Abstract
Phylogenies are a ubiquitous visual representation of core concepts in evolutionary biology and it is important that students develop an ability to read and correctly interpret these diagrams. However, as with any representation of complex disciplinary information, learning to correctly interpret phylogenies can be challenging, requiring that a diversity of educational strategies be deployed. Representational competence is the ability to develop and effectively use abstract representations. Accurately interpreting a phylogenetic tree as a presentation of evolutionary relationships requires that students develop general representational competence as well as knowledge of specific technical aspects of tree interpretation, such as knowing the graphical components of trees and what they represent. Here, we report on the development of a basic diagnostic tool of students' representational competence and technical skills with phylogenies, the Basic Evolutionary Tree-Thinking Skills Instrument (BETTSI). This short, multiple-choice instrument was designed to provide instructors with a quick diagnostic of students' ability to read and interpret phylogenies. It has been checked for reliability and validity and provides a convenient formative and summative assessment of students' understanding of evolutionary trees.