Transcript Biol 178 Lecture 32

Bio 178 Lecture 32
Evolution and the Origin of Species
J. Elson-Riggins
Reading
•
Chapters 21, 22, 23, 25, & 1
Quiz Material
•
Questions on P 452, 470, 490, 530, & 18
•
Chapters 21, 22, 23, 25, & 1 Quizzes on Text Website
(www.mhhe.com/raven7)
Changing Allele Frequencies (Cntd.)
• Genetic Drift
Random change in allele frequencies of a population as a
result of chance events.
Founder Effects
One or a few individuals leave a population and establish a
new one.
The alleles of these founders will be very significant in the
new population, even if they were rare in the original
population.
Eg. Galápagos Islands.
Founder Effect
Founder Effect
© S. Riggins
Genetic Drift (Cntd.)
Bottleneck Effect
Occurs when the population is drastically reduced to a few
individuals by a chance event - a random genetic sample of
the initial population will remain and genetic variability
will be restricted.
Eg. Northern elephant seal: ~ 20 animals ~1900, now
~130,000 animals.
Bottleneck Effect
Disseminated Intravascular Coagulation
Lungs from Infected NES
Changing Allele Frequencies (Cntd.)
• Selection
Process by which some organisms leave more offspring
than others.
Artificial Selection
Breeder selects the desired characteristics.
Natural Selection
Environment determines which individuals survive.
(Natural selection is one of several processes that can cause
evolutionary change).
Frequency Dependent Selection
Heterozygote Advantage
Fitness
Reproductive success of an individual.
Dependent on:
• Survival time
• Mating frequency
• Number of offspring per mating
Forms of Selection
Selective changes to the population depend on which
genotypes are favored.
• Disruptive Selection
Intermediate
phenotypes are
selected against, eg.
African fire-bellied
seedcracker finch.
Disruptive Selection
Forms of Selection (Cntd.)
• Directional Selection
Individuals of one extreme phenotype are selected against.
Forms of Selection (Cntd.)
• Stabilizing Selection
Individuals of
both extremes
are selected
against, eg.
Weight of human
newborns.
Stabilizing selection
Evidence for Evolution by Natural Selection
• Darwin’s Finches
Collection
In 1835, Darwin collected 31 individual finches from 3
Galápagos Islands - represented 13 species, all similar
except for their bills.
Importance of the Bill
The size and shape of bill correlated with their food source
 each bill type is adapted for its function  evidence for
natural selection.
Recent Evidence - P. and R. Grant
Read P 455.
Resource Partitioning In Darwin’s Finches
Finch from San Cristobal Island
©J. Elson-Riggins
Evidence for Evolution by Natural Selection
• Industrial Melanism and Peppered Moths
Biston betularia
Adults range from “peppered” to melanic - due to
different alleles in the population.
Black is dominant.
Pre-1850 Birmingham, England
Black moths rare.
Post-1850
Increasing proportion of black moths, up to 100% of
certain populations.
Biston betularia
Industrial Melanism (Cntd.)
Why did the Allele Frequency Change?
Read about Tutt’s hypothesis (1896) and Kettlewell’s
experiment (1950’s).
Industrial Melanism
Process by which darker individuals become more
frequent than lighter individuals in industrialized areas due to natural selection.
Selection Against Melanism
Has occurred since the Clean Air Act of 1956.
Current Controversy - What is the agent of Natural
Selection?
Read P 457.
Selection Against Melanism
Evidence for Evolution by Natural Selection
• Artificial Selection
By selecting for desirable phenotypic traits, humans have
produced evolutionary change over short periods of time.
Agriculture and Lab Experiments
Read P 458
Domestication
Example - domestic dogs. Selection for desirable traits has
resulted in huge phenotypic variation in only 10,000 years.
Domestic Dog Breeds
Fossil Evidence for Evolution
• The Fossil Record
Fossilization
Occurs rarely, but enough fossils have been found to
provide information on evolution.
Successive Evolutionary change
Fossil record documents life from the origin of eukaryotes
on.
Gaps in the Fossil Record
Due to problems with the fossilization process and
recovery.
Some major gaps filled recently, eg. Missing links in
cetacean evolution - recent discoveries of Ambulocetus,
Rodhocetus, & Pakicetus.
History of Life Revealed by Fossil Record
Missing Links in Evolution of Cetaceans
Evolution of Oyster Shell Shape
Fossil Evidence for Evolution
• Horse Evolution
Over 60 million years, the horse has evolved from a small
4-toed, short-legged mammal adapted to woodland, to its
current form, which is adapted for open grassland.
Hyracotherium sandrae
Although, due to lack of
horse diversity its evolution
appears linear, there were
actually 13 genera of horses
in N. America in the
Miocene epoch.
Horse Evolution - Body Size
Horse Evolution
Evidence for Evolution (Cntd.)
• The Anatomical Record
1. Sharing the Same Parts
* Homologous Structures
Structures that (although they differ in form and function)
are derived from the same body part of a common
ancestor.
Eg. Bones of vertebrate limbs.
* Analogous Structures
Features that resemble one another as a consequence of the
same selective pressures, but were formed from different
structures (not from a common ancestral origin).
Eg. Wings of insects and birds.
Homology - Vertebrate Bones
The Anatomical Record (Cntd.)
2. Development
Embryonic development of vertebrate embryos is similar suggests a common ancestor.
Eg. All at one stage have gills and a tail.
3. Imperfect Structures
Not all organisms are perfectly adapted to their
environments - a consequence of selection acting on the
variation available in the population (random rather than
by design).
Eg. Blind spot of vertebrate eye compared to mollusk eye,
giraffe neck vertebrae.
Vertebrate Development
Vertebrate and Mollusk Eyes
The Anatomical Record (Cntd.)
3. Vestigial Structures
Structures that had a function in the original ancestor, but
have no obvious function in the descendent (diminished
structure with reduced significance) - strong evidence for
evolution.
Examples:
Human appendix - Is the terminal part of the cecum. Is
small and vermiform, a vestige of the cecum of our
herbivorous ancestors.
Whale pelvic bones - reduced.
Cecum and Appendix of Mammals
http://www.talkorigins.org/faqs/vestiges/appendix.html
Whale Pelvic Bones
Evidence for Evolution (Cntd.)
• The Molecular Record
1. Sequence Divergence
Evolutionary changes occur by nucleotide change.
Hypothesis - More distantly related organisms expected to
have more differences in their DNA sequences than closely
related organisms.
Tested by comparing the sequence divergence of organisms
to the anatomical/fossil records - does the molecular record
match the anatomical/fossil records?
Use non-coding sequences - closely related organisms will
only have a similar sequence if evolution has occurred.
The Molecular Record (Cntd.)
2. Phylogenetic Trees
• Represent the evolutionary history of a group of
organisms. Can be based on a variety of characteristics.
Molecular data frequently used, eg. rRNA spacer regions.
• Anatomical/fossil and molecular data largely in
agreement.
Fig. 25.11
Molecular Clock of Cytochrome c
Suggests progressive change over time:
Evidence for Evolution (Cntd.)
• Convergent Evolution
The independent development of similar structures in
organisms that are not directly related.
Occurs as a consequence of the same selective pressures similar environments.
Example:
Marsupial-Placental Convergence
Despite isolation, Australian marsupials resemble
placental mammals occupying the same niches (functional
role in its environment) on other continents.
Convergent Evolution
Evidence for Evolution (Cntd.)
• Island Evolution
Organisms on islands tend to most closely resemble the
organisms living on the nearest continent - suggests that
they have common ancestors.
Eg. Darwin’s finches and Galápagos tortoises most closely
resemble S. American finches & tortoises.
Voyage of H.M.S. Beagle
Darwin (1809-1882) and his Evidence
Read P 8-14
• Fossils
Living organisms often resemble fossils found in the same
area - did one give rise to the other?
• Geographical Distribution
Characteristics of similar species vary
from place to place - do organisms change
as they migrate?
Criticism of the Theory of Evolution
Read P 468.
The Biological Species Concept
Ernst Mayr (1942)
“Species are groups of actually or potentially interbreeding
natural populations which are reproductively isolated
from other such groups”.
ie. A species is composed of populations that COULD
interbreed to produce fertile offspring. But, different
species are reproductively isolated.
• Problems with the BSC
Many problems (eg. asexual organisms)
 other species concepts exist. Read P
477.
The Process of Speciation
Similar populations diverge until reproductive isolation
results  Separate species
• Populations adapt to their environment or
random changes may occur in separate
populations.
• Adaptation or random changes result in the
accumulation of many differences between the
populations.
• Isolating mechanisms prevent population
hybridization.
• The populations are no longer capable of
interbreeding successfully.
Mechanisms of Reproductive Isolation
Liger
http://www.sierrasafa
rizoo.com/animals/li
ger.htm
Tigon
Behavioral Isolation
Classification of Organisms
• Binomial System (Carolus Linnaeus (1707-1778)
Each organism is given a 2 part name, genus and species.
Example:
Homo sapiens  H. sapiens
• Taxonomic Hierarchy
1. Species
5. Class
2. Genus
6. Phylum
3. Family
7. Kingdom
4. Order
8. Domain
Taxonomic Hierarchy
The Six Kingdom, 3 Domain System
Carl Woese (1990)
• Kingdoms
2 prokaryote kingdoms:
Archaebacteria
Eubacteria
4 eukaryote kingdoms:
Protista
Fungi
Plantae
Animalia
• Domains
Bacteria
Archaea
Eukarya
Evolutionary Relationship of the 3 Domains
The End!
© J. Elson-Riggins