Climbing around in the Tree of Life Learning Objectives: After this activity, participants will be able to: 1. Use phylogenetic trees to summarize the evolutionary history and organize the diversity of living organisms. 2. Explain how the current branching structure of the tree of life has become much more complex than the traditional kingdoms of older classifications. Introduction: This activity is intended to increase your familiarity with biological diversity, particularly the vast numbers of groups of organisms to which we seldom are exposed, and how that diversity is organized by phylogenetics. For example, the three kingdoms of older classifications — plants, animals, and fungi — together form just a small branch at the tip of one of the major divisions — Eukaryota— used in modern classifications. Even within the familiar groups, most branches are unfamiliar even to biologists. Evolutionary biologists have spent much of the last two centuries working out the relationships among organisms so that we can classify them. In the last few decades that effort explicitly searches for evidence of evolutionary relationship and the branching structure of our Tree has become much more complex as we have estimated those relationships. As you do this activity, I strongly encourage you to explore some of the side branches along the way. A second objective is to provide you with more experience working with phylogenies. Phylogenetic relationship forms the underlying framework for much of evolutionary biology. Here you will work with one way of drawing phylogenies, a cladogram. Cladograms show only the branching order of lineages, that is their “family tree,” without being concerned about the absolute time scale. You will be using the Tree of Life Project (http://tolweb.org). It is an international collaborative project (organized by twins David and Wayne Maddison) with each group of organisms or branch of the Tree being written by an expert on that group. The branches are connected by links that effectively let you climb up and down the Tree one set of branches at a time. This is almost the same as moving forwards and backwards through the history of life. Eventually, every lineage (branch) of life will be represented, including a separate page for every one of the more than 1 million known living and extinct species. At this point in time however, only parts of the Tree have been linked up. On each page is information about the taxon (a taxon is a unit of classification, e.g., Phylum Chordata, Class Mammalia, Order Primates, Genus Homo). Check them out as you explore. Note: each web page will have a small phylogeny that this assignment will call a “tree” (in lower case) which is just a small piece of the “Tree” (of Life, capitalized). Tree of Life image ©2007 Tree of Life Web Project, tolweb.org Procedure: Each person or group should pick up 6 slips of paper. One is a “From” species with the URL for its page in the Tree of Life. The other 5 are “To” species without URLs (you can increase this number to make for a more extensive activity, but less than 5 is really too few to see much of the Tree). The From and To species will belong to different Domains, or basal trunks, in the Tree (Archaea, Eubacteria, Eukaryota). Your assignment is to start at the From species by typing its URL into your web browser (it will be the only paper with a URL). Then follow links down the Tree to the Root (“Life on Earth”) and then go back up a different branch to find the To species. There are millions of possible combinations of species, so each group’s set will be different. 1: Type the “From” URL (http://…..) in the appropriate space of your web browser. 2: Write down on a sheet of paper the name of the species. 3: Use any of the navigation tools to climb down the Tree to the lower branch (e.g., click on “Down” button, the “<<=” sign at the base of the tree shown, or on the “Containing clade(s)” link; these all do the same thing). 4: On a sheet of paper, write down the name of this new clade (that is, taxon, which can be found as the headline at the top of the page. Draw a line connecting this taxon with the previous taxon (which can be thought of as the “daughter” taxon). Also, write down any characteristic features of the taxon (these will be mentioned just below the title, not all taxa will have characteristic features listed). 5: Repeat steps 3 and 4 until you reach the Root of the tree. 6: Click on the links at the tips of the branches on the tree to start moving up the Tree. Some tips will not have links; you do not have to worry about them. It may not be obvious which links to follow, explore as needed. 7: Write down the name of the new taxon and any characteristic features. 8: Draw a line connecting the parent taxon with the new daughter taxon. 9: Repeat steps 7 and 8 until you reach the first To species. 10: Go back down the Tree until you reach the point that the lineage leading to the second To species split from the first. 11: Repeat steps 7 and 8 until you reach the second To species. 12: Repeat for the remaining To species. 13: Redraw your entire tree to make it neat and legible. Poster paper is supplied for this purpose. You should have something that looks like this. You will probably need to redraw your notes so that your tree looks neat. In this case, Spirulina was the From species, lion was the first To species and wolf was the second To species. In many cases you will be faced with many unfamiliar choices for which branch to follow. You can often guess based on similarity of names (tribes, families, and higher levels are often named after a prominent genus, and I have chosen such species; for example, the house mouse Mus is in the tribe Murini, in the subfamily Murinae, in the family Muridae, and the superfamily Muroidea). You can also get hints from the description of the taxa (sometimes it helps to scroll down a page and read some of it), or from your own knowledge. Many links at the tips of trees include a rough list of their contents (e.g., “Hymenoptera (wasps, bees, ants, and sawflies)” one of the insect links). Other times, the To species is just one of a list on the page, and does not have it’s own page. Sometimes though, you just have to explore the other options until you can tell that they are not leading to your species. Exploration is part of the fun of science and is the real objective of this project. You can always search for new or different species to include as either From or To species should you use this in your class.