Stephanie Sang

PhD Student in Integrative Biology

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.

Towards predicting accurate morphological character sets in turritellines

Stephanie Sang, Sean C. Bell, Warren D. Allmon

Despite the ubiquity of molecular data, morphological characters remain the only source of phylogenetic information for fossils. However, we require methods of validating and understanding the accuracy of the information. In cases where molecular and morphological phylogenies conflict, the morphological characters may not be a reliable signal. Using turritellines, a group of morphologically-similar marine snails, we generate a computational method that predicts which morphological characters to use for analysis. Our method heuristically searches different combinations of morphological characters. It then finds the character set that produces the morphological tree most similar to the molecular tree.

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.