1. Adaptation
Psychology 3106

2. Introduction
Last class we looked at what you might call the ‘historical pathways’ that a behaviour or trait can take
Basically, how you get from one form to another
You can also look at the adaptive value (fitness consequence) of behaviour
As noted, these are related

3. Adaptation: A Definition
An adaptation is a heritable trait that:
Either spread because of Natural Selection and has been maintained by selection to the preesnt Or
Is currently spreading relative to alternative traits, due to Natural Selection

4. More Adaptation
Nice thing about this definition is that it can help us figure out if something is indeed an adaptation.
Does it increase fitness?? That is the question
What are the costs and benefits?

5. Not all traits are adaptations
The conditions that the trait evolved in may not exist
The trait may be a maladaptive side effect of an adaptive trait
The trait is a maladaptive expression of some adaptive trait
The trait may be an exaptation

6. Measuring Fitness Sometimes we can get direct measures of fitness :
Gamete production
Offspring survival
Rate of copulation
Fertilized egg production
Offspring production
Offspring independence

7. Measuring Fitness
Often we have to go to indirect measures of fitness :
Improved locomotion
Improved access to food
Improved survival chances
Improved access to territories
Better territories

8. An Example: Mobbing in Gulls
When you get near a nesting colony of gulls they get pretty angry….
Dive bombing
Swooping
Hitting!
A good guess is that this behaviour is an adaptation for defense of their young
But, as good as it sounds, does mobbing increase fitness?

9. Mobbing Gulls
OK, if mobbing is indeed an adaptation then, the degree of success experienced by mobbing gulls in protecting their eggs should be proportional to the degree to which predators are actually mobbed.
Kruuk (1964) tested this prediction.
Placed 10 hen eggs, every 10 m on a line leading from outside to inside a colony
The ones outside the colony were more likely to have been taken

10. Kruuuuuuuuuuuuuuuuk (1964)

11. Mobbing in Barn Swallows
Barn Swallows also mob.
Could be self defense
Could be mating advertisement
Could be an alternative to parental care
Shields (1984) placed a stuffed owl near a colony of barn swallows, and took note of who mobbed

12. Shields (1984)

13. The Comparative Method
Just as with looking at the history of some trait, the question of whether a behaviour is an adaptation or not can be (partially) answered with the Comparative Method
We would expect that birds that are cliff nesters would not mob, while those that were ground nesters would
Regardless of relatedness

14. Convergent and Divergent Evolution
This is in fact the case
The common ancestor of Gulls and Barn Swallows was ages ago!
Indeed, some colonial mammals mob!

15. Optimality Models
When does it make sense to use a particular strategy?
When does it make sense to evolve a particular strategy?
Look at the costs and benefits, thugh the use of optimality models
Basically looking at costs and benefits

16. Optimality Models
You might mob some of the predators some of the time…..
Top model looks only at costs and benefits
Bottom model looks at percentage of cautious and daring mobbers, they are dependent on each other!

17. Criticism of the Adaptationist Approach
Biggest critic was Stephen J. Gould
The only palaeontologist ever to appear on The Simpsons
Trait may be maladaptive now, but adaptive then
The trail may be a maladaptive byproduct of an previously adaptive (or presently adaptive) trait

18. More Criticisms by that baseball loving commie
Trait would never have occurred in the past, but new wacky conditions make it show up now
The trait is less than ‘perfect’ because it is constrained by past evolutionary events

19. Take that Dinosaur man
An assumption of adaptationism is that traits are adaptive, we then test the prediction.
It has never been about perfection Steve, I don’t know what you read
The point is not to be correct, but to be testable and proved wrong. You should have paid more attention in Philosophy of Science class. Science is not Essentialist!

20. Conclusions Don’t be a ‘rabid adaptationist’
Don’t fall for the naturalistic fallacy either!
Remember, its all about reproductive success in the end, so we really need this approach to test why something evolved.
This stuff is all intertwined with the stuff on the historical pathways of evolution that we talked about earlier