toxonomy and system a tics

8/14/2019 Toxonomy and System a Tics

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Copyright (c) The McGraw-Hill Com 1

CHAPTER 26

TAXONOMYAND SYSTEMATICS

Prepared by

Brenda Leady, University of Toledo


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Taxonomy

Hierarchical system involving successive

levels

Each group called a taxon

DomainHighest level

All of life belongs to one of 3 domains

Bacteria, Archaea, and Eukarya


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Domains similar but different

Scientists think all life originated from

primordial prokaryotic cells between 4.0

and 3.5 bya Soon after, 2 prokaryotic domains,

Bacteria and Archaea, diverged

2.5-2.0 bya first unicellular eukaryoticspecies

Multicellular eukaryotes arose about 1.5

bya


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These traits are universal because all 3

domains evolved from a common ancestor

Dissimilarities exist because majorevolutionary changes have occurred since

the time that the three domains diverged


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Domain BacteriaDiverse collection of many speciesSo widespread only generalizations about

their ecologyKey to success is metabolic diversityCome in a myriad of shapes and sizes

Domain ArchaeaLess diverse than BacteriaDiscovered in 1970s

Many found in extreme environmentsMost are extreme halophiles, methanogens or

hyperthermophilesNot entirely restricted to extreme

environments


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Domain Eukarya

4 traditional kingdomsProtista

Fungi

Plantae

Animalia


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Kingdom Protista

Simplest eukaryotes

Most unicellular but some are colonial or

simple multicellular

Some photosynthesize while others eat

bacterial or other protists

Most live in aquatic habitats

Leftover organisms not put in other 3

kingdoms


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Kingdom Fungi

Yeasts, molds, mushrooms

Present worldwide in aquatic and

terrestrial environments

Many symbiotic with plants

Cell walls contain chitin

Most multicellular

Mass of hyphae combine to make

mycelium


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Kingdom Plantae

Multicellular

Almost all capable of photosynthesis

Mosses, ferns, conifers, flowering plants

Cell wall made primarily of cellulose


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Kingdom Animalia Multicellular and eat others for food More than 1 million species

Sponges, worms, insects, mollusks, fish, amphibians,

birds, reptiles, mammals Most ingest food and digest it in an internal

cavity Bodies composed of cells organized into tissues

(except sponges) Capable of complex and rapid movement Nervous system Lack a rigid cell wall


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Systematics

Phylogeny evolutionary history of aspecies or group of species

Gather morphological or molecular data Use mathematical strategies to analyze

data

Construct evolutionary trees Molecular data has caused many revisions


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Monophyletic group or cladeGroup of species, taxon, consisting of themost recent common ancestor and all of itsancestors

Smaller and more recent clades aresubsets of larger clades

For larger taxa, common ancestor existed

a long time ago (kingdom) For smaller taxa, common ancestor more

recent (family or genus)


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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


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Molecular systematics/clocks

Analyzing genetic data to identify and

study genetic homology and reconstruct

phylogenetic trees DNA sequences from closely related

species are more similar to each other

than to sequences from more distantlyrelated species


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Primate evolution example Evolutionary relationships derived by comparing

DNA sequences in a mitochondrial gene 3 branch points to examine (A,D, E)

A- common ancestor diverges into siamangsand other speciesGene in siamangs more different than the gene in the

other 7 species Humans and siamangs have more differences

than humans and chimpanzees because therehas been more time for them to accumulatedifferences

2 chimp species diverged recently and have very

similar gene sequences


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Cladistic approach

Reconstructs phylogenetic tree byconsidering various possible pathways ofevolution and then proposing plausibletree

Phylogenetic trees or cladograms Compares traits shared or not sharedShared trait shared primitive character or

symplesiomorphyNot shared shared derived character or

synapomorphy


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Branch point 2 species differ in sharedderived characters

Ingroup monophyletic group we areinterested in

Outgroup species or group of speciesthat is most closely related to an ingroup

All traits shared by the outgroup and the

ingroup must have arisen in a commonancestor that predates the divergence ofthe 2 groups


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Cladogram can also

be constructed with

gene sequences

7 species called A- G

A mutation that

changes the DNAsequence is

analogous to a

modification of a

characteristic


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Constructing a cladogram

1. Choose species

2. Choose characters

3. Determine order of character states primitive or derived?

4. Group species (or higher taxa) based on

shared derived characteristics


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1. Build a cladogram based on

All species (or higher taxa) are placed on tips in thephylogenetic 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 unlessthe character is later modified

All shared derived characters appear together only

once in a cladogram unless they arose independently

during evolution more than once2. Choose the most likely cladogram among

possible options


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Strategies for a likely cladogram

Challenge in a cladistic approach is to determine thecorrect order of events

May not always be obvious which traits are ancestraland came earlier, and which are derived and came laterin evolution

Different approaches can be used to deduce the correctorder Analyze fossils and determine the relative dates that certain

traits arose

Assume that the best hypothesis is the one that requires thefewest number of evolutionary changes (principle of parsimony)

Maximum likelihood and Bayesian analysis for gene sequencedata


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Example

4 taxa (A-D)

A is the outgroupHas all the primitive

states

3 potential trees

Tree 3 requiresfewest number of

mutations so is the

most parsimonous


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Cooper and Colleagues Extracted DNA from Extinct

Flightless Birds and Then Compared It with DNA from

Modern Species to Reconstruct Their Phylogeny Ancient DNA analysis or molecular

paleontology

Under certain conditions DNA samples maybe stable as long as 50,000 100,000years

Discovery based sciences- gather data to

propose a hypothesis Sequences are very similar New Zealand colonized twice by the

ancestors of flightless birdsFirst by moa ancestor, then by kiwi ancestor


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Ideal goal of taxonomy to place organisms inmonophyletic groups


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Many recent models propose several major

groups, supergroups, as a way to organize

eukaryotes into monophyletic groups Shows that protists played a key role in the

evolution of diverse eukaryote species


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Due to Horizontal Gene Transfer, the

Tree of Life Is Really a Web of Life

Vertical evolution involves changes in species dueto descent from a common ancestor

Horizontal gene transfer is the transfer of genesbetween 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 havebeen a community of cell lineages


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