Intralocus sexual conflict
Encyclopedia
Intralocus sexual conflict is one of two genetic forms of sexual conflict
(the other being interlocus sexual conflict
). It occurs when selection on a shared allelic trait in one sex displaces the other sex from its phenotypic optimum. It arises because many shared traits have a common genetic basis but undergo contrasting selection
because they have opposite effects on the Darwinian fitness
of both sexes. A classic example is the human hip, where females need larger hips for childbirth as opposed to smaller hips (optimal for walking) for males. The genes that affect hip size must reach a compromise that is at neither the male optimum nor the female optimum.
In some cases, this conflict may be resolved by the restriction of the gene’s expression to only the sex that it benefits, resulting in sexual dimorphism
. Furthermore, evidence points to these sexually antagonistic genes being common in both plants and animals. Thus, intralocus sexual conflict is a widespread phenomenon.
on trait z in both sexes. Intralocus conflict then originates in the second phase when a change in physical or social conditions causes intense selection on trait z in males and/or females, and both sexes are displaced from their optimum. In the third phase, diverging selection
continues on both sexes, but is attenuated. In the fourth phase, intralocus conflict is fully resolved and sexual dimorphism has occurred.
Examples of this include sexually antagonistic selection on body size in collared flycatcher
s, leading to small males and large females, and sexually antagonistic selection on the beak color between male and female zebra finch
es. This dimorphism is the result of differential expression of the sexually antagonistic gene. Thus, intralocus sexual conflict often leads to and is resolved by dimorphism.
Sexual conflict
Sexual conflict occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, particularly the mode and frequency of mating, leading to an evolutionary arms race between males and females. The conflict encompasses the actions and behaviors of both sexes to influence...
(the other being interlocus sexual conflict
Interlocus sexual conflict
Interlocus sexual conflict is a type of sexual conflict that occurs through the interaction of a set of antagonistic alleles at one or more different loci in males and females, resulting in the deviation of either or both sexes from the fitness optima for the traits.Interlocus sexual conflict...
). It occurs when selection on a shared allelic trait in one sex displaces the other sex from its phenotypic optimum. It arises because many shared traits have a common genetic basis but undergo contrasting selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
because they have opposite effects on the Darwinian fitness
Fitness (biology)
Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
of both sexes. A classic example is the human hip, where females need larger hips for childbirth as opposed to smaller hips (optimal for walking) for males. The genes that affect hip size must reach a compromise that is at neither the male optimum nor the female optimum.
In some cases, this conflict may be resolved by the restriction of the gene’s expression to only the sex that it benefits, resulting in sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
. Furthermore, evidence points to these sexually antagonistic genes being common in both plants and animals. Thus, intralocus sexual conflict is a widespread phenomenon.
Development
Chenowith et al. proposed a 4 phase model for the development of intralocus sexual conflict, in which the first phase is stabilizing selectionStabilizing selection
-Description:Stabilizing or ambidirectional selection, , is a type of natural selection in which genetic diversity decreases as the population stabilizes on a particular trait value. This is probably the most common mechanism of action for natural selection...
on trait z in both sexes. Intralocus conflict then originates in the second phase when a change in physical or social conditions causes intense selection on trait z in males and/or females, and both sexes are displaced from their optimum. In the third phase, diverging selection
Disruptive selection
Disruptive selection, also called diversifying selection, describes changes in population genetics in which extreme values for a trait are favored over intermediate values. In this case, the variance of the trait increases and the population is divided into two distinct groups...
continues on both sexes, but is attenuated. In the fourth phase, intralocus conflict is fully resolved and sexual dimorphism has occurred.
Examples of this include sexually antagonistic selection on body size in collared flycatcher
Collared Flycatcher
The Collared Flycatcher, Ficedula albicollis, is a small passerine bird in the Old World flycatcher family, one of the four species of Western Palearctic black-and-white flycatchers. It breeds in southeast Europe and southwest Asia and is migratory, wintering in sub Sahara Africa...
s, leading to small males and large females, and sexually antagonistic selection on the beak color between male and female zebra finch
Zebra Finch
The Zebra Finch, Taeniopygia guttata, is the most common and familiar estrildid finch of Central Australia and ranges over most of the continent, avoiding only the cool moist south and the tropical far north. It also can be found natively in Indonesia and East Timor...
es. This dimorphism is the result of differential expression of the sexually antagonistic gene. Thus, intralocus sexual conflict often leads to and is resolved by dimorphism.