Transcript
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