BEACON Program Internship

Dr. Billie Swalla
University of Washington

The BEACON Program will fund up to four students. Students will work under the supervision of Dr. Billie Swalla.

Evolution of Development in Molgulid Ascidians

Ascidians are a fascinating clade of animals, spending their time filter-feeding, stuck to the benthos. These amazing animals are actually one of our closest related invertebrate cousins. Ascidians are invertebrate chordates that share a number of developmental features in common with the vertebrates including a branchial basket, an endostyle, and a notochord inside a functional swimming larval tail. Molgulids are a monophyletic clade of ascidians in which a tailless phenotype has evolved multiple times independently. We investigate the differential gene expression of two species of molgulids, Molgula oculata and Molgula occulta.

Molgula oculata, has a typical tailed phenotype, but its sister species, Molgula occulta, has lost the tail and notochord, developing 20 notochord cells that do not converge and extend, but sit on the side of the larvae in a “notoball”. The two species can be hybridized: if the egg of the tailless species is used, then some of the resulting hybrids have 20 notochord cells that, in some cases, do converge and extend into a short, non-functional half tail. We have sequenced the genomes and embryonic developmental transcriptomes of these two sister species as well as hybrid embryos, and are searching for differential gene expression of known notochord related genes to attempt to identify the developmental changes responsible for the loss of the tailed phenotype.









This is a model system for looking at the evolution and modification of complex features. We are using modern molecular techniques to search for changes in gene expression between the two species and identify the underlying mechanisms behind this drastic life history change. Understanding how the notochord has been altered will help us understand how evolution can alter complex structures and how the underlying gene networks can be modified while not effecting the survivability of the altered organism.

In the Swalla lab you will utilize gene detection techniques such as database searching to find notochord related genes, confirming their identity in NCBI, and gene alignments to confirm homology and quantify change. You will also learn molecular techniques such as gene cloning, running gels, creating molecular probes, performing in situ hybridization to detect gene expression, and how to visualize results using microscopy.

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