Date of Award

Spring 2012

Project Type


Program or Major

Natural Resources: Environmental Conservation

Degree Name

Master of Science

First Advisor

Marian K Litvaitis


We documented changes in the abundance and distribution patterns of cells involved in the allorecognition response in two species of colonial aplousobranch tunicates lacking a common vascular system. A histological examination of the fusion junction of isogeneic (CIAs) and allogeneic (CAAs) colony assays revealed that tunic cuticles were rapidly regenerated. The underlying tunic matrix fused readily in Didemnum vexillum in all assay and control types, however it did not fuse in CIAs in Polyclinum constellatum. We identified four and five different cell types in P. constellatum and D. vexillum, respectively. Phagocytic cells represented the most abundant cell type in both species and were most abundant in CAAs, followed by morula (or morula-like) cells. Additionally, the two cell types were more abundant at the fusion junction than at 120 mum or 240 mum from the junction (p<0.05 for P. constellatum; p=0.000 for D. vexillum). Hence, we concluded that phagocytes and morula cells are likely involved in the allorecognition reaction. Filopodial and granular cells, were present, although only at very low abundances. A layer of bladder cells was located immediately below the cuticle in D. vexillum. No bladder cells were found in P. constellatum. .