page_title: Sperm competition
section_title: Defensive adaptations
hierarchical_section_title: Sperm competition / Defensive adaptations
caption_attribution_description: Picture taken in the zoo of Wrocław (Poland): Neolamprologus pulcher (Trewavas &amp; Poll, 1952) This is one of the "Daffodil" populations, possibly a distinct species. Dysmorodrepanis (talk) 23:39, 25 August 2008 (UTC)
context_page_description: Sperm competition is the competitive process between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction. Competition can occur when females have multiple potential mating partners. Greater choice and variety of mates increases a female's chance to produce more viable offspring. However, multiple mates for a female means each individual male has decreased chances of producing offspring.
  Sperm competition is an evolutionary pressure on males, and has led to the development of adaptations to increase males' chance of reproductive success. Sperm competition results in a sexual conflict of interest between males and females. Males have evolved several defensive tactics including: mate-guarding, mating plugs, and releasing toxic seminal substances to reduce female re-mating tendencies to cope with sperm competition. Offensive tactics of sperm competition involve direct interference by one male on the reproductive success of another male, for instance by physically removing another male's sperm prior to mating with a female.
context_section_description: Mate-guarding is a defensive behavioral trait that occurs in response to sperm competition; males try to prevent other males from approaching the female (and/or vice versa) thus preventing their mate from engaging in further copulations. Precopulatory and postcopulatory mate-guarding occurs in birds, lizards, insects and primates. Mate-guarding also exists in the fish species Neolamprologus pulcher, as some males try to "sneak" matings with females in the territory of other males. In these instances the males guard their female by keeping them in close enough proximity so that if an opponent male shows up in his territory he will be able to fight off the rival male which will prevent the female from engaging in extra-pair copulation with the rival male.
  Organisms with polygynous mating systems are controlled by one dominant male. In this type of mating system, the male is able to mate with more than one female in a community. The dominant males will reign over the community until another suitor steps up and overthrows him. The current dominant male will defend his title as the dominant male and he will also be defending the females he mates with and the offspring he sires. The elephant seal falls into this category since he can participate in bloody violent matches in order to protect his community and defend his title as the alpha male. If the alpha male is somehow overthrown by the newcomer, his children will most likely be killed and the new alpha male will start over with the females in the group so that his lineage can be passed on.
  Strategic mate-guarding occurs when the male only guards the female during her fertile periods. This strategy can be more effective because it may allow the male to engage in both extra-pair paternity and within-pair paternity. This is also because it is energetically efficient for the male to guard his mate at this time. There is a lot of energy that is expended when a male is guarding his mate. For instance, in polygynous mate- guarding systems, the energetic costs of males is defending their title as alpha male of their community. Fighting is very costly in regards to the amount of energy used to guard their mate. These bouts can happen more than once which takes a toll on the physical well- being of the male. Another cost of mate-guarding in this type of mating system is the potential increase of the spread of disease. If one male has an STD he can pass that to the females that he's copulating with potentially resulting in a depletion of the harem. This would be an energetic cost towards both genders for the reason that instead of using the energy for reproduction, they are redirecting it towards ridding themselves of this illness. Some females also benefit from polygyny because extra pair copulations in females increase the genetic diversity with the community of that species. This occurs because the male is not able to watch over all of the females and some will become promiscuous.
  Eventually, the male will not have the proper nutrition which makes the male unable to produce sperm. For instance, male amphipods will deplete their reserves of glycogen and triglycerides only to have it replenished after the male is done guarding that mate. Also, if the amount of energy intake does not equal the energy expended, then this could be potentially fatal to the male. Males may even have to travel long distances during the breeding season in order to find a female which absolutely drain their energy supply. Studies were conducted to compare the cost of foraging of fish that migrate and animals that are residential. The studies concluded that fish that were residential had fuller stomachs containing higher quality of prey compared to their migrant counterparts  With all of these energy costs that go along with guarding a mate, timing is crucial so that the male can use the minimal amount of energy. This is why it is more efficient for males to choose a mate during their fertile periods. Also, males will be more likely to guard their mate when there is a high density of males in the proximity. 
caption: Neolamprologus pulcher
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