Intralocus sexual conflict

Throughout nature, males and females possess significantly different evolutionary interests, which are thought to be due to each sex occupying their different individual reproductive roles. The overall goal behind both sexes is reproductive success, which both male and female acquire through different techniques. For example, males do not mind dispensing their sperm into random females since their sperm are biologically less costly to produce and are found in abundance. They invest little time in the development of their offspring, and invest more energy on attaining their next mate. Male reproductive success is limited by the number of females he mates with, and not by the number of sperm that is produced. On the contrary, reproductive success in females is limited by the amount of eggs that are produced. The number of offspring created cannot exceed the number of eggs a female possesses. Unlike sperm, eggs are biologically very costly and numbered. In order for females to increase their reproductive success, they invest more time in creating high quality offspring and being choosy. Both sexes choose their mates based on favorable traits that are indicative of their mate's quality and fertility.

Natural selection leads offspring to inherit favorable traits from each parent. This will make them likely to succeed in competition of resources and reproduction. However, traits that may be optimal for the fitness of one sex may not be optimal for the other. Since many organisms have a shared set of chromosomes, organisms are restricted from individually reaching optima for their individual sex. This as a result causes sex-specific reductions in fitness, and sexual conflict between males and females.

Conflict between the two sexes commonly arises in one of two possible situations. Members of one sex can acquire characteristics that benefit their ability to successfully reproduce, while negatively impacting the fitness of the opposite sex. This process is referred to as Interlocus sexual conflict. In genetics, a locus refers to the exact location of a gene on a chromosome. This type of sexual conflict occurs at different loci in each sex. This may result in a counter adaptation in an attempt to reduce harm in the sex that experiences reduced fitness at a different locus. For example, a female may diminish detrimental consequences of being subjected to male accessory gland proteins during mating by waiting longer to re-mate, or she may develop an opposite physical adaptation of her reproductive tract Alternatively, sex-specific reductions of fitness may occur within the same locus. These specific reductions of fitness are caused by different selective pressures that exist between the sexes. These specific reductions are referred to as intralocus sexual conflict. Intralocus sexual conflict could ultimately displace the opposite sex, or both, from ever reaching a phenotypic optimum.

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