Stephanie Sang

PhD candidate in Integrative Biology

Development and evolution of paired fins

Stephanie Sang, Michael Coates, and Robert Ho

Paired appendages are fundamental to the gnathostome body plan, and the positioning of these appendages along the anteroposterior body axis is critical for defining the overall form and function of the organism. For my dissertation research, I will be investigating macroevolutionary patterns of paired fins in actinopterygians and using zebrafish Danio rerio as an experimental model to elucidate mechanisms behind paired fin development.

Meristem regulation and development in moss Physcomitrella patens

Stephanie Sang, Jill Harrison

Unlike in animals, plant cells cannot migrate, meaning that plant form is determined by how cellular division planes are initially oriented and how subsequent growth occurs. Because tissues and organs can only arise from meristems, modifications in meristem patterning and regulation are responsible for creating morphological complexity. Since the vast majority of research has focused on meristem maintenance in angiosperms, and earlier-diverging plants have different meristem organization, there is a considerable gap in our present knowledge of meristem function in all land plants. The appearance of the shoot apical meristem (SAM) in land plants allowed them to gain more complex forms than their algal ancestors. By determining how the most ancient land plant meristems were regulated, we can discover how such complexity arose during evolution.

For my MSc thesis, I investigated how meristems in Physcomitrella patens are regulated through staining gene expression reporter lines and beginning to construct amiRNA knockdown lines of candidate genes.

Inferring larval mode in Central American turritellines through a phylogenetic framework

Stephanie Sang, Warren D. Allmon

The closure of the Central American Seaway, which had connected the Atlantic and Pacific oceans, led to differing environmental conditions on both sides of the Central American Isthmus. Closely related marine species with a common ancestor, or geminate species, developed as a result of geographic separation and different selective pressures. This study builds total evidence (molecular and morphological) phylogenies of Central American turritellines and reconstructs larval developmental mode. The molecular phylogeny was calibrated using the final closure of the Isthmus and fossil data. We find that there are two geminate species pairs, and that protoconch size was generally larger in the Atlantic species. Overall, while transitions from planktotrophy to non-planktotrophy were common, reversals seldom occurred.