Date of Award

Spring 2009

Document Type

Restricted Thesis

Terms of Use

© 2009 Farah Hussain. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts


Biology Department

First Advisor

Elizabeth Ann Vallen


Corals are integral to many worldwide marine ecosystems but are threatened by bleaching, a process in which stress results in the loss of symbiotic zooxanthellae. To better understand the symbiont-host relationship, we studied the cytoskeleton of a related cnidarian, the sea anemone Aiptasia pallida in the presence and absence of zooxanthellae. We observed that zooxanthellae densely populated host gastrodermal cells, occupying the majority of intracellular space. This suggests that anemones must manipulate their cell shape and cytoskeleton in order to perform normal functions while accommodating symbionts. By staining cortical F-actin with a small-molecule dye, we observed that host cells harboring intracellular zooxanthellae were larger in cross-sectional area than aposymbiotic cells. There were also striking differences in the shape of these cells. Symbiotic gastrodermal cells exhibited compact curves that fit snugly over the intracellular symbionts. In contrast, aposymbiotic cells were smaller and polygonal. These observations indicate that the host rearranges its cytoskeleton and thus changes shape to accommodate symbionts. Microtubules visualized by immunofluorescence showed putative cilia on the surface of tentacles. In the ectoderm, staining showed potential outlines of nuclei, nematocyst capsules, and the outlines of vacuoles. Staining in the gastroderm was not reproducibly detectable, due most likely to problems with permeabilization. This investigation suggests that there are changes in cell shape and size as a result of the symbiosis between Aiptasia and zooxanthellae.