Deck 16: The Evolution of Sex

Question 1

Which of the following statements does NOT illustrate a potential cost of sexual reproduction?

A) Proteins in the seminal fluid of Drosophila males shorten the life expectancy of inseminated females.
B) Female birds of paradise inspect several males before deciding with whom to mate.
C) Male and female damselflies form characteristic mating wheels, which allow the partners to fly, albeit at slower speeds than single damselflies.
D) Pronghorn males do not actively search for mates, reducing their gene flow throughout the population.

Answer 1

D

Question 2

Would there be any disadvantage of sex if sexual reproduction was isogamous?

A) No; females would not pay the twofold cost of sex.
B) Yes; sex may break up coadapted gene complexes.
C) No; females would still transmit the same proportion of their genes to the next generation.
D) Yes; isogamous parents contribute unequally to gamete production, resulting in one parent experiencing a greater cost of reproduction.

Answer 2

B

Question 3

Are there any costs when asexual organisms reproduce automictically as opposed to apomictically?

A) Yes; recombination may disrupt coadapted gene complexes.
B) Yes; recombination is the cause of the twofold cost of sex.
C) No; both are forms of asexual reproduction.
D) No; recombination will produce more well-adapted individuals.

Answer 3

A

Question 4

In an experiment, Jokela and colleagues reared 14 replicate populations of a snail species that is polymorphic for sexual/asexual reproduction under controlled, identical conditions in the lab. Each population started with 35% asexual and 65% sexual individuals. The figure below shows the percentage of asexual individuals after a year-long experimental run. Which of the following statements is NOT a possible explanation for these results?

A) Asexual females survived better under the experimental conditions.
B) Asexual females produced more offspring per individual than sexual females.
C) Avoiding the cost of males allows faster population growth for the asexual subpopulation.
D) A novel mutation after the start of the experiment led to the increased survival of the asexual line with the mutations.

Question 5

What evolutionary model for the maintenance of sexual reproduction do the following data appear to support?

A) Muller's ratchet
B) the Red Queen hypothesis
C) the Fisher-Muller hypothesis
D) the environmental unpredictability hypothesis

Question 6

According to the reasoning of John Maynard Smith, in a mixed population of asexually reproducing females and sexually reproducing males and females, the number of asexuals should grow at twice the rate of the sexually reproducing individuals because

A) asexuals avoid the cost of producing males by producing offspring that do not need to be inseminated in order to reproduce, essentially only producing females.
B) the cost of sex per individual becomes smaller when sexuals become more rare in the population.
C) under Maynard Smith's model, populations are finite.
D) This scenario does not represent an accurate representation of real populations.

Question 7

Which of the following statements describes an element of the Fisher-Muller hypothesis for adaptive advantage of sexual reproduction?

A) Sex builds up linkage disequilibrium.
B) Sex slows down adaptive evolution by disrupting coadapted gene complexes.
C) Sex facilitates the combination of favorable mutations that originated in different individuals into advantageous genotypes.
D) Sex can increase the frequency of deleterious mutations.

Question 8

Why is sexual reproduction believed to be the ancestral state in eukaryotes?

A) Asexual reproduction is completely absent from basal unicellular eukaryotes.
B) Under the parsimony principle, the most common form of a trait's state is always the ancestral state.
C) The "twiggy" distribution of obligate asexual reproduction in phylogenetic trees suggests that asexuality is a derived trait.
D) Evolutionary models suggest that obligate asexual taxa are more prone to extinction than sexual ones.

Question 9

What are coadapted gene complexes?

A) genes that are located on the same chromosome
B) codominant alleles
C) favorable combinations of alleles at different loci
D) any epistatic interactions between different loci

Question 10

Which of the following is NOT a reason why the twofold cost of sex is sometimes referred to as the "cost of males"?

A) Males do not contribute genes to the next generation.
B) Males do not produce new offspring.
C) Males invest in sperm, most of which are wasted, rather than biomass.
D) Sperm cells do not contribute any substantial energy resources to the eggs they fertilize.

Question 11

Some mammals have demonstrated preferential attraction to individuals that carry immune system alleles that are complementary to their own. Which hypothesis does this observation support?

A) the Red Queen hypothesis
B) the Fisher-Muller hypothesis
C) Muller's ratchet
D) the attribution bias hypothesis

Question 12

Water fleas, Daphnia magna, can switch between asexual and sexual reproduction cycles. Which of the following observations support the hypothesis that sex is favored in unpredictable environments?

A) The introduction of predators triggers sexual reproduction.
B) D. magna reproduces asexually every other generation in a variety of habitats.
C) D. magna reproduces sexually when in stable water conditions.
D) Asexual D. magna strains outcompete introduced competitors.

Question 13

Why do some scientists consider automixis sexual reproduction?

A) It results in only heterozygous gametes.
B) It allows for crossing-over and can turn back Muller's ratchet.
C) Although the offspring are identical to their parents, it produces as much variation as sexual reproduction.
D) It reshuffles variation that originated in a bisexually reproducing population.

Question 14

Which of the following reproductive systems lends itself best to the study of the environmental factors that lead to the maintenance of sexual reproduction?

A) cyclical parthenogenetic populations that follow highly predictable seasonal patterns independent of environmental changes
B) obligate sexual species taxa, such as most birds
C) species that are polymorphic for sexual/asexual reproduction and show the same proportion of sexual reproduction in all environments
D) populations that respond to environmental changes with a change from asexual to sexual reproduction

Question 15

In a population that is polymorphic for sexual/asexual reproduction, a sexually transmitted disease has just eliminated most of the sexually reproducing individuals. When you expose samples of asexuals and sexuals from this population to harsh environmental conditions in the lab, you discover that the sexual individuals are worse at adapting to the new environment than the asexual individuals. (Note that your lab population is free from the sexually transmitted disease.) Which of the following statements is a likely explanation for your results?

A) All asexually reproducing strains independently acquired the same beneficial mutation that offset the advantage of the sexuals.
B) The bottleneck caused by the disease resulted in the fixation of many alleles in the sexually reproducing population.
C) Asexuals are favored under harsh environmental conditions.
D) The results support standard evolutionary theory.

Question 16

During bacterial conjugation, small circular chromosomes of DNA, called plasmids, are transferred from one bacterial cell to another. Why does this mechanism NOT fit the common definition of sexual reproduction?

A) No new offspring are produced.
B) No new allelic combinations are formed.
C) The cell receiving the plasmid does not contain genetic material from both parents.
D) The plasmid can recombine with the recipient cell's chromosome.

Question 17

The Amazon molly, Poecillia formosa, is a freshwater fish that is gynogenetic. In order to reproduce, individuals of this all-female species must mate with a male from a closely related species to initiate the development of their offspring. The male's genetic material does not, however, enter the Amazon molly's egg. What costs of sexual reproduction does the Amazon molly potentially experience?

A) None; it reproduces asexually.
B) It potentially experiences the costs associated with finding a mate and competing with other females for mates.
C) The female may risk incorporating a deleterious gene from the male.
D) It has no means of turning back Muller's ratchet.

Question 18

The figure shown illustrates the proportion of a particular asexual snail clone in a population and the degree to which it was infected with a particular parasite. Which prediction of the Red Queen hypothesis do these results appear to reflect?

A) a correlation between parasite load and sexual reproduction
B) oscillation in the relative frequency of asexual strains in the presence of parasites
C) emergent host defenses synchronously tracked by parasite responses
D) a general decline of asexual lineages in the presence of parasites

Question 19

What is the consequence of a deleterious mutation becoming fixed in a population?

A) Fixation of a deleterious mutation will automatically cause Muller's ratchet to move an additional turn.
B) Recombination cannot remove the mutation.
C) Mating between unrelated individuals can produce offspring that do not carry the mutation.
D) Muller's ratchet can no longer turn.

Question 20

The two figures represent an asexual and a sexual population. The letters indicate beneficial mutations. The shaded areas represent the frequency of particular combinations of mutations in the population over time. Why does it take longer for the beneficial allele combination of ABC to go to fixation in the asexual population than in the sexual population?

A) In the asexual population, new allelic combinations have to arise via de novo mutations.
B) There is no principal difference between asexual and sexual populations. In the sexual population shown, the favorable mutations just happen to be on different chromosomes.
C) The effective population size of both populations is the same.
D) Sexual populations tend to have higher mutation rates.

Question 21

Why are transduction, conjugation, and transformation sometimes referred to as sexual processes, but are not considered to be sexual reproduction?

A) Genetic material is exchanged, but the process does not involve meiosis and gamete fusion.
B) Genetic material is exchanged, but exchange can take place between organisms of the same sex.
C) Genetic material is not exchanged between two organisms; it is simply fused together into one new organism.
D) Genetic material is divided in the process of meiosis, resulting in two haploid individuals without exchange of genetic material.

Question 22

Birds of paradise are a family of tropical birds known for their striking sexual dimorphism. The males are famous for their elaborate, colorful plumage that combines with a variety of behaviors to attract females in their species for mating. Females choose the males based on their morphological and behavioral displays, providing an example of

A) intrasexual selection.
B) direct benefits.
C) intersexual selection.
D) Fisher-Muller evolution.

Question 23

Which step of the process of amphimixis produces new chromosomal variants?

A) gamete fusion
B) game production
C) recombination
D) meiosis

Question 24

In the crustacean genus Hyalella, females mate more often with males who have larger gnathopods. Males with larger gnathopods have been shown to be better protectors of females during amplexus. Which model of intersexual selection does this describe? A


B

A) good genes
B) direct benefits
C) Fisherian runaway selection
D) sensory bias

Question 25

How could the number of gametes produced relate to a reproductive success differential in males?

A) Males only produce a limited number of sperm; therefore, males that are choosy about their mates will have greater reproductive success.
B) Males that reproduce with more than one female will have greater opportunities for success because they attempt to fertilize multiple eggs.
C) Males chosen for reproduction by a females will have higher reproductive success because large numbers of eggs result in much higher probabilities of fertilization.
D) Males chosen by multiple females could have much higher reproductive success because of the large number of sperm produced by the male.

Question 26

What are two examples of asexual-like reproduction in the genomes of obligate sexually reproducing organisms?

Question 27

Could HIV infection be considered a cost of sexual reproduction? Keep your answer to one sentence.

Question 28

Several studies have looked at the different reproductive behaviors of male bluegill fish Lepomis macrochirus, identifying different morphs that exhibit different strategies when attempting to fertilize eggs. Which morph displays male-male competition through cuckoldry and sperm competition?

A) satellite
B) sneaker
C) paternal
D) territorial

Question 29

Which of the following is NOT a problem associated with distinguishing the Fisherian sexual selection model from the good genes model?

A) Neither the good genes model nor the Fisher model predict a positive correlation between male ornamentation and male viability.
B) The Fisher process operates on top of any good genes mechanism.
C) Linkage disequilibrium between female preference and a male trait is predicted by both models.
D) Neither model accounts for the effects of runaway sexual selection, which reinforces linkage disequilibrium.

Question 30

Counter the following argument: "Sexual reproduction is just an accident of evolution; once established it is irreversible. One does not need to postulate specific benefits to explain its maintenance."

Question 31

Under what conditions are asexual and sexual reproduction favored by the three evolutionary models shown in the figure, involving environmental unpredictability, number of niches, and parasite load? State whether a high or low value for each condition will favor sexual or asexual reproduction. A) Low environmental unpredictability
B) High environmental unpredictability
C) Low number of niches
D) High number of niches
E) Low parasite load
F) High parasite load

Question 32

Why is male reproductive success limited by the number of eggs?

A) Sperm are short lived compared to eggs and it is more expensive for males to reproduce because males produce a much greater number of gametes than there are eggs available to fertilize.
B) Eggs are much larger and scarcer than sperm, limiting the number of opportunities for reproductive success for males.
C) Eggs are smaller than sperm and short lived, limiting the number of opportunities for reproductive success for males.
D) Although eggs are not metabolically expensive to produce, most female organisms will only produce a small number of eggs during their life span.

Question 33

What did Curt Lively (1987) discover when applying the Red Queen hypothesis to snail populations in New Zealand?

A) Sexual reproduction was more common when the frequency of parasites was high, both in lakes and in streams.
B) Asexual reproduction was more common when the frequency of parasites was high, both in lakes and in streams.
C) Sexual reproduction was less common when the frequency of parasites was high, both in lakes and streams.
D) Sexual reproduction was more common when the frequency of parasites was high, but only in lake populations.

Question 34

How does recombination in sexually reproducing organisms reverse the effect of Muller's ratchet?

A) Recombination can undo fixation of deleterious mutations in either parent's chromosome.
B) Recombination can combine segments from each parent that have fewer deleterious mutations than were present in either parent's chromosome.
C) Recombination can reduce the rate of buildup of deleterious mutations in either parent's chromosome.
D) Recombination can reduce the number of deleterious mutations by promoting additional mutations that correct the original replication error.

Question 35

Do each of the following forms of reproduction represent asexual or sexual reproduction?
A. Amphimixis
B. Automixis
C. Apomixis

Question 36

For males, potential reproductive success is highest in a ________ mating system and lowest in a ________ mating system.

A) polygynandrous; monogamous
B) monogamous; polygynous
C) polygynous; polyandrous
D) monogamous; polyandrous

Question 37

What do these data about the offspring of peacocks tell us about the good genes model of intersexual selection? B


C

A) Chicks from fathers with feathers with large eyespots weighed more and had better rates of survival, indicating that tail length and ornamentation are indicators of male genetic quality.
B) Chicks from fathers with feathers with large eyespots weighed less and had lower rates of survival, indicating that tail length and ornamentation are indicators of male genetic quality.
C) Chicks from fathers with feathers with large eyespots weighed more and had better rates of survival, indicating that tail length and ornamentation are indicators of female genetic quality.
D) Chicks from fathers with feathers with large eyespots weighed less and had lower rates of survival, indicating that tail length and ornamentation are indicators of female genetic quality.

Question 38

You catalog all obligate asexual species within a family of insects and notice that asexual species are rare and are all members of genera that consist predominantly of sexual species. None of the genera consist exclusively of asexual species, and many of the asexual species have gone extinct. Your phylogenetic analysis shows that asexual species tend to be short "twigs" on the tree. What could you conclude from these results?

Question 39

Morphological or behavioral characteristics used to attract a mate can also have the consequence of drawing a predator's attention to the individual who possesses that trait, yet these so-called expensive traits persist in many species. This describes

A) the good genes hypothesis.
B) the Fisher process of sexual selection.
C) the handicap principle.
D) runaway sexual selection.

Question 40

What is the definition of "sexual reproduction"?

A) production of offspring from unfertilized gametes
B) unfertilized gametes produced by mitosis-like cell division, producing daughter cells with unreduced number of chromosomes
C) production of haploid gametes via meiosis, and diploidy restored by fusion of haploid nuclei from same meiosis
D) joining together of genetic material from two parents to produce an offspring with genes from each parent

Question 41

What is the relationship between male quality and tail length in peacocks? Why do extravagant and metabolically costly traits like peacocks' tails persist in population?

Question 42

Describe the three-step process of amphimixis.

Question 43

Why do pathogens tend to evolve faster than their hosts?

Question 44

Does Muller's ratchet apply to both apomictic and automictic asexual populations?

Question 45

What are the two immediate benefits to sexual reproduction in unpredictable environments, according to Alexey Kondrashov?

Question 46

Develop a short hypothetical explanation (one sentence) for the observed distribution of obligate asexual reproduction under the environmental unpredictability model.

Question 47

Explain how sexual reproduction overcomes the inherent disadvantage of generation time in the host of an asexually reproducing pathogen.

Question 48

Is it possible for a recombination event to turn Muller's ratchet "forward" in the population of chromosomes below? The dots on the chromosomes indicate deleterious mutations. Indicate the crossing-over event by placing an X on the figure.

Question 49

Why is the twofold cost of sex only seen in anisogamous organisms?