1 Chapter 21 Lecture and Animation Outline Copyright © McGraw-Hill Education. Permission required for reproduction or display. To run the animations you

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Chapter 21Lecture and

Animation Outline

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Darwin’s bark spider, Caerostris darwini, was discovered in 2010. The female of this species weaves an enormous web.

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Chapter 21

Taxonomy and Systematics

Taxonomy

Phylogenetic Trees

Cladistics

Molecular Clocks

Horizontal Gene Transfer

Chapter Outline:

Taxonomy Science of describing, naming, and classifying living

and extinct organisms

Systematics Study of diversity and evolutionary relationships

among organisms, both extinct and modern

Taxonomic groups are based on hypotheses regarding evolutionary relationships derived from systematics

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Taxonomy

Taxonomy

Hierarchical system involving successive levels

Each group at any level is called a taxon

Highest level is domain All of life belongs to one of 3 domains Bacteria, Archaea, and Eukarya

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Domains:

Eukaryoticsupergroups:

Typical protists:

Large eukaryotickingdoms:

Bacteria Archaea Eukarya

Excavata

Plantae

Land plants and relatives Alveolata Stramenopila Rhizaria Amoebozoa Opisthokonta

AnimaliaFungi

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

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Every Species Is Placed into a Taxonomic Hierarchy

Domain > Supergroup > Kingdom > Phylum> Class > Order > Family > Genus > Species

The plural of phylum is phyla

The plural of genus is genera

EVOLUTIONARY CONNECTIONS

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Taxonomicgroup

Gray wolffound in

Number ofspecies

Domain

Supergroup

Kingdom

Phylum

Class

Order

Family

Genus

Species lupus

Canis

Canidae

Carnivora

Mammalia

Chordata

Animalia

Opisthokonta

Eukarya ~4 –10 million

>1 million

>1 million

~50,000

~5,000

~270

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BIOLOGY PRINCIPLE

All species (past and present) are related by an evolutionary history

A goal of taxonomy is to relate the diversity of species according to their evolutionary

relationships.

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Binomial nomenclature

Genus name and species epithet

ex: Homo sapiens

Genus name always Capitalized

Species epithet never capitalized

Both names either italicized

Rules for naming established and regulated by international associations

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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

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Phylogenetic Trees

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 two or more

species13

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500

mil

lio

nP

rese

nt

1 b

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on

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 52 53 54 55 56 57 58 59 60 61 62 63 64

Mil

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Species (43)

34 35 36 37 38 39 40 45 46 47 48 49 50 5141 42 43 44

Family (species41–44)

Genus(species43–44)

Order (species41–48)

Class (species33–48)

Phylum (species 33–64)

Kingdom (species 1–64)

Monophyletic group or clade Group of species – a 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

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Homology

Similarities among various species that occur because they are derived from a common ancestor

ex: Bat wing, human arm and cat front leg

Genes can also be homologous if they are derived from the same ancestral gene

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Morphological analysis

First systematic studies focused on morphological features of extinct and modern species

Convergent evolution (traits arising independently due to adaptation to similar environments) can cause problems

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0

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Mil

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Hyracotherium

Pachynolophus

Propalaeotherium

Paleotherium

Orohippus

Epihippus

Mesohippus

Miohippus

Parahippus

AnchitheriumHypohippus

SinohippusArchaeohippus

Megahippus

Merychippus

Callippus

Pliohippus

Equus

Neohipparion

Nannippus

Hipparion

Stylohipparion

Tim

e

Hippidium andother genera

An analysis of fossilized bonesprovided the phylogenetic treedescribed here.

BIOLOGY PRINCIPLE

Structure determines function

The changes in structural features during horse evolution are related to changes in their functional needs. During this time, horse populations shifted

from feeding on leaves in forested regions to feeding on abrasive grasses in more wide-open spaces.

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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

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Study and classification of species based on evolutionary relationships

Cladistic approach discriminates among possible trees by considering the various possible pathways of changes and then choosing the tree that requires the least complicated explanation

Make phylogenetic trees or cladograms

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Cladistics

Cladistic approach compares homologous traits, also called characters, which may exist in two or more character states

Shared primitive character Shared by two or more different taxa and inherited from

ancestors older than their last common ancestor

Shared derived character Shared by two or more species or taxa and has

originated in their most recent common ancestor Basis of the cladistic approach is to analyze many

shared derived characters to deduce the pathwaythat gave rise to those species

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Branch point – two 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

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(b) Cladogram based on morphological traits

Mammaryglands

Tetrapod

Hinged jaw

Vertebrae

Notochord

Notochord Yes

Yes

Yes

Yes

No

Vertebrae

Hinged jaw

Tetrapod

YesMammary glands

YesYesYesYes

RabbitLizardSalmonLampreyLancelet

YesYesYes

YesYes

Yes

(a) Characteristics among species

NoNoNo

NoNo

NoNo

No

No

Lancelet Lamprey Salmon RabbitLizard


Cladogram can also be constructed with gene sequences

7 species called A-G

A mutation that changes the DNA sequence is analogous to a change of a characteristic

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GGTATAACCC

A6 T

E D G F A B C

T5 G

C10 G

G2 A

A7 T

C10 A

GGTATAACCC1 2 3 4 5 6 7 8 9 10

GGTATTACCC GGTAGTACCC GGTAGTACCA GATAGTACCC GATAGTTCCC GATA GTTCCG

Proposed primitivesequence

Constructing a cladogram

1. Choose species

2. Choose characters

3. Determine polarity of character states Primitive or derived?

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4. Analyze cladogram 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

5. Choose the most likely cladogram among possible options

6. Choose a noncontroversial outgroup as root

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 It may not always be obvious which traits are

primitive (came earlier) and which are derived (came later in evolution)

Fossils may be analyzed to help resolve

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Example

4 taxa (A-D)

A is the outgroupHas all primitive

states

3 potential treesTree 3 requires

fewest number of mutations so is the most parsimonous

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According to the principle of parsimony,

tree number 3 is themore likely choice

because it requires only five mutations.

Favorable mutations are rare, detrimental mutations are quickly eliminated – so most mutations are neutral

If neutral mutations occur at a constant rate they can be used to measure evolutionary time

Not perfectly linear over long periods of time Not all organisms evolve at the same rate Differences in generation times

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Molecular Clocks

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example: Primate evolution

Evolutionary relationships derived from DNA sequences for cytochrome oxidase subunit II Tends to change fairly rapidly on an evolutionary

timescale, so good for close relationships

Three branch points to examine (A, D, E)

Ancestor A This ancestor 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 species38

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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

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Horizontal gene transfer Any process in which an organism incorporates

genetic material from another organism without being the offspring of that organism

The transfer of genes between different species

In contrast to vertical evolution The traditional view of evolution Changes in groups due to descent from a common

ancestor42

Horizontal Gene Transfer

Tree of Life – really a “Web of Life”

Horizontal gene transfer plays a significant role in the 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

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1 Chapter 21 Lecture and Animation Outline Copyright © McGraw-Hill Education. Permission required for reproduction or display. To run the animations you