| Date | November 2020 | Marks available | 3 | Reference code | 20N.3.HL.TZ0.8 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 / no time zone |
| Command term | Explain | Question number | 8 | Adapted from | N/A |
Question
Male eastern bluebirds (Sialia sialis) display brilliant UV-blue feathers on their heads, backs, wings and tails. The brightness index of the male was calculated; the larger the score, the brighter the blue feathers. A brightness value of 0 indicates normal male brightness, so birds with negative scores are less bright than normal.
In an experiment to see the mating behaviour of bluebirds, scientists separated pairs of males and females and then allowed females to choose new partners.
The graph shows the relationship between male brightness index and choice of mate by females in eastern bluebirds.
[Source: Reprinted from Animal Behaviour, 78, Liu, M., Siefferman, L., Mays, H., Steffen, J.E. and Hill, G.E., A field test of
female mate preference for male plumage coloration in eastern bluebirds. pp.879–885. 2009 with permission from Elsevier
and The Association for the Study of Animal Behaviour. https://www.sciencedirect.com/journal/animal-behaviour.]
Evaluate the hypothesis that females prefer to mate with males whose feathers are a brighter blue.
Explain how natural selection can cause mate selection behaviour patterns to develop in a species such as eastern bluebirds.
Another type of behaviour is altruistic behaviour. Outline an example of altruistic behaviour.
Markscheme
Strengths:
a. (slight) increase in mate choice at higher male brightness index;
Weaknesses:
b. dots are scattered without a trend/no clear correlation
OR
most females choose mates around normal (brightness);
c. insufficient data/information provided;
Allow any other data-based statement.
a. natural selection favours specific types of mate selection/behaviour;
b. (behaviour/mate selection) increases the chances of survival/reproduction;
c. chosen organisms/males will leave more offspring;
d. pass on gene(s) for behavior to offspring;
e. (behaviour/allele) will become more prevalent/frequent in a population;
vampire bats share blood to ensure survival;
Other verified, outlined example.
Examiners report
Most candidates managed to provide at least one evaluation statement, but it was difficult for many to provide a complete evaluation.
It was difficult for many to provide focused answers for this question, although most candidates could provide valid partial explanations.
A large number of candidates could outline a valid example, but many answers lacked precision, either because "vampire" bats were not specified or the behaviour description was absent; a number of irrelevant examples were seen, including examples of human behaviour.
Syllabus sections
- 20N.3.HL.TZ0.8c: Another type of behaviour is altruistic behaviour. Outline an example of altruistic behaviour.
- 17N.3.HL.TZ0.06a: State the effect of simulated ship noise on foraging behaviour.
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17M.3.HL.TZ2.7b:
Suggest reasons for the length you stated in (a) being the most common length of M. edulis that C. maenas eat.
- 17M.3.HL.TZ2.7a: State the most common length of M. edulis eaten by the C. maenas population.
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18M.3.HL.TZ1.7c:
Distinguish between innate behaviour and learned behaviour in the development of birdsong.
- 19N.3.HL.TZ0.7a: Courtship behaviour leads to mate selection. Describe innate behaviour.
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18M.3.HL.TZ2.8:
Compare and contrast innate behaviour and learned behaviour.
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20N.3.HL.TZ0.8a:
Evaluate the hypothesis that females prefer to mate with males whose feathers are a brighter blue.
- 19N.3.HL.TZ0.7b: Explain the implications of courtship behaviour in natural selection.
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19M.3.HL.TZ2.6a.i:
Suggest a reason for the plateau in the graph when only one crab is present in the cage.
- 19M.3.HL.TZ2.6b: Outline the role of natural selection in animal behaviour.
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19M.3.HL.TZ2.6a.ii:
Determine whether foraging by crabs is dependent on number of prey (mussels) or number of predators (crabs).
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17N.3.HL.TZ0.06b:
Predict the consequences on C. maenas of increasing noise related to human activity.
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18M.3.HL.TZ1.7d:
Outline an example of a change in animal behaviour as a result of natural selection.
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18N.3.HL.TZ0.7:
The drawing shows male and female Emperor birds of paradise (Paradisaea guilielmi ) found in Papua New Guinea.
Suggest how the external features and courtship behaviour of these birds of paradise affect reproductive success.
