Chapter Summary

• Ivan Pavlov’s discovery of conditioned reflexes and B. F. Skinner’s research on operant conditioning as a model for learning led to an approach called behaviorism that mainly carried out laboratory experiments on rats and a few other animal models. Review Figure 52.1

• Ethology focuses on both the proximate causes of behavior (the immediate cause of the behavior, and how the behavior develops) and the ultimate causes (how the behavior affects the animal’s evolutionary fitness).

• A major focus of the ethologists was fixed action patterns and their releasers. They performed deprivation experiments as well as crossbreeding experiments to demonstrate that certain behaviors are genetically determined. Review Figure 52.2

• Genetic manipulations such as gene knockout experiments can reveal the roles of specific genes underlying a behavioral phenotype. Review Figure 52.3

• Most behaviors are complex traits involving many genes that function in cascades, offering many points for a change in a single gene to influence behavior. Review Figure 52.4

• Hormones can determine the pattern of behavior that develops and the timing of its expression. Review Figure 52.5

• Imprinting is a process by which an animal learns a specific set of stimuli during a limited critical or sensitive period. That critical period may be determined by hormones.

• The development and expression of song in white-crowned sparrows involve a genetic predisposition to learn the species-specific song, a critical period for imprinting of a song memory, and hormonally controlled timing of song expression. Social interactions may also play a role. Review Figure 52.7

• The ability to incorporate variations into species-specific behaviors may be important in establishing individuality and influencing mate choice. Review Investigating Life: Practice Makes Perfect

• An animal’s behavior involves a series of choices that influence its fitness. To make these choices, animals use environmental cues that are reliable predictors of the potential effects of their choice on their fitness.

• The cost–benefit approach can be used to investigate the fitness value of specific behaviors. The cost of a behavior typically has three components: energetic cost, risk cost, and opportunity cost. Review Figure 52.8, Animation 52.1

• According to optimal foraging theory, animals should practice feeding behaviors that maximize their energetic gain at the least cost. Review Animation 52.2

• Circadian rhythms control the daily cycle of behavior. Without environmental time cues, circadian rhythms free-run with a period that is genetically programmed. Circadian rhythms are normally entrained by the environmental light–dark cycle. Review Focus: Key Figure 52.11, Animation 52.3

• Circannual rhythms help organisms time their reproductive behavior to coincide with favorable times of year.

• Forms of navigation used by animals to find their way in the environment include piloting (orienting to landmarks), homing, distance–direction navigation, and bicoordinate navigation. Navigation mechanisms include celestial navigation and a time-compensated solar compass. Review Figures 52.13, 52.14 and 52.15, Animation 52.4, Activity 52.1

• The behaviors of individuals may become communication signals if the transmission of information benefits both the sender and the receiver. Review Figure 52.16, Activity 52.2

• Chemical communication signals (pheromones) can be highly specific and have different time courses. Visual signals can convey complex messages rapidly, but only if the recipient can see the sender. Acoustic signals can travel over long distances, do not require a focused recipient, and can be modified to reveal or conceal directional information. Tactile signals can convey complex messages when animals are in close proximity.

• Differences in parental investment can lead to different mating strategies for males and females.

• Polygynous mating systems, in which one male controls and mates with many females, can result in great variation in male reproductive success.

• Polyandry—a female mating with multiple males—can evolve in circumstances in which males make substantial contributions to the survival of offspring.

• The fitness an individual gains by producing offspring (direct fitness) plus the fitness it gains by increasing the reproductive success of relatives with whom it shares alleles (indirect fitness) is called inclusive fitness. Kin selection may favor altruistic behavior toward relatives, despite its cost to the performer, if it increases the performer’s inclusive fitness.

• As a result of haplodiploidy, the sex determination mechanism of hymenopteran insects, nonreproductive female workers (sisters) share more alleles with one another than reproductive females share with their own offspring. Review Figure 52.19

• Haplodiploidy has probably facilitated the evolution of eusocial behavior in the hymenopterans through kin selection. Eusociality has also arisen in diploid species in which chances of individual reproductive success are extremely low.

• Group living confers benefits such as greater foraging efficiency and protection from predators, but it also has costs, such as increased competition for food and ease of transmission of diseases.