Credit: R. ROBERTS, UNIV. MARYLAND

Science doi:10.1126/science.1174705 (2009)

Male cichlid fishes in East Africa's Lake Malawi have evolved striking coloration (top right) to compete for females. The objects of their affections, meanwhile, tend to sport inconspicuous brown scales (top left).

An exception is the 'orange-blotch' trait, which is found almost exclusively in females (bottom left) and provides them with camouflage. When it does occur in males, it disrupts their patterning (bottom right), reducing their fitness.

Thomas Kocher and his colleagues at the University of Maryland in College Park have found that this trait is caused by a mutation in the Pax7 gene, which is tightly linked to a new female-sex-determining gene. The close linkage between the mutated gene and the female sex determiner ensures that orange-blotch is expressed mainly in females. Such sexual conflicts can lead to the evolution of new sex-determining systems and many other traits, the team suggests.