cladistics Presentation

Cladistics Giovanni Mirarchi Which of these organisms are most likely related? Which two are most closely related? We’ll find out at the end of class…….. How many of you have heard of the word before??????? Let’s start from the beginning………. WHAT IS CLADISTICS????? Macro evolution- the large scale evolutionary changes including the formation of new species and new taxa The original single cell ancestors of all living things have resulted in millions of species that live today, and millions that have gone extinct In the Beginning…… THE TREE OF LIFE….. Taxonomy is the biological science that deals with arranging and naming groups and organisms. When Linnaeus first developed the form of taxonomy we use today, he based his system on morphological similarities and differences. The standard system of classification in which every organism is assigned a kingdom, phylum, class, order, family, genus, and species. This system groups organisms into ever smaller and smaller groups (Jacqueline described this last class) TAXA is a term used to denote any group or rank in the classification of organism TAXONOMY VS CLADISTICS Today, taxonomy is based on known phylogenetic relationships and similarities. PHYLOGENY is the study of evolutionary relatedness among various groups of organisms. We consider that if species evolve from common ancestors, closely related species have more traits in common than more distantly related species SYSTEMATICS is the process of trying to classify animals according to their phylogeny Willi Henning, a German entymologist, is seen as the father of cladistics He suggested that we classify organisms into group called CLADES which consist of an ancestor organism and all its descendants (and nothing else) SO WHAT IS CLADISTICS, AND WHEN DID IT APPEAR?? Cladistics is a way of hypothesizing the relationship among organisms Cladistics relies on the idea that members of a particular group share a COMMON EVOLUTIONARY RELATIONSHIP Members of the same group are more closely related to each other than to other groups. Groups are distinguished by sharing unique characteristics with others However, it is NOT enough for organisms to share characteristics – We run into some problems…. Cladistics Two organisms may share a great many characteristics and not be considered members of the same group. Back to our jellyfish, starfish, and human; Problems…… It is not just the presence of shared characteristics which is important, but the presence of shared derived characteristic Let’s take a look at Shared Derived characteristics Synapomorphies (shared derived characteristics) are derived character states shared by more than one species How can we fix this problem?? Cladograms are used to show evolutionary relationship (phylogeny) of taxa. Cladograms help us infer which groups are more closely related and the general sequence of events that gave rise to each group. They are Phylogenetic trees showing the order in which different lineages diverged from a common ancestor Cladograms can be made for any group of organisms CLADOGRAM Cladogram Shared Derived characteristic Original Ancestor Node Taxa Cladograms share many similarities with family trees. In family trees we trace back to our ancestors, and we can track our characteristics passed on from generation to generation Cladograms and Family Trees Like family trees, species have ancestors too. Ancestors may have died off, but they left their descendants behind. Unfortunately with cladograms sometimes there is no trace left of the ancestors. All we have is evidence of the offspring. Also in cladograms, an ancestor gives rise to only two species instead of multiple ones. This is called a splitting event, and the ancestors is assumed to have died after it has occurred Cladograms and Family Trees There are 3 assumptions that Cladists make 1. Any group of organisms are related by descent from a common ancestor. 2. There is a bifurcating, or branching, pattern of lineage-splitting. 3. Change in characteristics occurs in lineages over time. It is only when characteristics change that we are able to recognize different lineages or groups. Three Assumptions How do you classify change? We call the original state of the characteristic “primitive” or pleisomorphic. We call a change of characteristic “derived” or apomorphy Synapomorphy is when groups of species share a derived trait We display our results in a CLADOGRAM Change in characteristics occurs in lineages over time. Synapomorphy Older derived trait More recent derived trait 1. Choose your taxa Clades are a group of taxa that consist of ONLY an ancestor and ALL of its descendant taxa For example, one clade is Vertebrates Steps to creating a Cladogram 2. Determine the characters and examine each taxon to determine character states There a any number of characters you can choose from. For example, Hair, digits, bipedal etc. 3. Determine the order of evolution of each character Steps to creating a cladogram 4. Group taxas by synapomorphies – shared derived characteristics 5. Work out any conflicts that arise- Parsimony Parsimony is a principle that says that you should use the simplest explanation when constructing your tree. This means that we should create our tree using the least possible steps. 6. Build your tree Steps to creating a cladogram The most important feature when making a cladogram is making connections based on synapomorphies This can be very challenging because some synapomorphies can be lost, while other may turn out to be false. Examples Mammals- all mammals have evolved from species with hair, but whales have lost their hair. So the presence of hair is a good synapomorphy for distinguishing most but not all mammals from other vertebrates Bipedalism- humans and birds both walk on two legs, but this trait evolved independently, in both our ancestors and the birds. We must consider bipedalism two separate traits HOW TO MAKE AND INTERPRET CLADOGRAMS We include an outgroup, a taxon we know (or hypothesize) diverged from the common ancestor before the other taxa. Derived characters must be absent from the outgroup How do we resolve this problem? Scientists are able to apply cladistics to related organisms and determine their phylogenetic relationship based on SYNAPOMORPHIES They use very advanced software programs and large data sets from many sources that include a lot of genetic information. It is very important in understanding the evolution of new strains of disease- causing viruses and microorganisms. For example, cladistic analysis has shown that HIV evolved from SIV and has gone from chimpanzees and monkeys to humans on FIVE separate occasions HOW CLADISTICS IS USED IN Science We will use morphological evidence to construct a cladogram and describe the phylogeny of the organisms Example {5C22544A-7EE6-4342-B048-85BDC9FD1C3A}Animal Characteristics Digits Skin surface Forelimbs Tail Lemur Five digits Hair Grasping hands Present Deer Two digits Hair Non grasping Present Cow Two digits Hair Non grasping Present Chimpanzee Five digits Hair Grasping hands Absent Human Five digits Hair Grasping hands Absent Lizard* Five digits Scales Non grasping Present Morphological data *Lizard is our outgroup Step 1- We chose our taxa Step 2 Consider each characteristic and judge which trait is the more recently derived trait. This can usually be done by comparing the traits with the outgroup (LIZARD). This initial condition is called the PRIMITIVE CONDITION, and the recently evolved trait is the synapomorphy {5C22544A-7EE6-4342-B048-85BDC9FD1C3A}Animal Characteristics Digits Skin surface Forelimbs Tail Lemur Five digits Hair Grasping hands Present Deer Two digits Hair Non grasping Present Cow Two digits Hair Non grasping Present Chimpanzee Five digits Hair Grasping hands Absent Human Five digits Hair Grasping hands Absent Lizard Five digits Scales Non grasping Present Create a table of synapomorphies Organisms with the derived trait get a +, organisms without the trait get a – Ie. Two digits on each foot is a derived trait (having five digits is the primitive condition) Having hair is a derived trait (having scales like reptiles is primitive condition) Having grasping hands is a derived trait (have four non grasping feet is the primitive condition) The lack of a tail is a derived trait (have a tail is primitive) MAKING A CLADOGRAM {5C22544A-7EE6-4342-B048-85BDC9FD1C3A}Animal Digits Lemur Five digits Deer Two digits Cow Two digits Chimpanzee Five digits Human Five digits Lizard Five digits {5C22544A-7EE6-4342-B048-85BDC9FD1C3A}Synapomorphy- shared derived trait Animal Two digits Lemur - Deer + Cow + Chimpanzee - Human - Lizard - {5C22544A-7EE6-4342-B048-85BDC9FD1C3A}Animal Characteristics Digits Skin surface Forelimbs Tail Lemur Five digits Hair Grasping hands Present Deer Two digits Hair Non grasping Present Cow Two digits Hair Non grasping Present Chimpanzee Five digits Hair Grasping hands Absent Human Five digits Hair Grasping hands Absent Lizard Five digits Scales Non grasping Present H H H H H H H H H H H H h Step 3 Create a table of synapomorphies (shared derived traits) Animals Synapomorphies – Shared Derived Trait Two Digits Hair Hands No tail Lemur Deer Cow Chimpanzee Human Lizard Step 4 Draw a “V” with the outgroup at the upper left. The base of the V represents the common ancestor to all animals Step 5 All the animals except the lizard share the feature of having hair. We can indicate the evolution of hair on the right branch leading away from the lizard HAIR Lizard Step 6 The remaining animals fall into two groups- those with two digits those with grasping hands. H H H H H H H H H H H H h H H H H H H H H H H H H h Animals Synapomorphies – Shared Derived Trait Two Digits Hair Hands No tail Lemur Deer Cow Chimpanzee Human Lizard HAIR Lizard Deer Cow Two Digits Hands We therefore split the right branch into two and locate the evolution of these traits above the split. We can divide the deer/cow branch in two and place the names of the animals at the end of each branch Notice that when you split a branch, the choice of left or right branch for positioning the groups is arbitrary Step 7 The chimpanzee and human both lack a tail so we create a new branch and locate this derived trait above the split HAIR Lemur Deer Cow Two Digits Hands Human Chimpanzee No tail Lizard Based on the complete phylogeny, we can infer that the cow and the deer are more closely related to each than to other groups. Similarly, humans and chimpanzees are more closely related to each other than to other groups. We can also conclude that lemurs are more closely related to chimps and humans than to cows and deer Conclusions If we add an outgroup, we can see the evolutionary relationships. Let’s add a sponge How are humans and starfish more closely related then jellyfish? Sponges, jellyfish, and starfish all live in water and do not have backbones, therefore these are NOT derived characters. Backbones and living on land are unique to humans. We CAN’T use either of these characteristics in this cladogram All three have cells with flagella- so our common ancestor had cells with flagella Sponges have only one tissue layer. The other taxa all have multiple tissue layers. Sponges and jellyfish lack enclosed body cavities. (ancestral) Starfish and humans have enclosed body cavities. (derived) So our cladogram looks like this… What we can use Sponges Multiple tissue layers Humans Starfish Jellyfish Enclosed Body cavity Lamprey Jaw Lungs Bones Feathers Pike Lungfish Turtle Robin Together with your group you will create 2 separate cladograms; 1. With coins Activity Using the coins provided, create a table of synapomorphies (shared derived characteristics ) and using it create a cladograms which would theoretically map the “evolution” of the coin Using the pictures of our new species of insects, create a table of synapomorphies and use it to create a cladogram. Feel free to name your species of insects as you move along ? Next Activity Clark, N. (2005). Constructing a Cladogram. Retrieved from www.nclark.net/ConstructingACladogram.doc University of California Museum of Paleontology (2011). Understanding Evolution. Retrieved from . University of California Museum of Paleontology (1996). Implications of Cladistics. Retrieved from http://www.ucmp.berkeley.edu/clad/clad3.html Martin A. (Nd) Cladistics: Identifying branching points in evolution. Retrieved from http://www.elasmo-research.org/education/classification/cladistics.htm www.cabrillo.edu/~ncrane/bio1c/botPDFs/classification.pd Biology 11 (2011). Cladistics and phylogeny( pg 350-351).Nelson Education Canada. Resources Amoeba Sponge Earthworm Salmon Lizard Kangaroo Cat Multicellular Segmented Jaw Limbs Hair Placenta