Table 13.1Page 218

Extinction. End of the line for a species. Mass extinctions are catastrophic events in which major groups are lost abruptly and simultaneously.

Genetic disconnect

Basis of life’s diversity, as brought about by adaptive shifts, branchings, and radiations. Rates and times of change varied within and between lineages.

Genetic divergence

Basis of the unity of life. The biochemical and molecular basis of inheritance extends from the origin of first cells through all subsequent lines of descent.

Genetic persistence

Macroevolutionary Processes

Preserves or erodes species cohesion, depending on environmental pressures

Natural selection

Erodes species cohesionGenetic drift

Preserves species cohesionGene flow Stability or change in a species is the outcome of balances or imbalances among all of these processes, the effects of which are influenced by population size and by the prevailing environmental conditions.

Original source of allelesMutation

Microevolutionary Processes

Table 13.1  Summary of Processes and Patterns of Evolution

Speciation•Species- Individuals capable of successful interbreeding and producing fertile offspring.

• Speciation: process by which new species come into being

–Genetic divergence of reproductively isolated populations

time A time B time C time D

daughter species

parent species

time

Simplified diagram of genetic divergence

Reproductive Isolating Mechanisms

• Prezygotic Isolation– Ecological– Temporal– Behavioral– Gametic Mortality

• Postzygotic Isolation– Zygotic Mortality– Hybrid Inviability– Hybrid Infertility

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Temporal isolation

Mechanical isolation

Hybrid sterility

Behavioral isolation

Ecological isolation

Gamete mortality

Hybrid inviability

They interbreed anyway.

Zygotes form, but...

Different species!

No offspring or weak offspring that die before reproducing

Types of Speciation

• Sympatric Speciation- Isolation within a population– New species arises in the midst of the original population.

• Ex: Lake Victoria Cichlids

Allopatric Speciation- Geographical isolation– Thought to be most common means of speciation– A geographic barrier, such as a river or a mountain range,

causes the splitting of a population such that individuals of these now-separate populations can no longer interbreed.

• Ex: Grey Squirrels around the Grand Canyon

– Pioneering individuals may colonize a new habitat, such as an oceanic island.

• Ex: Hawaiian Honeycreeper

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The shared ancestor of allof Hawaii’s honeycreepersprobably looked like thishouse finch (Carprodacus)

Akepa(Loxops coccineus)

Maui parrotbill(Pseudonestor xanthrophrys)

Akohekohe(Palmeria doli)

Apap(Himatione sanguinea)

liwi(Vestiaria coccinea)

Alauahio(Paroreomyza montana)

Akekee(L. caeruleirostris)

Nihoa finch(Telespyza ultima)

Kauai Amakihi(Hemignathus kauaiensis)

Palila(Loxioides bailleui)

Akiapolaau(H. munroi)

1

23

4

A few individuals of a species on the mainland reach isolated island 1. Speciation follows genetic divergence in a new habitat.

1

2

Later in time, a few individuals of the new species colonize nearby island 2. In this new habitat, speciation follows genetic divergence.

1

23

4

Speciation may also follow colonization of islands 3 and 4. And it may follow invasion of island by genetically different descendants of the ancestral species.

Patterns of Speciation

– Phylogeny- The evolutionary relationships among living, or extinct, organisms.

– Evolutionary Trees- Summarize information about the continuity of relationships among species; summarize phylogenies

• Branching in the tree represents speciation.• Angling of a branch represents gradual change in a

lineage= phyletic evolution.• A straight line represents no change in a lineage.• Branches ending before the present represents

extinction. • Adaptive radiation- Burst of divergence (branches) from

a single lineage.

Patterns of Speciation

species 1

species 3species 2

suspected branching

branch point (time ofgenetic divergence,speciation under way)

a singlelineage;ancestralstock

Kingdom

Genus

Species

Family

Order

Class

Phylum

Plantae

Juniperus

J. occidentalis

Cupressaceae

Coniferales

Coniferopsida

Coniferophyta

Plantae

Vanilla

V. planifolia

Orchidaceae

Asparagales

Monocotyledonae

Anthophyta

Animalia

Musca

M. domestica

Muscidae

Diptera

Insecta

Anthropoda

Animalia

Homo

H. sapiens

Hominidae

Primates

Mammalia

Chordata

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‘Woodpecker’

‘Woodpecker’

Eubacteria Archaebacteria Protista Fungi Plantae Animalia

extreme

thermophiles

halophilesmethanogens cyanobacteria

ARCHAEBACTERIA

PROTISTANS

FUNGIPLANTS

ANIMALS

clubfungi

sacfungi

zygospore-forming

fungi

echinodermschordates

annelidsmollusks

flatworms

sponges

cnidarians

flowering plants conifers

horsetails

lycophytes

ferns

bryophytes

sporozoans

green algae amoeboidprotozoans

slime molds

ciliatesredalgae

brown algaechrysophytes

cycads

ginkgos

rotifers

arthropodsroundworms

chytrids

oomycotes

euglenoids

dinoflagellates

Gram-positive bacteria

spirochetes

chlamydias

proteobacteria

? crown of eukaryotes

(rapid divergences)

molecular origin of life

EUBACTERIAparabasalids

diplomonads(e.g., Giardia)

(alveolates)(stramenopiles)

chlorophytes

kinetoplastids

extreme

(e.g., Trichomonas)

Cladistics

• Cladistics- Classification based solely on evolutionary relationships.

– Classification of organisms matches their evolutionary history and expresses the history in branching trees known as cladogram.

– Clade-The entire portion of a phylogeny that is descended form common ancestor.

How do we construct evolutionary trees using cladistics?

• Identify ancestral and derived traits.– Ancestral traits- Traits shared with a common

ancestor• Most mammals have four limbs, having inherited this from

common ancestor.

– Derived traits- A trait that differs from the ancestral trait in a lineage.

• Homologous Traits- Traits derived from a common ancestor.

• Most mammalian limbs terminate in five digits, but in the hooved animals, there is only one. This trait, having only one digit, is a homologous trait and could be used to group all the hooved animals together.

1

1

1

1

1

1

2

2

2

2

2

2

2

3

3

3

3

3

3

3

4

4

4

4

4

5

5

5

5

early reptile

pterosaur

chicken

bat

porpoise

penguin

human

Archeaopteryx vs. Pigeon

Difficulties in determining homologous traits

• Not all resemblances are products of common ancestry.– Homoplasy- Some traits are the product of

convergent evolution, the evolution of the same trait in different lineages

• Ex: Australian mammals vs. N. American Mammals

Homoplasy

Species that share a common ancestor should share many

homologous traits

• Therefore, if two species share the same trait, systematists should, until proven otherwise, assume that the trait is homologous, i.e. none of the traits are the product of convergent evolution.

shark mammal crocodile bird

fur

heart

lungs

gizzard

feathers

Clades

Major Lineages

Constructing a Cladogram

• Assumptions– Evolution of traits is irreversible, i.e. an

ancestral trait can change into a derived one, but not the reverse.

– Each trait can change only once in a lineage.

Constructing a Cladogram

• Determine an outgroup, a taxon that is closely related to the group whose phylogeny is being constructed, but that branched off from the lineage of the group below its base on the evolutionary tree. – You know it’s different from the rest. It’s the one that’s “not like

the others”.

• Select traits that are believed to be homologous.• For each taxon, determine whether it has, or is lacking, that trait.

– (+) indicates the presence of the trait in that taxon.– ( - )indicates the lack of the trait in that taxon.

• Taxa with more homologous traits, have a more recent common ancestor, i.e. they are farther up the tree

plat

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, mon

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mes

rabb

its

rode

nts

prim

ates

hors

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ther

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soda

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deer

, oth

erar

tioda

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s

wha

les,

dol

phin

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carn

ivor

es

shre

ws,

oth

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sect

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es, b

ats

arm

adill

os

ante

ater

s

ma n

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scid

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kang

aroo

s, m

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ancestral mammal

CENOZOIC

MEZOZOIC