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Chapter 41 Opener. Concept 41.1 Behavior Has Proximate and Ultimate Causes.
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Concept 41.1 Behavior Has Proximate and Ultimate Causes In sexual cannibalism, one sex consumes the other during or following sexual reproduction. Usually it’s the female that consumes the male, and that’s the case for the Australian redback spider (Latrodectus hasselti), a relative of the black widow. The much smaller male courts the female for up to eight hours, strumming her web, and eventually mounting her. As sperm transfer begins, the male assumes a “headstand” position, assisting in self-sacrifice by dangling his abdomen over the female’s jaws. The female then begins slurping up the contents of the male abdomen. Following mating, the female produces a sac of 100–300 eggs, fertilized by male sperm. If females have mated with multiple males, egg sacs can have mixed paternity (multiple fathers).
Concept 41.1 Behavior Has Proximate and Ultimate Causes Discuss what you think might be the proximate versus ultimate causes of this extreme behavior. Consider the possible costs and benefits to males versus females of this unusual mating behavior.
Concept 41.1 Behavior Has Proximate and Ultimate Causes Which of the following statements provide a possible proximate explanation for cannibalism of males by females: a. The female eats the male because he dangles his abdomen right in front of her jaws. b. The female can produce more eggs in her egg sac if she eats the male. c. The female obtains nutrients from eating her mate.
Figure 41.4 The Mouse Vomeronasal Organ Identifies Gender (Part 1)
Figure 41.4 The Mouse Vomeronasal Organ Identifies Gender (Part 2)
Figure 41.7 Circadian Rhythms Are Entrained by Environmental Cues
Figure 41.7 Circadian Rhythms Are Entrained by Environmental Cues
Apply the concept p. 808 • Physiological mechanisms underlie behavior • Martin Ralph and colleagues used artificial selection to produce two strains of hamsters: one with a short circadian period and one with a long circadian period. When SCNs (suprachiasmatic nuclei) in some of these adult hamsters were destroyed, the animals became arrhythmic. After several weeks, the scientists transplanted SCN tissue from fetal hamsters into the brains of adult hamsters whose own SCNs had been destroyed. Long-period adult hamsters received tissue from short-period fetuses, and short-period adults received tissue from long-period fetuses. The effects of these treatments on the hamsters’ circadian periods are shown in the table.
Questions: • What did destroying the SCN make the adult hamsters arrhythmic? • What result would you expect if SCN tissue from a long-period fetal hamster were transplanted into a long-period adult whose own SCN was destroyed? • What do the results of the transplantation experiments tell you about where in the body the circadian rhythm phenotype (long vs. short) is expressed?
Figure 41.16 Group Living Provides Protection from Predators
Figure 41.16 Group Living Provides Protection from Predators (Part 1)
Figure 41.16 Group Living Provides Protection from Predators (Part 2)
Concept 41.4 Physiological Mechanisms Underlie Behavior Given what you have read in this chapter about biological rhythms and their physiological basis, discuss what you think the researchers might have found.
Concept 41.4 Physiological Mechanisms Underlie Behavior Given what you have read in this chapter about biological rhythms and their physiological basis, which of the findings below would you predict that the researchers might have found? a. There is no difference between spring, summer, fall, and winter in terms of sleep quality, mood, or alertness. b. Sleep difficulties are likely to be encountered in summer, when workers are exposed to only daylight during their morning and evening commutes. c. Sleep difficulties are likely to be encountered in winter, when workers are exposed to only darkness during their morning and evening commutes. d. Both b and c
Concept 41.5 Individual Behavior Is Shaped by Natural Selection Some plants produce mast crops of seeds (e.g., oaks, beeches, several species of conifers). In some years there is super-abundant seed production; in other years, none or very little. Periods of abundant seed production are called “masting.” Crossbills (genus Loxia) have uniquely shaped bills that allow them to probe inside the conifer cones and pull out the seeds. Crossbills don’t migrate north and south like many other birds, but rather have a nomadic lifestyle, moving from one site to another, tracking their primary food resource. In mast years, crossbills breed all winter long. (Most birds breed in summer only.) When seed crop diminishes, they move elsewhere.
Concept 41.5 Individual Behavior Is Shaped by Natural Selection Crossbills feed on a resource that is unpredictable in both time and space, and occurs in very clumped concentrations. Given what you have read about their habitat and food resources, as well as what you have learned about territorial behavior in Concept 41.5 of the textbook, discuss whether or not you would expect crossbills to defend feeding territories.
Concept 41.5 Individual Behavior Is Shaped by Natural Selection Crossbills feed on a resource that is unpredictable in both time and space, and occurs in very clumped concentrations. Given what you have read about their habitat and food resources, as well as what you have learned about territorial behavior in Concept 41.5 of the textbook, which of the following statements about crossbills would you expect to be true? a. They would strongly defend feeding territories. b. They would feed in flocks and would not defend feeding territories. c. They might defend small breeding territories. d. Since the food resource during masting is so abundant, the cost of defending a feeding territory would be greater than the benefit e. b, c, and e
Concept 41.6 Social Behavior and Social Systems Are Shaped by Natural Selection During argument about altruism, J. B. S. Haldane said he “would not be willing to risk his life to save his brother, but for two brothers or eight cousins, he would consider it.” Why would his individual fitness not be maximized by sacrificing himself for his brother? Why would sacrificing himself for two brothers or eight cousins be potentially beneficial to his evolutionary fitness?
Concept 41.6 Social Behavior and Social Systems Are Shaped by Natural Selection During argument about altruism, J. B. S. Haldane said he “would not be willing to risk his life to save his brother, but for two brothers or eight cousins, he would consider it.” Which of the following statements best explains his argument? a. His individual fitness would not be maximized by potentially sacrificing himself for his brother because he and his brother share only ½ of the same genetic material, so he gains more fitness by staying alive himself. b. Two brothers add up to ½ + ½ = 1, or 100% relatedness in terms of shared genetic material, so self-sacrifice would result in no net loss in terms of his genetic legacy. c. Eight cousins add up to ⅛ 8 = 1, or 100% relatedness in terms of shared genetic material, so self-sacrifice would result in no net loss in terms of his genetic legacy. d. All of the above e. None of the above
