Junior Biology, Geophysical Sciences major at The University of Chicago
REU Mentor: Dr. Scott Lidgard (Associate Curator, Geology)
Symposium Presentation Title: Bizarre biology: morphogenesis of the freshwater bryozoan Plumatella vaihiriae (Phylactolaemata)
Symposium Presentation Abstract: Bryozoans are a diverse phylum of aquatic small colonial invertebrates whose development, phylogenetic relationships, and reproductive biology are understudied and poorly understood compared to most other metazoan taxa. Within the same genetic individual - the colony - structural individuals called zooids are budded asexually. As zooids in some bryozoan groups are highly polymorphic, the study of these animals could shed light on the origin and evolution of polymorphism and functional specialization, the unique life histories of bryozoans, and the factors influencing colony growth and form. Morphogenesis in bryozoans is complex, potentially involving: embryonic development of a larva, catastrophic metamorphosis, iterative budding, and an asexually produced diapausal statoblast that subsequently germinates. Gene expression is a powerful tool for exploring the implications of these broad questions; we aim to construct a cDNA library for a species of phylactolaemate bryozoan, Plumatella vaihiriae, to complement an existing library for a cheilostome bryozoan, Bugula neritina. With B. neritina and then P. vaihiriae, we plan to investigate the expression of regulatory genes in bryozoans, and their role in patterning body plans in individual zooids and heterzooids, and colony morphology. In addition to this molecular work, we intend to collect a series of images and histological sections detailing the morphogenesis, budding, and sexual reproduction of P. vaihiriae as a model phylactolaemate bryozoan. Although the project is still in its initial stages, images of statoblast germination and ancestrula formation have been gathered, and techniques for rearing phylactolaemate bryozoans in the laboratory are being perfected.
Original Project Description: This project will employ collections of Bryozoa, the only wholly colonial phylum of animals, to address a fundamental biological question – how does evolution act to create new body plans? In bryozoans, sexually produced larvae with one body plan are released by a colony, settle, and undergo metamorphosis. From these larvae, asexually budded zooids together comprise the body of a single genetic individual, the colony. In many species, zooids are amazingly different morphologically (polymorphic), even though they are identical genetically. This life cycle and its polymorphism, in turn, can be seen as a laboratory to help discover how different body plans have come into being.
One part of studying this system involves microscopic imaging of zooid life stages—alive in their aqueous environment, using conventional histological techniques, and using scanning electron microscopy. The plan is to compare larval, zooid, and colony development in a few select species, some with and others without polymorphs, representing the phylogenetic breadth of the phylum. Molecular genetic and developmental protocols can now be used to compare gene regulation and patterning in feeding zooids and polymorphic zooids of colonies, as well as in earlier embryonic and larval stages. Principal goals are to relate a modern understanding of development to current bryozoan evolutionary biology and systematics; and to the broad contexts of development and diverse body plans among metazoans. This larger project, in collaboration with evolutionary developmental biologist Chris Lowe at Stanford University, is already underway with work on a highly derived polymorphic species. The summer internship will concentrate on a second, much "simpler" species representing freshwater bryozoans (Phylactolaemata, the most evolutionarily primitive group in the phylum) to begin erecting a evolutionary frame for anatomical and gene expression comparisons of the morphological genesis of genetically identical but morphologically diverse embryonic, larval, metamorphosing, and asexually budding life history stages.
Research methods and techniques: High-resolution digital images and cinematography of live freshwater bryozoan colonies (Phylactolaemata, the most evolutionarily primitive group in the phylum) will be used in the lab to document larval fission and release from the colony, settlement, metamorphosis, and zooid asexual budding. Specimens representing these different life history stages will be prepared, then analyzed using histological and SEM techniques. If time permits, the intern will assist with the use of a filter-based protocol to isolate total RNA from tissue samples of these different life stages. This is the first step in preparation of a cDNA library from which orthologs of regulatory genes can be recognized, and primers for visualization of gene expression can be constructed.