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Department of Geological Sciences | Indiana University Geol G-308 Paleontology and Geology of Indiana Bryozoa Evolutionary relationships 1 Porifera Phylogeny Brachiopoda (c) 2012, P. David Polly 1 0 0 0 P. David Polly Department of Geological Sciences Indiana University Bloomington, Indiana 47405 USA [email protected] 1 1 Department of Geological Sciences | Indiana University (c) 2012, P. David Polly Geol G-308 Paleontology and Geology of Indiana Objectives 1. Basic principles of phylogenetic trees 2. Terminology of phylogenetic trees and characters 3. Evidence for phylogeny 4. Evolution, descent with modification, and natural selection 5. Phylogeny reconstruction, traits, and parsimony 6. Metazoan phylogeny 7. Field gear Department of Geological Sciences | Indiana University (c) 2012, P. David Polly Geol G-308 Paleontology and Geology of Indiana Metazoan Phylogeny Valentine, JW, D Jablonski, DH Erwin, 1999. Fossils, molecules and embryos: new perspectives on the Cambrian explosion. Development, 126: 851-859. Department of Geological Sciences | Indiana University Geol G-308 Paleontology and Geology of Indiana (c) 2012, P. David Polly Phylogenetic trees show closeness of evolutionary relationship Evolutionary relationship is shown by branching patterns of the tree Taxa that share a common node (connection) share a common ancestor A B C D E Relationships can be drawn as tree or written as nested sets Examples: A and B are more closely related to each other than either is to C, D, or E C, D, and E are more closely related than any of the three are to A and B ((A,B), (C, (D,E))) A and B share a more recent common ancestor with each other than either does to C, D or E after Page and Holmes, 1998, Molecular Evolution: a Phylogenetic Perspective. Department of Geological Sciences | Indiana University Geol G-308 Paleontology and Geology of Indiana (c) 2012, P. David Polly Phylogenetic tree terminology Terminal node (leaf, tip) Internal node (hypothetical ancestor) Root Branch (edge) after Page and Holmes, 1998, Molecular Evolution: a Phylogenetic Perspective. Department of Geological Sciences | Indiana University Geol G-308 Paleontology and Geology of Indiana (c) 2012, P. David Polly Trees are like mobiles Only the branching order matters, not the graphical arrangement of the tree A B C D D = C B A B C D A = after Page and Holmes, 1998, Molecular Evolution: a Phylogenetic Perspective. Department of Geological Sciences | Indiana University (c) 2012, P. David Polly Geol G-308 Paleontology and Geology of Indiana Evidence for phylogeny Phylogeny, like all scientific knowledge, is based on inference supported by evidence. To be scientific a phylogenetic hypothesis must be testable. Evidence for phylogenetic relationships comes primarily from characteristics that are shared between taxa. Taxa can share characteristics because they share a common ancestor, from which they inherited the shared traits, or by convergent evolution in which they acquired the traits independently. Traits shared by common ancestry are the evidence for phylogenetic relationship. Testing is done by considering new sets of traits. Department of Geological Sciences | Indiana University Geol G-308 Paleontology and Geology of Indiana (c) 2012, P. David Polly Bryozoa Brachiopoda Porifera 1 1 0 1 Porifera Porifera 0 Brachiopoda Brachiopoda 1 1 Bryozoa Bryozoa Homology or synapomorphy 1 0 1 0 1 0 0 = no lophophore 1 = presence of lophophore Homology is a characteristic shared by two or more taxa that they inherited from a common ancestor. In phylogenetic analysis, a homologous trait is called a synapomorphy (syn=shared, apo=derived, morphy=characteristic) The lophophore of bryozoans and brachiopods is homologous. As a synapomorphy, it provides evidence that the two groups are closely related. after Page and Holmes, 1998, Molecular Evolution: a Phylogenetic Perspective. Department of Geological Sciences | Indiana University Geol G-308 Paleontology and Geology of Indiana (c) 2012, P. David Polly Character terminology Apomorphies are characters that evolved since the root of the tree. Also known as derived characters. Calcareous skeletons are apomorphies within metazoans. Apomorphies Plesiomorphies Synapomorphy = homology Plesiomorphies are characters present in the ancestor at the root of the tree. Also known as ancestral or primitive characters. DNA and cell nuclei are pleisiomorphies for all metazoans Synapomorphy is an apomorphic character that is shared by more than one taxon. Synapomorphies provide evidence for close relationship. Lophophores are synapomorphies of Autapomorphy Homoplasy =convergent evolution brachiopods and bryozoans. Autapomorphy is an apomorphic character found in only one taxon. The notocord Homoplasies are apomorphic characters that evolved on separate branches and are not inherited from a common ancestry. Calcareous skeletons are homoplasies within metazoans. after Page and Holmes, 1998, Molecular Evolution: a Phylogenetic Perspective. Department of Geological Sciences | Indiana University (c) 2012, P. David Polly Geol G-308 Paleontology and Geology of Indiana Darwin and the theory of natural selection A very conservative man, related to the Wedgwoods Traveled around the world as naturalist and captain’s companion on The Beagle, a British navy ship, in the 1830s. (Richard Owen described fossils collected by Darwin in South America. Visited Galapagos Islands. Determined how coral atolls are formed.) Published On the Origin of Species in 1859, explaining the concept of natural selection and outlining the evidence supporting it. Darwin’s work: • Explained homology as the similarity due to genetic relationship and specialization as difference due to adaptation. • Provided a scientific mechanism for how evolution works. • Explained that extinction could happen through failure to adapt to changing environments. Department of Geological Sciences | Indiana University (c) 2012, P. David Polly Natural selection as mechanism for evolution 1. Among individuals within every species there exists considerable variation. 2. Variable features found in parents are passed on to their offspring. 3. Every species produces more young than survive into the subsequent generation, therefore, competition for survival exists within species. 4. If one’s individual characteristics give an advantage in the competition, then that individual is more likely to survive into the next generation. 5. The characteristics possessed by the disadvantaged individuals are not passed into subsequent generations, but the characteristics of the advantaged ones are. Geol G-308 Paleontology and Geology of Indiana Department of Geological Sciences | Indiana University (c) 2012, P. David Polly Descent with modification Homologous structures are passed from each generation to the next, but natural selection filters variation at every step. Species become adapted to their environment because of the natural selection process. As environments change over geological time, natural selection continues to change species in response. When change is too rapid for adaptation to occur or when natural variation doesn’t include fit varieties, the species becomes extinct. Geol G-308 Paleontology and Geology of Indiana Department of Geological Sciences | Indiana University Geol G-308 Paleontology and Geology of Indiana (c) 2012, P. David Polly Phylogenetic analysis Synapomorphies are shared modified features, which indicate that two taxa descended from the same ancestor. Phylogenetic analysis finds the tree that maximizes the number of synapomorphies. 0 0 1 0 0 1 0 1 1 1 0 0 = no lophophore 1 = presence of lophophore 1 Porifera 1 Brachiopoda 1 Bryozoa 0 Hypothesis 3 Porifera Brachiopoda 1 Bryozoa Porifera 1 Hypothesis 2 Brachiopoda Bryozoa Hypothesis 1 1 0 Department of Geological Sciences | Indiana University Geol G-308 Paleontology and Geology of Indiana (c) 2012, P. David Polly Phylogeny of major Paleozoic animal phyla Bilateria Protostomia Chordata Echinodermata Mollusca Bryozoa Brachiopoda Cnidaria Porifera Lophophorata Ecdysozoa Deuterostomia Arthropoda Lophotrochozoa •bilateral symmetry (sometimes restricted to early developmental stages) •radial cleavage of early embryonic cell divisions •blastopore (opening in early embryo) becomes anus •blastopore becomes mouth •trochozoan larva (cilia around middle) •lophophore •exoskeleton that is shed Valentine, JW, D Jablonski, DH Erwin, 1999. Fossils, molecules and embryos: new perspectives on the Cambrian explosion. Development, 126: 851-859. Department of Geological Sciences | Indiana University Geol G-308 Paleontology and Geology of Indiana (c) 2012, P. David Polly Field tools Geological hammer Waterproof pen Handlens Notebook Chisels Specimen bags Department of Geological Sciences | Indiana University (c) 2012, P. David Polly Field notes Geol G-308 Paleontology and Geology of Indiana Department of Geological Sciences | Indiana University (c) 2012, P. David Polly Field tags Geol G-308 Paleontology and Geology of Indiana