what are taxonomy, classification, and systematics? · 1 topic 2: comparative method o taxonomy,...

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Topic 2: Comparative Method

o Taxonomy, classification, systematics

o Importance of phylogenies

o A closer look at systematics

o Some key concepts

o Parts of a cladogram

o Groups and characters

o Homology and homoplasy

What are taxonomy, classification,

and systematics?

o _________________ – The naming of

organisms and their categorization

o _________________ – The arrangement

of organisms into groups based on trait

similarity (justifying the groups)

o _________________ – The clustering of

groups and organisms based on a unifying

set of principles (evolutionary, or

otherwise)

How would you taxonomize, classify,

and systematize this cutlery?

© www.visualdicationary.com

Taxonomy – naming of taxa

Elk Wrasse Crested Gecko

Japalura Monitor Dog

Boa Goby Fly Solefugid

Photos © K.P. Bergmann

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Classification – categorization based on similarity


Mammals

Squamates

Fishes Arthropods

Systematics – clustering of taxa based on

unifying principles


What are taxonomy, classification,

and systematics?

o Taxonomy and classification are used

to _______________ things

o 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)

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What aspects of biology are

informed by systematics?


o Provides a

framework for

comparing species

o Accounts for non-

____________ of species

o Species pairs spent

different amount of time

evolving

o __________________

o __________________


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

2 Species 3 SpeciesThe Evolution of Fur

Some have it, some don’t Fur evolved after scales, scales

are ____________, fur is derived

A Closer Look at Systematics

o Systematics – The clustering of groups or

organisms based on a unifying set of

principles (evolutionary, or otherwise)

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

_____________________

o These underlying principles are typically

____________ and ______________

Key Concepts of Systematics

o _________________ – The guiding

principle of science, stating that the

simplest explanation that fits the evidence

is most likely the correct explanation

o __________________ – An

evolutionary branching

event, where new taxa arise

from a common ancestor

o ___________________ –

Evolutionary change in a

lineage through time (along

a branch)

Anagenesis

Cladogenesis

Key Concepts of Systematics

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Anatomy of a Cladogram

Operational

Taxonomic Unit (OTU)

Terminal Branch

NodeInternal Branch

Outgroup

Root

Clade: Amphibia

Ingroup

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

Topology

• Sister group

• Dichotomous

• Polytomy

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Types of Groups

o _________________ – A group containing an

ancestor and all of its descendents.

o _________________ – A group containing some, but

not all, of its descendents.

o _________________ – A group containing taxa that

lack a common ancestor.

Types of Characters

o A character can comprise any quality or

quantity that can be compared between the

taxa under study

o _______________

o Morphometrics

o _______________

o Ecology

o _______________

o Sonography

o __________________

o Allozymes

o Karyotype

o Protein structure

o Etc.

Types of Characters

o _____________________ – Alternate forms 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

Types of Characters

o ______________ – An ancestral feature,

common to taxa in the ingroup and outgroup

o ______________ – A shared derived feature,

common to clusters of taxa of the ingroup

o ______________ – A unique derived feature,

diagnostic of a taxon (OTU) in the ingroup

Sauropsids (‘Reptilia’ &

Aves)

Diapsida (Archosauria &

Lepidosauria)

Aves (Birds)

Plesiomorphy

Synapomorphy

Autapomorphy

Amniotic eggSingle centrale

bone in ankle

Of Diapsida:

2 temporal

foramina in skull

Of Aves:

Feathers

8

Single centrale

bone in ankle

2 temporal

foramina in

skull

2 temporal

foramina in

skull

Feathers

Types of Characters

Types of Characters

Taxon

Frog 0 0 0 0 0 0 0 0 1

Turtles 1 0 0 0 1 0 0 0 1

Lepidosaurs 1 0 1 1 0 0 1 0 1

Crocodylians 1 0 1 1 0 1 0 0 1

Birds 1 0 1 1 0 1 0 1 1

Monotremes 1 1 2 0 0 0 0 0 1

Marsupials 1 1 0 0 0 0 0 0 1

Eutherians 1 1 0 0 0 0 0 0 1

Modified from Liem et al 2001, Focus 1-2, Table A

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Types of Characters

Amniotic Egg

Single Centrale

Trunk in Shell

Fenestra in jaw

Diapsid Skull

Transverse Cloaca

Feathers

Digits on Limbs

Hair

Liem et al. 2001, Focus 1-2, Fig A

Frog

Turtle

Lepidosaur

Crocodilian

Bird

Monotreme

Marsupial

Eutherian

Digits on Limbs

Homology and Homoplasy

o _______________ – The fundamental similarity

of a character between taxa within a group

• Structures compared between taxa must be of the

same evolutionary origin (comparing apples to apples)

o Homology – comparing apples to apples

Modified from Linzey, 2001



_______________________ is when homologous structures occur

within an individual Examples:

• Vertebrae

• Feathers

• Hair

• Scales

• Teeth

• Front & Hind limbs

Examples:

• Testes & ovaries

• Glans penis & glans clitoridis

• Scrotum & labiae majorae

_______________ is when sexually dimorphic homologous structures

occur in males and females

o ____________________ – The similarity of a character or structure between taxa due to convergence

o Homoplasy can obscure relationships between taxa

by leading to erroneous:

o Statements of homology

o Coding of character states

o Phylogeny reconstruction


o Homoplasy is thought to occur due to:o _________________________ in different groups

o _________________ on the direction of evolution


Photos © PJB

Endothermy:

• Aves

• Mammalia

Allows sustained activity and

independence of metabolism

from environmental

temperatures

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Homology and

Homoplasy

Photos © PJB

Endothermy in Aves and

Mammalia has evolved

twice independently

Frog

Turtle

Lepidosaur

Crocodilian

Bird

Monotreme

Marsupial

Eutherian

Liem et al. 2001, Focus 1-2, Fig A

o Homoplasy is thought to occur due to:• Similar selective pressures in different groups

• Constraint on the direction of evolution


Modified from Linzey, 2001; Liem et al. 2001, Fig 1-9C

Homology or Homoplasy?

Aves Chiroptera Pterosauria

what are taxonomy, classification, and systematics? · 1 topic 2: comparative method o taxonomy,...

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