Coevolution or not? Crossbills, squirrels and pinecones

Abstract

This case reinforces the concept of coevolution as a reciprocal change in genetic structure between or among two or more populations, by having students analyze and interpret data, build a descriptive model of the system, and use data to make scientific arguments. The case study is designed for a single 50-minute class period after students have completed a brief pre-class reading assignment introducing coevolution. Students analyze evidence for interactions among red squirrels (Tamiasciurus hudsonicus), red crossbills (Loxia curvirostra), and lodgepole pines (Pinus contorta v. latifolia). The case describing the interactions among these species invites students to answer three questions: 1) What evidence is required for demonstrating coevolution? 2) What specific evidence supports the conclusion that that red squirrels, red crossbills, and lodgepole pines are coevolving (or not) in this system? 3) Why does the evidence support coevolution (or not)? In this discussion-and jigsaw-based case study, students advance both their core conceptual knowledge and their proficiency with scientific practices. Learning Goal(s) • Students will understand that species interact on evolutionary time scales. • Students will know that other organisms can be powerful agents of selection.