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Chapter 11: Sexual Selection

Chapter Study Questions

Chapter Study Questions


This activity contains 19 questions.

	Match the key terms in this chapter listed below with the phrase that is the best match for it. Using the pull-down menus, match each item in the left column to the corresponding item in the right column. intrasexual selection parental investment sexual dimorphism sexual selection intersexual selection 1.1 any consistent difference between males and females of a species (in physiology, behavior, morphology, etc.) A B C D E 1.2 differential reproductive success that is solely due to differences in the ability to attract mates A B C D E 1.3 the energy and time expended in creating and caring for offspring A B C D E 1.4 selection for the ability to compete directly with members of the same sex A B C D E 1.5 selection for the ability to attract the opposite sex A B C D E

	Three of the following correctly complete the statement, "Sexual dimorphism is __________" while the other three do not. Which three are correct?   An evolutionary consequence of different levels of investment of males and females in mating and parental care. A difference in the sexes that always takes the form of greater body size in males, and attractive features in females. Usually caused by sexual selection. Any difference between males and females, such as in morphology, physiology, or behavior. Any morphological feature that is influenced by reproductive hormones. Not present in humans.

	Which statement is correct?   Males are always choosy, and females are always competitive. Females are always choosy, and males are always competitive. Which sex is choosy or competitive usually depends on the strength of sexual selection for each sex.

	Parental care by males ________________________.   is associated with "choosiness" in females results in strong sexual selection on males is common in most birds is not common in any group of animals is common in most mammals (including humans)

	In the experiment on rough-skinned newts, why was it important that many males failed to mate at all, while all females mated at least once?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.

	We discussed two species in which males are larger than females: marine iguanas and humans. For which (if either) of these species did we see direct evidence that large males have reduced survival or health (i.e. the sexually selected trait of large body size is in opposition to natural selection)?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.

	For marine iguanas and humans, which (if either) of these species did we see direct evidence that large males attract more mates and/or have more offspring?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.

	For marine iguanas and humans, which (if either) of these species did we see direct evidence that large males have an advantage in combat with other males for access to females?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.

	Why have Catasetum orchids evolved to fire a pollinarium at a bee in a way that is apparently unpleasant for the bee?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.

	Sand gobies are a small, shallow-water marine fish in which males construct nests underneath empty mussel shells. Females come and lay eggs in the mussel shell nest, and males then guard the eggs until they hatch. Males fan water over the eggs with their fins while the eggs develop. The more eggs in their nest, and the more those eggs consume oxygen from the surrounding water, the more the male will fan the eggs. Kai Lindstrom and colleagues were curious about how females choose males. In a first experiment, females were placed in an aquarium from which they could view two males, one of whom had been provided with a small nest (a 6-cm-wide flowerpot nested within a 10-cm-wide flowerpot), and the other with a large nest (a 10-cm-flowerpot). Females were kept (with clear partitions) to the side of the nest so that they could not see the inside of the nest - from their point of view, the nests appeared identical. They could, however, see the male at the nest entrance. In a second experiment, low-oxygen water was piped into one of the nests. Again, the females could not perceive the difference in oxygen level from their location - all they could view from their vantage point was the male at the entrance of the nest. After the females had been given ample time to view the males, the small flowerpot removed (in the first experiment) and the low-oxygen-water-pipe turned off (in the second experiment. The female was then given access to entire aquarium. For the first time she was able to inspect the inside of the nest. What she saw was that both males had identical nests - 10-cm-wide flowerpots with normal oxygenation. Yet, in the first experiment, 82% of females chose the male who had had the larger nest earlier. In the second experiment, 73% of females chose the male who had had low-oxygen-wate r piped into his nest earlier. What explanation do you have for these results? How were females able to perceive differences in nests that they could not see, and why did they make the choices that they did?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.

	We take for granted that female humans develop breasts at puberty and retain them throughout life. And we take for granted the fact that men are often very interested in those breasts. However, this is a highly unusual trait. In other mammals, breasts (or udders) develop only when nursing young, regress at other times, and are generally not a feature that males are interested in. In humans, breasts develop under the influence of estrogen in puberty, and are composed (in non-nursing women) primarily of fat tissue. Why do you think women have evolved to have well-developed breasts throughout life? Which is the "choosier" sex in humans? How could you test your ideas?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.

	The “puzzle of sexual dimorphism” refers to the fact that   offspring differ from their parents. in many organisms, one sex or the other often exhibits traits that are not found in the other and that appear to be maladaptive. in many organisms (both plant and animal) males and females differ. Darwin was unable to explain sexual dimorphism.

	According to sexual selection theory, differences in reproductive investment lead to differences in factors that limit lifetime reproductive success. Based on the graph, of this species have the highest reproductive investment

	Why did Wikelski et al. infer that body size in male Galapagos marine iguanas was sexually selected? Use the graph to help identify the correct answer. In each histogram, asterisks mark the largest size at which individuals could maintain body weight in two different years.   Females are larger than males. Average male body size was larger than the optimal body size based on energetics. Marine iguanas are large. Iguanas on Santa Fe are larger than those on Genovesa.

	List and briefly describe three different traits that might be selectively favored in males facing sperm competition.   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.

	In African lions, infanticide seems to be adaptive for males because of the combination of _____ and _____.   short male residence time/short interbirth intervals short male residence time/long interbirth intervals long male residence time/short interbirth intervals long male residence time/long interbirth intervals

	Generalizing from the example of female choice for genetic quality in grey tree frogs, "good genes" models of sexual selection via female choice should include which of the following?   The quality of male ornamentation (song, color, behavioral display, etc.) is a reliable indicator of his genetic quality. Females receive direct benefits from ornamented males in the form of food, protection, or parental care for their young. Offspring of the most ornamented males will have performance/fitness advantages over offspring of less ornamented males. The first and third choices are correct.

	The chief prediction of the sensory exploitation hypothesis for female choice is that   female preference for a male trait evolves before the male trait itself. the males with the best ornaments or advertisements provide the best genetic benefits to the female's offspring. males with the best ornaments or advertisements provide nutrients, protection, or some other benefit to females. The second and third answers are both correct.

	Evidence that sexual selection explains some examples of sexual dimorphism in flowers through selection on male function (pollen donation) includes which of the following?   Stanton et al. found that, in wild radishes, reproductive success through pollen donation was limited by pollinator visits, whereas reproductive success through seed production was not. Delph et al. found that, in wind-pollinated plants, the sex with the largest reproductive parts always had the largest perianth. In 29% of 42 animal-pollinated plant species Delph et al. studied, females had the largest reproductive parts but males had the largest perianths. The first and third choices are both correct.

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