Download EVOLUTIONARY BIOLOGY BIOS 30305 EXAM #2 FALL 2016

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EVOLUTIONARY BIOLOGY BIOS 30305 EXAM #2 FALL 2016
There are 3 parts to this exam. Take your time and be sure to put your name on the top of each
page.
Part I. True (T) or False (F) (2 points each)(30 pts. total)
1)
Quantitative Trait Loci (QTL) studies based on crosses between divergent
individuals are used to estimate the number of genes (or genomic regions)
that influence phenotypic variation
T
F
Mate provisioning is an example of an indirect benefit driving the
evolution of female preference.
T
F
Sympatric speciation relies on geographic isolation of potentially
interbreeding populations.
T
F
Introgression is the exchange of alleles between species following
hybridization and backcrossing.
T
F
Antagonistic-Pleiotropy among fitness traits can maintain genetic
variance for fitness in natural populations
T
F
There is a higher opportunity for sexual selection in species with
strictly monogamous mating systems than in species with
polygynous mating systems.
T
F
Rapid divergence of secondary sexual characteristics in closely
related species provides evidence for reinforcement.
T
F
Male-male competition leads to a reduced variance in male
reproductive success
T
F
Similar ecological conditions can lead to parallel evolution of similar
phenotypes.
T
F
10) In small captive populations, doubling the effective size of the
population maintains twice the amount of additive genetic variation.
T
F
11) An estimate of the heritability of human I.Q. can tell us whether the
difference in I.Q. among different populations is due to environmental
factors.
T
F
12) Using Prices’ Rule, the selection differential (S) on relative fitness is
equal to the phenotypic variance (VP) in relative fitness.
T
F
2)
3)
4)
5)
6)
7)
8)
9)
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13) An analysis of Bateman’s Gradient in sex-role reversed pipefish
indicates that there is a greater opportunity for sexual selection in
females in this species.
T
F
14) Ring species demonstrate the development of instantaneous
reproductive isolation among adjacent populations.
T
F
15) On average, paternal half-siblings should resemble each other more
than grandparents and grandchildren.
T
F
Part II. Multiple Choice (3 points each)(45 pts total).
16)
When populations are in a rapidly changing environment they can,
A. Physically move to a more beneficial environment
B. Adapt to the changing environment and maintain high population fitness.
C. Adapt at a rate that is slower that the critical rate necessary to track the moving
optimum and eventually go extinct.
D. All of the above.
17)
Stabilizing selection occurs when…
A. The individuals with extremely small and large trait values have lower fitness
than those with intermediate trait values.
B. The individuals with intermediate trait values have lower fitness than those with
extremely small and large trait values.
C. The individuals with small trait values have lower fitness than those with larger trait
values.
D. All individuals have equal fitness.
18)
One form of the Good-Genes model for the evolution of female choice is the handicap
principle. Which of the following statements is NOT true under the handicap principle?
A. Handicaps are examples of honest signals since there is a true cost to elaborate
male traits.
B. Females who mate with males carrying an exaggerated trait will have female
offspring with decreased fitness.
C. The bigger the handicap, the higher the genetic quality of the male carrying the trait.
D. Female preference for exaggerated male traits can lead to a genetic correlation
between preference and trait.
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Which of the following statements about character displacement is/are TRUE?
A. Character displacement can promote rapid divergence among closely related
species.
B. Character displacement is the divergence of male and female traits involved in
sexual selection.
C. Character displacement can constrain divergence into occupied niches.
D. A and B.
E. A and C.
20)
What is the best definition of sexual selection?
A.
B.
C.
D.
21)
Anisogamy refers to,
A.
B.
C.
D.
22)
Mating occurs, but no gametes are transferred.
The backcross or F2 has reduced viability.
Mating occurs, gametes are transferred, but fertilization does not take place.
Populations are infected with different strains of the bacteria Wolbachia causing
reciprocal male sterility.
The observation that two loci are in linkage disequilibrium means…
A.
B.
C.
D.
24)
A positive relationship between size and fecundity.
A non-random mating process in which one sex competes for the other.
An asymmetry in the size of gametes, with one small type and one large type.
Asymmetrical sperm with a large amount of shape variation.
Which one of the following is NOT a prezygotic reproductive isolating mechanism?
A.
B.
C.
D.
23)
Selection related to any aspect of offspring production.
Selection that arises as a consequence of competition for access to mates.
Selection on the form and structure of gametes.
Selection that results in any type of difference between the sexes.
That they exhibit a non-random association of alleles.
That they are close to one another on a chromosome.
That the loci are functionally related.
That selection is operating on the loci.
Which of the following statements best describes the reason for barriers to gene flow
when there is postzygotic isolation?
A.
B.
C.
D.
Individuals from different populations meet but do not mate
Copulation occurs, but gametes are not transferred
Gametes are transferred, but eggs are not fertilized
Gametes are transferred, eggs are fertilized, but the zygote dies
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25)
Which of the following statements about heritability is TRUE?
A.
B.
C.
D.
26)
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Heritability is the additive genetic variance divided by the total genetic variance.
Traits that have a genetic basis always have high heritability.
Heritability is equal to the selection differential divided by the response to selection.
A higher heritability permits a greater evolutionary response to selection.
Which of the following statements is NOT true?
A. The selection differential is the covariance between phenotype and relative fitness.
B. The selection differential is the difference between the mean of selected parents and
the mean of the base population prior to selection.
C. The selection differential is the difference between the mean of the offspring of
selected parents and the mean of the offspring of all parents.
D. The selection differential is equal to the response to selection divided by the
heritability.
28)
Epistatic interactions are an important component of which of the following?
A. The build up of postzygotic reproductive isolating mechanisms.
B. The phenotypic covariance between half-sibs.
C. The almost universal observation of inbreeding depression in natural populations
following the mating of related individuals.
D. A and C.
29)
Which of the following statements best describes the three phases of Wright’s ShiftingBalance model of movement between peaks in an adaptive landscape?
A. Migration followed by random genetic drift and selection towards a new fitness
optima.
B. Selection towards a new fitness optima followed by random genetic drift and
migration.
C. Random genetic drift followed by selection towards a new fitness optima and
migration.
D. The appearance of a rare beneficial mutation followed by selection towards a new
fitness optima and migration.
30)
The Biological Species Concept (BSC) defines species as:
A. Actually or potentially interbreeding populations that are reproductively
isolated from other such populations.
B. Populations that form the smallest diagnosable cluster, or group, distinct from other
such clusters.
C. Both A and B
D. None of the above
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Part III. Short Answer (25 pts. total) Be concise and to the point, short focused answers
are better than long rambling ones.
31)
It is generally thought that it takes more than a single gene for the evolution of
reproductive isolation leading to speciation. What is the problem with a one locus model of
speciation? How does the Bateson-Muller-Dobzansky 2-locus model of speciation get around
this difficulty? (4 points)
The single-locus model requires that populations cross a fitness valley created by
heterozygote disadvantage. Since selection will always move a populations upwards on
a fitness landscape this model is unlikely since the initial mutation from A to a (or a to A)
in a single population will be deleterious and selection will prevent it from rising to high
frequency. In very small populations experiencing strong drift we know that gene
frequencies can move in the opposite direction from that favored by selection, so drift is
one possible way to “rescue” this single-locus model.
The B-M-D two-locus model of speciation circumvents the problem of the one-locus
model by the accumulation of independent mutations that are neutral or beneficial in the
genetic background they arise in, but have negative epistatic interactions when put in
the same genetic background. These negative epistatic interactions cause a decrease in
hybrid fitness that contributes to reproductive isolation.
Bonus (1 pt): How does Haldane’s Rule support the BMD model?
The dominance theory for Hadane’s rule relies on 1) multiple genes and 2) negative
epistatic interactions. Both are features of the 2-locus B-M-D Model.
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32)
Examine the plots above from the work of Coyne and Orr (1997). It appears that the
degree of prezygotic isolation is lower for allopatric pairs of species that have been
geographically isolated than for pairs that exist in sympatry. (4 points)
What is the likely explanation for this observation?
The work of Coyne and Orr (1997) comparing the patterns of pre- and postzygotic
isolation for species pairs of Drosophila best illustrates the action of REINFORCING
MECHANISMS. Sympatric species pairs develop prezygotic isolation at a faster rate
than do allopatric species pairs. The likely explanation is that REINFORCEMENT has
played a role in establishing reproductive isolation in sympatric, but not allopatric
species pairs. Allopatric populations cannot interbreed to create hybrids so a deficit in
hybrid fitness cannot cause a fitness loss to individuals in the two species. Sympatric
species can interbreed so a deficit in hybrid fitness leads to strong selection against
hybridization. If this reinforcing selection is not strong enough to counteract the
homogenizing effect of gene flow the species will reunite and will not be represented on
this plot.
The two key elements are 1) a defict in hybrid fitness, 2) reinforcement favoring
prezygotic isolating mechanisms that prevent the loss of fitness due to this deficit.
33)
Female preference for male traits can drive the evolution of exaggerated male traits. List
and explain three (3) theories for the evolution of female preference. (9 points)
There are a number of possible answers to this question. These include:
1) Direct Benefits (i.e., mate provisioning, nuptial gifts)
2) Indirect Benefits:
Good-genes Model: the key element of this model is preference by females for males
that are carrying high fitness genes
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Handicap Principle: this model is an example of “honest signaling” by males
advertising high-fitness genes that overcome a fitness handicap. The main
indirect fitness benefit for females is in daughters that inherit these high-fitness
alleles.
Fisherian Runaway Process: this model requires a genetic correlation between female
preference and male trait. This process begins with a pattern of assortative mating that
leads to linkage disequilibrium between preference and trait alleles.
Sexy-son Hypothesis: one way to couch the runaway process that emphasizes
that the indirect fitness benefit to females is sons with exaggerated traits and a
mating advantage
Antagonistic Coevolution: An alternative to the Good Genes Model is based on
Sexual Conflict. Just like the good genes models the genetic correlations created by
assortative mating can lead to a runaway process.
3) Sensory Bias: Pre-existing preferences that are “hard wired” due to the sensory machinery
in females.
Any three of these was acceptable. Full credit was not given if good Genes & Handicap
principle, or Sexy-son and Fisherian run away were used together since they are not distinct
from one another. For each, a reasonable explanation was required.
Bonus (1 pt): Which of these theories best explains the origin of female preference?
This question was evaluated based on what you had down for the first part. Sensory
Bias most directly addresses the question of the origin of female preference since it
does not require selection at all. Among the others, anytime there are direct benefits the
selection pressure on females will be the highest since there is a direct effect on her
individual fitness. Antagonistic coevolution also directly affects the female so this one
would be next. All the other categories are an indirect benefit and are more applicable to
the evolution of female preference and male trait after they are established in a
population. Among these, a good genes model is the best choice.
34)
The rapid diversification of species is a hallmark of an Adaptive Radiation.
Paleontologist G. G. Simpson suggested that two main factors contribute to an Adaptive
Radiation. List and explain these two factors, and provide an example from an actual
adaptive radiation for each factor. (8 points)
Two factors suggested by the paleontologist G. G. Simpson that play a role in adaptive
radiations are:
1) ECOLOGICAL OPPORTUNITY - Can be the result of the invasion of unoccupied
territory, or the extinction of a competitor opening up an available niche. The main
feature is the availability of unoccupied niches. When there is open niche space for
species to diversify into, mechanisms like character displacement can rapidly promote
diversification. There are many examples of ecological opportunity that could be used.
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2) KEY INNOVATION- The evolution of a novel trait can lead to an adaptive radiation by
opening up new niches and exposing organisms to novel selection pressures promoting
divergence. There are many examples of key innovations that could be used.
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Extra Work Space:
Section 1
Section 2
Section 3
Total
/30
/45
/25
/100
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Components of Phenotypic Variation:
VP  VG  VE , where VP is the total phenotypic variance, VG is the total genetic variance and VE is
the environmental variance.
Components of Genetic Variation:
VG  VA  VD  VI , where VG is the total genetic variance, VA is the additive genetic variance, VD is
the dominance genetic variance, and VI is the epistatic genetic variance.
Slope of a regression line of two variables x and y:
b
Cov x, y 
Var x 
Heritability:
h2 
VA
VA

VP VG  VE 
The Univariate Breeder’s Equation:
R  h 2 S , where R is the response to selection, h2 is the heritability, and S is the selection
differential.
Price’s rule: S = Cov(relative fitness, phenotype)
S
1
N
 w  w P  P 
i
i
VA under drift-mutation equilibrium:
VA  2 NVm , where Vm is the genetic variance due to the input by mutation
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