Meeting Abstract
Lineage-specific genes-those conserved within one group but absent in outgroups-may contribute to novelty. Studies of these genes are rare, especially those restricted to ancient clades. We bioinformatically identified genes specific to the large superphyletic clade Spiralia, and examined their expression in a mollusc. Strikingly, two of 20 genes were specifically expressed in the ciliary band of the larva. Many spiralians have prominent ciliary bands, suggesting that such bands are an important spiralian character; however, it is not clear whether these bands are homologous, or why they are so prevalent in this group. We then carried out a comparative survey across the Spiralia, examining one or both of these genes in two polychaete annelids, two nemerteans, a brachiopod, a phoronid and a rotifer. In most taxa, the genes were specifically expressed in the major ciliary bands in the larva (annelids, phoronid, and brachiopod). In the case of the rotifer, the gene studied was present in the corona, a prominent ciliary band in the adult, and in the case of the phoronid, the gene studied was expressed in the developing lophophore, an adult ciliary feeding structure found in several spiralian groups. Nemerteans are thought to have secondarily derived ciliary bands, and in a representative of this group, the gene studied was expressed in association with, but not specific to, the primary ciliary bands. We are currently testing these genes’ functions. These are the first genetic data that potentially unite the diverse ciliary structures of spiralians, and suggest roles in spiralian-specific aspects of ciliary biology. This provides a rare example of lineage-specific genes participating in a key trait in an ancient metazoan clade.
