Premed · Premed · General Biology 2
Lecture 24: Animal Behavior
General Biology II — Organismal, Evolution & Ecology
Learning Objectives
By the end of this lecture, students will be able to:
- Distinguish between innate and learned behaviors and provide examples of each
- Explain the concept of fixed action patterns and their role in behavior
- Describe the major types of learning including habituation, classical conditioning, operant conditioning, and imprinting
- Explain how natural selection shapes behaviors related to foraging, mating, and communication
- Describe the costs and benefits of social behaviors including altruism
- Apply inclusive fitness and kin selection theory to explain cooperative and altruistic behavior
- Explain how game theory concepts apply to animal behavioral strategies
Lecture Content
I. What Is Behavior?
Behavior — an action carried out by muscles or glands under the control of the nervous system in response to a stimulus. Behavior has both proximate and ultimate explanations: Proximate causation — the "how" questions: what stimulus triggers the behavior? What physiological mechanisms underlie it? How does it develop during the organism's lifetime? Ultimate causation — the "why" questions: what is the evolutionary significance? How does the behavior contribute to survival and reproduction (fitness)? Tinbergen's four questions provide a framework for studying behavior: Causation (mechanism) — what triggers the behavior? Development (ontogeny) — how does the behavior change with age and experience? Adaptive value (function) — how does the behavior affect survival and reproduction? Evolutionary history (phylogeny) — how did the behavior evolve?
II. Innate Behavior
Innate behaviors — genetically programmed; performed correctly the first time without prior experience; highly stereotyped. Fixed action pattern (FAP) — a sequence of innate behaviors that, once initiated by a specific stimulus (sign stimulus or releaser), runs to completion regardless of feedback. Example: egg-rolling behavior in greylag geese — a rounded object near the nest triggers the goose to roll it back with its bill; once started, the motion continues even if the egg is removed. Example: male three-spined stickleback — red belly of an intruding male triggers aggressive territorial behavior; even crude red-bellied models elicit the response. Supernormal stimuli — exaggerated sign stimuli can produce exaggerated responses (e.g., birds preferring larger artificial eggs over their own) Kinesis — a change in the rate of random movement in response to a stimulus (non-directional) Example: woodlice move faster in dry conditions, slower in moist conditions → tend to accumulate in moist areas. Taxis — a directed movement toward or away from a stimulus. Positive phototaxis — movement toward light (moths) Negative phototaxis — movement away from light (cockroaches) Chemotaxis — movement toward or away from a chemical. Circadian rhythms — innate ~24-hour behavioral cycles regulated by internal biological clocks. Suprachiasmatic nucleus (SCN) of the hypothalamus — master circadian clock in mammals. Entrained by environmental cues (zeitgebers), primarily the light-dark cycle. Influence sleep-wake cycles, feeding, hormone release, body temperature. Migration — seasonal movement between habitats; often innate navigational ability: Navigation cues: sun compass, star compass, Earth's magnetic field, landmarks, olfactory cues. Example: monarch butterflies, arctic terns, salmon homing.
III. Learning
Learning — a modification of behavior based on experience. Types of learning:
A. Habituation
Decrease in response to a repeated, inconsequential stimulus. Simplest form of learning; adaptive — conserves energy by ignoring irrelevant stimuli. Example: prairie dogs stop alarm-calling in response to repeated non-threatening stimuli.
B. Classical Conditioning (Associative Learning)
An organism learns to associate an arbitrary stimulus with a significant one. Pavlov's experiments: dogs learned to associate a bell (conditioned stimulus) with food (unconditioned stimulus) → salivation in response to the bell alone (conditioned response).
C. Operant Conditioning (Trial and Error)
An organism learns to associate a behavior with a consequence (reward or punishment) Positive reinforcement increases behavior frequency; negative consequences decrease it. Example: a rat learns to press a lever for food; a bird learns to avoid brightly colored toxic prey.
D. Imprinting
A form of learning that occurs during a specific critical (sensitive) period early in life; largely irreversible. Filial imprinting — young birds form an attachment to the first moving object they see (usually the parent) Konrad Lorenz demonstrated greylag goslings imprinting on him. Sexual imprinting — early exposure influences later mate preferences.
E. Spatial Learning and Cognitive Maps
Learning the spatial structure of the environment. Cognitive map — an internal representation of spatial relationships. Example: Clark's nutcrackers cache thousands of seeds and remember locations months later; digger wasps learn landmarks around their nests.
F. Social Learning and Culture
Learning by observing and imitating others. Example: young chimpanzees learn tool use (termite fishing) by watching adults; Japanese macaques learned potato washing from an innovator. Cultural transmission — behaviors passed between individuals by learning rather than genetics; can lead to behavioral traditions in animal populations.
IV. Foraging Behavior
Optimal foraging theory — natural selection favors foraging strategies that maximize net energy intake per unit time. Animals make decisions about: which prey to pursue, where to forage, when to leave a patch. Marginal value theorem — a forager should leave a food patch when the rate of energy gain drops to the average rate for the habitat. Risk-sensitive foraging — when energy reserves are low, animals may prefer risky (variable) food sources; when reserves are high, they prefer predictable sources. Example: shore crabs preferentially select mussels of the size that yields maximum energy per unit handling time.
V. Communication
Communication — transmission of a signal from one animal (sender) to another (receiver) that influences the receiver's behavior. Signal modalities: Visual — body coloration, posture, facial expression, bioluminescence (fireflies) Auditory — bird song, frog calls, whale song, cricket chirping. Chemical (pheromones) — sex pheromones (moths: bombykol), alarm pheromones (ants), trail pheromones, territorial marking. Tactile — grooming, antenna contact in insects, waggle dance vibrations. Electrical — weakly electric fish (Gymnotiformes, Mormyridae) Honest signals — signals that reliably indicate the quality or condition of the sender; maintained by natural selection because they are costly to fake. Handicap principle (Zahavi) — elaborate traits (peacock tail) are honest signals of genetic quality because only high-quality individuals can afford the cost. Deceptive signals — signals that mislead the receiver; can be maintained when deception is rare relative to honest signaling. Example: firefly females of genus Photuris mimic the flash patterns of other species' females to lure and eat the males.
<image>A four-panel diagram illustrating different modes of animal communication with examples. Panel A (Visual): A male peacock displaying its elaborate tail feathers in a fan formation to a female peahen. Structural coloration and eyespots on the feathers are highlighted, with a caption about honest signaling and the handicap principle. Panel B (Auditory): A spectrogram (frequency versus time) of a bird song showing the complex syllable structure, with a perched male songbird next to the spectrogram. Arrows indicate that song complexity signals territory quality and mate fitness. Panel C (Chemical): A female moth releasing pheromone molecules from an abdominal gland, with a concentration gradient (plume) shown drifting downwind. A male moth several meters away is depicted with large feathery antennae detecting the pheromone molecules and flying upwind along the gradient. Panel D (Tactile): A honeybee performing the waggle dance on the vertical surface of a comb inside the hive. The figure-eight pattern is diagrammed, with the angle of the waggle run relative to vertical indicating the direction of the food source relative to the sun, and the duration of the waggle indicating distance. Nearby worker bees follow the dancer and decode the information.</image>
VI. Mating Systems and Sexual Selection
Sexual selection — selection driven by variation in mating success (reviewed in Lecture 2); leads to sexual dimorphism. Intrasexual selection — competition among individuals of the same sex (usually males) for access to mates: combat, display, sperm competition. Intersexual selection (mate choice) — one sex (usually females) chooses mates based on traits that signal quality. Mating systems: Monogamy — one male with one female; both may provide parental care; common when biparental care increases offspring survival. Polygyny — one male mates with multiple females; often in species where males defend territories or resources (e.g., elephant seals, red-winged blackbirds) Polyandry — one female mates with multiple males; rare; males provide parental care (e.g., jacanas, pipefish) Promiscuity — both sexes mate with multiple partners; no pair bonds. Parental investment theory (Trivers) — the sex that invests more in offspring (usually females — eggs are expensive) is choosier; the sex that invests less (usually males) competes for access to mates. Sexual conflict — evolutionary conflict between the reproductive interests of males and females.
VII. Social Behavior and Altruism
Agonistic behavior — contest behavior involving threat, aggression, and submission; often determines dominance hierarchies. Dominance hierarchies reduce costly fighting — subordinates defer to dominants. Territoriality — defense of a space; adaptive when benefits (resources, mates) exceed costs (energy, injury risk) Altruism — behavior that decreases the fitness of the altruist while increasing the fitness of the recipient. Evolutionary puzzle: how can natural selection favor self-sacrificing behavior?
Explanations for Altruism:
Kin selection (Hamilton's rule) — altruism evolves when directed toward relatives who share genes: Hamilton's rule: altruistic behavior is favored when rB > C; r = coefficient of relatedness between altruist and recipient. B = reproductive benefit to the recipient. C = reproductive cost to the altruist. Inclusive fitness — an individual's total fitness = direct fitness (own offspring) + indirect fitness (additional offspring of relatives attributable to the altruist's actions) Example: eusocial insects (honeybees, ants, termites) — workers forgo reproduction to help the queen (their mother); in haplodiploid species, sisters share 75% of genes (r = 0.75), more than they would share with their own offspring (r = 0.5) Example: Belding's ground squirrels — females give alarm calls when predators approach; callers are at higher risk but warn close kin nearby. Reciprocal altruism — altruism between unrelated individuals when there is a high probability of future reciprocation: Requires repeated interactions, individual recognition, and ability to detect cheaters. Example: vampire bats share blood meals with roostmates who have failed to feed; individuals who fail to reciprocate are excluded from future sharing. Group selection — controversial; traits that benefit the group may be favored if differential group extinction/survival occurs; most biologists favor individual/kin-level explanations.
VIII. Game Theory and Evolutionary Stable Strategies
Evolutionary game theory — models behavioral strategies as games where fitness payoffs depend on what strategy other individuals in the population use. Evolutionary stable strategy (ESS) — a strategy that, once common in a population, cannot be invaded by an alternative strategy. Hawk-Dove game — models contest behavior: Hawks always fight; Doves always retreat. If all Hawks: frequent costly injuries → Dove strategy benefits. If all Doves: a single Hawk wins every contest → Hawk strategy benefits. ESS: mixed strategy — stable population with both Hawks and Doves at a frequency where fitness payoffs are equal. Prisoner's dilemma — models cooperation vs. defection: In one-time interactions, defection is favored. In repeated interactions (iterated prisoner's dilemma), cooperative strategies (tit-for-tat) can be ESS → basis for reciprocal altruism.
<image>A diagram illustrating Hamilton's rule and kin selection. The top section shows a family pedigree with coefficients of relatedness labeled: parent to offspring r = 0.5, full siblings r = 0.5, half siblings r = 0.25, grandparent to grandchild r = 0.25, cousins r = 0.125. In haplodiploid species (below), a separate pedigree shows a queen and her daughters (sisters) with r = 0.75 highlighted between sisters, r = 0.5 between mother and daughter, and r = 0.25 between sisters and brothers, explaining why workers in haplodiploid species gain more inclusive fitness by helping raise sisters than by producing their own offspring. At the bottom, the Hamilton's rule inequality rB > C is presented with a worked example: a ground squirrel alarm call scenario where C = slight reduction in caller survival, B = increased survival of nearby kin, and r = 0.5 for siblings, showing that the inequality is satisfied and alarm calling is therefore favored by kin selection.</image>
