Molgulid Ascidians Share a Unique Gene Complex

Abstract

Typical chordate features found in ascidian tadpole larvae have been evolutionarily lost several times independently within the Molgulidae family. While tailed molgulids retain a tail with muscle cells, a notochord, and a dorsal neural tube, the notochord and muscle cells have been lost within the tail-­‐less species. Of the ascidians, there are just two extant species with tail-­‐less larvae other than the in the Molgulidae, which are found in the related Styelidae. A locus containing an unusual gene arrangement of the Bobcat gene within the first intron of the Manx gene has been shown to be essential for the development of chordate features in molgulid tadpole larvae. We propose that the unique rearrangement that took place in the molgulid ancestor may be responsible for the numerous instances of the evolution of tail-­‐lessness found in the Molgulidae.