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263 Cards in this Set

  • Front
  • Back
What is homoplasy?
This is a convergent character that arose
independently in two taxa
What animal are whales most closely related to? (Deer, Hippopotamus, Pig, Camel?)
What was a special characteristic of the exterior of dinosaurs?
What is an example of a feather extand dinosaur?
Birds today!
What is the basic taxonomy of birds in order?
Domain- Eukarya
Kingdom- Animalia
Phylum- Chordata
Class- Aves
Superoder- Dinosauria
Suborder- Theropoda
Order- Passeriformes
When did the mass extinction event occur that wiped out many of the dinosaurs?
65 million years ago
What is a misconception about the mass extinction?
It only killed non-avian dinosaurs. That is how birds are still alive today (which are ancestors of dinosaurs).
What is the K-T boundary?
This is the time between the Tertiary and the Crestaceous Periods when the mass extinction occurred that wiped out 50% of the animal/plant species.
How is the geologic time scale organized in general eras from oldest to earliest?
Precambrian, [Paleozoic, Mesozoic, Cenozoic]
What periods (and MYA) is the Mesozoic Era divided into (oldest to earliest)?
Triassic (245 MYA)
Jurassic (208 MYA)
Cretaceous (144 MYA)
What periods (from oldest to earliest in MYA) is the Cenozoic Era divided into?
Tertiary (65 MYA)
Quarternary (65 MYA)
What is the unique development occurred during the Triassic Period?
First dinosaurs and mammals appeared
What is the unique development occurred during the Jurassic Period?
Origin of birds
What is the unique development occurred during the Cretaceous Period?
Evolution of flowering plants
What is the unique development occurred during the Tertiary Period?
Divergence of modern mammals and birds
What is the unique development of the Quarternary Period?
The earliest human fossils (this is the period that continues into today)
What is the outline form of the taxonomic arrangement of birds?
I. Amphibia
II. Amniota
A. Mammalia
B. Reptilia
1. Testudines
2. Diapsida
a. Lepidosauria
b. Archosauria
i. Crocodylia
ii. Aves
What is more closely
related to pterosauria? Theropoda or Crocodilia? (consider slide 21 of lecture 1)
Theropoda- the last common ancestor of a Pters and Crocs lived long ago, and ancestors of Thers and Pters lived more
recently-- so a more recent
common ancestor means
Thers and Pters are more
closely related
What are molecular evidence was studied and used to support the relationships of certain historic creatures with animals today?
studied the amino acid
sequence of collagen proteins
from t-rex and mastodon fossil
What were the conclusions of the molecular studies of the t-rex and mastodon fossils?
t-rex sequence similar to
extant chickens (matched better with birds than modern reptiles)

mastodon sequence similar
to more closely related to
extant mammals
What is an Important synapamorphic character of Maniraptors?
semilunate carpal in the wrist allows for a flexible seizing function: preflight motion of the hands
What branches from Maniraptors on its taxonomic tree?
Dromaeosaurids, then Archaeopteryx, and finally Other birds
What dinosaur is the most recent common ancestor of modern birds?
Birds are descendants of theropod maniraptoran dinosaurs, probably something similar (but not identical) to a small dromaeosaur like velociraptor
Researchers have found fossils of Theropod species in
Montana. Deeper deposits contain larger species, and more
recent deposits contain smaller species. How does this
observation support the theory of evolution?
A) It suggests that species are unchanging and of ancestral
B) It proves that environments have changed over time
C) It provides evidence that lineages change over time
D) It shows that all species are related to each other
C) It provides evidence that lineages change over time
Why did Darwin argue that evidence of extinction
supports the theory of evolution?
A) It shows that reproduction is more important
than survival of the fittest
B) It shows that lower organisms have died to
make way for humans
C) It shows that nothing lasts forever
D) It shows that the number and types of species
have changed over time
D) It shows that the number and types of
species have changed over time
Evolutionary theory predicts that species are related, not
independent. Four of the following examples provide support
for this prediction, but one is irrelevant. Which one of these
examples does not support the claim that species are related?
A) Many dinosaurs and other organisms went extinct
following a huge asteroid impact at the end of the
B) The endostyle of lancelets (invertebrate chordates) and
the thyroid gland of vertebrates develop similarly, and both
produce iodinated proteins
C) All prokaryotes and eukaryotes use DNA to carry their
genetic information.
D) Ground squirrel species found on the north and south
sides of the Grand Canyon are very similar to each other
E) Before synthetic insulin was available, diabetics used
injections of purified pig insulin to manage their disease
A) Many dinosaurs and other organisms went extinct
following a huge asteroid impact at the end of the
The best definition of Darwinian fitness is:
A. the ability of an individual to survive
B. the ability of a population of organisms to persist
C. the ability of an individual to stay healthy by
eating well-balanced meals and exercising
D. the ability of an individual to survive and
reproduce compared to others in the population
D. the ability of an individual to survive and
reproduce compared to others in the population
If you were to take a Yellow feather and a Blue feather and
crush each one into a powder, what color powder would
each feather yield?
A) yellow, gray-white
B) gray-white, gray-white
C) yellow, blue
D) gray-white, blue
A) yellow, gray-white
What is the Archaeopteryx recognized as?
This was the first "bird" fossil from about 150 MYA during the Jurassic Period.
What is true about the Archaeopteryx's feathers and what does this tell us?
Archaeopteryx’s wing feathers were asymmetrically vaned for flight;
--not informative about where feathers came from, or about their primitive function
What is hypothesis I of the evolution of feathers? Is it viable?
Feathers evolved for flight
--Predicts that feathers evolved from elongated
reptilian scales (Probably not)
What is hypothesis II of the evolution of feathers? Is it viable?
Feathers evolved for insulation
--Predicts that feathers were a
fuzz that covered entire body (Possible)
What is hypothesis III of the evolution of feathers? Is it viable?
Feathers evolved for color signaling (i.e., communication)
--Predicts that early feathers were a colorful fuzz (Possible)
What is some evidence that
dinosaurs may have evolved feathers for insulation before they were used for flight?
--Downy feathers (not used for flight) covered the whole body of a therapod fossil discovered
--Downy feathers covered
body, and ornamental
tail feathers not for flight
--Evidence that dinosaurs may have evolved feathers for display (elaborate tail feathers)
What is something that should be noted about depictions of dinosaurs today?
Dinos had FEATHERS; the colors are based on the whim of artist; sometimes there may be evidence of bands of dark and light but not the intense color choices some artists use
What branches off after Coelurosaurs in its taxonomic tree?
Tyrannosaruoids; then at the tips of those branches after it are Dromaeosaurs, Archaeopteryx, and Other birds
Hierarchically, birds are classified as:
A) Theropod, Coelurosaurs
B) Archeosaur, Dinosaur, Saurishia, Theropod,
Coelurosaur, Maniraptor, Aves
C) Dinosaur, Theropod, Coelurosaur, Aves
D) All the above
D) All the above
What does fossil evidence suggest about the development of feathers?
Feathers develop
from a ‘tubular’ feather germ
and follicle and therefore predicted that diversification of feathers proceeded through a
series of derived evolutionary
novelties in developmental
What is the significance of a Theropod discovered with patterned feathers?
(Simple bristles only found on its head, midline of the back, and tail -- and so feathers
could have only a limited function in insulation)
*Feather bristles showed evidence of banding pattern--a
potential signal!
Based on the finding of melanosomes (in a particular
arrangement) in the feather keratin, what color could they
postulate that the feathers were:
A) Orange
B) Yellow
C) Blue
D) Iridescent
D) Iridescent-melanin pigments make black, grey, brown, rufous colors, but also contribute to structural iridescence
What are three important facts about melanin or melanosomes?
-Melanin pigments are deposited in feathers as
organelles called melanosomes
- melanosomes are preserved in fossil feathers
- different melanasomes have different shapes
What is Eumelanin?
It is a type of melanosome: rod shaped and usually makes black, gray
What is Pheomelanin?
It is a type of melanosome: round and usually makes brown, rufous
What is true about melanin and its affect on birds?
--Melanin pigments are widely
distributed in extant birds
--Produce blacks, grays, and
brown-red colors
What was the first step in trying to figure out how to color a dinosaur?
First, researchers compared the shape and density of
melanosomes in extant birds to those found in their Theropod dinosaur
What did researchers use SEM for when trying to figure out how to color a dinosaur?
With SEM, they imaged
samples of feathers from black, gray, and rufous plumage
What did researchers graph when trying to figure out how to color a dinosaur and what did they notice?
--Researchers plotted
melanosome shape vs.
density from feathers of
different colors
--Using color-coordinated points to their sampled feathers, they found a clear
clustering of color types
How did researchers actually assign color to dinosaurs? (the last step of the research process?)
Using the same techniques for the dinos and the extant birds, researchers mapped
melanosomes onto the graph made from extant bird feathers
--assigned color to each numbered point from the dino
-painted colors on fossil reconstruction based on where the melanosomes were
What concluding statement can be made after considering all of the hypotheses and evidence of dinosaur feathers?
Color display likely played an important role in the early evolution of feathers.
Given a population that contains genetic variation, what is
the correct sequence of the following events, under the
influence of natural selection?
1. Well-adapted individuals leave more offspring than do
poorly adapted individuals.
2. A change occurs in the environment.
3. Genetic frequencies within the population change.
4. Poorly adapted individuals have decreased survivorship.
A) 2 → 4 → 1 → 3
B) 4 → 2 → 1 → 3
C) 4 → 1 → 2 → 3
D) 4 → 2 → 3 → 1
E) 2 → 4 → 3 → 1
A) 2 → 4 → 1 → 3
To observe natural selection's effects on a population,
which of these must be true?
A) One must observe more than one generation of
the population.
B) The population must contain genetic variation.
C) Members of the population must increase or
decrease the use of some portion of their anatomy.
D) A and C only
E) A and B only
E) A and B only
Which of the following must exist in a population before
natural selection can act upon that population?
A) Genetic variation among individuals
B) Variation among individuals caused by
environmental factors
C) Sexual reproduction
D) B and C only
E) A, B, and C
A) Genetic variation among individuals
Which statement best describes the evolution of pesticide
resistance in a population of insects?
A) Individual members of the population slowly adapt to
the presence of the chemical by striving to meet the new
B) All insects exposed to the insecticide begin to use a
formerly silent gene to make a new enzyme that breaks
down the insecticide molecules.
C) Insects observe the behavior of other insects that
survive pesticide application, and adjust their own
behaviors to copy those of the survivors.
D) Offspring of insects that are genetically resistant to the
pesticide become more abundant as the susceptible
insects die off.
D) Offspring of insects that are genetically resistant
to the pesticide become more abundant as the
susceptible insects die off.
What is the most important concept in biology? Who proposed it?
The theory of evolution by natural selection, jointly
proposed by Charles Darwin and Alfred Russel Wallace in
1858, is the most important concept in all of biology
What did Darwin base his arguments on?
Darwin had no examples of the action of natural selection, so he based his arguments
on artificial selection by plant and animal breeders
What is the definition of Evolution?
Gene (or allele) frequency change over time
What are the major mechanisms of evolution?
• Natural Selection (differential reproduction)
• Gene flow (migration)
• Genetic drift (random events)
• Mutation
If organisms could increase their number geometrically, why don't they?
their resources are limited (behind the logic of natural selection)
What is true about populations and their growth?
Populations have a capacity for exponential growth
What was Thomas Malthus quoted saying about populations and their growth?
“Population, when unchecked, increases in a geometrical ratio.
Subsistence only increases in an arithmetical ratio.”
What is another logic behind natural selection concerning individuals in a population?
Variation exists among individuals in every species
What is true about communication signals within species (specifically looking at individuals)? What is an example of this?
--Communication signals are highly variable
--Face patterns of wasps communicate dominance
What is true about variations concerning the logic behind natural selection?
Many such variations within species can be transmitted from parent to offspring
What is true about communication signals within species concerning relatedness between offspring and parents? What evidence supports this idea?
--Communication signals are heritable.
--Offspring develop similar coloration to genetic parents, even when raised by foster mothers. (owls)
What is true about variations that result in greater survival?
This will mean these variations will have higher numbers of reproduction and the variation will increase in frequency as time passes
What is true about strong or "attractive" communication signals?
They result in greater reproduction and more ornamented individuals will have more offspring which means that parents will pass on these same traits to their offspring
Does natural selection occur in a Lamarckian manner?
NO! Individuals do not change during natural selection, populations do!
What is the definition of natural selection?
Natural selection is the differential success in survival and reproduction among individuals that vary in their
heritable traits, causing a change in the genetic makeup of a population
Can evolution occur without
natural selection?
YES-there are other
mechanisms of evolution
Can natural selection occur
without evolution?
YES-some traits that cause
differential reproduction are
not heritable
What does natural selection explain?
It explains the diversity of life?
What gives rise to adaptation?
Only Natural Selection
What is the definition of a phenotype?
Phenotype: A trait (or value of a trait, i.e., longer tail) that confers higher fitness to individuals within the population with that trait/trait value
What is the definition of a process?
A process of genetic change in
a population where, due to natural selection, the average state of a trait becomes improved with reference to a
specific function
How do we recognize adaptations?
1. Fit of form and function
2. Comparative method (convergent vs. divergent evolution)
What is convergent evolution?
Evolution of similar traits in similar environments, in
distantly related organisms
What is divergent evolution?
Evolution of differing traits in different environments, in
closely related organisms
What is important to note about adaptations?
Important to realize that not all features originally evolved
as adaptations for their current function
- Original function can be co-opted to serve a new function
Selection is blind to the _______,
but acts on the _______
A) phenotype, genotype
B) genotype, phenotype
C) genotype, population
D) population, phenotype
B) genotype, phenotype OR
D) population, phenotype
Which of the following is the most predictable outcome
of increased gene flow between two populations?
A) Lower average fitness in both populations
B) Higher average fitness in both populations
C) Increased genetic difference between the two
D) Decreased genetic difference between the two
E) Increased genetic drift
D) Decreased genetic difference between the two
Which populations would be affected most by
random genetic drift?
A) Large populations
B) Small populations
C) Migrating populations
D) Fixed populations
B) Small populations
Random genetic drift affects allele frequencies more
drastically as population size decreases
A population is _____.
A) Many individuals of the same species
B) A group of individuals of the same species that
live in the same area and can potentially interbreed
C) A group of interacting species that live in the same
D) Two or more groups that regularly interbreed
B) A group of individuals of the same species that
live in the same area and can potentially interbreed
Which of the following examples of natural selection in
action would tend to increase the genetic variation in the
A) Natural selection causes dragonflies to evolve
longer tails.
B) Lupines evolve large flowers above the
timberline and small flowers below the timberline.
C) Natural selection simultaneously selects against
heavy field mice (they starve during winter) and
light field mice (they freeze during winter).
D) Natural selection acts on beak size in finches such
that those individuals able to eat small, soft seeds
survive through the winter.
B) Lupines evolve large flowers above the
timberline and small flowers below the timberline.
Disruptive selection or selection for extreme phenotypes
tends to increase variation in that trait
An earthquake decimates a ground-squirrel population.
The surviving population happens to have broader stripes
on average than the initial population. If broadness of
stripes is genetically determined, what effect has the
ground-squirrel population experienced during the
A) Directional selection
B) Disruptive selection
C) A founder event
D) A genetic bottleneck
E) Gene flow
D) A genetic bottleneck - a type of genetic drift
What is the first limit to adaptation that concerns genes?
Natural selection can only lead to evolutionary change when there is genetic variation for traits that affect fitness
-A change selection pressures (e.g., due to change in the
environment) can only lead to adaptation for traits
already present in the gene pool.
What might happen as a result of strong natural selection for a certain trait?
Under strong selection
for a certain phenotype/genotype, the
genetic diversity in the
population disappears
-Less successful
genotypes disappear
from a population
What causes the phenotypic variation between parents and their offspring?
this phenotypic variation could be due to genetic variation or environmental variation
Are traits perfectly heritable?
NO--Traits are generally not perfectly heritable
-Offspring are not a perfect representation of their parents (consider humans)
What is the definition of heritability?
Proportion of phenotypic variation (in a given population) due to genetic variation
What is the heritability equation? What does it do?
This estimates the role of genes in phenotypic variation. Equation: h2 = VG/VP
What is the range of h2 values?
h2 values range: 0 to 1
What are two methods that can be used to estimate heritability in addition to the heritability equation?
1) Parent-offspring regression
2) Response to selection (breeder’s equation)
What is a parent-offspring regression?
It is a scatterplot graph of Midparent Trait Value (x) vs. Offspring Trait Value (y) and the slope of the line = h2
What is the breeder's equation?
Use to assess how much shift in phenotype is possible
following selection.

Breeder’s Equation:
h2 = R / S
R = Response to selection
S = Selection differential
What does the S in the breeder's equation stand for and how do you calculate it?
Selection differential (S): ABS
difference b/t mean of selected
individuals and initial mean (ex:
Initial mean=10, Subset chosen for breeding mean= 16, 16-10=6)
What does the R in the breeder's equation stand for and how do you calculate it?
Response to selection (R)=ABS difference in means (ex: Initial mean=10, New generation’s mean=14, 14-10=4)
In studies of genetically identical inbred
animals, all traits have ____ heritability
A) moderately low
B) very low
C) moderately high
D) very high
E) zero
E) zero: if all were genetically
identical, there would be no genetic
variance, so VG=0 (h2 = VG/VP)
What is one potential environmental cause to a high heritability number?
h2 HIGH can result from lack of environmental variation (consider the example of wintertime high heritability of skin color because children are not tanned at the beach)
Is heritability fixed?
h2 is not a fixed measure. It can vary with environment:
Exposure of kids, but not parents to sun (at beach)
decreases heritability over time in the same population
Say you’re a zookeeper monitoring two populations of lions, one with all robust individuals (Tanzania), and one with all scrawny individuals (Kenya). You find that there are high values of
heritability for body-condition in both populations.
h2 = 0.82
h2 = 0.85
Does this mean that body condition is largely
genetically determined, and so you should select breeding stock from Tanzania population?
A. Yes
B. No
C. I don’t have the foggiest clue
B. No--High h2 could be due to a lack of environmental variation within each population
(one could be constantly good, the other constantly bad)-- condition could still
respond to environment
What is the definition of genetic drift?
Random change in allele
frequencies over generations brought about by chance
How does genetic drift limit adaptation?
How drift limits adaptation
In the absence of other forces, drift leads to loss of genetic diversity
-alleles that are beneficial but occur at low frequencies can become lost
What is fixation?
This is related to genetic drift where some alleles can either become fixated or dissappear due to random changes.
What is the affect of genetic drift on small populations?
Magnitude of drift is greatest in small populations
-Small populations reach fixation quickly
What is an example of evolutionary history being a limit to adaptation?
Adaptation is be subject to historical constraints.
EX: Both food and air pass
through the pharynx
= Choking hazard
What is the definition of pleiotropy?
Pleiotropy: a single gene affects multiple phenotypic traits
What is the consequence to pleiotropy?
Consequence: Selection in one direction on one trait
can be constrained by selection in another direction
for a different trait
Why is fox domestication a good example of pleiotropy?
Artificial selection for a single
behavioral trait – tamability – resulted in a suite of changes
• Gene(s) for tamability have
pleiotropic effects
– tamability highly regulated by
hormones, which alter much of
morphology and physiology
What physical traits changed with the fox domestication experiment?
Loss of pigmentation, floppy ears, rolled tails, skulls smaller (less sexual dimorphism), snouts shorter and wider
What physiological traits changed in the fox domestication experiment?
– ↓ adrenaline (less flight response)
– ↓ corticosteroids (less stress)
– ↑ serotonin (inhibition of aggressive behavior)
What was the impact of hormonal changes in the fox domestication experiment?
Retention of juvenile physical characteristics
How might the "Frizzle" gene be a good example of pleiotrophy?
Pleiotropic ‘Frizzle’ gene produces feathers that curl
outward, BUT ALSO causes: abnormal body temperatures, higher metabolic rate, and fewer eggs
Why is testosterone in dark-eyed juncos not held at physiological maximum, even though males do benefit from elevated T?
Selection for greater male solicitation of extra-pair paternity, would have pleiotropic effects on a suite of other fitnessdepressing traits, including:
--less paternal care given at home nest
--less defense of predators
--more stress response (may lead to lower survivorship)
How can pleiotropy be “broken”?
For example, mutations can
arise for gene duplication (within gene families) which can lead to copies that can separately code for each trait
What is another limit to adaptation concerning selective pressures?
How are trade-offs a limit to adaptation?
Trade-offs: Multiple selective pressures can act on a given trait
- Phenotype is determined by a trade-off between conflicting
What is a good example of a trade-off? (think of Darwin)
Darwin’s Finches use their bills for:
- Food gathering
- Song
-Selection for increasing bill
size leads to a decrease in
singing performance
How is reproduction a limit to adapation? What are the consequences of fast and slow reproduction?
Reproductive capacity limits a population’s ability to adapt
-If reproduce quickly (insects, bacteria) then population can
adapt to changes in a short time
-If reproduce slowly (elephants, tigers, corals) then it takes thousands or millions of years to adapt
What is a limit to adaptation considering time?
Time lag: Response to selection takes many generations,thus many current traits may have evolved in response to
a different past environment and are in the process of
being selected against
Which of the following could be a vicariance event
for a species?
A) The level of water in a lake recedes, creating
two lakes where there used to be one
B) Some insects get blown in a storm to a new
mountain range, where they lay eggs
C) Radiation near Chernobyl increases mutation
rate, causing an increase in migration behavior
D) All of the above
A) The level of water in a lake recedes, creating two lakes where there used to be one
A subset of a population of birds leaves its habitat on the
mainland and colonizes a nearby island. The birds, after a
period of time, become reproductively isolated. The island
sinks and the population of birds that lived on the island
returns to its original habitat. Which of the following
statements about these bird populations is true?
A) The populations will not be able to interbreed because
they are different species
B) The birds were separated by a vicariance event
C) The populations were sympatric while they diverged
D) The populations will be able to interbreed even though
they are different species
A) The populations will not be able to interbreed
because they are different species-they already became
reproductively isolated (i.e., some genetic difference that
prevents interbreeding)
A small number of birds arrive on an island from a
neighboring larger island. This small population
begins to adapt to the new food plants available on
the island, and their beaks begin to change. About
twice a year, one or two more birds from the
neighboring island arrive. What effect do these new
arrivals have?
A) Their arrival speeds the process of speciation
B) Their arrival tends to promote adaptation to the
new food plants
C) Their arrival tends to retard adaptation to the
new food plants
D) Their arrival represents a colonizing event
C) Their arrival tends to retard adaptation to
the new food plants-Increased gene flow
homogenizes differences between populations
When is reinforcement beneficial?
A) when populations would otherwise fuse over time
B) when hybrids have lower fitness than either
parent population
C) when prezygotic isolating mechanisms are in
D) when one population could be overwhelmed by
the other
E) reinforcement is beneficial under all of the above
B) when hybrids have lower fitness than either parent population-Natural selection for traits that keep distinct populations from reproducing with each other (because of costs of hybrids) is called
Imagine two populations descended from a single bird species.
After a period of isolation in allopatry, the populations resume
inhabiting the same region. Assuming that the only differences
between the populations are those listed, which of the following
factors would most likely prevent interbreeding?
A) Population A rests in the upper branches of trees during
foraging bouts; population B rests on the ground.
B) Population A forages by picking insects off leaves;
population B forages by tearing open ant nests.
C) Population A performs its mating calls in the upper
branches of trees; population B performs them on the ground.
D) Population A nests in oak trees; population B nests in
maple trees.
C) Population A performs its mating calls in the upper
branches of trees; population B performs them on the
ground. -- this is only option that leads to reproductive isolation
What is directional selection?
Changes average value
of a trait (increase or
decrease) in a population
What is stabilizing selection?
Stabilizing selection
Maintains intermediate phenotypes in a population (note average remains the same)
What are the consequences of stabilizing selection?
Reduces population genetic diversity over time as alleles
that specify extreme forms are eliminated
What is a consequence of directional selection?
Reduces population
genetic diversity over time
What was the blue tit experiment and what was it testing?
**Has selection
optimized avian clutch size?**
• Changing (adding &
subtracting) number
of eggs will reduce
fitness (i.e. offspring
• Experiment:
• Add and remove
chicks to test whether
optimal clutch size is
what we see in nature
What does a cost-benefit analysis graph look like?
It is a graph of clutch size (x) vs. units of fitness (y) where the benefits are represented linearly and costs rise in a gentle upward curve.
What is the general conclusion of a cost-benefit analysis?
No organism has an infinite amount of energy to spend
on its activities.
What is disruptive selection?
Intermediate phenotypes
are selected against and
extremes are favored
What are the consequences of disruptive selection?
--Increases population genetic diversity over time.
--Disruptive selection can cause populations to diverge
and this can lead to new species (aka speciation)
What are the benthic and limnetic three-spined sticklebacks examples of?
--They are examples of disruptive selection! ('large' benthic living in littoral zone *shoreline*; 'small' limnetic living in limnetic zone *open water*)
--Descended from common
--Assortative mating led to
speciation (mating like with
like; non-random mating)
What is assortive mating?
This is mating like with like, aka non-random mating.
Which of the following does not tend to promote
A) the founder effect
B) gene flow
C) natural selection
D) drift
B) gene flow
How likely is divergence of populations? What would you use to estimate this?
The amount of gene flow between groups relative to
the strength of divergent selection combine to determine whether speciation can occur.
--Use a graph of probability of speciation (x) vs. strength of process (y) for positive linear slope of "intensity of divergent selection" and a negative linear slope "degree of gene flow" of cross in an X where speciation is more likely on the right side of the graph.
What is the narrow definition of a species?
a large and distinct gene pool
What is the broad definition of a species?
group of organisms that share a common evolutionary history and are capable of interbreeding within their group and are not capable of interbreeding with other groups
If the Happy Face Spiders look so different, why do we consider them to be the same species?
They can interbreed
What is a morphological species?
Morphological species: a group of organisms with a
distinct form from other groups of organisms
What are the pros of the Morphological Species Concept?
--Easy to administer
--Can be used for asexual
sp. and for fossils
What are the cons of the Morphological Species Concept?
--Morphology is not a great indicator of ancestry (problem with convergence)
--Morphology is not always a great indicator of affiliation within a species
What is a phylogenetic species?
Phylogenetic species: Smallest diagnosable cluster of organisms within which there is a shared pattern of ancestry and descent (i.e., the smallest monophyletic group)
What are the cons of the Phylogenetic Species Concept?
--Phylogenies are unavailable for most groups (constructing
rigorous phylogenies is difficult, expensive and time consuming)
What are the pros of the Phylogenetic Species Concept?
--Species defined by shared
evolutionary history
--Can be used for asexual sp.
and for fossils
Does the Phylogentic Species Concept "split" species indefinitely?
NO--Ex: The 3 “C” populations
cannot be distinguished
by unique, derived characters. Thus, they represent a single
phylogenetic species
A storm brings two formerly separated populations of
amazonian frogs together. They look very similar. Under
the biological species concept, which of the following
would suggest that the two populations are different
A) One population breeds in spring, the other in fall.
B) Males of the two populations have different call
patterns in courtship.
C) When individuals from the two populations mate with
each other in the laboratory, the eggs fail to hatch.
D) All of the above is correct.
E) None of the above is correct.
D) All of the above is correct.
The common edible frog of Europe is a hybrid between two
species, Rana lessonae and Rana ridibunda. The hybrids have a
wide distribution across central Europe. When hybrids mate, their
offspring are rarely successful in producing offspring. What can
you infer from this information?
A) Postzygotic isolation exists between the two frog species.
B) Prezygotic isolation exists between the two frog species.
C) These two species are likely in the process of fusing back
into one species.
D) The hybrids form a separate species under the biological species concept.
A) Postzygotic isolation exists between the two frog
Imagine two North American tree frog species that contact
each other as the southern species moves northward during
a period of global warming. These two species do not mate
much, due to differences in their courtship calls. The
northern frog does not tolerate the warmer temperatures well
but is limited in its ability to move north because it does not
normally disperse much. Based on this information, which is
the most likely outcome?
A) fusion of the populations
B) reinforcement
C) hybrid zone formation
D) extinction of one of the species
E) creation of a new species
D) extinction of one of the species
Male leopard frogs give calls that attract female frogs to
approach and mate. Researchers examined mating calls of
closely related leopard frogs in South America. What
outcomes can occur where the ranges of two species
A) The species will interbreed, eventually fusing over time.
B) A stable hybrid zone will form if hybrids are better
adapted to the area of overlap than either parent species is.
C) Species will continue to diverge and be isolated by
behavioral or genetic mechanisms.
D) All of the above is possible outcomes.
E) None of the above is a possible outcome.
D) All of the above is possible outcomes.
What is a biological species?
Biological species: groups of actually or potentially
interbreeding natural populations that are reproductively isolated from other such groups
What are the pros to the Biological Species Concept?
--Defined by actual, or potential for, gene flow between populations
--Can be tested in the field
What are the cons to the Biological Species Concept?
--Can not be used for asexual sp. and for fossils
--Difficult to determine reproductive isolation of allopatric populations (i.e., not clear how to categorize species with disjointed ranges)
--Interbreeding populations may still be evolving independently
What is speciation?
Speciation: a lineage-splitting event that produces two or
more separate species (i.e., evolution of two or more
species from a single ancestral species)
What is anagenesis?
Anagenesis = gradual changes in an ancestral species lead to its eventual "replacement" by a novel form (not usually
considered speciation)
What is cladogenesis?
Cladogenesis = splitting of a lineage (speciation)
What two ways cause speciation?
1. Isolation: gene flow is restricted between previously
cohesive groups
2. Divergence: evolutionary forces alter traits differently
in each group
What are the mechanisms that lead to genetic divergence in populations that become isolated from one another?
--Genetic drift: especially in small populations, strongest during founder effect
--Natural selection: especially if isolation leads to different selection pressures
--Sexual selection: if female mate-preference and male ornaments diverge between populations
What is allopatric speciation?
Allopatric speciation:
Something extrinsic prevents two or more groups from mating with each other. Isolation might occur due to great separating distance, or a physical barrier (such as a desert, river, glacier)
What are the two general forms of geographic isolation (allopatric speciation)?
1) Vicariance- A previously
cohesive population is split
via a physical barrier
2) Peripatry- A dispersal event occurs, and usually a small number of individuals colonizes a new habitat
What is vicariance?
Vicariance: a previously
cohesive population is split
via a physical barrier
Examples: changing river
courses, rising of mountains, drying of seas, forest fragmentation, lava flows
What is peripatry?
Peripatry: A dispersal event occurs, and usually a small number of individuals colonizes a new habitat
Founders are often different from main population due to genetic drift (founder effect)
What is parapatry or parapatric speciation?
Parapatry (not Peripatry)
There are no specific
extrinsic barrier to gene flow.
The population is continuous,
but the population does not
mate randomly: Individuals
are more likely to mate with
their geographic neighbors
What is a ring species?
Ring species: species with
a geographic distribution that forms a ring and overlaps at the ends.
What is an example of parapatric speciation?
Subspecies of Ensatina
salamanders (in California and the differences between those on the coast and inside the state)
What is sympatric speciation?
Sympatric speciation:
Speciation that occurs between populations occupying the same
What are the 7 prezygotic isolating mechanisms?
1). divergent selection and
assortative mating by type
ex) sticklebacks limnetic & benthic, Amazonian frog
2) difference in timing of mating
3) mechanical differences: Usually due to physical
differences in copulation structures
4) ecological or habitat differences: populations
occur in the same geographic area (on a
macroscale) but use different habitats within
5) behavioral differences
6) ornamentation differences
7) Gamete incompatibility: gamete transfer occurs
but fertilization does not. Often due to factors such
as cellular architecture variation
What are postzygotic isolating mechanisms?
hybrid sterility, reduced hybrid fertility, increased hybrid mortality (ex: sterile mule which is offspring of male donkey and female horse)
What happens if groups that diverged reconnect?
If groups reconnect, evolved differences are accentuated
by selection (change from allopatric to sympatric but do not interbreed which means that speciation has occurred)
Considering character displacement, what is reinforcement?
Reinforcement: avoid mating with other incipient species to avoid costs of hybridization. Often favors traits that promote assortative mating
What is niche based character displacement?
Niche based character
displacement: species become
more different so as to fit into
respective ecological niches
(reduces competitive overlap)
How do females tell the difference between Western and Eastern Meadowlarks that
appear to be identical with overlapping ranges?
their distinct songs prevent females from choosing wrong species as a mate
How do the songs of sympatry and allopatry compare?
Songs in sympatry are more different from songs in allopatry
A biologist doing a long-term study on tail length in a
population of motmots observes increased variation in
tail length over time. She hypothesizes that the
population is experiencing ________.
A) directional selection.
B) stabilizing selection.
C) disruptive selection.
D) sexual selection.
E) genetic drift.
C) disruptive selection.
Male turkeys have a snood, which is a flap of skin that
hangs across their beak. Snood length is negatively
correlated with parasite load (i.e., males with longer
snoods have fewer parasites), and females prefer to mate
with long-snooded males. This is an example of:
A) the fundamental asymmetry of sex.
B) sexual selection via female choice.
C) sexual selection via male-male competition.
D) stabilizing selection.
E) all the above.
B) sexual selection via female choice
Which statement most fully characterizes the fundamental
asymmetry of sex?
A) Female fitness is limited mostly by the ability to get
resources for producing eggs and rearing young, while male
fitness is limited by the ability to attract females.
B) Female fitness is limited mostly by the ability to attract
males, while male fitness is limited by the ability to get
resources for provisioning the female.
C) Female fitness is limited mostly by the ability to get
resources for producing eggs and rearing young, while male
fitness is limited by the ability to get resources for provisioning
the female.
D) Female fitness is limited mostly by the ability to attract
males, and male fitness is limited by the ability to attract
A) Female fitness is limited mostly by the ability to get
resources for producing eggs and rearing young, while
male fitness is limited by the ability to attract females.
Sexual dimorphism is most often a result of
A) pansexual selection.
B) stabilizing selection.
C) intrasexual selection.
D) disruptive selection.
E) artificial selection.
C) intrasexual selection.
What are the 2 types of behavioral research
1). Proximate = HOW?
2). Ultimate = WHY?
What is proximate behavioral research?
Proximate = HOW?
how does behavior develop;
how do genetic, physiological,
and anatomical mechanisms
underly the behavior?
What is ultimate behavioral research?
Ultimate = WHY?
why did behavior evolve: from
an ancestral perspective what
gave rise to the behavior
(evolutionary history); why
does the behavior increase
What is the nature vs. nuture debate?
There IS NOT one! It's BOTH! Behavioral traits are the result of complex interactions between genetic and environmental factors
What does artifical selection show about behavioral genetics?
Artificial selection shows that behavioral differences among individuals often result from genetic differences
– Genetics of learning (ex: fast and slow rat populations)
What is vasopressin (VP)? What experiment was it used with?
This is a hormone that effects memory. Only prairie voles responded to VP because this species has genes for many VP receptors. Transgenic mice had similar responses to prairie voles.
What is anisogamy?
This is the inherent difference in gamete size between males and females.
What is the fundamental asymmetry of the sexes?
females usually invest more (fewer eggs that require much more energy to make) in offspring than do males (lots of sperm and require less energy to make)
What are the 3 important consequences of anisogamy?
***Consequence 1:
--Female reproductive success is limited by access
to resources (each egg is precious)
--Male reproductive success is limited by access to mates (sperm are not costly)
***Consequence 2:
--Males have far higher potential maximum reproductive success than females
***Consequence 3
--Male reproductive success is more variable than female
reproductive success
--Result: differential reproduction due to phenotypic
variation is far greater in males! This is sexual selection.
What is sexual selection?
Sexual selection: Differential reproduction (due to phenotypic variation) that arises from the acquisition of more mates, or better quality mates
What does anisogamy lead to? (differences in gamete investment between males and females)
Higher mating competition in the sex whose reproduction is limited by access to mates (usually males)
--Males selected to invest in traits that increase probability of mating: ornaments & armaments
--Female selected to invest in traits that increase probability of offspring survival as each offspring is limited (i.e., parental care, choosing ‘best’ mate)
What are the two main kinds of sexual selection?
1) Intrasexual selection: “Contest-competition”
--usually male vs male
2) Intersexual selection: “Mate-choice-competition”
--usually male vs male
What is intrasexual selection?
--usually male vs male
What is intersexual selection?
--usually male vs male
What does sexual selection lead to?
Sexual Dimorphism: differences between males and females
What are the direct benefits females gain from choice?
Direct benefits: Actual resources that males provide (i.e., food, paternal care: feeding or protection of offspring)
What are the indirect benefits females gain from choice?
Indirect benefits: Females chose males that provide heritable beneficial traits to their offspring (i.e. good genes)
What do extra-pair copulations (EPCs) in Red-winged Blackbirds tell us about female choice?
--Females seek good-genes.
--Although half of all nests contained at least one EPC hatchling, females gain NO DIRECT benefits from EPC males
What are the evolutionary advantages of extra-pair copulations? (EPCs)
--Males: increased reproductive success
--Females: offspring receive genes from genetically superior
Which of the following is an example (or are examples)
of intersexual sexual selection?
A) male katydids choosing larger female katydids
B) large male elephant seals monopolizing female
C) female junglefowl preferring dominant males
D) a and c
E) all the above
D) a and c
Which of the following describes an organism’s
relative fitness?
a) survival
b) number of matings
c) adaptation to the environment
d) successful competition of resources
e) relative number of offspring
e) relative number of offspring
During breeding season, one should expect female house
finches to prefer to mate with males with the brightest red
feathers. Which of the following terms are appropriately
applied to this situation?
A) Intrasexual selection
B) Handicap signaling
C) Direct benefits
D) Only B and C
E) All the above
D) Only B and C
What is true about offspring that are born from more ornamented males?
Offspring that are from more
ornamented males grow faster and have higher survival
What is an example of sexual selection with color signaling of birds?
Size of bright patches
influences male territory size
and thus, attractiveness (Yellow-browed Warbler)
Considering animal communication, what are signals?
--Signals are adaptations used for communication
--Specifically, they are behavioral, physiological, or
morphological characteristics maintained by natural selection because they convey information
What is true about the reciever of a signal?
-- The signal must modify behavior of the receiver
-- Receiver response, on average, must benefit the sender (but no requirement with respect to receiver’s fitness)
Are signals also known as cues?
NO! Cues are any feature of the world, animate or inanimate, that can be used
as a guide to future action
What are cues?
Cues are any feature of the world, animate or inanimate, that can be used as a guide to future action
If something is intended to provide information is it a cue or a signal?
What are some examples of cues?
Examples of cues:
–Owl hears mouse rustling in leaves
–Your CO2 exhalations reveal your location to mosquitos
How do male birds use their songs as signals? What are two examples?
1). Fighting- Males communicate with males to defend territory
2). Flirting- Males communicate with females to attract partners
Is animal communication cooperative interaction?
Generally NO...Interest of sender and receiver are often incongruent
How are sender and recievers of signals incongruent between animals?
--Courtship: females often want best male, males want any/more matings
--Fighting: intimidate rivals without having to fight (fighting is risky)
Concerning honesty in signals, what is the sender's perspective?
Often it would pay to convey information that is
incomplete or even false (i.e., deception, dishonesty)
Concerning honesty in signals, what is the reciever's perspective?
Given that some signals are deceptive, this should impose selection pressure on receivers to extract reliable information from signals, and thus disregard unreliable information
How can receivers distinguish
deceitful signals from reliable
signals? (hint: there are 3)
Three signal types that maintain
signal honesty, and are thus
favored by receivers:
–1). Handicap signals
–2). Index signals
–3). Conventional signals
What is the handicap model of signal evolution?
only high quality
individuals can bear the cost of a large handicap
--Thus, males with the highest viability can display the
highest trait value
What is a vulnerability handicap?
--Performance places
sender at risk of attack: only
high quality males can fly
with an extravagant tail and
avoid predation (ex: long-tailed widowbird)
What is a quality handicap?
--Display intensity correlated with signaler quality
--Signal production is condition dependent
--Smaller differential benefit for low quality individuals (i.e., low quality individuals have pay a relatively higher cost for a given trait compared to higher quality individuals)
What does the graph of the condition-dependent costs look like?
It is a graph of signal intensity (x) vs. costs and benefits (y) where the benefits line is an increasing downward curve and cost is a positive linear line.
What happens to the condition-dependent signal cost graph with low quality individuals compared to high quality?
The costs for low quality signalers has a higher slope so there is a smaller difference between the benefit and the cost lines. That also means that the optimal signal strength is different (generally closer to the origin).
What is the optimal signal strength in the condition-dependent signal cost graph?
This is the point on the graph when the difference between the benefits and the costs are greatest.
What are the production costs (costs when signal used/displayed) of signaling?
--Conspicuousness to predators & parasites
--Energetic costs
What are the development costs of signaling?
--Energetic costs
(growth of antlers, long tails)
--Loss of limited nutrients
What are the maintenance costs of signaling?
(flying with long tail, preening)
Which of the below costs is least likely to impose
honesty on bird song
A) use of energy
B) loss of time spent foraging
C) testosterone as immuno-suppressant
D) tradeoff of brain space devoted to song production
E) attracting predators
D) tradeoff of brain space devoted to song production
Natural selection will favor senders who elicit _________
response(s). From the signalers perspective, a display
may be viewed as a means of __________
A) beneficial, manipulation
B) costly, manipulation
C) beneficial, mutualism
D) costly, mutualism
E) any kind of, avoiding costs
A) beneficial, manipulation
Honesty can be maintained if _________
individuals pay _________ for a given level of
signal intensity than do high-quality individuals
A) high-quality, lower costs
B) low-quality, higher costs
C) high-quality, lower costs
D) low-quality, higher costs
E) average-quality
B) low-quality, higher costs
If all birds in a population signaled at same signal
intensity (e.g., same coloration), would that
signaling system be maintained by selection?
A) yes
B) no
C) not enough information to decide
B) no
What is true about the trade-off between allocation of carotenoids(C) to immune function and ornamentation?
--Only males that can gain a C-rich diet, or that have a strong immune system, are capable of bearing the costs of using Cs for immune function while still have Cs left for ornamentation
What happened in the experiment with the infected birds and their bill color?
--Males infected & C+ supplemented maintained bill color
--Males infected & non-supplemented lost bill color
What does plumage redness indicate? What does this tell us about males in general?
--Plumage redness indicates foraging ability and viability (survival)
--Only males capable of bearing the cost of gaining access to ample quantity/quality of food (via competition) are capable of
exaggerated ornamentation
What does the natural variation in male
house finch color look like?
Their belly and head colors move from yellow to orange to red.
What were the effects of experimental manipulation of the diets of captive birds?
Their diet altered the color of their plumage.
--Carotenoid deficient diet (lightest orangeish brown color)
diet (more orange color)
diet (deep red color)
If redder male birds molt faster, then what does that suggest about them?
Indicates that colorful
males are are nutritionally
What is also true about redder males and their survival rate?
Redder males have higher
survival rates
--Average color increased
after an epidemic
What is one visible trait that many female birds use to choose mates?
"redness"; there was an experiment where male birds were lightened and darkened in their red color and the darkened males had more pairings that took less time to get.
What is an index signal? What are some examples?
The honesty of an index signal is maintained because the
signals is physiologically or physically constrained (i.e. they are unbluffable)
–EX: Depth of pitch and body size is correlated in many frogs, Scratch marks by grizzlies or tigers; Body size or armament size plays a role in contest competition: size of armament cannot be faked; Tracheal length constrained by body size: makes
especially loud, resonant noises
What is a conventional sign? What are some examples?
The honesty of a conventional signal is maintained by the threat
of receiver retaliation (i.e. if you bluff you get attacked). These signals convey information about dominance
EX: Black badge size indicates dominance,
What are the 6 things that birds are saying with their vocalizations?
1).Territorial defense
2).Resource defense (can be territory defense)
3).Species recognition
4). Individual recognition: Parent-offspring & mate recognition
5). Individual recognition: Neighbor/stranger recognition
6).Mate attraction
What is the affect of experimental muting of birds?
Experimental muting of
territorial male leads to greater intrusion rate by other males, and eventual loss of territories
What do many voice rattles and variety tell you about a male?
Only males with high
testosterone (high physiological investment in
aggression) vocalize with many rattles
What is necessary in a computer generated song concerning bird responses?
Birds respond to computer-generated songs only when they contained species-typical features (because songs announce what species birds are)
What is the "Dear Enemy Effect?"
Essentially, if neighbors move or change places, this causes the subject to freak out and increase the intensity and frequency of his songs. (remember the graphs from the slide)
What aspects of vocalizations are informative, and what
kinds of information do they provide?
Features of song to which receivers respond:
--Song output (duration or rate)
--Song complexity (repertoire size: syllables or song types)
--Vocal performance (the ability to push limits of physical and physiological
What does birds' song complexity often correlate with?
Song complexity often correlates with reproductive success
What type of songs do female birds prefer? Why?
Females prefer males with complex songs
--Repertoire size indicative of parasite load
--Only males with good genes for (e.g., for immune system,
or to buffer stress of infection) can develop a complex song
What is the affect of malaria on song birds during development?
--Malaria infection reduces song complexity in canaries
--Birds infected with malaria during critical phases of development of higher vocal center (HVC) in the brain produced less complex
songs and had smaller HVCs
What does the RA in a canary stand for?
RA = Robust nucleus of the
Arcopallium (involved in adult
song production)
What does HVC in a canary stand for?
HVC = Higher Vocal Center nuclei (involved in song development)
What is the affect of food and hormonal stress on birds?
Food and hormonal stress during development reduce the size of the HVC in zebra finches
What can song complexity signal about a bird's brain?
Song complexity can signal neural complexity
What can song complexity signal about a bird's brain?
Song complexity can signal neural complexity
What is the significance of Ornithurine birds according to the Zhou 2004 reading?
Ornithurine birds are the only group of Mesozoic birds to have survived the K/T extinction
How would you describe the heritability of male peacock's sexual dimorphisms according to the Petrie et al 2009 reading?
All three traits associated with
sexual selection, train length, eyespot diameter and number
of eyespots, showed high levels of heritability in male peacocks (however only train length showed a significant value).
What is the difference between an adaptation and an exaptation according to the Ketterson & Nolan 1999 reading?
adaptation- A biological adaptation is an anatomical structure, physiological process or behavioral trait of an organism that has evolved over a period of time by the process of natural selection such that it increases the expected long-term reproductive success of the organism. (ex: giraffes evolving longer necks to reach tree leaves)

exaptation- an evolutionary process in which a given adaptation is first naturally selected for, and subsequently used by the organism for something other than its original, intended purpose (ex: evolving wings which would be useful for body temperature control, but useless for flying (they're too small) until they evolved larger)
What is Oxytocin and what is it an example of according to the Ketterson & Nolan 1999 reading?
Oxytocin (OT) is a peptide
hormone produced in the brain that has an effect on various behaviors and cell functions of rats/mice/etc which means that it is an example of pleiotropy.
What is significant about Testosterone and what does it exemplify according to the Ketterson & Nolan 1999 reading?
This not only exemplifies pleiotropy, but it also shows how in avian studies, testosterone has enhanced mating effort, suppressed parental effort, and
produced physiological consequences expected to shorten life span (conundrum of testosterone because although it is sexually selected for, it is selected against in natural selection).
What was the result of the experiments about female choice in the Barraclough et al 1995 article?
They tested the theory that predicts that sexual dichromatism in passerines has evolved through the action of female choice.

However, their results were inconclusive as to whether these sexually dimorphic traits evolved solely due to female choice. They suggested that part of the evolution could have occurred due to male plumage in addition to female choice. They cannot support the hypothesis that sexual selection by female choice has promoted cladogenesis (breaking off into two different species basically at a node)
What are the three "lines of evidence" that the Boul et al 2007 article refers to and what conclusion does it make?
1). sexual selection has promoted divergence in male mating calls and female preferences for calls between neighbouring populations
2). phylogenetic
analysis indicates that populations have become fixed for alternative call types several times throughout the
species’ range
3). estimated gene flow demonstrates genetic divergence and incipient speciation
Therefore, sexual selection is
driving behavioural isolation and speciation among populations of an Amazonian frog.
What conclusions do the field studies on house finches in the Hill 1991 article come to?
Field studies show that female house finches prefer to mate with colorful males. Also, plumage brightness and coloration correlates with a male's capacity for parental care and generally its genotypic quality.
What did the McGraw & Ardia 2007 reading end up discovering about testosterone?
Testosterone (T) is an important honesty reinforcer of animal sexual signals because of its immunosuppressive effects; only those individuals that can immunologically withstand
high T levels can develop the most exaggerated traits. Also, their findings show that those zebra finches with carotenoid supplementation were able to mobilize carotenoids for their immune system and the high cost of T (T-implants) while maintaining high levels of ornamentation.
What resulted from the blackbird experimentation reported about in the Baeta et al 2008 reading? Why is this significant?
They used a host-parasite model to show that supplemented males circulated more carotenoids in the blood and developed more brightly coloured bills than unsupplemented males. This is significant because this shows how animals face a trade-off in carotenoid allocation between immune functions and degree of ornamentation.
What are the 7 "limiting costs or constraints" of bird songs that are mentioned in the GIl & Gahr 2002 reading?
1). energy
2). social aggression
3). predation
4). age/experience
5). Neural costs
6). Immune/Hormonal costs
7). Physical and developmental constraints
What was significant about the experiment and the conclusions that the Nowicki et al 2002 reading come to about male bird songs? What myth did they address in their work?
Their results provide the first experimental demonstration that variation in learning abilities among males plays a functionally important part in the expression of a sexually selected trait (bird songs), and further provide support for the hypothesis that song functions
as an indicator of male quality because it rejects variation in response to early developmental stress. They addressed the idea that male traits are based on a complex combination of environmental and genetic factors (correcting the nature vs. nurture myth).