Concept 41.1 Behavior Has Proximate and Ultimate Causes

• Questions about animal behavior can be grouped into four interrelated categories: causation, development, function, and evolution. The first two refer to proximal causes of behavior and the later two to ultimate causes of behavior.
   
• Behaviorism originated in the study of conditioned reflexes and focused on this phenomenon as a mechanism of learning. By contrast, ethology focused on fixed action patterns and the nature of stimuli, called releasers, that trigger those genetically inherited behavior patterns. Review Figures 41.1 and 41.2
   

Concept 41.2 Behaviors Can Have Genetic Determinants

• Breeding experiments can reveal whether a behavioral phenotype is inherited. A simple Mendelian ratio of traits in offspring indicates a small number of responsible genes for a behavioral difference. Review Figure 41.3
   
• Induced mutations can reveal genetic determinants of a behavior. However, a mutation may affect a behavior because it is a transcription factor influencing the expression of many genes, or because it is a gene in a cascade of gene expression that underlies a behavior.
   
• Gene knockout experiments can reveal the roles of specific genes underlying a behavior. An example is the knockout of genes re-sponsible for pheromone detection in mice. Review Figure 41.4
   

Concept 41.3 Developmental Processes Shape Behavior

• Hormones can determine the pattern of behavior that develops and the timing of its expression. Review Figure 41.5
   
• 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 involves 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 41.6
   

Concept 41.4 Physiological Mechanisms Underlie Behavior

• Circadian rhythms control the daily cycle of behavior. Without environmental time cues, circadian rhythms free-run with a period that is genetically programmed. They are normally entrained to the light-dark cycle by environmental cues. Review Figure 41.7 and ANIMATED TUTORIAL 41.1
   
• Two forms of navigation used by animals to find their way in the environment are piloting (orienting to landmarks) and distance–direction navigation. Bicoordinate navigation may also be used by some animals. Navigation mechanisms include celestial navigation and a time-compensated solar compass. Review Figures 41.8, 41.9, 41.10, ANIMATED TUTORIAL 41.2, and INTERACTIVE TUTORIAL 41.1
   
• The behaviors of individuals may become communication systems if the transmission of information benefits both the sender and the receiver.
   
• Chemical communication signals (pheromones) can be highly specific and have different time courses depending on their volatility and diffusibility. Visual signals can convey complex messages rapidly, but the recipient must be looking at the sender. Acoustic signals travel well over distances, do not require a focused recipient, and can be modified to reveal or conceal directional information. Tactile signals are used by animals in close proximity and can convey complex messages. Review Figure 41.11 and WEB ACTIVITY 41.1
   

Concept 41.5 Individual Behavior Is Shaped by Natural Selection

• An animal's behavior is 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 choices 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.
   
• Different types of territorial behavior can be understood in terms of the costs and benefits of defending resources, among them nesting sites, food, and even mates. Review Figure 41.12 and ANIMATED TUTORIALS 41.3 and 41.4
   

Concept 41.6 Social Behavior and Social Systems Are Shaped by Natural Selection

• The evolution of mating systems can be understood by looking at the fitness costs and benefits incurred by each partner in the species' environment. 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 a male can make a substantial contribution to the survival of his offspring. Review Figure 41.13
   
• The fitness an individual gains by producing offspring (individual fitness) plus the fitness it gains by increasing the reproductive success of relatives with whom it shares alleles 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. Review Figure 41.14
   
• As a result of haplodiploidy, the sex determination mechanism of the Hymenoptera, nonreproductive workers share more alleles with one another than females share with their own offspring. Haplodiploidy has probably facilitated the evolution of eusocial behavior in this group through kin selection. Eusocial behavior has also risen in diploid species in which chances of individual reproductive success are extremely low. Review Figure 41.15
   
• 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. Review Figure 41.16
   

See WEB ACTIVITY 41.2 for a concept review of this chapter.