University of Tokyo researchers have revealed the whole genome sequences of two swallowtail butterflies Papilio polytes, the females of which mimic the unpalatable butterfly Pachliopta aristolochiae, and Papilio xuthus, which does not show this Batesian mimicry, and determined the responsible gene and molecular mechanism for the mimicry.
Only the females of the swallowtail butterfly Papilio polytes, which inhabits the Okinawa islands, resemble the unpalatable butterfly Pachliopta aristolochiae, and are able to avoid predators as a result. It was also known that some female Papilio polytes did not show Batesian mimicry, but the genes responsible for this mimicry and the molecular mechanism remained unknown.
Based on genome data analyses, Professor Haruhiko Fujiwara and Project Researcher Shinichi Nishikawa at the Graduate School of Frontier Sciences and their colleagues have determined that the responsible region for the mimicry is a supergene, a large region including multiple genes covering more than 130kb of the genome, and that the supergene includes the doublesex gene which is usually involved in sex differentiation. The orientation of the supergene on the chromosome of the mimetic female was the reverse of the non-mimetic female. The researchers speculate that this inverted structure was produced some tens of millions of years ago. In addition, the research group showed that the doublesex gene from the mimetic female but not from the non-mimetic female caused the mimetic wing color pattern.
This research solves the mystery of why Batesian mimicry is limited to females and is the first to demonstrate the complete structure and function of a supergene. This is a significant contribution to the progress of evolutionary genetics and evolutionary developmental biology.
This research was published in Nature Genetics (April 2015, Volume 47 No. 4).
Source: University of Tokyo