Improving Tree-Thinking One Learnable Skill at a Time

Kristy Lynn Halverson 0 5018, Hattiesburg, MS 39402, USA 1 ) Department of Biological Sciences, University of Southern Mississippi, 118 College Dr Representations are a critical way to communicate scientific knowledge. Systematists biologists are acknowledged as expert tree thinkers who can both read and build phylogenetic trees (e.g., cladograms) accurately. The purpose of this study was to identify the core skills essential to help college students overcome tree-thinking challenges. In this study, I used pre/posttests, interviews, weekly reflective journal entries, field notes from course observations, and student responses to coursework to learn how upper-level college biology students developed representational competence with phylogenetic trees. I identified essential core skills by investigating students' tree-thinking progression over the course of the semester. Three major patterns emerged from the data: (1) students became better tree readers than tree builders by the end of the plant systematics course; (2) core skills are essential for students to develop tree-thinking competence; and (3) tree reading skills developed before tree building skills. By diagnosing challenges students face with tree-thinking, identifying core skills necessary to overcome these challenges, and developing a starting point for a context-based framework for representational competence, this study adds to our understanding of critical elements necessary for designing effective instructional interventions and improving student learning with phylogenetic trees. - representations to express their understandings of the evolutionary relationships they are investigating (Matuk 2007). In systematic biology, biological information is organized using phylogenetics and evolutionary trees serve not only as tools for biological researchers across disciplines but also as the main framework within which evidence for evolution is evaluated (Baum et al. 2005). Evolutionary biologists interpret phylogenetic trees in accordance with how they illustrate evolutionary histories or inferred evolutionary relationships among a set of taxa (Baum and Offner 2008). Scientists compare phylogenetic representations in search of similar patterns to provide support for hypothesized relationships among taxa. They find similarities by comparing monophyletic groups, or clades, across representations. Being able to correctly interpret and compare phylogenetic trees is a critical component to developing tree-thinking. A second component of tree-thinking involves generating phylogenetic trees by isolating and interpreting informative data into evidence of evolutionary relationships. There are many different styles of representations an expert could generate if asked to draw a visual representation illustrating the relationships among taxa (e.g., Matuk 2007). In addition, scientifically accurate phylogenetic representations share the following features: relationships are grouped based on evolutionary histories and common ancestry, all organisms are related and are connected within a single representation, taxa are placed at the terminal tips assuming hypothetical ancestors at nodes, and consensus nodes are used when relationships are uncertain. People must share this common understanding of how to accurately interpret the representation in order to effectively communicate. Theoretical Framework Representations provide a different way of presenting information than verbal lectures and are critical for communicating abstract science concepts (Gilbert 2005; Mathewson 1999; Patrick et al. 2005). Comprehension of verbal descriptions is aided by both accompanying visualizations and when learners generate visualizations from a series of descriptive statements. These types of visualizations help develop a deeper understanding of the relationships among phenomena. The primary importance of using such visual tools to facilitate learning is that the visualization itself, animated or still, should explain, not merely show, content. For example, in science, graphic representations such as phylogenetic trees are used to display data, organize complex information, and promote a shared understanding of scientific phenomena (Kozma and Russell 2005; Roth et al. 1999). Students must learn how to use representations to construct meaning through interpretations of underlying ideas rather than rely primarily on the surface features of representation to derive meaning (Chi et al. 1981). Kozma and Russell (2005), in the context of chemical representations, proposed a set of core skills that must be developed in order to develop competence in the use of visual representations. These skills include an individual being able to use, generate, describe, and compare appropriate representations when communicating with a particular discipline. Once these skills are developed, a learner should be able to effectively use a variety of representations, thereby achieving representational competence. When a learner achieves representational competence, he/she can begin shifting the external representation into an internal representation, or a mental image that can be manipulated (e.g., scanned and rotated) to improve performance on visual tasks, memory tasks, and cognitive problem solving (Botzer and Reiner 2005; Clement et al. 2005; Gilbert 2005). Although Kozma and Russell (2005) proposed the core skills for chemistry education, these skills have not been empirically tested in or beyond chemistry. A major aspect of learning to read and to construct representations involves determining which features are and are not pertinent (Van Fraassen 2008). Unfortunately, phylogenetic trees are not well understood by students (Baum et al. 2005; Gregory 2008; Halverson 2010a; Meir et al. 2007; Omland et al. 2008; Sandvik 2008; Thanukos 2009). For example, students often misinterpret phylogenetic trees because they focus on superficial features. This focus leads many students to misinterpret phylogenetic trees by reading across the tips and assuming more intervening nodes equals more distantly related, basing evolutionary relationships on the physical proximity of species to one another in the representation (see Baum et al. 2005; Gregory 2008; Meir et al. 2007; Perry et al. 2008). These errors prevent students from tracing implied taxa lineages that can be mapped from the tip to the root of the tree (Halverson 2009, 2010b). But not all superficial tree reading errors are based on proximity. Students do not always recognize that altering the orientation of a tree or format of the branches (e.g., straight, bent, or circular) does not alter the relationships represented (Catley et al. 2009; Halverson et al. 2011; Novick and Catley 2008). Furthermore, branches on a phylogenetic tree can swivel around nodes and still represent the same branching pattern, thus the same relationships among taxa. Tree-thinking is not restricted to interpreting and building single represe (...truncated)