Figure 4.3 (b)
24 The Origin of species
Species and Speciation
• Fundamental unit of classification is the species.
• Species = a group of populations in which genes are
actually, or potentially, exchanged through interbreeding.
• Problems
– Reproductive criterion must be assumed based on
phenotype and ecological information.
– Asexual reproduction
– Fossil
– Geographical isolation
• The origin of new species, or speciation
– Is at the focal point of evolutionary theory,
because the appearance of new species is the
source of biological diversity
• Evolutionary theory
– Must explain how new species originate in
addition to how populations evolve
Microevolution, Macroevolution, and
Evidence of Macroevolutionary change
~ Bacteria gain resistance to antibiotics over time
• A change in frequency of alleles in populations over time
is called Microevolution.
• Over longer timescales, microevolutionary processes
result in large scale changes that result in formation of
new species called Macroevolution (species level)
• Evidence of Macroevolution- patterns of plant and animal
distribution, fossils, anatomical structures, and
developmental processes
• Concept 24.1: The biological species
concept emphasizes reproductive isolation
• Species
– Is a Latin word meaning “kind” or
“appearance”
Reproductive isolation leads to Speciation
- the formation of new species
• Requirement
– Subpopulations are prevented from
interbreeding
– Gene flow does not occur (Reproductive
isolation)
• Reproductive isolation can result in evolution
• Natural selection and genetic drift can result in
evolution
Speciation of Darwin’s Finches
Warbler
Large ground finch
(a)
Similarity between different species.
The eastern and western meadowlark (Sturnella
magna, left) (Sturnella neglecta, right)
songs and other behaviors are different enough
to prevent interbreeding
(b)
Diversity within a species. As diverse as we
may be in appearance, all humans belong to
a single biological species (Homo sapiens),
defined by our capacity to interbreed.
Figure 24.3 A, B
Reproductive Isolation
• Reproductive isolation
– Is the existence of biological factors that
impede members of two species from
producing viable, fertile hybrids
– Is a combination of various reproductive
barriers
• Prezygotic barriers
– Impede mating between species or hinder the
fertilization of ova if members of different
species attempt to mate
• Postzygotic barriers
– Often prevent the hybrid zygote from developing
into a viable, fertile adult
Prezygotic barriers impede mating or hinder fertilization if mating does occur
Habitat
isolation
Behavioral
isolation
Temporal
isolation
Individuals
of different
species
Mechanical
isolation
Mating
attempt
• Prezygotic and postzygotic barriers
HABITAT ISOLATION
TEMPORAL ISOLATION
MECHANICAL ISOLATION
(g)
BEHAVIORAL ISOLATION
(b)
(d)
(e)
(f)
(a)
(c)
Figure 24.4
Gametic
isolation
Hybrid
breakdown
Reduce
hybrid
fertility
Reduce
hybrid
viability
Viable
fertile
offspring
Fertilization
GAMETIC ISOLATION
REDUCED HYBRID FERTILITY
REDUCED HYBRID
VIABILITY
(k)
(j)
(m)
(l)
(h)
(i)
HYBRID BREAKDOWN
Limitations of the Biological
Species Concept
• The biological species concept cannot be
applied to
– Asexual organisms
– Fossils
– Organisms about which little is known
regarding their reproduction
Other Definitions of Species
• The morphological species concept
– Characterizes a species in terms of its body shape, size,
and other structural features
• The paleontological species concept
– Focuses on morphologically discrete species known only
from the fossil record
• The ecological species concept
– Views a species in terms of its ecological niche
• The phylogenetic species concept
– Defines a species as a set of organisms with a unique
genetic history
• Concept 24.2: Speciation can take place
with or without geographic separation
• Speciation can occur in two ways
– Allopatric speciation
– Sympatric speciation
Figure 24.5 A, B
(a) Allopatric speciation. A (b) Sympatric speciation. A small
population becomes a new species
population forms a new
species while geographically without geographic separation.
isolated from its parent
population.
Allopatric (“Other Country”)
Speciation
• In allopatric speciation
– Gene flow is interrupted or reduced when a
population is divided into two or more
geographically isolated subpopulations
• Once geographic separation has occurred
– One or both populations may undergo
evolutionary change during the period of
separation
A. harrisi
Figure 24.6
A. leucurus
Sympatric (“Same Country”)
Speciation
• In sympatric speciation
– Speciation takes place in geographically
overlapping populations
Habitat Differentiation and
Sexual Selection
• Sympatric speciation
– Can also result from the appearance of new
ecological niches
• In cichlid fish
– Sympatric speciation has resulted from
nonrandom mating due to sexual selection
EXPERIMENT
Researchers from the University of Leiden placed males and females of Pundamilia pundamilia and
P. nyererei together in two aquarium tanks, one with natural light and one with a monochromatic orange
lamp. Under normal light, the two species are noticeably different in coloration; under monochromatic orange
light, the two species appear identical in color. The researchers then observed the mating choices of the fish
in each tank.
Monochromatic
Normal light
orange light
P. pundamilia
P. nyererei
RESULTS
CONCLUSION
Figure 24.10
Under normal light, females of each species mated only with males of their own species. But
under orange light, females of each species mated indiscriminately with males of both species.
The resulting hybrids were viable and fertile.
The researchers concluded that mate choice by females based on coloration is the main
reproductive barrier that normally keeps the gene pools of these two species separate. Since
the species can still interbreed when this prezygotic behavioral barrier is breached in the
laboratory, the genetic divergence between the species is likely to be small. This suggests
that speciation in nature has occurred relatively recently.
Allopatric and Sympatric
Speciation: A Summary
• In allopatric speciation
– A new species forms while geographically
isolated from its parent population
• In sympatric speciation
– The emergence of a reproductive barrier
isolates a subset of a population without
geographic separation from the parent species
Adaptive Radiation
• Adaptive radiation
– Is the evolution of diversely adapted species
from a common ancestor upon introduction to
new environmental opportunities (typical for
long-distance dispersal)
Black noddy tern
Australian coast
• The Hawaiian archipelago
– Is one of the world’s great showcases of
adaptive radiation
1.3 million years
Dubautia laxa
MOLOKA'I
MAUI
KAUA'I
5.1
million
years
Argyroxiphium sandwicense
O'AHU
3.7
million
years
Dubautia waialealae
LANAI
HAWAI'I
0.4
million
years
13
• The punctuated equilibrium model
– Contrasts with a model of gradual change
throughout a species’ existence
Time
(a)
Gradualism model. Species
descended from a common
ancestor gradually diverge
more and more in their
morphology as they acquire
unique adaptations.
(b)
Punctuated equilibrium
model. A new species
changes most as it buds
from a parent species and
then changes little for the
rest of its existence.
25 Phylogeny and Systematics
• Overview: Investigating the Tree of Life
• This chapter describes how biologists
trace phylogeny
– The evolutionary history of a species or group
of related species
• Biologists draw on the fossil record
– Which provides information about ancient
organisms
Figure 25.1
• Biologists also use systematics
– As an analytical approach to understanding
the diversity and relationships of organisms,
both present-day and extinct
• Currently, systematists use
– Morphological, biochemical, and molecular
comparisons to infer evolutionary
relationships
Figure 25.2
• Concept 25.1: Phylogenies are based on
common ancestries inferred from fossil,
morphological, and molecular evidence
The Fossil Record
• Sedimentary rocks
– Are the richest source of fossils
– Are deposited into layers called strata
1 Rivers carry sediment to the
ocean. Sedimentary rock layers
containing fossils form on the
ocean floor.
2 Over time, new strata are
deposited, containing fossils
from each time period.
3 As sea levels change and the seafloor
is pushed upward, sedimentary rocks are
exposed. Erosion reveals strata and fossils.
Younger stratum
with more recent
fossils
Figure 25.3
Older stratum
with older fossils
• The fossil record
– Is based on the sequence in which fossils have
accumulated in such strata
• Fossils reveal
– Ancestral characteristics that may have been
lost over time
• Though sedimentary fossils are the most
common
– Paleontologists study a wide variety of fossils
(c) Leaf fossil, about 40 million years old
(b) Petrified tree in Arizona, about
190 million years old
(a) Dinosaur bones being excavated
from sandstone
(d) Casts of ammonites,
about 375 million
years old
(f) Insects
preserved
whole in
amber
Morphological and Molecular
Homologies
• In addition to fossil organisms
– Phylogenetic history can be inferred from
certain morphological and molecular similarities
among living organisms
• In general, organisms that share very similar
morphologies or similar DNA sequences
– Are likely to be more closely related than
organisms with vastly different structures or
sequences
Sorting Homology from Analogy
• A potential misconception in constructing a
phylogeny
– Is similarity due to convergent evolution,
called analogy, rather than shared ancestry
• Convergent evolution occurs when similar
environmental pressures and natural
selection
– Produce similar (analogous) adaptations in
organisms from different evolutionary lineages
Marsupial Australian
mole
Eutherian North Am.
mole
Figure 25.5
• Analogous structures or molecular
sequences that evolved independently
– Are also called homoplasies
1
Ancestral homologous
DNA segments are
identical as species 1
and species 2 begin to
diverge from their
common ancestor.
1 C C A T C A G A G T C C
2 C C A T C A G A G T C C
Deletion
2
3
4
Figure 25.6
Deletion and insertion
mutations shift what
had been matching
sequences in the two
species.
Homologous regions
(yellow) do not all align
because of these mutations.
Homologous regions
realign after a computer
program adds gaps in
sequence 1.
1
C C A T C A G A G T C C
2
C C A T C A G A G T C C
G T A
Insertion
1
C C A T
C A
2
C C A T
G T A
1
2
A G T C C
C C A T
C C A T
G T A
C A G
A G T C C
C A
A G T C C
C A G
A G T C C
• Concept 25.2: Phylogenetic systematics
connects classification with evolutionary
history
• Taxonomy
– Is the ordered division of organisms into
categories based on a set of characteristics
used to assess similarities and differences
Binomial Nomenclature
• Binomial nomenclature
– Is the two-part format of the scientific name of
an organism
– Was developed by Carolus Linnaeus 17071778 (Father of Taxonomy or Systematics)
• The binomial name of an organism or
scientific epithet
– Is latinized
– Is the genus and species
Hierarchical Classification
• Linnaeus also introduced a system
– For grouping species in increasingly broad
Panthera
Species pardus
categories
Panthera
Genus
Felidae
Family
Carnivora
Order
Class
Phylum
Kingdom
Figure 25.8
Domain
Mammalia
Chordata
Animalia
Eukarya
Panthera
pardus
(leopard)
Mephitis
mephitis
(striped skunk)
Lutra lutra
(European
otter)
Panthera
Mephitis
Lutra
Figure 25.9
Order
Family
– In branching
phylogenetic trees
Species
• Systematists depict
evolutionary
relationships
Genus
Linking Classification and
Phylogeny
Felidae
Mustelidae
Carnivora
Canis
familiaris
(domestic dog)
Canis
lupus
(wolf)
Canis
Canidae
• Each branch point
– Represents the divergence of two species
Leopard
Domestic cat
Common ancestor
• Concept 25.3: Phylogenetic systematics informs
the construction of phylogenetic trees based on
shared characteristics
• A cladogram
– Is a depiction of patterns of shared characteristics
among taxa
• A clade within a cladogram
– Is defined as a group of species that includes an
ancestral species and all its descendants
• Cladistics
– Is the study of resemblances among clades
Cladistics
• Clades
– Can be nested within larger clades, but not all
groupings or organisms qualify as clades
• A valid clade is monophyletic
– Signifying that it consists of the ancestor
species and all its descendants
Grouping 1
E
D
J
H
G
F
C
I
B
A
(a) Monophyletic. In this tree, grouping 1,
consisting of the seven species B–H, is a
monophyletic group, or clade. A monophyletic group is made up of an
ancestral species (species B in this case)
and all of its descendant species. Only
monophyletic groups qualify as
legitimate taxa derived from cladistics.
Figure 25.10a
K
• A paraphyletic clade
– Is a grouping that consists of an ancestral
species and some, but not all, of the
descendants
Grouping 2
G
E
D
C
J
H
I
F
B
A
(b) Paraphyletic. Grouping 2 does not
meet the cladistic criterion: It is
paraphyletic, which means that it
consists of an ancestor (A in this case)
and some, but not all, of that ancestor’s
descendants. (Grouping 2 includes the
descendants I, J, and K, but excludes
B–H, which also descended from A.)
Figure 25.10b
K
• A polyphyletic grouping
– Includes numerous types of organisms that
lack a common ancestor
D
E
G
J
H
K
Grouping 3
I
F
C
B
A
(c) Polyphyletic. Grouping 3 also fails the
cladistic test. It is polyphyletic, which
means that it lacks the common ancestor
of (A) the species in the group. Furthermore, a valid taxon that includes the
extant species G, H, J, and K would
necessarily also contain D and E, which
are also descended from A.
Figure 25.10c
Shared Primitive and Shared
Derived Characteristics
• In cladistic analysis
– Clades are defined by their evolutionary
novelties (new chars)
Outgroups
• Systematists use a method called
outgroup comparison
– To differentiate between shared derived
(unique to a clade but not found in beyond
that taxon) and shared primitive (ancestral)
characteristics
• As a basis of comparison we need to
designate an outgroup
– which is a species or group of species that is
closely related to the ingroup, the various
species we are studying
• Outgroup comparison
– Is based on the assumption that homologies
present in both the outgroup and ingroup must
be primitive characters that predate the
divergence of both groups from a common
ancestor
• The outgroup comparison
– Enables us to focus on just those characters
that were derived at the various branch
points in the evolution of a clade
Lamprey
Tuna
Turtle
Leopard
Salamander
Lancelet
(outgroup)
CHARACTERS
TAXA
Hair
0
0
0
0
0
1
Amniotic (shelled) egg
0
0
0
0
1
1
Four walking legs
0
0
0
1
1
1
Hinged jaws
0
0
1
1
1
1
Vertebral column (backbone)
0
1
1
1
1
1
Turtle
Figure 25.11a, b
(a) Character table. A 0 indicates that a character is absent; a 1
indicates that a character is present.
Leopard
Hair
Salamander
Amniotic egg
Tuna
Four walking legs
Lamprey
Hinged jaws
Lancelet (outgroup)
Vertebral column
(b) Cladogram. Analyzing the distribution of these
derived characters can provide insight into vertebrate
phylogeny.
•
The
Universal
Tree
of
Life
The tree of life
– Is divided into three great clades called domains: Bacteria,
Archaea, and Eukarya
• The early history of these domains is not yet clear
Billion years ago
Bacteria
Eukarya Archaea
0
4
Symbiosis of
chloroplast
ancestor with
ancestor of green
plants
1
3
Symbiosis of
mitochondrial
ancestor with
ancestor of
eukaryotes
2
Possible fusion
of bacterium
and archaean,
yielding
ancestor of
eukaryotic cells
1
Last common
ancestor of all
living things
4
2
3
2
3
1
Origin of life
Figure 25.18
4
26 The Tree of Life
An Introduction to Biological Diversity
• Overview: Changing Life on a Changing
Earth
• Life is a continuum
– Extending from the earliest organisms to the
great variety of species that exist today
• Geological events that alter environments
– Change the course of biological evolution
• Conversely, life changes the planet that it
inhabits
Figure 26.1
e 26.10
• The analogy of a clock
– Can be used to place major events in the
Earth’s history in the context of the
geological record
Cenozoic
Humans
Land plants
Origin of solar
system and
Earth
Animals
4
1
Proterozoic
Eon
Archaean
Eon
Billions of years ago
2
3
Multicellular
eukaryotes
Prokaryotes
Single-celled
eukaryotes
Atmospheric
oxygen
Concept 26.3: As
prokaryotes evolved, they
exploited and changed
young Earth
The oldest known fossils
are stromatolites
– Rocklike structures
composed of many layers
of bacteria and sediment
– Which date back 3.5 billion
years ago
The First Prokaryotes
• Prokaryotes were Earth’s sole inhabitants
– From 3.5 to about 2 billion years ago
Electron Transport Systems
• Electron transport systems of a variety of
types
– Were essential to early life
– Have: some aspects that possibly precede life itself
Photosynthesis and the Oxygen
Revolution
• The earliest types of photosynthesis
– Did not produce oxygen
• Oxygenic photosynthesis
– Probably evolved about 3.5 billion years ago
in cyanobacteria
Figure 26.12
• When oxygen began to accumulate in the
atmosphere about 2.7 billion years ago
– It posed a challenge for life
– It provided an opportunity to gain abundant
energy from light
– It provided organisms an opportunity to exploit
new ecosystems
• Concept 26.4: Eukaryotic cells arose from
symbioses and genetic exchanges between
prokaryotes
• Among the most fundamental questions in
biology
– Is how complex eukaryotic cells evolved from
much simpler prokaryotic cells
The First Eukaryotes
• The oldest fossils of a simple eukaryotic
cell
– Date back 2.1 billion years
Endosymbiotic Origin of
Mitochondria and Plastids
• The theory of endosymbiosis
– Proposes that mitochondria and plastids were
formerly small prokaryotes living within larger
host cells
• The prokaryotic ancestors of mitochondria
and plastids
– Probably gained entry to the host cell as
undigested prey or internal parasites
Cytoplasm
DNA
Plasma
membrane
Ancestral
prokaryote
Infolding of
plasma membrane
Endoplasmic
reticulum
Nucleus
Nuclear envelope
Engulfing
of aerobic
heterotrophic
prokaryote
Cell with nucleus
and endomembrane
system
Mitochondrion
Mitochondrion
Ancestral
heterotrophic
eukaryote
Figure 26.13
Engulfing of
photosynthetic
prokaryote in
some cells
Plastid
Ancestral
Photosynthetic
eukaryote
• In the process of becoming more
interdependent
– The host and endosymbionts would have
become a single organism
• The evidence supporting an
endosymbiotic origin of mitochondria and
plastids includes
– Similarities in inner membrane structures and
functions
– Both have their own circular DNA
• Concept 26.5: Multicellularity evolved
several times in eukaryotes
• After the first eukaryotes evolved
– A great range of unicellular forms evolved
– Multicellular forms evolved also
The Earliest Multicellular
Eukaryotes
• Molecular clocks
– Date the common ancestor of multicellular
eukaryotes to 1.5 billion years
• The oldest known fossils of eukaryotes
– Are of relatively small algae that lived about 1.2
billion years ago
• Larger organisms do not appear in the fossil
record
– Until several hundred million years later
• Chinese paleontologists recently described
570-million-year-old fossils
– That are probably animal embryos
Figure 26.15a, b
(a) Two-cell stage
150 m
(b) Later stage 200 m
The Colonial Connection
• The first multicellular organisms were
colonies
– Collections of autonomously replicating cells
Figure 26.16
• Some cells in the colonies
– Became specialized for different functions
• The first cellular specializations
– Had already appeared in the prokaryotic
world
Colonization of Land by Plants,
Fungi, and Animals
• Plants, fungi, and animals
– Colonized land about 500 million years ago
• Robert Whittaker proposed a system with
five kingdoms
– Monera, Protista, Plantae, Fungi, and
Animalia
Plantae
Fungi
Protista
Figure 26.21
Monera
Animalia
Reconstructing the Tree of Life: A
Work in Progress
• A three domain system
– Has replaced the five kingdom system
– Includes the domains Archaea, Bacteria, and
Eukarya
• Each domain
– Has been split by taxonomists into many
kingdoms