Chapter 26: Taxonomy and Systematics
- 1. CHAPTER 26 LECTURE SLIDES Prepared by Brenda Leady University of Toledo To run the animations you must be in Slideshow View. Use the buttons on the animation to play, pause, and turn audio/text on or off. Please note: once you have used any of the animation functions (such as Play or Pause), you must first click in the white background before you advance the next slide. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
- 2. Taxonomy and systematics Taxonomy Science of describing, naming, and classifying living and extinct organisms and viruses Systematics Study of biological diversity and the evolutionary relationships among organisms, both extinct and modern Taxonomic groups are now based on hypotheses regarding evolutionary relationships derived from systematics 2
- 3. Taxonomy Hierarchical system involving successive levels Each group at any level is called a taxon Domain Highest level All of life belongs to one of 3 domains Bacteria, Archaea, and Eukarya 3
- 4. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Domains: Bacteria Archaea Eukarya Eukaryotic Excavata Land plants and algal relatives Alveolata Stramenopila Rhizaria Amoebozoa Opisthokonta supergroups: Large eukaryotic Plantae Fungi Animalia kingdoms: 4
- 5. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Taxonomic Gray wolf Number of group found in species Domain Eukarya ~ 4– 10 million Supergroup Opisthokonta >1 million Kingdom Animalia >1 million Phylum Chordata ~50,000 Class Mammalia ~5,000 Order Carnivora ~270 Family Canidae 34 Genus Canis 7 Species lupus 1 5
- 6. Binomial nomenclature Genus name and species epithet Genus name always capitalized Species epithet never capitalized Both names either italicized or underlined Rules for naming established and regulated by international associations 6
- 7. Phylogenetic trees Phylogeny – evolutionary history of a species or group of species To propose a phylogeny, biologists use the tools of systematics Trees are usually based on morphological or genetic data 7
- 8. Phylogenetic tree Diagram that describes phylogeny A hypothesis of evolutionary relationships among various species Based on available information New species can be formed by Anagenesis – single species evolves into a different species Cladogenesis – a species diverges into 2 or more species 8
- 9. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Present F I G J H K B E Millions of years ago (mya) 5 C Time D B 10 A 9
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- 11. Monophyletic group or clade Group of species, taxon, consisting of the most recent common ancestor and all of its ancestors Smaller and more recent clades are nested within larger clades that have older common ancestors Paraphyletic group Contains a common ancestor and some, but not all, of its descendents 11
- 12. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H I J K L M N O H I J K L M N O H I J K L M N O D E F G D E F G D E F G B C B C B C A A A (a) Monophyletic (b) Paraphyletic (c) Polyphyletic 12
- 13. Over time, taxonomic groups will be Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. KEY reorganized so only Orders Classes monophyletic groups and snakes and snakes Crocodiles Crocodiles are recognized Lizards Lizards Turtles Turtles Birds Birds Reptiles were a paraphyletic groups because birds were excluded Reptiles (a) Reptiles as a (b) Reptiles as a Reptiles paraphyletic taxon monophyletic taxon 13
- 14. Homology Similarities among various species that occur because they are derived from a common ancestor Bat wing, human arm and cat front leg Genes can also be homologous if they are derived from the same ancestral gene 14
- 15. Morphological analysis First systematic studies focused on morphological features of extinct and modern species Convergent evolution (traits arise independently due to adaptations to similar environments) can cause problems 15
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- 17. Molecular systematics Analysis of genetic data, such as DNA and amino acid sequences, to identify and study genetic homologies and propose phylogenetic trees DNA and amino acid sequences from closely related species are more similar to each other than to sequences from more distantly related species 17
- 18. Cladistics Study and classification of species based on evolutionary relationships Cladistic approach discriminates among possible phylogenetic trees by considering the various possible pathways of evolutionary changes and then choosing the tree that requires the least complex explanation for all of the available data Phylogenetic trees or cladograms 18
- 19. Cladistic approach compares homologous traits, also called characters, which may exist in two or more character states Shared primitive character or symplesiomorphy Shared by two or more different taxa and inherited from ancestors older than their last common ancestor Shared derived character or synapomorphy Shared by two or more species or taxa and has originated in their most recent common ancestor 19
- 20. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. D E F G B C A 20
- 21. Branch point – 2 species differ in shared derived characters Ingroup – group we are interested in Outgroup – species or group of species that is assumed to have diverged before the species in the ingroup An outgroup will lack one or more shared derived characters that are found in the ingroup 21
- 22. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lancelet Lamprey Salmon Lizard Rabbit Notochord Yes Yes Yes Yes Yes Vertebrae No Yes Yes Yes Yes Hinged jaw No No Yes Yes Yes Tetrapod No No No Yes Yes Mammary No No No No Yes glands (a) Characteristics among species Lancelet Lamprey Salmon Lizard Rabbit Mammary glands Tetrapod Hinged jaw Vertebrae Notochord 22 (b) Cladogram based on morphological traits
- 23. Cladogram can also be constructed with gene sequences 7 species called A-G A mutation that changes the DNA sequence is analogous to a modification of a characteristic 23
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- 25. Constructing a cladogram 1. Choose species 2. Choose characters 3. Determine polarity of character states Primitive or derived? 25
- 26. 4. Analyze cladogram based on All species (or higher taxa) are placed on tips in the phylogenetic tree, not at branch points Each cladogram branch point should have a list of one or more shared derived characters that are common to all species above the branch point unless the character is later modified All shared derived characters appear together only once in a cladogram unless they arose independently during evolution more than once 4. Choose the most likely cladogram among possible options 5. Choose a noncontroversial outgroup as root 26
- 27. Principle of parsimony Preferred hypothesis is the one that is the simplest for all the characters and their states Challenge in a cladistic approach is to determine the correct polarity of events Itmay not always be obvious which traits are primitive and came earlier and which are derived and came later in evolution Fossils may be analyzed 27
- 28. Example 4 taxa (A-D) A is the outgroup Has all the primitive states 3 potential trees Tree 3 requires fewest number of mutations so is the most parsimonous 28
- 29. According to the principle of parsimony, tree number 3 is the more likely choice because it requires only five mutations. 29
- 30. Molecular clocks Favorable mutations rare and detrimental mutations eliminated Most mutations are neutral If neutral mutations occur at a constant rate they can be used to measure evolutionary time Longer periods of time since divergence allows for a greater accumulation of mutations Not perfectly linear over long periods of time Not all organisms evolve at the same rate Differences in generations times 30
- 31. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nucleotide differences in a homologous gene between different pairs of species 0 Evolutionary time since divergence of pairs of species 31 (millions of years)
- 32. Primate evolution example Evolutionary relationships derived by comparing DNA sequences for cytochrome oxidase subunit II Tends to change fairly rapidly on an evolutionary timescale 3 branch points to examine (A, D, E) Ancestor A Thisancestor diverged into two species that ultimately gave rise to siamangs and the other five species 23 million years for siamang genome to accumulate changes different from other 5 species 32
- 33. Ancestor D This ancestor diverged into two species that eventually gave rise to humans and chimpanzees Differences in gene sequences between humans and chimpanzees are relatively moderate Ancestor E This ancestor diverged into two species of chimpanzees Two modern species of chimpanzees have fewer differences in their gene sequences 33
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- 35. Cooper and Colleagues Extracted DNA from Extinct Flightless Birds and Modern Species to Propose a New Phylogenetic Tree Ancient DNA analysis or molecular paleontology Under certain conditions DNA samples may be stable as long as 50,000 – 100,000 years Discovery based sciences- gather data to propose a hypothesis Sequences are very similar New Zealand colonized twice by the ancestors of flightless birds First by moa ancestor, then by kiwi ancestor
- 38. Horizontal gene transfer Any process in which an organism incorporates genetic material from another organism without being the offspring of that organism Vertical evolution Changes in groups due to descent from a common ancestor 38
- 39. Due to Horizontal Gene Transfer, the Tree of Life Is Really a “Web of Life” Vertical evolution involves changes in species due to descent from a common ancestor Horizontal gene transfer is the transfer of genes between different species Significant role in phylogeny of all living species Still prevalent among prokaryotes but less common in eukaryotes Horizontal gene transfer may have been so prevalent that the universal ancestor may have been a community of cell lineages
- 40. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bacteria Archaea Eukarya Fungi Animals Plants KEY Vertical evolution Horizontal gene transfer Common ancestral community of primitive cells
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