Counter Intuitive Darwinian Logic of Natural Selection on Behaviour

Question 1

Hanuman langurs: Infanticide background

Answer 1

• Langurs live in social groups
• 1 large male and several females
• When a new males takes over the group the infants in the group are killed

Question 2

Hanuman langurs: Infanticide. Is this an adaptive behaviour or is it social pathology that has arisen due to overcrowding?

Hypothesis 1

Answer 2

H 1: Non-adaptive

• E.g. Social pathology brought on by overcrowding

Question 3

Hanuman langurs: Infanticide. Is this an adaptive behaviour or is it social pathology that has arisen due to overcrowding?

Hypothesis 2

Answer 3

H 2: Favoured by natural selection, at individual level

• Infanticide frees females to become pregnant sooner. The male becomes a father sooner, and has more offspring before he is himself overthrown by another male.
• Most likely hypothesis

Question 4

Hanuman langurs: Infanticide. Is this an adaptive behaviour or is it social pathology that has arisen due to overcrowding?

Hypothesis 3

Answer 4

H 3: Favoured by natural selection, group level

• Infanticide reduces overcrowding which would cause the group to overexploit its food or other resources.
• Can theoretically occur but very rare

Question 5

what is the logic of group selection?

Answer 5

• Selection at the level of the group
• Avoidance of overexploitation of resources
• Must be an advantage at the group level
• Individual selection will be stronger as any individual within a group will prosper if they are ‘selfish’
• Rare

Question 6

When is the altruistic type favoured over the selfish type in group selection?

Answer 6

• Non-restraining ‘selfish’ type is favoured within groups
• Restraining ‘altruistic’ type is favoured between groups

Question 7

Self sacrifice in worker bees: what are the mechanisms for this?

Answer 7

• Barbed sting
• Goes in easy - difficult to get out
• Most effective when detatched from worker
• Sends out alarm pheremone which guides other workers to intruder and makes them more likely to sting.

Question 8

What does autotomy mean?

Answer 8

Casting off of a body part E.g. Bee sting

Question 9

Why do worker bees honey bees self sacrifice?

Answer 9

• Honeybee workers rarely reproduce
• They rear close relative so their genes are passed on indirectly
• By sacrificing themselves they save their reproductive investment
• Kin selection

Question 10

Sex change in Anthias fish: The mechanisms

Answer 10

• Females change into males when large dominant males die and leave an opening in the population
• Increasing their reproductive output
• Individual selection

Question 11

Redback Spider: Copulation. What is the behaviour and how is it adaptive?

Answer 11

• Males purposely place themselves in a females jaw after copulation and sacrifice themselves.
• Females have multiple mating so there is sperm competition.
• If first male is cannibalised → 6/9 females reject second male (67%)
• If first male is not cannibalised → 1/23 females reject second male (4%)
• Male increases his chances of gaining paternity if he canabalises himself

Question 12

Redback spider self sacrifice: Males that are cannibalised vs not, outcome

Answer 12

• In second matings (females that have already mated)
• Males that are cannibalised copulate longer than those that are not cannibalised.
• Second males gain over 90% paternity over females offspring.
• Both first and second mated males gain benefits from self cannibalising

Question 13

Bean weevil (Callosobruchus maculatus): Spiny penis

Answer 13

• Uses spines on end of penis to damage female during copulation
• Penetration damages lining of digestive tract
• A damaged tract reducing chance that female will mate again, thus increasing males chances of fathering offspring.
• Reduces sperm competition
• Female kicking behaviour reduces damage to reproductive tract