Building trees

1. Building trees

2. The Great Clade Race • Long, long ago, in a place far, far away, eight runners (A–H) met in the woods for a foot race. All the runners began the race at a single starting point, but, at various points, the course forked. Each series of forks led to a separate finish line at the other end of the woods. At each fork, runners chose which path to take. • To keep track of the race, each runner carried a card that was stamped at check-in stations distributed at various points along the paths. Each runner had his or her card stamped at each check-in station they passed. • Use these cards to try and reconstruct the course of each runner and the placement of check-in stations.

3. The Great Clade Race 1. All runners completed the race, i.e., nobody stopped midday along a path. 2. When the paths split, they forked into two new paths, not three or more. 3. Once paths diverged, they never reunited. 4. Check-in stations were located between forks in the paths.

4. Bony Ray Amniotic Skeleton fins Egg Lactation Perch 1 1 0 0 Guppy 1 1 0 0 Shark 0 0 0 0 Cat 1 0 1 1 Dog 1 0 1 1 Lizard 1 0 1 0

5. Terms for cladistic tree building • Character • Character state • Ancestral character state (Plesiomorphic) • Symplesiomorphy • Derived character state (Apomorphic) • Synapomorphy • Autapomorphy

6. Synapomorphies are marked Examples of symplesiomorphies?

7. How can we determine synapomorphy vs. symplesiomorphy?

8. Outgroups • Outgroups are the most common method for rooting trees • Outgroup criteria 1. “Outside” the group of study • Closely related enough to be informative