Lecture 2 - counter intuitive behaviour

Question 1

Hanuman langurs live in social groups, when a new male takes over a group they kill all the existing offspring - this is risky because if he is caught the females are likely to attack him - give 3 hypotheses to explain this behaviour

Answer 1

1) non adaptive - males lash out at youngsters due to overcrowding
2) favoured by natural selection at the individual level - frees females to become pregnant sooner
3) favoured by natural selection at the group level - Infanticide reduces overcrowding which would cause the group to overexploit its food or other resources

Question 2

explain the likelihood of each of the 3 hypotheses about infanticide in the hanuman langurs?

Answer 2

1) overcrowding - not likely as it is not more frequent in bigger groups
2) NS at individual level - very likely
3) NS at group level - can theoretically occur but mechanisms favouring group selection are rare

Question 3

describe the logic of group selection

Answer 3

• Group selection suggests an individual’s behaviours are adaptations that assist the survival of their “group”. e.g, reproducing less to avoid overexploiting resources.
• Groups with individuals that practice self restraint or do something else beneficial to the group survive better.

Question 4

what is the problem with group selection?

Answer 4

Individual selection will usually be stronger. Groups with the characteristics necessary for group selection are rare

Question 5

what is the difference between selfish and altruistic types?

Answer 5

altruistic types don’t reproduce as rapidly so they can protect the group

Question 6

describe how individual selection (competition WITHIN groups for spaces or resources) and group selection works ( competition BETWEEN groups for limited space and resources) on selfish and altruistic individuals

Answer 6

• individual selection works best on selfish individuals

- group selection works best on altruistic individuals - therefore a group with more altruists has the advantage

Question 7

describe the requirements of a group for group selection to occur?

Answer 7

• inter group competition has to be high

- must have a long lived well established group

Question 8

when was it thought group selection first occurred?

Answer 8

in the evolution of man

Question 9

what is Alcock known for?

Answer 9

discussing infanticide in other species, including giant waterbugs and jacanas were the females carry out infanticide because they compete for males

Question 10

• meerkats live in social groups with a dominant female and subordinates- pregnant females kill the pups of other females- describe the results of the experiment explaining this infanticide in meerkats?

Answer 10

• dominant female litters were less likely to survive if one or more subordinate females were pregnant when the litter was born
• subordinate litters were less likely to survive if a dominant female was pregnant when the litter was born
• individual selection to save meerkat offspring from having to compete

Question 11

describe self sacrifice (kin selection) in worker honey bees?

Answer 11

• honey bee workers rarely reproduce instead they rear close relatives so their genes are passed on indirectly
• sting is more effective when detached from worker but results in workers death
• by sacrificing themselves they save their reproductive investment by protecting their family

Question 12

describe the proximate and ultimate mechanisms of self sacrifice in worker bees?

Answer 12

proximate - sting more effective for protection

ultimate - protects family to pass on genes

Question 13

describe the evolutionary advantage of sex change in anthias fish

Answer 13

Females change into males when a large dominant male dies and leaves an opening in the population
- best to be female when small and best to be dominant male when large to maximise reproductive success

Question 14

describe some techniques of male spiders to stop female attacking them and allowing them to mate

Answer 14

garden spider - males are much smaller - they wait for females to mature and carefully pluck the web to signal to female it isn’t food

• some spiders give nuptial gifts because the female is less likely to attack if she’s full
• black widow females eat partner after copulation

Question 15

describe canabilism in the redback spider

Answer 15

• Female much larger than male
• Female longer lived than male
• Male matures at a younger age
• Many males per female
• Multiple mating by females occurs
• the male deliberately places himself in females jaws after copulation - they arent large enough to be a food source it is because the female is less likely to remate if she cannibalises the first male because the copulation duration is longer when cannibalised and longer periods of copulation help paternity

Question 16

describe the battle of the sexes in bean wevils?

Answer 16

• spines on penis to damage the female reproductive tract
• the damage discourages her from wanting to remate as damage is alot worse 2nd time
• during copulation females start to kick off males to reduce damage as the damage reduces the females lifespan
• battle of the sexes with the system in a dynamic state