Animal Behaviour: Instinct, Learning, Mating, Social Life and Communication

Practice questions (18)

Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.

1. A researcher identifies which hormones and brain nuclei must be active for a male canary to sing. Which of Tinbergen’s four questions is being addressed?

   1. Function: how singing raises the male’s survival and reproductive success
   2. Evolution: how song arose and changed across related finch species
   3. Causation: which internal and external mechanisms trigger the song
   4. Development: how the song is acquired as the young bird matures
   Show answer

   Answer: C — Causation: which internal and external mechanisms trigger the song

   Hormones and neural circuits that switch a behaviour on are its immediate mechanism, Tinbergen’s question of causation, a proximate question. Development is the tempting alternative because it is also proximate, but it asks how the ability arises during the bird’s life (hearing tutors, practising), not what triggers singing in the adult. Function and evolution are the ultimate questions.

2. Woodlice in a chamber with a humidity gradient move faster and turn more often in dry air and slow down in moist air, without heading towards the moist end; within an hour most of them are in the moist end. This behaviour is

   1. a kinesis, because humidity changes the rate of movement, not its direction
   2. a positive taxis, because the animals steer along the gradient towards moisture
   3. a fixed action pattern released by the sign stimulus of high humidity
   4. operant learning, because moist air rewards the animals that reach it
   Show answer

   Answer: A — a kinesis, because humidity changes the rate of movement, not its direction

   The animals do not orient to the stimulus; they simply move and turn more where conditions are bad and less where they are good, so they accumulate in the favourable zone. That undirected change in speed (orthokinesis) or turning (klinokinesis) defines a kinesis. A taxis is the tempting answer because the end result looks directed, but a taxis needs steering towards or away from the source, which the stem excludes.

3. A brooding greylag goose sees an egg outside its nest and starts rolling it back with the underside of its bill. If the egg is removed partway, the goose still completes the rolling movement towards the nest. This shows that egg-rolling is

   1. a learned habit, kept up because it was rewarded in earlier breeding seasons
   2. a taxis guided throughout by continuous visual feedback from the egg
   3. a reflex of the bill muscles that needs constant contact with the egg
   4. a fixed action pattern that, once released, runs to completion without feedback
   Show answer

   Answer: D — a fixed action pattern that, once released, runs to completion without feedback

   The sight of an egg outside the nest is the sign stimulus; once released, the stereotyped retrieval movement continues to the end even with no egg, the defining property of a fixed action pattern. If the movement depended on feedback from the egg, as a taxis or a contact reflex would, it would stop when the egg was removed. First-time breeders roll eggs correctly, so it is not a learned habit.

4. Fischer’s lovebird carries nest strips in its bill, whereas the peach-faced lovebird tucks them into its rump feathers. Hybrids between them at first try repeatedly to tuck strips but fail to secure them, and only after long practice carry most strips in the bill, still turning the head towards the rump before flying. The best conclusion is that strip-carrying

   1. is entirely learned, since the hybrids end up carrying strips like one parent
   2. has a genetic basis and is also modified by learning with experience
   3. is entirely innate, since experience does not change what the hybrids do
   4. is copied from the foster parents, so the hybrids’ genes play no part in it
   Show answer

   Answer: B — has a genetic basis and is also modified by learning with experience

   The hybrids’ confused, intermediate tucking appears without any model to copy and mixes the two parental patterns, so genes inherited from both species shape it. Their slow improvement with practice shows learning, and the persisting head turn shows that learning modifies but does not erase the inherited pattern. “Entirely learned” is the tempting choice because of the eventual improvement, but it cannot explain the initial intermediate behaviour or the head turn; “entirely innate” is contradicted by the improvement itself.

5. A shore crab feeds on two sizes of mussel. Large mussels yield 300 J and take 20 s to handle; small ones yield 60 J and take 10 s. While searching, the crab meets large mussels at 1 per 40 s and small mussels at 1 per 20 s. Using the long-term intake rate R = Σλᵢeᵢ ÷ (1 + Σλᵢhᵢ), where λ is the encounter rate during search, e the energy and h the handling time, the intake rate (J s⁻¹) of a crab that eats both sizes whenever it meets them is ____ (to two decimal places).

   Numerical answer — type the value.

   Show answer

   Answer: 5.25

   λ_large = 1/40 s⁻¹, λ_small = 1/20 s⁻¹. Numerator: 300/40 + 60/20 = 7.5 + 3 = 10.5 J s⁻¹. Denominator: 1 + 20/40 + 10/20 = 1 + 0.5 + 0.5 = 2. R = 10.5 ÷ 2 = 5.25 J s⁻¹. Check against the prey model: a large-only specialist gets 7.5 ÷ 1.5 = 5.00 J s⁻¹, and small mussels have profitability 60/10 = 6 J s⁻¹, which exceeds 5.00, so including them should raise the rate, as it does. Forgetting the 1 in the denominator gives 10.5, the usual slip.

6. Which of the following statements about forms of learning are correct?

   1. Habituation is a stimulus-specific decline in response to a repeated harmless stimulus, not muscular fatigue
   2. Filial imprinting occurs most readily during a brief sensitive period soon after hatching
   3. In classical conditioning, whether the reward arrives depends on the animal’s own response
   4. Conditioned taste aversion needs many pairings in which illness follows the taste within seconds
   Show answer

   Answer: A — Habituation is a stimulus-specific decline in response to a repeated harmless stimulus, not muscular fatigue; B — Filial imprinting occurs most readily during a brief sensitive period soon after hatching

   Habituation is specific to the repeated stimulus (a different stimulus still evokes the full response, which rules out fatigue), and imprinting is confined to a sensitive period early in life. Making reward depend on the animal’s action defines operant conditioning; in classical conditioning the US follows the CS whatever the animal does. Taste aversion is the classic exception to contiguity: one pairing suffices even with illness hours later.

7. Aplysia given repeated tail shocks over several days normally shows both short-term (minutes) and long-term (days) sensitization of its gill-withdrawal reflex. If a protein-synthesis inhibitor is present throughout training, the expected result is that

   1. both short- and long-term sensitization are lost, since each needs newly made proteins
   2. long-term sensitization forms normally but short-term sensitization is lost
   3. short-term sensitization occurs but long-term sensitization fails to form
   4. habituation replaces sensitization, because serotonin can no longer be released
   Show answer

   Answer: C — short-term sensitization occurs but long-term sensitization fails to form

   Short-term sensitization works by serotonin → cAMP → PKA modifying proteins already present in the sensory neuron, so it survives the inhibitor. Long-term sensitization needs CREB-dependent transcription, new proteins and new synaptic connections, so it fails. The tempting “both lost” ignores this two-stage mechanism; serotonin release itself does not depend on new protein synthesis during training.

8. Rats explore a maze for ten days without any reward. When food is then placed in the goal box, from the next trial they run to it with as few errors as rats rewarded from the start. This illustrates

   1. latent learning: the maze was learnt without reward and shown once reward appeared
   2. insight learning: the rats solved the maze suddenly by reasoning without experience
   3. classical conditioning: the maze became a conditioned stimulus paired with food
   4. imprinting: the rats fixed on the maze during a sensitive period early in life
   Show answer

   Answer: A — latent learning: the maze was learnt without reward and shown once reward appeared

   Tolman’s experiment showed that rats form a spatial map while exploring unrewarded; the learning stays hidden until a reason to use it appears. Insight is the tempting distractor because performance improves suddenly, but the rats were drawing on ten days of experience, not solving a new problem by reasoning. Food was never paired with the maze during exploration, so it is not classical conditioning.

9. In pheasant-tailed jacanas, females are larger than males, each female defends a territory holding several males, and the males alone incubate the eggs and care for the chicks. This mating system is best described as

   1. resource-defence polygyny, because one sex defends a territory holding many mates
   2. a lek, because the larger sex displays on an arena to attract many partners
   3. social monogamy with occasional extra-pair matings by the larger sex
   4. polyandry with sex-role reversal, as the males invest more in the young
   Show answer

   Answer: D — polyandry with sex-role reversal, as the males invest more in the young

   One female mating with several males is polyandry, and because males provide all the parental care, the usual roles flip: females compete, are larger and defend territories, while males are the limiting, choosier sex. Resource-defence polygyny is the tempting answer because of the territory, but polygyny means one male with several females. A lek offers no resources and no territory with resident mates.

10. Which of the following statements about mating and territorial behaviour are correct?

    1. Territorial defence is expected only when the resources it secures outweigh the costs of defending them
    2. On a lek, males give females nothing but sperm, and a few males obtain most of the matings
    3. Because eggs are cheaper to make than sperm, females are usually the competing sex and males the choosy sex
    4. Under the handicap principle, costly ornaments are unreliable signals because weak males can easily fake them
    Show answer

    Answer: A — Territorial defence is expected only when the resources it secures outweigh the costs of defending them; B — On a lek, males give females nothing but sperm, and a few males obtain most of the matings

    Economic defensibility predicts territoriality only when benefits exceed costs, and leks are display arenas where females choose males for genes alone, producing a strongly skewed mating success. Eggs, not sperm, are the costly gametes, which is why females are usually choosy and males compete. The handicap principle argues the opposite of the last claim: a trait is reliable precisely because it is too costly for low-quality males to bear.

11. A nectar-feeding sunbird defends a patch of flowers when nectar production is moderate, but abandons defence both when nectar is very scarce and when it is extremely abundant. The best explanation is that

    1. territoriality is a fixed action pattern released only by one particular nectar concentration
    2. defence pays only when the extra nectar it secures exceeds the energy spent on defending
    3. at both extremes the bird is too weak to fight, as nectar intake controls its muscle strength
    4. intruders are absent at both extremes, so there is nothing for the owner to defend against
    Show answer

    Answer: B — defence pays only when the extra nectar it secures exceeds the energy spent on defending

    This is the economic-defensibility argument. When nectar is very scarce, even an exclusive patch cannot repay the energy spent chasing intruders; when nectar is superabundant, the bird gets all it needs whether or not it excludes others, so defence adds cost without extra gain. Only at intermediate levels does the nectar saved from intruders exceed the cost. A fixed action pattern would not track costs and benefits in this way, and nothing in the stem suggests intruders vanish at the extremes.

12. In a haplodiploid ant species the queen mates only once. A worker that gives up rearing 4 daughters of her own can instead help the queen rear extra full sisters. Taking helping to be favoured when (r to a full sister) × (extra sisters reared) > (r to an own daughter) × 4, the smallest whole number of extra sisters for which helping is favoured is ____.

    Numerical answer — type the value.

    Show answer

    Answer: 3

    Sisters of a once-mated queen get identical paternal genomes (the haploid father passes on all his genes) and share half the maternal genes on average: r = ½ × 1 + ½ × ½ = 0.75. A mother’s r to her own daughter is 0.5. Helping is favoured if 0.75 × B > 0.5 × 4 = 2, so B > 2.67, and the smallest whole number is 3. Using the diploid sibling value r = 0.5 gives B > 4, so 5, the usual slip.

13. In an outbred diploid ground squirrel, giving an alarm call lowers the caller’s expected future offspring by 0.05, while each maternal half-sibling nearby gains 0.04 expected offspring from the warning. Using Hamilton’s rule rB > C, with B the total benefit to all half-siblings present, the smallest whole number of half-siblings that must be present for calling to be favoured is ____.

    Numerical answer — type the value.

    Show answer

    Answer: 6

    Maternal half-siblings share a mother but have different fathers: r = ½ (a given gene came from the shared mother) × ½ (the half-sibling received the same maternal copy) = 0.25. With n half-siblings, rB = 0.25 × 0.04 × n = 0.01n. Calling is favoured if 0.01n > 0.05, so n > 5. At n = 5 the two sides are equal and calling is not favoured, so the answer is 6. Using r = 0.5 (full siblings) would give 3.

14. Eusociality means cooperative care of young, overlapping generations and a reproductive division of labour with non-breeding workers. Which of the following are eusocial?

    1. Termite colonies, in which a king and a queen breed while non-breeding workers and soldiers help
    2. Naked mole-rat colonies, with one breeding female and non-breeding helpers
    3. Honeybee colonies, with a queen, non-breeding female workers and seasonal drones
    4. Flocks of domestic hens, in which every hen lays eggs within a pecking order
    Show answer

    Answer: A — Termite colonies, in which a king and a queen breed while non-breeding workers and soldiers help; B — Naked mole-rat colonies, with one breeding female and non-breeding helpers; C — Honeybee colonies, with a queen, non-breeding female workers and seasonal drones

    Termites (diploid in both sexes), naked mole-rats (a mammal) and honeybees (haplodiploid) all have a reproductive caste, non-breeding helpers, overlapping generations and shared brood care, which shows that eusociality is not confined to haplodiploid insects. A hen flock has a dominance hierarchy, but every hen breeds and there is no non-breeding worker caste, so it is social but not eusocial.

15. On the vertical comb inside a dark hive, a honeybee forager’s waggle runs point 40° to the left of straight up. Where is the food source?

    1. 40° to the left of the direction directly away from the sun
    2. 40° to the right of the sun’s azimuth, since the dance is mirror-imaged
    3. 40° to the left of the sun’s azimuth, as seen from the hive entrance
    4. 40° above the horizon, in the same compass direction as the sun
    Show answer

    Answer: C — 40° to the left of the sun’s azimuth, as seen from the hive entrance

    In the dark hive, gravity stands in for the sun: “straight up” on the comb means “towards the sun’s azimuth”, and the angle of the waggle run from vertical equals the angle of the food from the sun, on the same side. So 40° left of vertical means 40° left of the sun. The direction away from the sun would be signalled by a run straight down; the dance is not mirror-imaged, and it encodes direction on the ground, not elevation.

16. When researchers play back a recording of a vervet monkey’s eagle alarm call with no eagle present, the listening vervets typically

    1. look up into the sky and run into dense bushes
    2. climb out onto the thin ends of tree branches
    3. stand on their hind legs and scan the ground
    4. ignore it, since no predator can be seen anywhere
    Show answer

    Answer: A — look up into the sky and run into dense bushes

    Each vervet alarm call evokes the escape suited to its predator even in a playback with no predator, which shows the call itself carries information about predator type. The eagle call makes vervets look up and hide in bushes, away from open sky. Climbing into trees is the response to the leopard call (leopards cannot follow onto thin branches), and standing up to scan the ground is the response to the snake call.

17. Which of the following statements about pheromones are correct?

    1. Bombykol, released by female silkworm moths, is a releaser pheromone that attracts males
    2. Honeybee queen mandibular pheromone acts as a primer by suppressing ovary development in workers
    3. Pheromones are secreted into the blood and act on target organs of the same individual
    4. Primer pheromones produce immediate, short-lived behavioural responses such as attraction or alarm
    Show answer

    Answer: A — Bombykol, released by female silkworm moths, is a releaser pheromone that attracts males; B — Honeybee queen mandibular pheromone acts as a primer by suppressing ovary development in workers

    Bombykol triggers immediate upwind flight in males, the defining action of a releaser, and queen mandibular pheromone causes a slow physiological change in workers, the defining action of a primer. Pheromones are released outside the body and act on other members of the species; acting inside the producer’s own body through the blood describes a hormone. Immediate behavioural responses are the mark of releasers, not primers.

18. A female mouse that has just mated is housed on bedding soiled by an unfamiliar male, and her pregnancy fails before implantation. This phenomenon is

    1. the Whitten effect, in which male urine synchronises oestrus among grouped females
    2. the Lee–Boot effect, in which females housed together suppress one another’s cycles
    3. the Coolidge effect, in which a new female renews a male’s sexual interest
    4. the Bruce effect, a primer pheromone action detected by the vomeronasal organ
    Show answer

    Answer: D — the Bruce effect, a primer pheromone action detected by the vomeronasal organ

    Pregnancy block by the chemical cues of a strange male is the Bruce effect, a primer action processed by the vomeronasal (accessory olfactory) system; the familiar stud male’s odour does not cause it. The Whitten effect is the tempting distractor because it is also a male-urine primer effect, but it induces and synchronises oestrus in females that are not pregnant rather than ending a pregnancy.