Sexual Conflict Resolved by Invasion of a Novel Sex Determiner in Lake Malawi Cichlid Fishes

Sexual Blotch Sexual conflicts may provide selection pressures that facilitate invasion of new genetic sex determiners. Roberts et al. (p. 998 , published online 1 October) describe data obtained from several species of sexually dimorphic cichlid fishes found in Lake Malawi that support this model. An orangeblotch color pattern has evolved among the females of rock-dwelling species because it provides effective camouflage against the algae-coated rocks. Blotched males (OB) are rare, possibly because the trait interferes with the normal male color pattern of blue stripes that are important cues for mate selection. The pigmentation pattern that creates this conflict between natural selection in females and sexual selection in males is caused by mutation in the cis -regulatory region of the Pax7 gene and is tightly linked to a dominant female sex determiner. When bred in the lab, the OB males inherit the intact maternal OB haplotype and their OB-carrying chromosome determines female sex in the offspring; the males seem to be sex-reversed by another mechanism.