User interface language: English | Español

Date November 2020 Marks available 2 Reference code 20N.3.HL.TZ0.8
Level Higher level Paper Paper 3 Time zone TZ0 / no time zone
Command term Evaluate 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.

[2]
a.

Explain how natural selection can cause mate selection behaviour patterns to develop in a species such as eastern bluebirds.

[3]
b.

Another type of behaviour is altruistic behaviour. Outline an example of altruistic behaviour.

[1]
c.

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.

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;

b.

vampire bats share blood to ensure survival;

Other verified, outlined example.

c.

Examiners report

Most candidates managed to provide at least one evaluation statement, but it was difficult for many to provide a complete evaluation.

a.

It was difficult for many to provide focused answers for this question, although most candidates could provide valid partial explanations.

b.

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.

c.

Syllabus sections

Option A: Neurobiology and behaviour » Option A: Neurobiology and behaviour (Additional higher level topics) » A.6 Ethology
Option A: Neurobiology and behaviour » Option A: Neurobiology and behaviour (Additional higher level topics)
Option A: Neurobiology and behaviour

View options