Sexual selection 2- Week 3, part 3- Choice for indirect benefits (Runaway selection). Flashcards
What is split into two categories?
What is the first category?
What is it?
What are the traits?
Preferences for indirect benefits.
Good genes sexual selection.
Females choosing males based on traits that indicate something about their quality.
Indicators.
What is the second category?
What is it?
What do both explanations imply?
When offspring get indirect benefits, what does it lead to?
Runaway or chase-away sexual selection.
Traits are arbitrary (random)- tells you nothing about the males quality.
Indirect benefits.
Enhanced ability to compete, survive and reproduce.
Runaway sexual selection:
Who made runaway sexual selection?
What did Fisher state?
When will this only happen?
What else is this theory called?
Ronald Fisher.
Females who mate with attractive males will have attractive sons.
If attractiveness is heritable.
Sexy son or good-taste theory.
Continuation from the runaway sexual selection:
What happens if the females have a tendency to mate with attractive males?
What will happen if a females preference for a trait is heritable + they have sexy sons?
Tendency to mate with attractive males- will pass good taste to daughters- daughters will have sexy sons.
Coevolution- of the male trait + female preference for the trait.
Coevolution:
What happens if females find a characteristic attractive?
Consequently, who else will have greater fitness?
What is this all called?
What can happen to the trait?
Males with that characteristic will have greater fitness than those without it.
Females who have a preference for that characteristic- will produce sons with it.
Runaway process.
It can be exaggerated.
Continuation with the runaway process:
How does the runaway get started?
What happens once the preference is established?
What will then happen?
Females- attracted to feature with survival value- gets exaggerated.
Any arbitrary can get exaggerated.
Traits get exaggerated- over many generations- way beyond the point of usefulness.
Long-tailed widowbirds preference:
Who did a study on widowbirds?
What did he want to see?
Is there an issue with having a long tail?
What is generally seen with widowbirds (not related to this study)?
Andersson (1982).
What happened if you made their tails longer or shorter.
Yes- burden- become vulnerable to predators.
Males with longer tails- mate with more females.
Continuation with Andersson’s (1982) study:
How many groups did he split them into?
What were the 4 groups?
What did they look at after manipulating the tail length?
- 1) Elongated- lengthened it.
2) Control 1- tails cut and glued back on the exactly the same as before- just to see if tail effected the males behaviour.
3) Control 2- Tails untouched.
4) Short- shortened it.
Number of active nests.
Continuation with Andersson’s (1982) study:
What did this study give evidence for?
What could successful males do?
Females prefer males with longer tails.
Get females to set up nests with them + lay eggs.
Continuation with Andersson’s (1982) study:
What is three limitations of Andersson’s (1982) study?
1) Were long-tailed males actually fertilising eggs?- Females engaged in extra pair copulations, do not know who is fertilising their eggs.
2) Extreme changes in length- would not see this in the real world.
3) Experimental manipulations may have affected other confounding variables- e.g. how they fought off other males, maybe females were looking at this.
What countered the limitation of Andersson’s (1982) study?
What type of bird is this?
How is this experiment better?
How many conditions in this study?
What was found?
Experiment with Jackson’s widow birds by Andersson (1992).
Lek breeding bird.
Removed confounding variables of territory.
Two- short and long.
Males with longer tails = more copulations- females preferred it.
What does long tail go under?
Sexy son mechanism- mating with long-tailed males is beneficial- sons will have it- they will be successful.
Sexy son theory (daughters):
In terms of this long tailed widow birds, what will happen to daughters?
What are the daughters called?
What will increase for daughters?
What must be expressed in a sex-limited fashion?
They will inherit the preference for long-tailed males (good taste).
Daughters will good taste.
Fitness.
Traits and preferences.
Continuation from sexy son theory (daughters):
Over many generations, what will happen?
What will eventually happen?
What is two costs of having a long tail?
What is this process called?
Tails will get longer.
Tails will get so long- more costs than benefits.
Get eaten by predators + too much energy to grow it.
Run away selection.
Runaway selection:
What does a trait not need to have?
How can a trait start?
Explain how the trait of having a long tail could have developed.
Survival value for males.
Start due to a sensory bias- can spread harmful traits.
Some males start off with slightly longer tails than average- could help flying for example (females preferred this)- started the process- then it ran away.
