A. Starlings decorate their nests with fresh sprigs of nearby greenery. Why??
B. Research has shown that this is not for camouflage, nor is it for insulation; rather, it is to reduce the number of parasitic mites that may be in the nesting hole. Evidence for this?
I. The Heritable Basis of Behavior: (Review Chapter 10!)
A. Genes and Behavior
1. Animal behavior involves coordinated responses to external and internal stimuli, using interactions among nervous, endocrine, and skeletal-muscular systems.2. Genes contribute in an indirect way to behavior by influencing development of the nervous system.
3. Illustration: Feeding preferences of garter snakes in California show&endash;
a. Newborn offspring of coastal parents readily ate banana slugs; offspring of inland parents rejected them.b. Offspring "hybrid" snakes responded more to banana slug scent but less than did typical newborn coastal snakes.
B. Hormones and Behavior
1. Hormones are signaling molecules that can affect a series of behavioral responses.2. Illustration: Changing photoperiod causes the pineal in songbirds to reduce its melatonin secretion, which in turn allows the gonads to release their hormones.
a. Estrogen in males influences the development of the "sound system."b. During the breeding season, testosterone triggers the singing.
C. Instinctive Behavior Defined
1. In instinct behavior, components of the nervous system allow an animal to accomplish complex, stereotyped responses to certain sign stimuli (cues); fixed action pattern.2. Newly hatched cuckoos push their foster parents’ eggs out of the nest.
3. Human infants mimic the smiling face of an adult, or a face mask with two eyelike spots.
II. Learned Behavior
A. Learned behavior incorporates information that has been gained from specific experiences.
1. A toad flips out its tongue at moving objects but learns to avoid black and yellow ones that sting&endash;bumblebees.2. Experiments with sparrows show that the ability to produce distinctive songs is both instinctive and learned.
B. Other categories of learned behavior include:
1. Classical conditioning in which animals learn to associate a stimulus (such as a bell) with food and later salivate at the sound without the presence of food.2. Operant conditioning in which an animal learns to associate a voluntary activity with it consequences.
3. Habituation in which an animal learns NOT to respond to a situation if the response has neither positive nor negative consequences.
4. Spatial or latent learning in which the animal acquires a mental map of some region.
5. Insight learning in which an animal abruptly solves some problem without trial-and-error attempts at the solution.
III. The Adaptive Value of Behavior
A. Definitions used in describing behavioral evolution:
1. Natural selection is a measure of the difference in survival and reproduction among individuals that differ in heritable traits.2. Reproductive success refers to the survival and production of offspring.
3. Adaptive behavior promotes reproductive success.
4. Social behavior is the cooperative, interdependent relationships among individuals of the same species.
5. Selfish behavior occurs when an individual increases its chances of producing offspring.
6. Altruistic behavior is self-sacrificing behavior that helps others and decreases the individual’s own chance to reproduce.
B. Is there a relationship between selection and feeding behavior?
1. Natural selection seems to favor the individual more than the species.2. Studies of ravens show that a raven feeding outside its own territory will call loudly to attract other nonterritorials and thus attempt to overwhelm any defensive behavior of resident ravens.
IV. Communication Signals
A. The Nature of Communication Signals
1. Social behavior requires communication signals provided by signalers and signal receivers.2. Pheromones are chemicals released into the environment to elicit intraspecific communication.
a. Signaling pheromones may bring about an immediate behavioral response such as alarm behavior or sexual attraction.b. Priming pheromones, as detected in rodents, elicits a physiological response such as female estrus.
3. Acoustical signals include distinctive sounds made by striking a body part against a substrate or songs generated by a special vocal apparatus.
B. Examples of Communication Displays
1. Visual signals are observable actions or cues used by animals that are active in daytime.a. Male baboons may show a threat display to a rival with a "yawn."b. Courtship displays in birds often involve contorted posturing.
c. Fireflies use bioluminescent signals for signaling at night.
2. Tactile signals can be used to communicate at close range as when a foraging honeybee performs her round dance or waggle dance to inform the bees touching her of the distance and direction of a food source.
C. Illegitimate Signalers and Receivers
1. Sometimes the wrong animal (illegitimate receiver) will intercept a communication signal as when termites respond with defensive behavior when they detect chemicals coming from an invading ant.2. Illegitimate signalers like assassin bugs will place dead termites on their bodies to acquire the termite scent and fool the termites into letting them in to the nest.
V. Mates, Parents, and Individual Reproductive Success
A. Sexual Selection Theory and Mating Behavior
1. Sexual selection involves competition for access to a mate and also choosiness in selecting a mate.2. Reproductive success for a male depends on how many eggs he fertilizes; for females it is the quality (not quantity) of the mate.
a. Male hanging flies present food that the females evaluate before mating.b. Male sage grouses stake out a small territory (lek) and advertise for females, one of which will mate with one male only and then leave to make a nest.
c. Male bighorn sheep who lose in head-butting contests will regroup and overwhelm the victor’s capacity to protect his territory.
B. Costs and Benefits of Parenting
1. Parental care takes time and energy, yet it benefits the individual by improving the likelihood that the current generation of offspring will survive.2. The benefit of immediate reproductive success may outweigh the cost of reduced reproductive success later on.
VI. Benefits of Living in Social Groups
A. Cooperative Predator Avoidance
1. A group of animals simply provides more pairs of eyes to detect predators; they may also engage in group counterattack.2. Example: When disturbed, sawfly caterpillars collectively rear up, writhe about, and regurgitate toxic fluids.
B. The Selfish Herd
1. Some animals live in groups simply to "use" others as a shield against predators.2. Example: The largest, most powerful bluegill fish protect the eggs in the center of the nest while smaller males assemble around them and bear the predatory attacks that may come from bass.
C. Dominance Hierarchies
1. Members of some social groups help other individuals survive and reproduce at personal cost but individuals may not be giving up their reproductive success entirely.2. A dominance hierarchy exists in which some individuals have adapted a subordinate status to others in order to increase survival or reproduce eventually.
VII. Costs of Living in Social Groups
A. Evolutionary biologists evaluate the range of social behavior using the cost-benefit approach.
1. Sometimes costs to the individual may outweigh the benefits of life in a social group.2. Large nesting colonies of gulls may present cannibalizing opportunities, strain resource availability, and encourage the spread of contagious diseases.
B. Individuals also may risk being exploited or having their offspring killed by others in the social group.
VIII. Evolution of Altruism
A. In altruistic behavior, the "helper" reduces its own reproductive potential while the "helped" has increased its reproductive success.
B. A nonreproducing subordinate member of a group can indirectly propagate its genes by helping to preserve and produce more relatives.
1. The theory of indirect selection proposes that caring for nondescendant relatives favors genes associated with helpful behavior&endash;an extension of parental behavior.2. In insect societies like bees, sterile guards may protect the queen by stinging an intruder and then committing suicide, thereby sacrificing their own reproductive chances and increasing the number of genetically similar offspring produced.
IX. Focus on Science: Why Sacrifice Yourself?
X. An Evolutionary View of Human Social Behavior
A. Adaptive does not mean the same thing as moral; it means that the behavior is valuable in the transmission of an individual’s genes.
B. Hypotheses about "selfish" and "altruistic" behavior of humans can be similarly tested without attempts to justify the behavior; for example: adopting children.