Nature and location of modifier alleles determine the resolution of intralocus sexual conflict

When selection favours different levels of expression for a shared trait in males and females, the population is said to be in Intralocus Sexual Conflict (IaSC). In a landmark study, Connallon and Clark (2010) showed that modifiers (alleles at a different locus that alter the expression of the trait under IaSC in a sex-specific manner), effectively resolve IaSC. Their model assumed that modifier alleles are “perfect”; i.e., they fully rescue the harmful effects of the deleterious allele while leaving the positive effects of the beneficial allele unaffected. In the present study, we relaxed this assumption to include more realistic “imperfect” modifier alleles. Imperfect modifiers are those that reduce the expressions of both detrimental allele and beneficial allele to different extents in a given sex. We also ask whether autosomes or X chromosomes are more conducive to resolution of IaSC. Our results suggest that the resolution of IaSC may not always be guaranteed when the modifier allele is “imperfect.” Interestingly, IaSC gets resolved more easily on autosomes only when modifier alleles are “perfect” or near “perfect” in concordance with the assumption made by Connallon and Clark (2010). However, in general, X chromosomes are more conducive to the resolution of IaSC.