Interlocus contest evolution

Interlocus contest evolution (ICE) is a process of intergenomic conflict by which different loci within a single genome antagonistically coevolve. ICE supposes that the Red Queen process, which is characterized by a never-ending antagonistic evolutionary arms race, does not only apply to species but also to genes within the genome of a species.

Because sexual recombination allows different gene loci to evolve semi-autonomously, genes have the potential to coevolve antagonistically. ICE occurs when "an allelic substitution at one locus selects for a new allele at the interacting locus, and vice versa." As a result, ICE can lead to a chain reaction of perpetual gene substitution at antagonistically interacting loci, and no stable equilibrium can be achieved. The rate of evolution thus increases at that locus.

ICE is thought to be the dominant mode of evolution for genes controlling social behavior. The ICE process can explain many biological phenomena, including intersexual conflict, parent-offspring conflict, and interference competition.

A fundamental conflict between the sexes lies in differences in investment: males generally invest predominantly in fertilization while females invest predominantly in offspring. This conflict manifests itself in many traits associated with sexual reproduction. Genes expressed in only one sex are selectively neutral in the other sex; male- and female-linked genes can therefore be acted upon separated by selection and will evolve semi-autonomously. Thus, one sex of a species may evolve to better itself rather than better the species as a whole, sometimes with negative results for the opposite sex: loci will antagonistically coevolve to enhance male reproductive success at females’ expense on the one hand, and to enhance female resistance to male coercion on the other. This is an example of intralocus sexual conflict, and is unlikely to be resolved fully throughout the genome. However, 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.

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