How does a polymorphic colony divide labor among its modules? Colonial development in the marine invertebrate, Bugulina stolonifera

Abstract

Bryozoans are a diverse phylum of marine and freshwater colonial invertebrates containing approx- imately 6,000 described living species. Bryozoans grow by budding new physiologically connected colony members (zooids) from a metamorphosed larva. Interestingly, these modules often come in different shapes and sizes and are specialized to serve different tasks within the colony. Zooids range in function from feeding to reproduction, defense, and colony attachment. A complex interaction of genotype, environment, and developmental pathway shapes zooid formation, however, the spe- cific mechanisms underlying the establishment of this division of labor remain unknown. In this thesis, I present the first characterizations of differential gene expression between poly- morphic zooids of a bryozoan colony. I explored the development of different zooid types of lab- cultured Bugulina stolonifera colonies using RNA sequencing, de novo transcriptome assembly, and differential gene expression analysis. I developed a technique to extract high quality mRNA from small colony structures which enabled me to build cDNA libraries for zooid types at different developmental stages. High throughput sequencing of cDNA libraries yielded an average of 20.1 million paired-end reads per sample, from which I filtered all low-quality and potential contami- nant sequences, resulting in an average of 14.9 ± 1.3 (SE) million paired-end reads per sample. Here, I present data for the first de novo transcriptome assemblies of B. stolonifera and the first characteri- zation of genes involved in the formation and maintenance of zooid types within a bryozoan colony. De novo assembly resulted in an average of 250,000 transcripts per sample, with an average N50 contig size of 956 base pairs. In a comparison between autozooid and avicularium tissues, I uncov- ered 1,097 significant differentially expressed genes. To further explore the development of the avic- ularium from bud to mature state, I used confocal imaging to define morphological stages of avicu- larian ontogeny. Taken together, this work provides a much-needed foundation for a new approach to understanding the mechanisms involved in the development of zooids and the establishment of division of labor of B. stolonifera, and contributes new insights into the evolution of polymorphism in bryozoans.