Ch. 16 Sex and Sexual Selection Homework

apomixis

A form of asexual reproduction in which an unfertilized gamete undergoes a single mitosis-like cell division, producing two daughter cells that have an unreduced number of chromosomes and that are genetically identical to those of the mother. -a form of asexual reproduction in which daughter cells are genetically identical to the parent cell

automixis

A form of asexual reproduction in which haploid gametes are produced via meiosis, and then diploidy is restored by one of several asexual mechanisms.

sexual selection

A form of natural selection that refers to selection for traits and behaviors that confer mating success (as opposed to survival).

sexual conflict

A phenomenon in which selection operates differently on males and females, typically with respect to mating behavior.

polygamy

Males mate with more than one female every breeding season.

monogamy

One male and one female mate only with each other during a given breeding season.

Polygynandry

Both males and females have more than one mate in a breeding season, and several males form pair bonds with several females simultaneously.

Which of the following statements most accurately describes what evolutionary biologists mean by "the cost of producing males" in sexually reproducing organisms?

In a population consisting of both sexuals and asexuals, the number of asexually reproducing individuals should grow more rapidly than the number of sexually reproducing individuals.

Which of the following statements best explains how anisogamy differs from isogamy in terms of parental investment in offspring biomass?

In an isogamous system, both sexes contribute to offspring biomass, whereas in anisogamy, only females make this gametic investment.

For which reason does recombination in sexually reproducing organisms prevent the accumulation of deleterious mutations via Muller's ratchet?

It breaks up haplotypes and can combine chromosomal segments containing beneficial alleles.

The potential reproductive success of the most successful males in a population depends on social structure and mating system. Place the following mating systems in increasing order of potential male reproductive success (from lowest to highest).

Lowest: polyandry (one female with multiple male partners) monogamy (one male with one female partner) polygynandry (one male with 2 female partners) Highest: polygamy (one male having multiple female partners)

diploid

having two copies of each type of chromosome

Because they represent competitive strategies rather than traits that serve as criteria for female choice, alternative reproductive morphs, such as sneaker and satellite males in bluegill sunfish, most likely evolve under what type of selection?

intrasexual

What term describes the form of sexual selection in which members of one sex (typically males) compete directly for access to mates?

intrasexual selection

syngamy

the union of gametes from different individuals during sexual reproduction

Muller's Ratchet Hypothesis

genetic drift and mutation lead to accumulation of harmful mutations that sex can solve.

sexual reproduction

-A reproductive process that involves two parents that combine their genetic material to produce a new organism, which differs from both parents -An individual in which a deleterious mutation arises can produce offspring that do not have that mutation. -Deleterious mutations are associated with reductions in fitness.

asexual reproduction

-Process by which a single parent reproduces by itself -Production of offspring from unfertilized gametes -Deleterious mutations build up irreversibly due to Muller's ratchet. -Deleterious mutations are associated with reductions in fitness.

3 steps of amphimixis:

1. Recombination: the crossover between homologous chromosomes, which produces new chromosomal variants. 2. Gamete production: the production of haploid gametes by diploid individuals via reductive meiotic division. 3. Gamete fusion: gametic exchange between individuals, in which haploid gametes fuse to produce a diploid offspring.

Sexual reproduction is associated with costs. Indicate which of the following statements is/are consistent or inconsistent with this statement.

Consistent: Sexually reproducing organisms incur an energetic cost associated with finding and courting potential mates. Recombination associated only with sexual reproduction can break up favorable allelic combinations/haplotypes. Sexually reproducing individuals pass on a smaller proportion of their genes to each offspring than do asexual individuals. Inconsistent: The number of sexually reproducing individuals in a population should grow more rapidly than the number of asexually reproducing individuals.

Drag each statement to the correct box to indicate whether or not it describes the figure to the right, which depicts the expected evolutionary trajectories of sexual and asexual lineages coexisting with a parasite that has a much shorter generation time than the host.

Correct: A new asexual lineage with genetically based defenses against the parasite is at an initial competitive advantage over sexual lineages. If a mutation arises that allows the parasite to overcome resistance in an abundant asexual host lineage, the asexual clone is at a disadvantage relative to genetically variable sexual hosts. Incorrect: High parasite loads favor asexual reproduction over sexual reproduction in populations where both reproductive modes can occur.

Drag each of the following statements to the correct box to indicate whether it is correct or incorrect of Petrie's experiments on mate choice in peafowl.

Correct: Because elaborate tails are energetically costly, they are likely honest indicators of male quality, in keeping with Zahavi's handicap principle. Male offspring of males with more elaborate tails are healthier (heavier) and offspring regardless of sex survive better than offspring of males with less elaborate tails, hypothetically because they have inherited genes that enhance their ability to fight infectious disease. Incorrect: The results shown in the graph indicate that female preference for large eyespots most likely evolved under the direct benefits model since offspring weight (an indicator of health) is positively correlated with the mean size of eyespots in the father. Evidence from Petrie's study suggests that elaborate tails in peacocks evolved under intrasexual rather than intersexual selection.

Drag each statement to the correct box to indicate whether or not it reflects the differences between the two figures depicting fixation in a large population with the advantageous mutations A, B, and C. Assume that these three loci are physically linked in the genome.

Correct: In sexual reproduction, the assembly of the most advantageous haplotype involves the breakdown of linkage disequilibrium at the three loci under consideration. In asexual reproduction, the A allele can come together with the B allele in the same haplotype only if B arises in an individual that already carries A. Incorrect: Natural selection fixes the most advantageous haplotype more rapidly in asexual reproduction than in sexual reproduction.

Drag each statement to the correct box to indicate whether or not it is a likely advantage of sexual reproduction when the environment is spatially or temporally unpredictable.

Correct: Production of genetically variable offspring increases opportunities to exploit different niches and could thus reduce resource competition among siblings. Production of genetically variable offspring increases the probability that some progeny will be well suited to new environmental conditions. Incorrect: A sexually reproducing lineage will grow in number faster than an asexually reproducing lineage that is equally well adapted to the environment.

Drag each statement to the correct box to indicate whether or not it is a distinction between the good genes model and the Fisherian runaway model of sexual selection.

Distinction: Both the good genes model and the Fisherian model predict linkage disequilibrium between loci associated with female preference and loci that govern the male trait. Not distinction: The good genes model is an example of intersexual selection, whereas the Fisherian model is an example of intrasexual selection. Both the good genes model and the Fisherian model assume that the preferred male trait covaries with some other indicator of male genetic quality. The good genes model predicts that male viability will be positively correlated with male ornamentation, whereas the Fisherian model predicts a negative correlation between ornamentation and viability.

polyandry

Females mate with more than one male every breeding season.

direct benefits

Selection favors females that choose mates based on traits associated with resource provisioning rather than genetic contributions to offspring.

good genes

Selection favors females that choose mates with traits that are honest indicators of genetic quality.

Fisherian runaway selection

Selection favors females with a preference for a male ornament that is in linkage disequilibrium with the genes underlying the female preference.

sensory bias

Selection favors male traits that tap into a preexisting female sensitivity to some stimulus.

Muller's ratchet

The irreversible buildup of deleterious mutations in asexual populations.

Which feature of the graph most directly supports the Fisher-Muller hypothesis of adaptive evolution?

The sexual lineage increases in fitness more quickly than the asexual lineage.

Which of the following predictions of the Red Queen hypothesis is most strongly and directly supported by the results shown in the figure? The gold bars in the graph represent the frequency of the asexual lineage, and the red line represents the frequency of all parasites in a natural population.

There will be a time lag between the appearance of host resistance and the evolution of a mechanism by which the parasite can overcome that defense.

Male Drosophila transfer accessory gland proteins along with sperm during normal mating. Experiments implicate these proteins in sexual conflict because they increase female egg production but decrease female survival. If accessory gland proteins are responsible for depressed female survival, which of the treatments shown in the table below must have generated the curve marked with an arrow? (Lowest female survival) Assume that none of the males could produce sperm.

Treatment A: males produce accessory gland proteins and males mate normally with females.

Drag each statement to the correct box to indicate whether it is true or false of the phylogenetic distribution of sexual and asexual reproduction in eukaryotes.

True: Few eukaryotes reproduce only asexually. Almost no multicellular eukaryotic taxa consist entirely of asexually reproducing species. False: Modern eukaryotes that reproduce asexually most likely retain the ancestral reproductive mode of eukaryotes. Sexual taxa tend to go extinct more quickly than asexual taxa.

Drag each statement to the correct box to indicate whether it is true or false of how anisogamy translates into different selective pressures on males and females.

True: In a system that does not involve effective parental care of offspring as a factor in the success of those offspring/matings, we expect males that mate with numerous females to leave many more offspring than males that mate with few females. We expect males to compete for access to mates and for females to be more discriminating than males about mate choice. False: We expect females that mate with numerous males to leave many more offspring than females that mate with few males. Mating success is typically more variable in females than in males.

Drag each statement to the box to indicate whether it is true or false of the evolutionary phenomenon known as Muller's ratchet.

True: Muller's ratchet depends on a genetic system in which deleterious mutations arise and mutations from deleterious back to advantageous alleles are negligibly rare. Muller's ratchet is the phenomenon whereby deleterious mutations accumulate irreversibly in asexual populations. False: Muller's ratchet occurs because new deleterious alleles are fixed rapidly in asexual populations. Muller's ratchet is characterized by fluctuation in the number of deleterious alleles present in an asexually reproducing population.

Drag each statement to the box to indicate whether it is true or false of the evolutionary phenomenon known as Muller's ratchet.

True: Muller's ratchet is the phenomenon whereby deleterious mutations accumulate irreversibly in asexual populations. Muller's ratchet depends on a genetic system in which deleterious mutations arise and mutations from deleterious back to advantageous alleles are negligibly rare. False: Muller's ratchet occurs because new deleterious alleles are fixed rapidly in asexual populations. Muller's ratchet is characterized by fluctuation in the number of deleterious alleles present in an asexually reproducing population.

The graph depicts the association between sexual reproduction and parasite load in lake and stream populations of the snail Potamopyrgus antipodarum, which can reproduce either sexually or asexually. The study that generated the data was designed to test hypotheses regarding the evolutionary advantage conferred by sexual reproduction. Drag each statement to the correct box to indicate whether it is true or false of the results in the graph.

True: The results of this study are not consistent with the predictions of the environmental unpredictability hypothesis. Sexual reproduction is more common in lake populations than in stream populations, as predicted by the multiple niche hypothesis. False: Greater parasite load is associated with less sexual reproduction, as predicted by the Red Queen hypothesis.

Drag each statement to the correct box to indicate whether it is true or false as you consider the information in the graph depicting the results of a competition experiment with sexual and asexual snails.

True: These experimental results illustrate what Maynard Smith called the "twofold cost of sex." We can assume that the asexual snails used in the experiment were female. False: If the experimenters were to grow these snails in the presence of parasites for multiple generations, we would expect essentially the same outcome. These experimental results illustrate the evolutionary advantage of anisogamy.

The freshwater crustacean Daphnia magna is a cyclical parthenogen in which individuals normally reproduce asexually but occasionally reproduce sexually. Experiments have demonstrated that females shift to sexual reproduction in response to introduction of a new predator, a decrease in food quality, and cues related to drying up of a temporary pond. Drag each of the statements below to indicate whether it is true or false of these reproductive shifts in Daphnia.

True: These results are consistent with the hypothesis that sexual reproduction confers an advantage in temporally variable and unpredictable environments. When the environment is stable, asexual reproduction allows a well-adapted lineage to grow at a higher rate than a similarly adapted sexual lineage. False: A shift to sexual reproduction decreases the ability of a population to respond to new selection pressures and is thus a puzzling phenomenon in Daphni

Given the distribution of female reproductive success as shown, which of the following graphs is most likely to represent the reproductive success of males in the same sexually reproducing population with anisogamy?

When females in a population have high reproductive success, males in the same sexually reproducing population tend to have varying reproductive success.

isogamy

When individuals in a population produce one type of gamete—each parent produces mid-sized gametes that, when they fuse, are together the size of the large gametes produced by anisogamous females. With isogamous sexual parents, investment again goes to biomass rather than "wasted" sperm, and the lineage is able to grow at the same rate as an asexual lineage.

meiosis

a series of two cell divisions that generates haploid gametes

The production of gametes of two different masses in sexually reproducing species is called _______. Under such a system, only the _______ sex invests in offspring biomass. In asexual reproduction, all individuals in the population invest completely in offspring production, and as a consequence, we expect an asexual population to grow _________ than a sexual population. Evolutionary biologist John Maynard Smith called this cost of producing males and the effects on population growth rate "the twofold cost of sex."

anisogamy; female; faster

Two types of asexual reproduction

apomixis and automixis

Female isopods in the species Hyalella azteca prefer to mate with males that have large gnathopods, with which the males grasp the females and hold them for an extended period during mating. Based on the information in the graph and your understanding of sexual selection, which model of intersexual selection most likely explains the evolution of large male gnathopods? Note that male body size is positively associated with gnathopod size.

direct benefits, because females that choose males with large gnathopods gain a survival advantage

What mode of selection favors the evolution of anisogamy?

disruptive selection

Sexual selection is a type of selection in which traits found in one sex increase in frequency as a consequence of their beneficial effects on _________ alone. _________ selection results in the increase in the frequency of traits that favor the ability of members of one sex, typically males, to directly compete with each other for access to mates. This type of selection is often implicated in the evolution of male weapons and armor. _________ selection results in the increase in the frequency of traits that favor the ability of members of one sex to choose among members of the other sex. This form of selection is sometimes called "female choice" because females pick mates based on some aspect of male phenotype such as color or ornamentation. Both forms of sexual selection are associated with the evolution of _____________, in which males and females differ in phenotype.

mating success; intrasexual; intersexual; sexual dimorphism

True sexual reproduction involves recombination, production of haploid gametes via the cell division process known as ________, and gametic fusion, or syngamy. These steps, which as a whole make up the process called _________, produce a diploid zygote with a set of chromosomes inherited from each parent. Species that only reproduce asexually are ________ among eukaryotes, and asexually reproducing lineages typically go extinct more ________ than sexual lineages over evolutionary time.

meiosis; amphimixis; rare; quickly

Which types of sexually reproducing females have the highest reproductive success?

polyandrous and polygynandrous

Anisogamy

sexual reproduction involving different sized gametes; small sperm and large eggs

amphimixis

sexual reproduction which involves alternating phases of meiosis and gamete fusion (syngamy)

Imagine a hypothetical marine animal population that produces a range of gamete sizes as shown in Panel A. Members of this species release their gametes into the water, and pairs of gametes fuse upon encountering each other. The relationship between zygote fitness and zygote size, shown in Panel B, indicates that the fittest zygotes would result from fusion of two large gametes. However, if we assume a ________ between the number and size of gametes that an individual can produce, and if large gametes are the_______ motile, the probability that two such gametes will find each other is low. Under these conditions, _______ selection is expected to favor the evolution of two classes of gametes, a condition known as ________.

trade-off; least; disruptive; anisogamy