IB Biology 5 5 Cladistics All syllabus statements

IB Biology 5. 5 Cladistics All syllabus statements ©IBO 2007 All images CC or public domain or link to original material. http: //en. wikipedia. org/wiki/File: Tree_of_life_SVG. svg

The value of classifying organisms 1. Identification of Organisms Unknown organisms are easily identified if data about organisms is organised. Classification allows for the creation of keys.

2. Evolutionary Links Classification allows us to see evolutionary relationships. Organisms that are grouped together share a lot of similar features (homologous structures). These shared characteristics help us see how organisms have evolved from a common ancestor. e. g. Llamas were originally compared to sheep but a study of their morphology later placed them in the camel family http: //www. flickr. com/photos/mrapplegate/2423991076/ http: //www. flickr. com/photos/doug 88888/3458057235/

3. Prediction of Characteristics that are shared by organisms within a group would be expected to be found in other species that are closely related. e. g. no doubt more fossils that can be categorised in the Homo genus will be found. We can expect them to have relatively big brains (crazy “Hobbit” finds excepted!) http: //commons. wikimedia. org/wiki/File: Hominins_2002. png

The universality of DNA and protein structures provides evidence for the common ancestry of living organisms 1) All known organisms use DNA as genetic material The genetic code is universal. Gene sequences inserted in different organisms express the same proteins http: //commons. wikimedia. org/wiki/File: Bdna. gif

2) The same 20 amino acids are used to make all proteins http: //commons. wikimedia. org/wiki/File: Protein_primary_structure. svg

variations in specific molecules can indicate phylogeny Example: protein cytochrome c. It is not identical in all species due to mutations. • humans and chimpanzees have the identical cytochrome c molecules • rhesus monkeys share all but one of the amino acids • This suggests that humans and chimpanzees are more closely related to each other than to rhesus monkeys I didn’t want to be closely related to stinking humans anyway! http: //www. flickr. com/photos/stuffinhergoose/571672799

This is part of a molecular phylogeny of all of the living primates. It clearly shows chimpanzees (Pan) as being more closely related to humans than to gorillas. It was made by comparing 34, 927 base pairs sequenced from 54 genes taken from each of a single species in each genus.

biochemical variations can be used as an evolutionary clock An evolutionary clock involves calculating the time since species diverged by comparing the number of differences in their DNA and/or protein sequences. http: //commons. wikimedia. org/wiki/File: Nature_Clock. gif

The assumption is that these changes occur at a regular rate. (which may not always be the case) Therefore if species A had 5 differences from species B and 10 differences from species C, then the lineages for A and C must have split twice as long ago as for A and B C B A Time

Cladistics Clade- a group of organisms evolved from a common ancestor, including all species alive today, common ancestral species, and now extinct species that evolved from the common ancestor. http: //www. flickr. com/photos/aussiegall/4149475009/

For example, birds, dinosaurs, crocodiles, and all descendants (living or extinct) of their most recent common ancestor form a clade Wikipedia http: //www. flickr. com/photos/kev http: //www. flickr. com/photos/mo http: //www. flickr. com/photos/tam om/photos/emraya/2929959881/

3 Characteristics change over time, thus the amount of change can help determine relationships Groups of organisms are descended from a common ancestor Assumptions There is a branching pattern in the evolution of species and when a split occurs, two distinct species eventuate.

Shelled eggs Hair Each clade is determined by common characteristics of its members that are different from that of the other species from which it has diverged Amniotic Egg Four Limbs Bony Skeleton Vertebrate http: //bridgeurl. com/xrmmmk/all

These traits which tie the clades together are called shared derived characters http: //www. flickr. com/photos/29448992@N 08/2970804257/

analogous and homologous characteristics Homologous structures are inherited from a common ancestor http: //www. flickr. com/photos/opoterser/4189239614/

e. g. The fly on the previous page and the mosquito on this page have mouthparts adapted to their food sources but the basic components were inherited from a common ancestor Other examples include pentadactyl limbs and finches’ beaks http: //www. flickr. com/photos/kclama/102002644/

Analogous structures have similar form and function due to convergent evolution, they do not stem from a common ancestor Bats… http: //www. flickr. com/photos/tjt 195/105694980/

…birds… http: //www. flickr. com/photos/patrickwilken/112947862/

…and bugs all have wings for flight that evolved independently Other examples include: -Streamlined shape for dolphins , sharks and ichthyosaurs -Long snout and tongue for capturing ants on the anteater and echidna http: //www. flickr. com/photos/hhoyer/3758550410/sizes/o/in/photostream/

Outline the methods used to construct cladograms and the conclusions that can be drawn from them AND Construct a simple cladogram • These two cladograms are identical (although they don’t look it) • The shape and the order of the terminal nodes does not matter. • The only information to be gathered from the cladograms below is the order of nesting of sister clades and the relative relatedness of species http: //commons. wikimedia. org/wiki/File: Identical_cladograms. svg

Sister clades: have a common ancestor Terminal nodes Human Chimp Gorilla Nodes: Common ancestors Root Chimp Human Out group: Defines the ancestral characters Gorilla

Branches on a cladogram can be scaled or unscaled. If the branches are scaled, the length of the branch often indicates how much evolutionary change has occurred in a species since it split from it’s sister clade at the last node http: //www. ncbi. nlm. nih. gov/About/primer/phylo. html

Rooted cladograms show evolutionary relationships. Unrooted trees just show the relationships between clades http: //www. ncbi. nlm. nih. gov/About/primer/phylo. html

Cladograms are made by compiling data on homologous characteristics shared by species. These characteristics can be structural, physiological and/or biochemical. With increasing taxa comes increasing complexity. Number of taxa 23 4 5 6 7 8 9 10 N Possible number of rooted 1 3 15 105 945 10, 395 135, 135 2, 027, 025 34, 459, 425 1*3*5*7*. . . *(2 N-3) cladograms So software is often used to find the best possible tree that has the fewest evolutionary steps.

This cladogram for bacteria is computer generated

1) Compile a table of the characters being compared Characters Shark Frog Kangaroo Human Vertebrae X X X X X Two pairs of limbs Mammary glands Placenta X Modified from: http: //www. bu. edu/gk 12/eric/cladogram. pdf

2) Use the data to construct a Venn diagram, Start with the characteristic shared by all taxa in the biggest circle and work inwards Vertebrae: Shark Two Pairs of Limbs: Frog Mammary Glands: Kangaroo Placenta: Human

3) Convert the Venn diagram into a cladogram Shark Frog Kangaroo Human Placenta Mammary Glands Lungs Vertebrae

Now you try! Make a Venn diagram for this data. Characters Sponge Jellyfish Flatworm Earthworm Snail Fruit fly Starfish Human Cells with flagella X X X X X X Mesoderm X X X Head develops first X X X Symmetry Bilateral symmetry Anus develops first Segmented body Calcified shell Chitinous Exoskeleton Water Vascular system Vertebrae X X X

It should look something like this: Cells with flagella: Sponge Symmetry: Jellyfish Bilateral symmetry: Flatworm Mesoderm Head develops first Segmented Body: Earthworm Chitinous exoskeleton: Fruit fly Calcified Shell: Snail Anus develops first Water Vascular system: Starfish Vertebrae: Human now make the cladogram

It should look something like this: Sponge Flat. Jellyfish worm Snail Earthworm Fruit fly Starfish Calcified shell Chitinous shell Water vascular system Human Vertebrae Segmented body Head develops first Some of the characteristics in the data table were unnecessary for the construction of this cladogram. Can you identify them? Anus develops first Mesoderm Bilateral symmetry Symmetry Flagella

Sponge Flat. Jellyfish worm Snail Unnecessary to use two characteristics to differentiate between Starfish and Human. Either would do the trick Earthworm Fruit fly Starfish Calcified shell Chitinous shell Water vascular system Human Vertebrae Segmented body Head develops first Unnecessary to differentiate Snail is the only species with head develops first and without segmented body Anus develops first Unnecessary to use two characteristics Bilateral symmetry to split lineages Mesoderm Symmetry Flagella

D. 5. 9 Analyse cladograms in terms of phylogenetic relationships A B C 1 D Of the three nodes, 3 is most recent and 1 3 occurred earliest. Node 3 is the most recent 2 common ancestor for C and D Node 2 is the most recent common ancestor for B and C Node 3 is the common ancestor of all taxa And so on…

D. 5. 10 Discuss the relationship between cladograms and the classification of living organisms Mammals have the unique homologous characteristic of producing milk They form a clade http: //www. flickr. com/photos/chavals/3720930469/

Likewise, birds share the common characteristic of feathers They too form a clade http: //www. flickr. com/photos/bestrated 1/47581481/

Lizard Tortoise Reptiles, as a group, consist of the crocodilians, lizards and snakes, tortoises and turtles and tuatara. However, they are not a clade. One of them is actually more closely related to birds. Crocodile Tuatara Care to guess which one? http: //www. flickr. com/photos/audreyjm 529/155024495/ http: //www. flickr. com/photos/mg-muscapix/3288435589/ http: //www. flickr. com/photos/8363028@N 08/2665814123 / http: //www. flickr. com/photos/sidm/5253662054/

rd s a (L iza (T ur tle s a nd to nd sn ak rto es ise ) s) Crocodiles are more closely related to birds than to lizards! Monophyletic: A recent common ancestor and all it’s descendants Paraphyletic: Does not include all descendants from a common ancestor Polypheletic: A group of organisms that does not include the most recent common ancestor What this doesn’t show is that birds are the last descendants of the dinosaurs! http: //en. wikipedia. org/wiki/File: Phylogenetic-Groups. svg