Phylogeny Bryozoa Brachiopoda Porifera 16 - Phylogeny.pdfBryozoa Brachiopoda Porifera Bryozoa...

Department of Geological Sciences | Indiana University(c) 2012, P. David Polly Paleontology and Geology of Indiana

Geol G-308

P. David PollyDepartment of Geological SciencesIndiana UniversityBloomington, Indiana 47405 [email protected]

Bryozoa

Brachiopoda

Porifera

01 1

0 1

0 1

Evolutionary relationships

Phylogeny

mailto:[email protected]

mailto:[email protected]

Objectives


Geol G-308

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


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Valentine, JW, D Jablonski, DH Erwin, 1999. Fossils, molecules and embryos: new perspectives on the Cambrian explosion.

Development, 126: 851-859.

Metazoan Phylogeny


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A B C D E

((A,B), (C, (D,E)))

after Page and Holmes, 1998, Molecular Evolution: a Phylogenetic Perspective.

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

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 and B share a more recent common ancestor with each other than either does to C, D or E


Geol G-308

Root

Branch(edge)

Internal node(hypotheticalancestor)

Terminal node(leaf, tip)


Phylogenetic tree terminology


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A B C D ABCD AB C D

= =


Trees are like mobilesOnly the branching order matters, not the graphical arrangement of the tree


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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.


Geol G-308

Bryozoa

Brachiopoda

Porifera

Bryozoa

Brachiopoda

Porifera

0 = no lophophore1 = presence of lophophore

0

0

1

01 1

Bryozoa

Brachiopoda

Porifera

01 1

0 1

11


Homology or synapomorphy

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.


Geol G-308

Apomorphies PlesiomorphiesSynapomorphy

= homology

AutapomorphyHomoplasy

=convergent evolution


Character terminologyApomorphies are characters that evolved since the root of the tree. Also known as derived characters. Calcareous skeletons are apomorphies within metazoans.

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 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.


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Darwin and the theory of natural selectionA 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.


Geol G-308

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.


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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

Phylogenetic analysisSynapomorphies 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.

Bryo

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Bra

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Po

rife

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0 = no lophophore

1 = presence of lophophore

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Bryo

zo

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Bra

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Po

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Bryo

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Hypothesis 1 Hypothesis 2 Hypothesis 3


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Porifera

Cnidaria

Brachiopoda

Bryozoa

Mollusca

Arthropoda

Echinodermata

Chordata

Lophotrochozoa Ecdysozoa Deuterostomia

Protostomia

Bilateria

Lophophorata

Valentine, JW, D Jablonski, DH Erwin, 1999. Fossils, molecules and embryos: new perspectives on the Cambrian explosion.

Development, 126: 851-859.

Phylogeny of major Paleozoic animal phyla

•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


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Field tools

Handlens

Notebook

Waterproof pen

Geological hammer

Specimen bags

Chisels


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Field notes


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Field tags

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