SYSTEMATICS

• The reconstruction and study of evolutionary relationships

Taxonomy• Two main objectives:

– to sort out organisms into species– to classify species into higher taxonomic levels

• Species that appear to be closely related are grouped into the same genus.

• the leopard, Panthera pardus, belongs to a genus that includes the African lion (Panthera leo) and the tiger (Panthera tigris).

• Taxon = a named taxonomic unit at any level; (taxa = plural)– ex: Mammalia is a taxon at the Class level

TAXONOMY• taxonomic system developed by Linnaeus

in the 18th century– binomial = Genus species– classification system

• Domain Eukarya• Kingdom Animalia• Phylum Chordata• Class Mammalia• Order Primates• Family Hominidae• Genus Homo• speciessapiens

DomainEukarya

KingdomAnimalia

PhylumChordata

SubphylumVertebrata

ClassMammalia

OrderRodentia

FamilySciuridae

GenusSciurus

SpeciesSciurus

carolinensis

Sciuruscarolinensis

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Did

King

Phillip

Come

Over

For

Great

Sex?

5

Limitations of the Linnean System

Many hierarchies are being re-examined based on the results of molecular analysis

-Linnaean taxonomy does not take into account evolutionary relationships

-The phylogenetic and systematic revolution is underway

PHYLOGENY

• Hypothesis of the evolutionary history of a group

• represented by pictures: phylogenetic trees– time goes from the bottom up– read from bottom up, NOT LEFT TO RIGHT– branch “length” = the number of changes

Fig. 23.1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Variations of a Cladogram

Gibbon Human Chimp Gorilla Orangutan Gibbon Orangutan Gorilla Human Chimp

Chimp

Human

Gorilla

Orangutan

Gibbon

13

1

2

2

3

3

2

1

Version 1 Version 2

b.a.

Version 3

Reproduced by kind permission of the Syndics of Cambridge University Library, Darwin’s Notebook ‘B’, ‘Tree of Life’ Sketch, p. 36 from DAR.121 D312

11

Phylogenies depict evolutionary relationships

• Phylogenetic trees reflect the hierarchical classification of taxonomic groups nested within more inclusive groups.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 25.8

Approaches to Constructing Phylogenies

• Cladistics– uses shared derived characteristics

(synapomorphies) to classify organisms– Not shared ancestral characteristics

(symplesiomorphies)– not overall similarity

• Because evolution is not steady paced, not unidirectional, may be convergent

14

Examples of ancestral versus derived characters• Presence of hair is a synapomorphy (shared

derived feature) of mammals• Presence of lungs in mammals is a

symplesiomorphy (an ancestral feature); also present in amphibians and reptiles

Cladistics

Building CladogramsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Traits:Organism

Jaws Lungs AmnioticMembrane

Hair No Tail Bipedal Lamprey Shark Salamander Lizard Tiger Gorilla Human

Lamprey

Shark

Salamander

Lizard

Tiger

Gorilla

Human

0 0 0 0 0 0

1

1

1

1

1

1

0

1

1

1

1

1

0

0

1

1

1

1

1 1 1

1 1 0

1 0 0

0 0 0

0

0 0 0

0 0

Jaws

Lungs

Amnioticmembrane

Hair

Tail loss

Bipedal

a. b.

Can also use molecular dataCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

G

Site

Species A

Species B

Species C

Species D

Outgroup

DNA Sequence

1 2 3 4 5 6 7 8 9 10

A T A T C C G T A T

A C A G C C G C A T

A C A T C G G T G G

G C A T A G T G T

Outgroup Species B Species D Species A Species C

Homologousevolutionarychanges

Homoplasticevolutionarychanges

2:T C

4:T

8:T

G

C

10:T G

8:T C

9:A

6:C

G

G

5:C A

1:A G

G C A T A G G C G T

PHYLOGENY

• systematists prefer monophyletic taxa– a single ancestor gave rise to all species in that

taxon and to no species in any other taxa

18Monophyletic Group

Systematics and Classification

19Paraphyletic Group

Systematics and Classification

20Polyphyletic Group

Systematics and Classification

21

Old plant classification system

Systematics and Classification

22

New plant classification system

Systematics and Classification

Evidence used to reconstruct phylogenies

• Comparative anatomy, morphology, embryology, etc.– problems of homology vs homoplasy (analogy)

• homology = likeness due to common ancestry• homoplasy or analogy = likeness due to convergent

evolution

Fig. 23.9Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Monotremes

MarsupialsPlacentals

Phylogeny of MammalsC

arni

vore

s

Carnivores

Felines

Nimravids

Sabe

r-to

othe

dca

t

Hye

nas

Civ

ets

Mon

goos

es

Sabe

r-to

othe

d ni

mra

vid

Phylogeny of Carnivores

How many times have saber teeth evolved in mammals?

Hypothesis: Saber teeth are homologous and have only evolved once in mammals (or, conversely, saber teeth are convergent and have evolved multiple times in mammals).

Phylogenic Analysis: Examine the distribution of saber teeth on a phylogeny of mammals, and use parsimony to infer the history of saber tooth evolution (note that not all branches within marsupials and placentals are shown on the phylogeny).

Result: Saber teeth have evolved at least three times in mammals: once within marsupials, once in felines, and at least once in a group of now-extinct cat-like carnivores alled nimravids.

Interpretation: Note that it is possible that saber teeth evolved twice in nimravids, but another possibility that requires the same number of evolutionary changes (and thus is equally parsimonious) is that saber teeth evolved only once in the ancestor of nimravids and then were subsequently lost in one group of nimravids.(Note that for clarity, not all branches within marsupials and placentals are shown in this illustration.)

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Sabe

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SCIENTIFIC THINKING

Question:

Evidence used to reconstruct phylogenies

• Protein comparisons• DNA comparisons

– DNA-DNA hybridization, restriction mapping, DNA sequencing

29A Cladogram: DNA

Can Have Homoplastic Molecular Data

Character Mapping

• Once you have a phylogeny you can trace the evolution of characters or traits in that group

• use the rules of parsimony– the simplest is the best

Parental CareCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

a. b.

a: Image #5789, photo by D. Finnin/American Museum of Natural History; b: © Roger De La Harpe/Animals Animals

33Parsimony and Homoplasy

Classification System

35

Arc

ha

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Ch

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• Excavata (organisms lacking typical mitochondria)• Chromalveolata (organisms with chloroplasts obtained through

secondary endosymbiosis)• Archaeplastida (organisms with chloroplasts for photosynthesis)• Rhizaria (organisms with slender pseudopods used for movement)• Amoebozoans (organisms with blunt pseudopods used for movement)• Opisthokonts (fungi, animal ancestors, and animals)

Six Supergroups Within Eukarya

38

Grouping OrganismsCarl Woese proposed a six-kingdom system

Prokaryotes Eukaryotes

KINGDOMS• Monera = Archaebacteria & Eubacteria

– prokaryotic• Protista

– eukaryotic• Plantae

– eukaryotic, multicellular, autotrophic, cell walls• Fungi

– eukaryotic, multicellular, heterotrophic, cell walls• Animalia

– eukaryotic, multicellular, heterotrophic, no cell walls