Understanding Life History Trade-offs: Key Questions Explained

Multiple Choice Questions Answers can be found at the end of the book. 1. Which statement is the best way to explain why an understanding of life history trade-offs is important when examining the fitness of an organism? 1. Individuals need to live longer, so they will not produce the maximum number of offspring each season. 2. When individuals need offspring, they can choose whether to reproduce or not. 3. Individuals may not be producing the maximum number of offspring they possibly can in any particular breeding season. 4. In any particular breeding season, individuals may need to produce fewer offspring to enhance their own survival. 2. What was Austad’s prediction regarding opossums on Sapelo Island? 1. Opossums on Sapelo Island would mature later and have fewer offspring per season than opossums on the mainland. 2. Opossums on Sapelo Island would have more offspring per season than opossums on the mainland because there were no predators. 3. Natural selection would favor opossums with more stretchable muscle fibers on Sapelo Island. 1374 d. Opossums on Sapelo Island would have higher fitness than opossums on the mainland. 3. Use Figure 12.5 to predict the evolution of life history traits that a population of lake trout (a popular food fish) might experience after a new lakeside fishing resort was built. 1. Because the fishermen act like predators, the lake trout should produce more offspring that are bigger in size.

2. Because the fishermen act like predators, the lake trout will spend less time breeding and should produce fewer offspring. 3. Because the fishermen act like predators, the lake trout should produce more offspring that are smaller in size and the trout will mature at smaller sizes. 4. Nothing will happen to the lake trout. 4. Why do male gobies dig up and devour eggs in their nests? 1. The male needs the nutrition, and he can always mate again later. 2. If there is not enough oxygen in the water, the young won’t survive anyway. 3. Male gobies that devour some of their eggs in response to poor environmental conditions tend to have more surviving offspring than male gobies that do not. 4. The male eats the young for the betterment of the species. 5. Which of these statements about gene imprinting is true? 1. Gene imprinting is a male reproductive strategy that can reduce the lifetime reproductive success of females. 2. Gene imprinting is a female reproductive strategy that can reduce the lifetime reproductive success of males. 3. Gene imprinting is found only in placental mammals. 4. Both a and b.

1375 6. How does an evolutionary perspective help us understand the aging process? 1. The theory of evolution allows scientists to compare closely related species that differ in how they invest in reproduction and in body maintenance to test for effects on the aging process. 2. The theory of evolution generates predictions about how individuals with certain suites of life history characteristics might fare in the aging process when compared to other individuals without those characteristics. 3. The theory of evolution provides insight into the historical development of adaptations, such as the number of offspring an individual has, that may contribute to life history trade- offs, such as aging. 4. All of the above. 7. Do all scientists agree that menopause is adaptive? 1. Yes. Menopause has to be adaptive because life history theory predicts that women should not outlive their reproductive capacity, so menopause must have some function.

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2. Yes. Menopause has to be adaptive because humans, not chimpanzees, experience menopause, and humans are evolutionarily more advanced than chimpanzees. 3. No. Several hypotheses for menopause as an adaptation have been proposed, but they have not been tested. 4. No. Several hypotheses for menopause as an adaptation have been proposed, but more evidence is necessary to support any one of them. 8. Investment in reproduction can come at the expense of a. growth. 1376 b. body maintenance. c. future fertility. d. All of the above. 9. The Trivers–Willard hypothesis predicts which of the following? 1. Greater investment in male offspring by parents in good condition. 2. Greater investment in female offspring by parents in good condition. 3. Equal investment in male and female offspring by parents in good condition. 4. Equal investment in male and female offspring by parents in poor condition. 10. Senescence describes all of the following conditions except a. aging cells accumulating malformed proteins. b. a less effective immune system. c. the onset of Alzheimer’s disease. d. higher rates of cancer. Interpret the Data Answers can be found at the end of the book. 11. The figures that follow show data on the distribution of reproductive success (number of offspring sired, or number of mates) across individuals within a population. Which sex has the greater variance in reproductive

success in each case? Why is this relevant to the strength and direction of sexual selection likely to be acting in each species? 1377 Description Bar graph A plots number of offspring over a male’s lifetime on the horizontal axis, ranging from 0 to 100 in increments of 5; and percentage of males on the vertical axis, ranging from 0 to 100 in increments of 25. The bar with a horizontal range from 0 to 1 has a vertical maximum of approximately 90. All other bars have a vertical maximum of

approximately 8 or less, sometimes 0. Referring to the horizontal range, text reads: Range equals 0 to 100. 1378 Bar graph B plots number of offspring over a female’s lifetime on the horizontal axis, ranging from 0 to 100 in increments of 5; and percentage of females on the vertical axis, ranging from 0 to 100 in increments of 25. The bar with a horizontal range from 0 to 1 has a vertical maximum of approximately 65. All other bars have a vertical maximum of approximately 12 or less, reaching 0 by 10 offspring. Referring to the horizontal range, text reads: Range equals 0 to 10. In bar graph C, all values are approximate. Bar graph C plots number of mates on the vertical axis, ranging from 0 to 1 in increments of 1, for both males and females; and frequency on the vertical axis, ranging from 0 to 0.8 in increments of 0.2. Males, 0 mates: 0.2 frequency. Females, 0 mates: 0.55 frequency. Males, 1 mate: 0.8 frequency. Females, 1 mate: 0.22 frequency. Males, 2 mates: no data. Females, 2 mates: 0.06 frequency. Males, 3 mates: no data. Females, 4 mates: 0.03 frequency. Males, 4 mates: no data. Females, 4 mates: 0.17 frequency. Short Answer Questions Answers can be found at the end of the book. 12. How does natural selection act to optimize reproductive fitness of individuals in light of life history trade-offs? 13. Discuss how sexual conflict may shape the reproductive strategies of male and female gulf pipefishes. 1379 14. From your understanding of the mechanisms of sex ratio adjustment, how might you test whether natural selection may be operating to drive sex ratios in Seychelles warblers? What is your hypothesis? 15. Based on your understanding of genomic imprinting, how might you explain the parent-of-origin effect observed when horses and donkeys are hybridized?

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16. What is senescence? Give an example of how evolutionary factors are affecting senescence in a species. 17. Does the following statement accurately reflect the current understanding of the evolution of life histories? Why or why not? “An individual female chooses how many pups to raise because she needs to have high fitness over her lifetime.”

Chapter 12 - Questions

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