[Seminar] Tail loss in two independent tunicate lineages: a comparative genomics perspective

Speakers:

Rin Okaji - Masters student at the Molecular Invertebrate Systematics and Ecology Laboratory, Ryukyu University.

Abstract:

Tunicates, the sister group of vertebrates, comprise appendicularians (including Oikopleura dioica), thaliaceans, and ascidians. Most tunicates have a tail with a notochord at some stage of their life cycle, but some ascidian species develop without a tail throughout their life. Tail loss has evolved independently several times within the family Molgulidae, whereas it has rarely been reported in other ascidian lineages. Genomes are available for both tailed and tailless Molgula species, and comparisons between them have shown that tail loss is associated with the pseudogenization of muscle actin and tyrosinase genes and the loss of notochord expression of genes such as Col1/2a. However, only a few such genes have been identified, and why certain lineages repeatedly lose their tails remains unclear. We found that an ascidian species inhabiting Japan develops without a tail, and phylogenetic analysis placed this species in the family in which tailless development has not been reported before (manuscript in preparation). This tail loss, independent of Molgulidae, provides an excellent opportunity to investigate the molecular basis of convergent tail loss in ascidians. In this talk, we will introduce this system and discuss genomic approaches to identify features shared among tailless species.