Meeting Abstract
Tunicates, more specifically ascidians, offer an opportunity to investigate the mechanisms underlying adaptation. Two closely related ascidians, Corella inflata and Corella willmeriana allow us to specifically explore evolutionary changes in reproductive strategies. Ascidians are usually hermaphroditic and self-infertile. Strikingly, C. willmeriana appears to have conserved this ancestral trait, while C. inflata has acquired the ability to self-fertilize. There exists a known mechanism for self-sterility in Ciona Robusta that involves two pairs of hyper-variable allorecognition proteins – s-Themis and v-Themis that are associated with the sperm and vitelline coat respectively. Here we show that these genes are present in both Corellid transcriptomes but the acquisition of self-fertility in C. inflata is associated with paralog loss and potential degeneration. We performed alignments between the C. Robusta Themis genes and orthologs from the Correlid transcriptomes. We found that C. willmeriana may possess an extra v-Themis paralog whereas C. inflata may have lost one. Additionally, we found a substantially lower level of sequence conservation in the C. inflata orthologs. The apparent conservation of self-sterility genes in C. inflata suggests that the Themis genes are pleiotropic. We have begun long-read sequencing of Correlid genomic DNA to improve genome assembly and confirm our Themis ortholog predictions. We expect that our findings will provide insights into the evolution of hyper-variable genes in association with loss of traits involving allorecognition.
