Unique Tunicate Traits Possibly Encoded by Horizontally Transferred Genes

While horizontal gene transfer (HGT) is common among prokaryotes, its prevalence and impact among metazoans are debatable. A clear example of HGT in animals is the cellulose synthase gene in tunicates, invertebrate chordates that possess the unique ability to produce a cellulose-containing tunic, despite sharing a conserved larval body plan with vertebrates. To investigate evolutionary roles of HGT in animals, we surveyed the genome of a tunicate and identified eight groups of candidate genes that are unlikely to have been vertically transferred. Notably, these candidates encode proteins potentially associated with physiological and structural features unique to tunicates, suggesting that integration of foreign genetic material has contributed to emergence of adaptive traits unique to the tunicate lineage.