Animal Behaviour Questions and Answers

Answer: C

Besides melatonin, the hormone involved is Thyroxine.

In photoperiodic breeders, long or short days are signalled by the duration of nightly melatonin secretion. In mammals melatonin acts on the pars tuberalis, which releases thyroid-stimulating hormone; in birds the light signal acts on the same pathway directly. The resulting change in local deiodinase enzymes alters how much thyroxine (T4) is converted to active T3 in the mediobasal hypothalamus, and that local thyroid hormone signal switches the reproductive axis on or off.

GnRH is the final output of the reproductive axis that the thyroid hormone signal controls, not the hormone that reads day length. Growth hormone and ACTH have no established role in measuring photoperiod.

Answer: B

The hypothesis is validated if sexual receptivity is regained only in E2 treated females.

Removing the gonads removes the animal's own estradiol, so it serves as the control for the hormone. If E2 is needed to induce the pheromones that make females receptive, then replacing E2 should restore receptivity and giving the vehicle alone should not. That is a clear positive result with a negative control.

Receptivity only in vehicle-treated females would contradict the hypothesis. Receptivity regardless of treatment would show that E2 is not required. No receptivity in any group would show that E2 alone is not sufficient, so neither of the last two would support the claim.

Answer: B

The correct match is P-(iv)-c, Q-(iii)-d, R-(ii)-a, S-(i)-b.

• Torpor is a short drop in metabolism and body temperature within the daily cycle; hummingbirds enter it every night to save energy (iv-c).
• Hibernation is a deep fall in metabolism and body temperature lasting weeks or months, as in ground squirrels (iii-d).
• Winter sleep, or winter dormancy, is long inactivity in which body temperature stays close to normal; denning polar bears are the example (ii-a).
• Aestivation is dormancy during long dry periods, as in Australian burrowing frogs, which wait out droughts underground (i-b).

Options A and C give hibernation to polar bears or hummingbirds and aestivation to ground squirrels, and option D attaches the definitions to the wrong behaviours.

Answer: C

Innate behaviour is a behavior that is determined by heredity.

Innate (instinctive) behaviour is genetically programmed: it appears fully formed the first time the animal meets the right stimulus, without learning or practice, as in a spider spinning its first web or a newly hatched gull chick pecking at its parent's bill.

Behaviour trained by parents and behaviour learnt by trial and error are learned behaviours. A response merely triggered by an environmental change describes any behaviour's stimulus, learned or innate, so it does not define innate behaviour.

Answer: D

The mating system is polygynandry.

In polygynandry both sexes have several mates in a breeding season: each male mates with several females and each female with several males.

Monogamy is one male with one female. Polyandry is one female with several males, and polygyny one male with several females; each describes only one sex having multiple partners, which does not match the question.

Answer: D

The brood parasite is the cuckoo.

A brood parasite lays its eggs in the nests of other species and leaves the hosts to incubate the eggs and raise the young. Many cuckoos, such as the common cuckoo and the Asian koel, do exactly this: the female lays an egg that often mimics the host's, and the cuckoo chick may push the host's own eggs or chicks out of the nest.

Pigeons, sparrows and geese all build nests (or scrapes) and incubate and rear their own young, so none of them is a brood parasite.

Answer: C

In species with precocial young, the father is more likely to be polygamous.

Precocial young, such as the chicks of fowl, ducks and many waders, hatch with open eyes and down and can walk and feed themselves almost at once. One parent, usually the female, can raise them alone, so the male gains more by seeking other mates than by staying to help, and polygyny is common.

Altricial young, helpless at hatching, need both parents to feed them, and that is where monogamy is most common, as in most songbirds. Polyandry describes a female with several males, not the father's strategy, and 'monoandrous' likewise describes a female mating with one male.

Answer: C

The key's answer is the lagena.

The lagena is a small end organ of the inner ear in birds, fish and reptiles, separate from the hearing organ, with sensory hair cells under an otolithic membrane. It has been proposed as a site of the avian magnetic sense: iron-rich structures are found in its hair cells, and in pigeons the lagena has been linked experimentally to responses to magnetic fields.

The cochlea is the hearing organ, and the columella and extracolumella are the rod-like middle-ear bones that carry sound to the inner ear; none of them is associated with magnetoreception.

Answer: D

The master clock is in the suprachiasmatic nucleus (SCN) of the hypothalamus.

The SCN, a pair of small nuclei just above the optic chiasm, receives light information directly from the retina. It keeps its own near-24-hour rhythm and synchronises the peripheral clocks of the liver, heart and other organs through nerve signals, hormones and body temperature cycles. Destroying the SCN abolishes the coordinated circadian rhythms of the whole animal.

The pineal gland secretes melatonin under the SCN's control; it is an output of the clock, not the master. The hypophysis (pituitary) and its anterior lobe, the adenohypophysis, are endocrine glands, not the circadian pacemaker.

Answer: B

Inclusive fitness is a measure of the reproductive fitness of an organism and its relatives.

W. D. Hamilton's idea adds to an individual's own (direct) reproductive success the indirect fitness it gains by helping relatives reproduce, each weighted by the coefficient of relatedness. It underlies Hamilton's rule, \(rB \gt C\): an altruistic act can spread if the benefit to the relative, weighted by relatedness, exceeds the cost to the actor. This explains, for example, sterile workers in social insects.

It is not group fitness, which is the subject of group selection, and it does not concern assortative mating or stabilising selection.