Abstract Detail

Teaching

Huang, Sophia [1], Whittall, Justen Bryant [2].

Santa Clara University’s Tree of Trees: Using campus tree diversity to integrate molecular, organismal and evolutionary biology.

The Tree of Life provides a fundamental roadmap to understanding biodiversity, yet requires a unique perspective known as “tree thinking”. Tree thinking can be challenging for undergraduates at the introductory biology level because of the unique structure of phylogenetic trees and vast amounts of comparative data stored therein. In order to increase students’ tree thinking skills, we developed a 65-minute discussion activity for freshman biology majors that integrates molecular, organismal, and evolutionary biology utilizing campus tree diversity. Campus trees represent numerous branches of the plant Tree of Life, exhibit fascinating adaptive traits, and are native to a diversity of regions on Earth. We identified 67 trees in a particularly diverse region of Santa Clara University’s campus and developed a custom dichotomous key to assist with their identification. There were 54 angiosperms, 12 gymnosperms and one fern. Each tree was scored for several morphological traits including reproductive mode and fruit type. We then downloaded and aligned 18S ribosomal DNA sequences for these taxa or their closest relatives from Genbank. For 45% of the taxa (30/67), we found sequences for the exact same species. For another 39% of the taxa (26/67), we used the closest representative from the same genus. For the remaining taxa (11/67), we used sequences from the closest representative from the same family. The master SCU Tree of Trees was built with RAxML and is largely congruent with our current perspective on angiosperm relationships. We mapped the evolution of reproductive mode (flowers or cones) and fruit type (dry or fleshy) using parsimony to illustrate homology and homoplasy, respectively. In preparation for the discussion activity, each student identified two trees using the dichotomous key and brought in samples or images of their trees. In discussion, pairs of students used the morphological similarities among their four trees to generate a phylogenetic hypothesis (with tree ferns as an outgroup). Then, we provided students with an alignment of the first 21 variable sites of the 18S rDNA for their four taxa plus tree fern to build a molecular phylogeny by hand using maximum parsimony. After building their molecular tree, they compared their topologies with the master SCU Tree of Trees to identify instances of molecular and morphology homology and homoplasy. After our first roll-out of this activity (February 2016), student narrative evaluations scored this discussion higher than most other activities in its ability to contribute to their understanding of evolutionary and tree thinking.

1 - Santa Clara University, Biology, 500 El Camino Real, Santa Clara, CA, 95053, United States
2 - Santa Clara University, Department Of Biology, 500 El Camino Real, Santa Clara, CA, 95053, USA

Keywords:
Trees
phylogeny
pedagogy
tree thinking.

Presentation Type: Poster
Session: P, Teaching Section Poster Session
Location: Exhibit Hall/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
Time: 5:30 PM This poster will be presented at 6:15 pm. The Poster Session runs from 5:30 pm to 7:00 pm. Posters with odd poster numbers are presented at 5:30 pm, and posters with even poster numbers are presented at 6:15 pm.
Number: PTE008
Abstract ID:556
Candidate for Awards:None