multiple sperm will fuse its nucleus with the nucleus of the egg. Physiological polyspermy is present in some species of vertebrates and invertebrates. Some species utilize physiological polyspermy
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across the surface of the egg, which is caused by the fusion of the first sperm with the egg. Unfertilized sea urchin eggs have a negative charge inside, but the charge becomes positive upon fertilization. When sea urchin sperm encounter an egg with a positive charge, sperm-egg fusion is blocked.
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The cortical reaction occurs due to calcium oscillations inside the oocyte. What triggers such oscillations is PLC-zeta, a phospholipase unique to sperm that is very sensitive to calcium concentrations. When the first spermatozoa get inside the oocyte, it brings in PLC-zeta, that is activated by
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Polyspermy is very rare in human reproduction. The decline in the numbers of sperm that swim to the oviduct is one of two ways that prevents polyspermy in humans. The other mechanism is the blocking of sperm in the fertilized egg. According to
Developmental Biology Interactive, if an egg becomes
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by the induction of free calcium ion concentration in the cytoplasm of the egg. This induction plays a very critical role in both physiological polyspermy and monomeric polyspermy species. The rise in calcium causes activation of the egg. The egg will then be altered on both a biochemical and
355:. On the one hand, polyspermy creates inviable zygotes and lowers female fitness, but on the other, defenses may prevent fertilization altogether. This leads to a delicate compromise between the two, and has been suggested as one possible cause for the relatively high
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Mio, Y., Iwata, K., Yumoto, K., Kai, Y., Sargant, H. C., Mizoguchi, C., … Nishikori, K. (2012). Possible mechanism of polyspermy block in human oocytes observed by time-lapse cinematography. Journal of
Assisted Reproduction and Genetics, 29(9), 951–956.
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oocyte's basal calcium concentrations, initiates the formation of IP3 and causes calcium release from endoplasmic reticulum stores, generating the oscillations in calcium concentration that will activate the oocyte and block polyspermy.
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Thus, after the first sperm contacts the egg and causes the change, subsequent sperms are prevented from fusing. This "electrical polyspermy block" is thought to result because a positively charged molecule in the sperm surface
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Unlike physiological polyspermy, monospermic fertilization deals with the analysis of the egg calcium waves, as this is the typical reproduction process in all species. Species that undergo physiological polyspermy have
656:
Gabbett, Michael T.; Laporte, Johanna; Sekar, Renuka; Nandini, Adayapalam; McGrath, Pauline; Sapkota, Yadav; Jiang, Peiyong; Zhang, Haiqiang; Burgess, Trent; Montgomery, Grant W.; Chiu, Rossa; Fisk, Nicholas M. (2019).
315:). In species without an electrical block, polyspermy is usually prevented by secretion of materials that establish a mechanical barrier to polyspermy. Animals such as sea urchins have a two-step polyspermy prevention
331:. This may be the result of the female genital tract being adapted to minimize the number of sperm reaching the egg. Nevertheless, polyspermy preventing mechanisms are essential in mammals; a secretion reaction, the "
145:, one from each parent. The cell resulting from polyspermy, on the other hand, contains three or more copies of each chromosome—one from the egg and one each from multiple sperm. Usually, the result is an unviable
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morphological level. In mammals as well as sea urchins, the sudden rise in calcium concentration occurs because of the influx of calcium ions within the egg. These calcium ions are responsible for the
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Miao, YL & Williams CJ. 2012. Calcium signaling in mammalian egg activation and embryo development: the influence of subcellular localization. Molecular
Reproduction & Development 79:742-56.
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rates seen in mammalian species. In some species, polyspermy is allowed to happen to result in more than one sperm entering the egg creating viable offspring without detrimental effects.
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fertilized by multiple sperm, the embryo will then gain various paternal centrioles. When this happens, there is a struggle for extra chromosomes. This competition causes disarrayment in
790:(Gardner, A.J, Evans, J.P. 2006. Mammalian membrane block to polyspermy: new insights into how mammalian eggs prevent fertilization by multiple sperm. "Reprod Fertil Dev."
268:, which respond to the acceptance of one sperm by inhibiting the successful penetration of the egg by subsequent sperm. Similar defenses exist in other
765:, M. Gould. 1985. Polyspermy-preventing mechanisms. In C. B. Metz & A. Monroy (editors) Biology of Fertilization. Academic, New York. pp. 223-250.
827:, Morrow, E. H., G. Arnqvist, T. E. Pitcher. 2002. The evolution of infertility: Does the hatching rate in birds coevolve with female polyandry?
847:"The biology and evolution of polyspermy: insights from cellular and functional studies of sperm and centrosomal behavior in the fertilized egg"
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During physiological polyspermy, the egg accepts multiple sperms but only allows one sperm to fuse its nucleus with the egg's nucleus.
215:-preventing mechanisms that act inside the egg. This is quite different from the normal polyspermy block on the outside of the egg.
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Grandin, N; Charbonneau, M (1992). "Intracellular free Ca2+ changes during physiological polyspermy in amphibian eggs".
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149:. This may occur because sperm are too efficient at reaching and fertilizing eggs due to the selective pressures of
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1989. Evidence that the voltage-dependent component in the fertilization process is contributed by the sperm.
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Jaffe, L. A. & M. Gould. 1985. Polyspermy-preventing mechanisms. In C. B. Metz & A. Monroy (editors)
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Braden, A. W. H. 1953. Distribution of sperms in the genital tract of the female rabbit after coitus.
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In mammals, in which fertilization occurs internally, fewer sperm reach the fertilization site in the
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as the proper mechanism for developing their offspring. Some of these animals include birds,
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Female defenses select for ever more aggressive male sperm, however, leading to an
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The prevention of polyspermy in sea urchins depends on a change in the electrical
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to avoid this situation. The defenses are particularly well characterized in the
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Electrical polyspermy blocks operate in many animal species, including
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Snook, Rhonda R.; Hosken, David J.; Karr, Timothy L. (2011-12-01).
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Female
Control: Sexual Selection by Cryptic Female Choice
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551:"Polyspermy in birds: sperm numbers and embryo survival"
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Proceedings of the Royal
Society B: Biological Sciences
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is repelled by the positive charge at the egg surface.
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Fertilization in Fishes and the
Problem of Polyspermy
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formation and the normal consequence is death of the
713:. Princeton University Press, Princeton, New Jersey.
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Chicken and zebra finch eggs require multiple sperm
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335:" modifies the extracellular coat of the egg (the
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16:Fertilization of an egg by more than one sperm
908:. Academic, New York.Brendon magero; 223–250.
493:https://www.ncbi.nlm.nih.gov/books/NBK10033/
410:"Egg activation in physiological polyspermy"
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621:http://doi.org/10.1007/s10815-012-9815-x
471:. Sunderland, Mass: Sinauer Associates.
391:. Princeton University Press, Princeton
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598:Bhanoo, Sindya N. (2 November 2015).
635:"Fertilization: Avoiding Polyspermy"
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190:of their yolky eggs. Sperm triggers
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178:or anamniote, including
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467:Gilbert, Scott (2000).
408:Iwao, Yasuhiro (2012).
897:Ginzberg, A. S. 1972.
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567:10.1098/rspb.2015.1682
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864:10.1530/REP-11-0255
429:10.1530/rep-12-0104
235:Blocking polyspermy
605:The New York Times
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184:cartilaginous fish
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58:"Polyspermy"
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723:Jaffe, L.A.
633:Priore, C.
507:Development
357:infertility
741:Iwao, Y.,
375:References
270:eukaryotes
266:sea urchin
213:polyploidy
172:ctenophora
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