Supergene evolution via gain of autoregulation

Area of Science:

• Evolutionary developmental biology
• Genetics
• Entomology

Background:

• Species evolve multiple phenotypes, often controlled by supergenes—linked loci regulating development.
• Identifying mutations causing functional differences in supergene alleles is challenging.
• The doublesex (dsx) gene regulates insect sexual differentiation and acts as a supergene in Papilio butterflies.

Purpose of the Study:

• To elucidate the genetic mechanisms underlying supergene evolution in Papilio alphenor butterflies.
• To identify the specific mutations responsible for divergent dsx allele function in mimetic and non-mimetic phenotypes.

Main Methods:

• Investigated cis-regulatory elements (CREs) controlling dsx expression in Papilio alphenor.
• Analyzed the binding of the DSX transcription factor to dsx CREs.
• Utilized genetic and molecular techniques to assess the function of identified CREs.

Main Results:

• The Papilio alphenor supergene evolved through the recruitment of six novel CREs.
• These new CREs mediate allele-specific dsx expression, controlling distinct female wing phenotypes.
• Four of the six novel CREs are bound by the DSX transcription factor, suggesting autoregulation.

Conclusions:

• Experimental evidence supports classic supergene theory regarding the evolution of complex traits.
• Autoregulation by the DSX transcription factor may be a key mechanism for supergene origination.
• This study highlights how pleiotropic genes can be co-opted into new developmental roles through regulatory evolution.