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Sexual conflict or sexual antagonism occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, particularly over the mode and frequency of mating, potentially leading to an evolutionary arms race between males and females.〔 For instance, males may benefit from multiple matings, while multiple matings may harm or endanger females.〔 The development of an evolutionary arms race can also be seen in the chase-away sexual selection model, which places inter-sexual conflicts in the context of secondary sexual characteristic evolution, sensory exploitation, and female resistance. According to chase-away selection, continuous sexual conflict creates an environment in which mating frequency and male secondary sexual trait development are somewhat in step with the female’s degree of resistance.〔 It has primarily been studied in animals, though it can in principle apply to any sexually reproducing organism, such as plants and fungi. Sexual conflict/antagonism can be in two forms: #Interlocus sexual conflict is the interaction of a set of antagonistic alleles at one or more loci in males and females. An example is conflict over mating rates. Males frequently have a higher optimal mating rate than females because in most animal species, they invest fewer resources in offspring than their female counterparts. Therefore, males have numerous adaptations to induce females to mate with them. Another well-documented example of inter-locus sexual conflict is the seminal fluid of ''Drosophila melanogaster'', which up-regulates females' egg-laying rate and reduces her desire to re-mate with another male (serving the male's interests), but also shortens the female's lifespan reducing her fitness. #Intralocus sexual conflict This kind of conflict represents a tug of war between natural selection on both sexes and sexual selection on one sex. For example, the bill color in Zebra finches etc. Ornamentation could be costly to produce, it is important in mate choice but also makes an individual vulnerable to predators, the alleles for such phenotypic traits are under antagonistic selection and this conflict is resolved via elaborate sexual dimorphism thus maintaining sexually antagonistic alleles in the population. Evidence indicates that intralocus conflict may be an important constraint in the evolution of many traits.〔 Sexual conflict may lead to antagonistic co-evolution, in which one sex (usually male) evolves a favorable trait that is offset by a countering trait in the other sex. Similarly, interlocus sexual conflict can be the result of what is called a perpetual cycle. The perpetual cycle begins with the traits that favor male reproductive competition, which eventually manifests into male persistence. These favorable traits will cause a reduction in the fitness of females due to their persistence. Following this event, females may develop a counter-adaptation, that is, a favorable trait that reduces the direct costs implemented by males. This is known as female resistance. After this event, females' fitness depression decreases, and the cycle starts again.〔 Interlocus sexual conflict reflects interactions among mates to achieve their optimal fitness strategies and can be explained through evolutionary concepts. Sensory exploitation by males is one mechanism that involves males attempting to overcome female reluctance. It can result in chase-away selection, which then leads to a co-evolutionary arms race. There are also other mechanisms involved in sexual conflict such as traumatic insemination, forced copulation, penis fencing, love darts and others. Female resistance traditionally includes reducing negative effects to mechanisms implemented by males, but outside the norm may include sexual cannibalism, increased fitness in females on offspring and increased aggression to males. Animal species that are not in a state of sexual conflict are more likely to be in sync to the male dominance hierarchy as the females are more docile in these organizations such as wolves, common rabbits and crocodiles. Others, such as spiders, ants and orcas are female-dominated. Some regard sexual conflict as a subset of sexual selection (which was traditionally regarded as mutualistic), while others suggest it is a separate evolutionary phenomenon.〔T Lodé "la guerre des sexes chez les animaux" Eds O Jacob, Paris, 2006, ISBN 2-7381-1901-8〕 == Conflicts of interests between sexes == The differences between male and female general evolutionary interests can be better understood through the analysis of the various factors that affect sexual conflict. In situations involving a male and female, only the relative positions of the optimal trait values are important as it is their comparative positions that provide insight into the resulting conflict. The trait value bar at the bottom of the accompanying figure indicates the relative intensity of each trait. The left side represents the poorly developed end of intensity range, while the right side represents the strongly developed end of the range. Males and females differ in the following general components of fitness, thus leading to sexual conflict. Refer to the accompanying figure in this section. Mating rate: Males generally increase their fitness by mating with multiple mates, while females are on the middle section of the range because they do not favor a particular side of the spectrum. For instance, females tend to be the choosier sex, but the presence of female sexual promiscuity in Soay sheep show that females do not have an established mating preference. Female stimulation threshold: Generally, females benefit from being more selective than males would like them to be. For example, the Neotropical spider, ''Paratrechalea ornata'', displays nuptial gift-giving behaviors during courtship as a part of their male mating efforts. These nuptials gifts allow the male to control copulation duration and to increase the speed of female oviposition. Degree of female fidelity: Because female fidelity depends on the species’ particular mating system, therefore they are in the middle section of the spectrum. However, males seeking mates have different preferences depending on whether they are unpaired or paired. Paired males benefit from high female fidelity, while unpaired males benefit from low female fidelity in order to increase their mating frequencies. Toxicity of seminal fluid: Females benefit from low seminal fluid toxicity, while males benefit from a high toxicity level as it increases their competitive edge.〔 Female fecundity: Males benefit from a high female fecundity as it means that females can produce more offspring and have a higher potential for reproduction. It is important to note that females also benefit from high fecundity, and thus this trait is probably more affected by classical natural selection. Maternal investment: In many species, males benefit from high maternal investment as it allows them to preserve more energy and time for additional matings rather than investing their resources on one offspring. Females are expected to invest a certain amount of time and resources, but it can also be detrimental to the female if too much maternal investment is expected. 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「sexual conflict」の詳細全文を読む スポンサード リンク
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