Topic 2: Systematics I...1 Topic 2: Systematics I What is the difference between taxonomy, classification, systematics? Why is systematics important? Terminology of systematics What

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Topic 2: Systematics I

� What is the difference between taxonomy,

classification, systematics?

� Why is systematics important?

� Terminology of systematics

� What are important terms related to cladograms,

groups & characters?

� What are homology and homoplasy?

� What is the difference between anagenesis &

cladogenesis?

� What are the schools of thought of systematics?

What are taxonomy, classification, and

systematics?

� __________________ – The naming of

organisms and their categorization.

� _________________ – The arrangement

of organisms into groups based on trait

similarity (justifying the groups).

� __________________ – The clustering

of groups or organisms based on a

unifying set of principles (evolutionary, or

otherwise).

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How would you taxonomize, classify

and systematize this cuttlery?

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Taxonomy – naming and categorizing

Elk Wrasse Crested Gecko

Japalura Monitor Dog

Boa Goby Fly Solefugid

Photos © K.P. Bergmann

Classification – categorization based on similarity

Photos © K.P. Bergmann

Mammals

Squamates

Fishes Arthropods

Systematics – clustering of taxa based on unifying principles

Photos © K.P. Bergmann

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What are taxonomy, classification, and

systematics?

� Taxonomy and classification are

used to ________________ things

� Systematics is used to ___________

things

Why is systematics important?

“Nothing in biology makes sense except in the light

of evolution.”

- Dobzhansky, 1973.

“The task of systematics is the creation of a general

reference system and the investigation of the relations

that extend from it to all other possible and necessary

systems in biology.”

- Hennig, 1950 (1966).

What aspects of biology are

informed by systematics?

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Why is systematics important?

� Provides a

framework for

comparing species

� Accounts for ________

______________ of species

� Species pairs spent different

amount of time evolving

� ___________________

� ___________________

Photos © K.P. Bergmann

Why is systematics important?

Photos © K.P. Bergmann

� Informs about direction of evolution, how species can be compared

2 Species 3 SpeciesThe Evolution of Fur

____________________

____________________

_________________________

_________________________

The Terminology of Systematics

Anatomy of a “Cladogram”

Operational

Taxonomic Unit (OTU)

Modified from Pough et al., 2002. Fig. 1-3.

Topology

• Sister group

• Dichotomous

• Polytomy

• Rooted vs unrooted

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What are the types of taxonomic groups?

� ____________________ – A group containing

taxa that lack a common ancestor

� ____________________ – A group containing

an ancestor and all of its descendents

� ____________________ – A group containing

some, but not all, of an ancestor’s descendents

What are characters?

�A character can comprise any quality or

quantity that can be compared between the

taxa under study.

What are the different types of characters?

� _______________ – A unique derived feature,

diagnostic of a taxon (OTU) in the ingroup

� _______________ – An ancestral feature,

common to taxa in the ingroup and outgroup

� _______________ – A shared derived feature,

common to clusters of taxa of the ingroup

The Terminology of Systematics –

Types of Characters

Sarcopterygii

(Lobe-finned

fishes)

Tetrapoda Amniota

Plesiomorphy

Synapomorphy

Autapomorphy

Two sets of

paired fins

Shoulder

girdle

Of Tetrapoda:

2 bones in

zygopodium

Shoulder

girdle

2 bones in

zygopodium

2 bones in

zygopodium

Of Amniota:

Cleidoic egg

Cleidoic egg

,

What are character states?

� Character States – ___________________ of a

character in the taxa being studied

� These represent the variation that is analyzed

by systematic methods

© K.P. Bergmann

e.g. Pupil

shape

Round Slitted Slit & pin-hole

What is character polarity?

� Polarity – A character is polarized when the ancestral state

is determined

� This can give us information about the order of

character state transformation

� Approaches:

� _______________________

� Clues from ontogeny

� Ancestral state widespread

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What is character polarity?

� Polarity – A character is polarized when the ancestral state

is determined

� __________________________ is most prevalent

� Gives information about the order of character

state transformation

© K.P. Bergmann

What do we mean by homology & homoplasy?

� Homology – The fundamental similarity of a

character between taxa within a group

� Specifically, for a character to be valid,

structures compared between taxa must be

of the ______________________________

(comparing apples to apples)

� Homology – comparing apples to apples.

Modified from Linzey, 2001.

What do we mean by homology & homoplasy?

What is homoplasy & how does it differ

from homology?

� Homoplasy can obscure relationships

between taxa by leading to erroneous

� Statements of homology of characters, or

� Coding of character states

� Homoplasy – The similarity of a character or structure between taxa due to _______________

What is homoplasy?

Gekko vittatus Anolis cuvieri Prasinohaema virens

Williams and Peterson, 1982.

© Afco Zoological Suppliers© USDA© K.P. Bergmann

� Homoplasy is also an important evolutionary

phenomenon

What is parsimony?

� Parsimony – The guiding principle of

science, stating that the _____________

explanation that fits the _____________

is most likely the correct explanation

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What is the difference between

cladogenesis & anagenesis?

Anagenesis

Cla

do

ge

ne

sis

� Cladogenesis – An

evolutionary ____________

event, where new taxa

arise from a common

ancestor

� Anagenesis – Evolutionary

change in a lineage through

time (________________

______________)

What are the different schools of

systematics?

� Systematics – The clustering of groups or

organisms based on a unifying set of

principles (evolutionary, or otherwise)

� If the system is based on evolution, then it is

phylogenetic

� These underlying principles are typically evolution

and parsimony

What are the different schools of

systematics?

1. Evolutionary Systematics

(phylogenetic)

2. Phenetics (not phylogenetic)

3. *Cladistics (= “Phylogenetic

Systematics”)

4. *Model-based approaches

(phylogenetic)

* Currently used approaches