Question 20N.3.HL.TZ0.b
| Date | November 2020 | Marks available | [Maximum mark: 3] | Reference code | 20N.3.HL.TZ0.b |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | Explain | Question number | b | Adapted from | N/A |
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.]
Explain how natural selection can cause mate selection behaviour patterns to develop in a species such as eastern bluebirds.
[3]
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;
It was difficult for many to provide focused answers for this question, although most candidates could provide valid partial explanations.
