Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 17
Processes of Evolution
(Sections 17.11 - 17.14)
Albia Dugger • Miami Dade College
17.11 Allopatric Speciation
• In allopatric speciation, a geographic barrier arises and
ends gene flow between populations – genetic divergences
then give rise to new species
• allopatric speciation
• Speciation pattern in which a physical barrier that
separates members of a population ends gene flow
between them
Barriers to Reproduction
• Whether a geographic barrier can block gene flow depends
on whether and how an organism travels (e.g. by swimming,
walking, or flying), and how it reproduces (e.g. by internal
fertilization or by pollen dispersal)
• Example:
• When the Isthmus of Panama formed, it cut off gene flow
among populations of aquatic organisms in the Pacific and
Atlantic oceans
Allopatric Speciation
in Snapping Shrimp
Allopatric Speciation in Snapping Shrimp
Alpheus nuttingi (Atlantic)
Isthmus
of Panama
Alpheus millsae (Pacific)
Fig. 17.20, p. 272
Allopatric Speciation in Snapping Shrimp
Atlantic
Ocean
Mexico
Pacific
Ocean
Isthmus
of Panama
Columbia
Fig. 17.20a, p. 272
Allopatric Speciation in Snapping Shrimp
Alpheus nuttingi (Atlantic)
Fig. 17.20b, p. 272
Allopatric Speciation in Snapping Shrimp
Alpheus millsae (Pacific)
Fig. 17.20b, p. 272
Speciation in Archipelagos
• Archipelagos are isolated island chains formed by volcanoes,
such as the Hawaiian and Galápagos Islands
• Archipelagos were populated by a few individuals of mainland
species whose descendants diverged over time
• Selection pressures within and between the islands can foster
even more divergences
The Hawaiian Islands
Hawaiian Honeycreepers
• The first birds to colonize the Hawaiian Islands found a near
absence of competitors and predators and an abundance of
rich and vacant habitats, which encouraged rapid speciation
• The many species of honeycreepers, unique to the Hawaiian
Islands, have specialized bills and behaviors adapted to feed
on certain insects, seeds, fruits, nectar, or other foods
Honeycreeper Diversity
Honeycreeper
Diversity
Akepa
(Loxops
coccineus)
Insects,
spiders, nectar;
high mountain
rain forest
Fig. 17.21a, p. 273
Honeycreeper
Diversity
Akekee
(Loxops
caeruleirostris)
Insects, spiders,
nectar; high
mountain rain
forest
Fig. 17.21b, p. 273
Honeycreeper
Diversity
Nihoa finch
(Telespiza ultima)
Insects, buds,
seeds, flowers,
seabird eggs;
rocky or shrubby
slopes
Fig. 17.21c, p. 273
Honeycreeper
Diversity
Palila Maui
(Loxioides bailleui)
Mamane seeds,
buds, flowers,
berries, insects;
high mountain
dry forests
Fig. 17.21d, p. 273
Honeycreeper
Diversity
Maui parrotbill
(Pseudonestor
xanthophrys)
Insect larvae,
pupae, caterpillars;
mountain forests,
dense underbrush
Fig. 17.21e, p. 273
Honeycreeper
Diversity
Apapane
(Himatione
sanguinea)
Nectar,
caterpillars and
other insects,
spiders; high
mountain forests
Fig. 17.21f, p. 273
Honeycreeper
Diversity
Poouli
(Melamprosops
phaeosoma)
Tree snails,
insects in
understory; last
one died in 2004
Fig. 17.21g, p. 273
Honeycreeper
Diversity
Maui Alauahio
(Paroreomyza
montana)
Bark or leaf
insects, high
mountain rain
forest
Fig. 17.21h, p. 273
Honeycreeper
Diversity
Kauai Amakihi
(Hemignathus
kauaiensis)
Bark-picker;
insects, spiders,
nectar; high
mountain rain
forest
Fig. 17.21i, p. 273
Honeycreeper
Diversity
Akiapolaau
(Hemignathus
munroi)
Probes, digs
insects from big
trees; high
mountain rain
forest
Fig. 17.21j, p. 273
Honeycreeper
Diversity
Akohekohe
(Palmeria dolei)
Mostly nectar
from flowering
trees, some
insects, pollen;
high mountain
rain forest
Fig. 17.21k, p. 273
Honeycreeper
Diversity
Iiwi
(Vestiaria coccinea)
Mostly nectar (ohia
flowers, some
nectar; lobelias,
mints), some
insects; high
mountain rain
forest
Fig. 17.21l, p. 273
ANIMATION: Allopatric speciation on an
archipelago
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ANIMATION: Models of speciation
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17.12 Sympatric and
Parapatric Speciation
• Populations sometimes speciate even without a physical
barrier that bars gene flow between them
• In sympatric speciation, populations in physical contact
speciate
• With parapatric speciation, populations in contact along a
common border speciate
Sympatric Speciation
• Sympatric speciation can occur instantly with a change in
chromosome number – many plants are polyploid (e.g. wheat)
• Sympatric speciation can also occur with no change in
chromosome number (e.g. mechanically isolated sage plants)
• sympatric speciation
• Pattern in which populations inhabiting the same
geographic region speciate in the absence of a physical
barrier between them
Sympatric Speciation in Wheat
Sympatric Speciation in Wheat
A Einkorn has a diploid chromosome
number of 14 (two sets of 7, shown
here as 14 AA). Wild einkorn
probably hybridized with another
wild species having the same
chromosome number (14 BB) about
11,000 years ago. The resulting
hybrid was diploid (14 AB).
Triticum
monococcum
(einkorn)
14 AA
Unknown
species of
Triticum
X
14 BB
14 AB
B About 8,000 years ago, the
chromo-some number of an AB
hybrid plant spontaneously
doubled. The resulting species,
emmer, is tetraploid: it has two
sets of 14 chromosomes (28
AABB).
spontaneous
chromosome
doubling
T. turgidum
(emmer)
28 AABB
C Emmer probably hybridized
with a wild goatgrass having a
diploid chromosome number of
14 (two sets of 7 DD). The
resulting common bread wheat
has six sets of 7 chromosomes
(42 AABBDD).
T. tauschii
(goatgrass)
X
14 DD
T. aestivum
(common
bread
wheat)
42 AABBDD
Fig. 17.22, p. 274
Examples of Sympatric Speciation
• Lake Victoria cichlids (sexual selection)
• In the same lake, female cichlids of different species
visually select and mate with brightly colored males of
their own species
• Warblers around the Tibetan plateau (behavioral isolation)
• Two populations overlap in range, but don’t interbreed
because they don’t recognize one another’s songs
Male Cichlids of Lake Victoria
Parapatric Speciation
• Parapatric speciation may occur when one population
extends across a broad region with diverse habitats
• Example: Two species of velvet walking worm with
overlapping habitats in Tasmania: Where they interbreed,
their hybrids are sterile
• parapatric speciation
• Speciation model in which different selection pressures
lead to divergences within a single population
Comparing Speciation Models
Key Concepts
• How Species Arise
• Speciation varies in its details, but it always involves the
end of gene flow between populations
• Microevolutionary events that occur independently lead to
genetic divergences, which are reinforced by reproductive
isolation
ANIMATION: Sympatric Speciation in
Wheat
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17.13 Macroevolution
• A central theme of macroevolution is that major evolutionary
novelties often stem from the adaptation of an existing
structure for a completely different purpose (exaptation)
• exaptation
• Adaptation of an existing structure for a completely
different purpose; a major evolutionary novelty
Patterns of Macroevolution
• Macroevolution includes patterns of evolution above the
species level, such as one species giving rise to multiple
species, origin of major groups, and major extinction events
• Four patterns of macroevolution:
• Stasis
• Adaptive radiation
• Coevolution
• Extinction
Stasis
• With the simplest macroevolutionary pattern, stasis, a lineage
persists for millions of years with little or no change
• Example: Coelacanths
• stasis
• Evolutionary pattern in which a lineage persists with little
or no change over evolutionary time
Coelacanth: Fossil and Living
Mass Extinctions
• More than 99% of all species that ever lived are now extinct
• There have been more than twenty mass extinctions, which
are simultaneous losses of many lineages, including five
catastrophic events in which the majority of species on Earth
disappeared
• extinct
• Refers to a species that has been permanently lost
Adaptive Radiation
• In adaptive radiation, a lineage rapidly diversifies into
several new species
• Adaptive radiation can occur after individuals colonize a new
environment that has a variety of different habitats with few or
no competitors (e.g. Hawaiian honeycreepers)
• adaptive radiation
• A burst of genetic divergences from a lineage gives rise to
many new species
An Example of Adaptive Radiation
• This evolutionary tree
diagram shows how one
ancestral species gave
rise to the Hawaiian
honeycreepers
• Only 41 of many
hundreds of species are
represented here
(orange are extinct)
Adaptive Radiation (cont.)
• Adaptive radiations also occur after geologic or climatic
events eliminate some species from a habitat
• Example: Mammals were able to undergo an adaptive
radiation after the dinosaurs disappeared
Adaptive Radiation (cont.)
• A key innovation can result in an adaptive radiation, or rapid
diversification into new species
• Example: evolution of lungs opened the way for an adaptive
radiation of vertebrates on land
• key innovation
• An evolutionary adaptation that gives its bearer the
opportunity to exploit a particular environment more
efficiently or in a new way
Coevolution
• In coevolution, close ecological interactions between two
species cause them to evolve jointly
• Over evolutionary time, two species may become so
interdependent that they can no longer survive without one
another (e.g. the large blue butterfly (Maculinea arion) and
red ant (Myrmica sabuleti))
• coevolution
• Joint evolution of two closely interacting species
• Each species is a selective agent for traits of the other
• Each adapts to changes in the other
Coevolved Species
• The ant eats honey
exuded by the butterfly
larva and carries it to its
nest
• The caterpillar lives in
the ant nest and eats
ant larvae until it
pupates
Evolutionary Theory
• Many biologists disagree about how macroevolution occurs
• Dramatic jumps in morphology may be the result of mutations
in homeotic or other regulatory genes
• Macroevolution may be an accumulation of many
microevolutionary events, or it may be an entirely different
process
Key Concepts
• Macroevolution
• Patterns of genetic change that involve more than one
species are called macroevolution
• Recurring patterns of macroevolution include the origin of
major groups, one species giving rise to many, and mass
extinction
ANIMATION: Adaptation to What?
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ANIMATION: Animal evolution in Phyla
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ANIMATION: Evolution of Horses
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17.14 Phylogeny
• Instead of trying to divide the diversity of living organisms into
a series of taxonomic ranks, most biologists are now focusing
on evolutionary connections
• Cladistics allows us to reconstruct evolutionary history
(phylogeny) by grouping species on the basis of their shared
characters
Key Terms
• phylogeny
• Evolutionary history of a species or group of species
• cladistics
• Method of determining evolutionary relationships by
grouping species into clades based on shared characters
• character
• Quantifiable, heritable characteristic—any physical,
behavioral, physiological, or molecular trait of a species
Examples of Characters
Ranking Versus Grouping
• The result of a cladistic analysis is a cladogram, a type of
evolutionary tree used to visualize evolutionary patterns
• Each line represents a lineage, which may branch into two
sister groups at a node, which represents a shared ancestor
• Every branch ends with a clade, a species or group based on
a set of shares characters
• Ideally, each clade is a monophyletic group that comprises
an ancestor and all of its descendants
Key Terms
• evolutionary tree
• Type of diagram that summarizes evolutionary
relationships among a group of species
• cladogram
• Evolutionary tree that shows a network of evolutionary
relationships among clades
• clade
• A species or group of species that share a set of
characters
Key Terms
• sister groups
• The two lineages that emerge from a node on a cladogram
• monophyletic group
• An ancestor and all of its descendants
Cladograms
Cladograms
A
earthworm
earthworm
multicellular
tuna
tuna
multicellular with a backbone
lizard
lizard
multicellular with a backbone and legs
mouse
mouse
human
human
multicellular with a backbone,
legs, and fur or hair
B
Fig. 17.27, p. 278
ANIMATION: Interpreting a cladogram
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How We Use Evolutionary Biology
• Hawaiian honeycreepers illustrate how evolution works:
• Isolation that spurred honeycreepers’ adaptive radiations
also ensured they had no built-in defenses against
predators or diseases from the mainland
• Specializations became hindrances when habitats
suddenly changed or disappeared
• At least 43 species of honeycreeper that thrived on the
islands before humans arrived were extinct by 1778 -today, 32 of the remaining 71 species are endangered,
and 26 are extinct
Going, Going, and Gone
• Destruction of food
sources and avian
malaria decimated the
palila and akekee
• The poouli is probably
now extinct
Key Concepts
• Cladistics
• Evolutionary tree diagrams are based on the premise that
all species interconnect through shared ancestors
• Grouping species by shared ancestry better reflects
evolutionary history than do traditional ranking systems
Rise of the Super Rats (revisited)
• The allele that makes rats resistant to warfarin is adaptive
when warfarin is present, and maladaptive when it is not
• Periodic exposure to warfarin maintains a balanced
polymorphism of the resistance gene in rat populations