page_title: Sperm heteromorphism
section_title: Sperm competition
hierarchical_section_title: Sperm heteromorphism / Possible functions of sperm heteromorphism / Sperm competition
caption_attribution_description: English: Scanning electron microscopic image of immature parasperm lancet of Fusitriton oregonensis showing the tail brush still present, which later develops into part of the body of the parasperm.
context_page_description: Sperm heteromorphism is the simultaneous production of two or more distinguishable types of sperm by a single male. The sperm types might differ in size, shape and/or chromosome complement. Sperm heteromorphism is also called sperm polymorphism or sperm dimorphism. Typically, only one sperm type is capable of fertilizing eggs. Fertile types have been called "eusperm" or "eupyrene sperm" and infertile types "parasperm" or "apyrene sperm".
  One interpretation of sperm polymorphism is the "kamikaze sperm" hypothesis, which has been widely discredited in humans. The kamikaze sperm hypothesis states that the polymorphism of sperm is due to a subdivision of sperm into different functional groups. There are those that defend the egg from fertilization by other male sperm, and those that fertilize the egg. However, there is no evidence that the polymorphism of human sperm is for the purpose of antagonizing rival sperm.
context_section_description: Non-fertile sperm increase the fertilisation success of the male producing them when sperm competition occurs. This might be offensive (e.g. displacing or even killing rival fertilising sperm) or defensive (e.g. by blocking areas of the female tract or creating a hostile pre-fertilisation environment).
caption: Scanning electron microscopic image of immature parasperm lancet (infertile sperm morph) of Fusitriton oregonensis showing the tail brush still present, which later develops into part of the body of the parasperm. It is producing when sperm competition occurs.
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