Bio94 Discussion Activity week 3: Chapter 27 Phylogenies and the History of Life 1. Constructing a phylogenetic tree using a cladistic approach Construct a phylogenetic tree using the following table: Outgroup: Species A: Species B: Species C: Species D: Species E: Trait Lobe-finned fish Frog Kangaroo Mouse Turtle Human Dorsal Nerve Cord Yes Yes Yes Yes Yes Yes Legs No Yes Yes Yes Yes Yes Nature of egg Hard shell prevents drying Nature of development In egg In egg Marsupial Placental In egg Placental Hair No No Yes Yes No Reduced Presence of pouch* Bidpedal posture No No Yes No No No No No Yes No No Yes * A pouch is a saclike structure, such as the external abdominal pocket in which marsupials carry their young. Phylogenetic tree: Outgroup A (frog) D (turtle) B (kangaroo) C (mouse) E (human)
Indicate in the tree one branch, one node and one tip. What do they represent? Node (most recent common ancestor) Branch (population) Tip (group of living organisms) Place an X anywhere there is a synapomorphy. Trait Outgroup: Species A: Species B: Species C: Species D: Species E: Lobe-finned fish Frog Kangaroo Mouse Turtle Human Dorsal Nerve Cord Yes Yes Yes Yes Yes Yes Legs No Yes Yes Yes Yes Yes Nature of egg Hard shell prevents drying Nature of development In egg In egg Marsupial Placental In egg Placental Hair No No Yes Yes No Reduced Presence of pouch* Bidpedal posture No No Yes No No No No No Yes No No Yes Outgroup A (frog) Dorsal nerve cord Legs D (turtle) B (kangaroo) Hair Placenta C (mouse) E (human)
Circle a monophyletic group. What is/are the shared derived character(s) present in your monophyletic group. There are 5 possible monophyletic groups. Outgroup A (frog) D (turtle) B (kangaroo) C (mouse) E (human) Match the following organisms with the species A to E: turtle, mouse, human, frog and kangaroo. Do you need help? A trait (character) can have different states. For example, for the trait hair, the possible states may be present (yes) and absent (no). To construct a phylogenetic tree, first determine which traits are ancestral and which are derived. This is usually done by comparison with a more distantly related organism termed the outgroup. It is hypothesized that traits shared with the outgroup are likely to be ancients ; traits that differ from the outgroup are likely to be derived. Second, group taxa by shared derived character states (synapomorphies). 2. Adaptive radiation Case 1: Find the correct chorological order of the following events. C. A population arrives to an island. B. The original colonizing group encountered new and novel types of resources. E. With few competitors, the descendants of the colonizing group are able to grow in a wide range of habitats. A. Over time, some organisms become specialized to grow in certain habitats and diverge. D. There is a rapid speciation triggered by ecological opportunity.
Case 2: B. A lineage evolves a key morphological trait. A. With this new morphological trait the descendants can exploit new sources of food. D. The fitnesses of the derived organisms increase in their corresponding environment. C. There is a rapid speciation triggered by morphological innovation.
3. Life s time line Eons Eras Periods Important dates Phanerozoic Eon Proterozoic Eon Cenozoic Era Mesozoic Era Paleozoic Era Neogene Paleogene Cretaceous Jurassic Triassic Permian Carboniferous Devonian Silurian Ordovician Cambrian Major events - Angiosperms/mammals - Extinction that killed 60 to 80% of species. END-CRETACEOUS EXTINCTION - Gymnosperms/dinosaurs - Extinction that killed over 90% of species. END-PERMIAN EXTINCTION - Appearance and diversification of animals, land plants and appearance of land organisms. - Appearance of every major group of animals (adaptive radiation). CAMBRIAN EXPLOSION Oxygen levels gradually increase. Geological events - Pangea breaks apart - Supercontinent Laurentia to the north and Gondwana to the south Precambria n Archaean Eon Hadean Eon 3.5 billion years ago Origin of life. First oceans. 4.6 billion years ago Earth started to form.
Arrange the following information in the table: Appearance and diversification of animals, land plants and appearance of land organisms. 3.5 billion years ago. Extinction that killed 60 to 80% percent of existing species and was caused by an asteroid impact (extinction of the dinosaurs). Supercontinent Pangea breaks apart. Origin of life. 4.6 billon years ago. Oxygen levels gradually increase. Angiosperms were the most important plants and mammals were the most important vertebrates. Earth started to form. Extinction that killed over 90% of existing species. Supercontinent of Laurentia to the north and Gondwana to the south. First oceans. Gymnosperms were the most important plants and dinosaurs were the most important vertebrates. Appearance of every major group of animals (adaptive radiation).