Download How New Species Evolve

Chapter 17
Speciation and Macroevolution
1
17.1 How New Species Evolve
• Macroevolution is best observed within
the fossil record
 Requires the origin of species, also called
speciation.
 Speciation is the final result of changes in
the gene pool’s allelic and genotypic
frequencies.
2
How New Species Evolve
• Every species has its own evolutionary
history
• Species Concepts
 Refers to the different ways in which a
species is defined.
3
How New Species Evolve
• Morphological species concept
 Based on analysis of diagnostic traits
distinguishing one species from another.
• Can be distinguished anatomically
• Method used by Linnaeus
• Most species are described this way
4
How New Species Evolve
• The evolutionary species concept
distinguishes species from one another
based on morphological (structural) traits
 Critical traits for distinguishing species are
called diagnostic traits
• The phylogenetic species concept
relies on the identification of species
based on common ancestry.
 A common ancestor for two or more
different groups.
5
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Evolutionary
Species
Concept
Orcinus orca
Hindlimbs too
reduced for walking
or swimming
Rodhocetus kasrani
Ambulocetus natans
Hindlimbs used
for both walking
on land and
paddling in water
Tetrapod with limbs
for walking
Pakicetus attocki
6
How New Species Evolve
• Biological Species Concept
• Populations of the same species breed only
among themselves
• Experience reproductive isolation from other
such populations
• Very few species are actually tested for
reproductive isolation
7
How New Species Evolve
• Reproductive isolating mechanisms inhibit
gene flow between species
• Two general types:
 (1) Prezygotic Isolating Mechanisms – prevent
mating attempts or make it unlikely that fertilization
will be successful
• Habitat Isolation - species occupy different habitats
• Temporal Isolation - each reproduces at a different time
• Behavioral Isolation - courtship patterns for recognizing
mates
• Mechanical Isolation - incompatible animal genitalia or plant
floral structures
• Gamete Isolation - gametes that meet do not fuse to
become a zygote
8
Reproductive Barriers
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Prezygotic Isolating Mechanisms
Premating
Postzygotic Isolating Mechanisms
Mating
Habitat isolation
Species at same locale
occupy different habitats.
species 1
Temporal isolation
Zygote mortality
Mechanical isolation
Genitalia between
species are unsuitable
for one another.
Species reproduce at
different seasons or
different times of day.
species 2
Fertilization
Fertilization occurs, but
zygote does not survive.
Hybrid sterility
hybrid
offspring
Hybrid survives but is
sterile and cannot
reproduce.
Gamete isolation
Behavioral isolation
In animal species,
courtship behavior differs,
or individuals respond to
different songs, calls,
pheromones, or other
signals.
Sperm cannot reach
or fertilize egg.
F2 fitness
Hybrid is fertile, but F2 hybrid
has reduced fitness.
9
Temporal Isolation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Mating Activity
high
low
March 1
April 1
May 1
June 1
July 1
10
How New Species Evolve
• Reproductive Isolating Mechanisms (cont.)
 Postzygotic Isolating Mechanisms - Prevent
hybrid offspring from developing or breeding
• Hybrid Inviability - hybrid zygote is not viable and
dies
• Hybrid Sterility - hybrid zygote develops into a
sterile adult
– Ex. Mule (Female Horse and Male Donkey), Ligers
11
17.2 Modes of Speciation
• Speciation:
 The splitting of one species into two, or
 The transformation of one species into a new
species over time
• Two modes:
 (1) Allopatric Speciation
• Two geographically isolated populations of one
species become different species over time
• Can be due to differing selection pressures in
differing environments
• Stickleback Speciation
12
Allopatric Speciation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Ensatina eschscholtzi picta
1
Members of a northern ancestral
population migrated southward.
Ensatina eschscholtzi
oregonensis
2
Subspecies are separated by
California’s Central Valley .Some
interbreeding between populations
does occur.
Central
Valley
Barrier
Ensatina eschscholtzi platensis
Ensatina eschscholtzi
xanthoptica
Ensatina eschscholtzi
croceater
Ensatina eschscholtzi
eschscholtzii
3
Evolution has occurred, and in the
south, subspecies do not
interbreed even though they live in
the same environment.
Ensatina eschscholtzi
klauberi
13
Allopatric Speciation Among
Sockeye Salmon
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Lake male
River male
Lake female
River female
a. Sockeye salmon at Pleasure Point Beach, Lake Washington
b. Sockeye salmon in Cedar River .The river connects with
Lake Washington.
14
Modes of Speciation
• Two modes (continued):
 (2) Sympatric Speciation
• One population develops into two or more
reproductively isolated groups
• No prior geographic isolation
• In plants, sympatric speciation often involves
polyploidy (a chromosome number beyond the
diploid [2n] number)
– Tetraploid hybridization in plants
» Results in self fertile species that are reproductively
isolated from either parental species
15
Modes of Speciation
 (2) Sympatric Speciation
• A polyploid plant can reproduce with itself, but cannot
reproduce with the 2n population because not all the
chromosomes would be able to pair during meiosis.
• Two types of polyploidy are known:
– Autoploidy - diploid plant produces diploid gametes due to
nondisjunction during meiosis.
» If diploid gamete fuses with a haploid gamete, a triploid plant
results.
» A triploid (3n) plant is sterile and cannot produce offspring
because the chromosomes cannot pair during meiosis.
– Alloploidy - more complicated process than autoploidy
» Requires two different but related species of plants
» Hybridization is followed by doubling of the chromosomes.
16
Autoploidy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2n = 14
2n = 10
Clarkia concinna
Clarkia virgata
hybrid
doubling of chromosome number
2n = 24
Clarkia pulchella
(C. pulchella): © J. L. Reveal; (C. concinna): © Gerald & Buff Corsi/Visuals Unlimited; (C. virgata): ©: Dr. Dean Wm. Taylor/Jepson Herbarium, UC Berkeley
17
Modes of Speciation
• Adaptive Radiation
 Occurs when members of a species invade several
new geographically separate environments
 The populations become adapted to the different
environments
 Many new species evolve from the single ancestral
species
• Ex. Galapagos Finches, Hawaiian Honeycreepers
18
Adaptive Radiation in
Hawaiian Honeycreepers
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
* Lesser Koa finch
Palila
Laysan
finch
* Greater
Koa finch
Ou
* Kona
finch
Maui parrot bill
Akiapolaau
* Kauai
akialoa
Nukupuu
* Akialoa
Genus Loxops
Anianiau
(lesser
amakihi)
Great
amakihi
(green
solitaire)
* Extinct species or subspecies
Alauwahio
(Hawaiian
creeper)
Akepa
Amakihi
19
Modes of Speciation
• Convergent Evolution
 Occurs when a similar biological trait evolves in two
unrelated species as a result of exposure to similar
environments.
• Traits evolving in this manner are termed analogous traits.
– Similar function, but different origin
– Ex: bird wing vs. bat wing
20
21
Convergent Evolution of
Africa Lake Fish
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Lake Tanganyika
Lake Malawi
Lake Tanganyika
Lake Malawi
Reprinted by permission from Macmillan Publishers Ltd on behalf of Cancer Research UK: RC Albertson, TD
Kocher (2006) Genetic and developmental basis of cichlid trophic diversity. Heredity vol. 97 (3) pp. 211-221
22
17.3 Principles of
Macroevolution
• Macroevolution
 Evolution at the species or higher level of
classification
 Some evolutionists support a gradualistic
model
• Evolution at the species level occurs gradually
• Speciation occurs after populations become
isolated
• Each group continues its own evolutionary pathway
• The gradualistic model suggests that it is difficult to
indicate when speciation occurred
23
Principles of Macroevolution
• Macroevolution
 Some paleontologists support the punctuated
equilibrium model
• Species can appear quite suddenly
– Species then remain essentially unchanged phenotypically
during a period of stasis (sameness) until they undergo
extinction.
• This model states that periods of equilibrium are
punctuated by speciation
24
Gradualistic and Punctuated
Equilibrium Models
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
new
species 1
new
species 1
ancestral
species
ancestral
species
transitional link
ancestral
species
new
species 2
Time
a. Gradualistic model
stasis
new
species 2
Time
b. Punctuated equilibrium
25
Principles of Macroevolution
• Developmental Genes and Macroevolution
 Genes can bring about radical changes in body
shapes and organs.
• Gene expression can influence development
– A change in gene expression could stop a developmental
process or continue it beyond its normal time.
• Using modern technology, researchers discovered
genes whose differential expression can bring about
changes in body shapes and organs.
–
–
–
–
Pax6 in eye development
Tbx5 in limb development
Hox genes in development of overall shape
Hox genes Video
26
Pax6 Gene and Eye
Development
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(Left): © Carolina Biological Supply/Photo Researchers, Inc.; (Center): © Vol. OS02/PhotoDisc/Getty Images; (Right): © Aldo Brando/Peter Arnold, Inc.
27
Study of Pax6 Gene
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Courtesy Walter Gehring, reprinted with permission from Induction of Ectopic Eyes by Target Expression of the Eyeless Gene in Drosophila, G. Halder, P. Callaerts, Walter J. Gehring, Science Vol. 267, © 24
March 1995 American Association for the Advancement of Science
28
Hox6 Genes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(Both): © A. C. Burke, 2000
29