There may be plenty of fish in the sea but the medaka knows what it likes. A single gene mutation that causes the Japanese Killifish to be born a drab grey colour has proved to be a turn-off to members of the opposite sex. By over-expressing the ‘ginger gene’ in the medaka ‘super attractive’ bright orange variants were created . These fish induced hyper-sexual activity in members of the opposite sex resulting in the other potential mates being ignored almost completely
Found commonly in Southeast Asia, the medaka exists in a wide range of colours; from brown, to more uncommon orange and grey variations. The grey medaka were often observed to be rejected in favour of their brown or orange rivals. “This is the first demonstration of a single gene that can change both secondary sexual characteristics and mating preferences” said Shoji Fukamachi, who led a team of researchers from the University of Konstanz, Germany and the University of Tokyo.
The greys, however, need not be completely despondent at these findings, as the study also showed that they were preferentially selective for each other. The attraction seen in the different coloured fish for their colour counterparts, suggests a potential window for sympatric speciation.
The orange colour observed in medaka is due xanthophores, a type of pigmented structure. The grey fish have a mutation in the xanthophore gene resulting in under-expression.
The study published in the open access journal BMC Biology concludes, “This discovery should further facilitate molecular dissection/manipulation of visual-based mate choice”.