L13- Manipulation and Spite

Manipulation-

• falls within altruism category

  

• an individual that is tricked or coerced into behaving cooperatively towards another

• all behaviours have a degree of manipulation but we are focusing on situations where an actor incurs a very large cost for the benefit of the recipient

Brood parasites-

• parasites manipulate their hosts to be altruistic

• e.g. intraspecific- starling females lay eggs in nests of conspecifics

  

• e.g. interspecific- cuckoo finches parasitise prinia, armsrace seen in eggs

  

What happens after hatching?

e.g. reed warbler-

• reed warblers are parasitised by european cuckoos, cuckoo chick evicts host chicks from nest

• build nest in reeds over water, low predation rate

• parents decide how hard they will feed their brood based on signals from the chicks:

  • visual signal- bright yellow gapes:

    

    • the hungrier chicks get, the wider they gape

    • as chicks get bigger, they can display a larger visual signal

      

  • vocal signal- calls:

    • the hungrier chicks get, the louder they call

    • as chicks get bigger, they can display a larger vocal signal

      

• do parents respond to these signals?

  • measured provisioning x vocal signal size

  • results→ parents always feed 4 chicks more than 2 chicks and work harder when there are extra chicks

    

  → parents respond to amplified signals from their brood

• how do cuckoos persuade their host parents to feed them?

  • cuckoos are fed at a similar rate to 4 reed warbler chicks

    

  → cuckoos are just as good as reed warblers to persuade their parents to feed them

• how do cuckoos do this?

  • gape of cuckoo is not as large as 4 reed warbler chicks

  

  • cuckoo chick mimics begging calls of more than 4 reed warbler chicks

  

  • older cuckoos work harder to beg than 4 reed warbler chicks→ are heavier compared to 1 rw

    

• cuckoos are deficient in their gape area but compensate this by having more calls:

  

e.g. Horsefield’s hawk-cuckoo-

• cuckoo chick evicts host chicks from nest

• nests are built on the ground, high rate of nest predation, cannot call loudly

• instead chicks display both gape and yellow patch on underside of wing to host parents

  

  • wing display increases as chick gets hungrier

  • significantly lower feeds when underside was black

    

→ parasites have to tap into hosts behavioural decision making rules to persuade them to invest in them

Mutualism→ Interspecific manipulation:

• larva (blue butterfly) is parasitic with social insects :

  

  • ants feed on secretions provided by larva (from the nectary organ)

  • ants defend larva against predators

• however, found that ants that fed on the larva for a while were significantly less mobile:

  

  • butterfly is manipulating ant to be a standing guard

  • used a manipulative drug that decreases dopamine→ causes ants to be more aggressive and stay on the larva

  → butterfly is tapping into the neural system of the ant to manipulate it

Interspecific manipulation→ mutualism:

• great-spotted cuckoo parasitise the carrion crow

  

• found that the success rates of nests with parasite was greater than nests without parasites (lower predation rate, more likely to survive to fledgling):

  

• realised hands always smell after handling cuckoos

• hypothesise→ cuckoos benefit hosts by emitting a foul-smelling secretion that repels predators

• experiment→ removed a cuckoo from a nest and placed in another nest

• results→ removed cuckoo nest is more likely to be predated, added cuckoo nest is less likely to be predated:

  

Spite:

• actor performs a costly act with the aim of having a negative effect on the recipient:

  

• Hamilton’s rule→ expect spiteful behaviour to evolve when rB > c, B is negative, C is positive so r has to be negative

How can r be negative?

• relatedness coefficient→ genes shared identically by descent

• measured relative to the population (geometric measure of relatedness)

• r < 0 → individual shares genes with the actor at a lower frequency than expected at random compared to the population as a whole

  

Spiteful gene-

• gene can spread through a population if it harms individuals not carrying the gene (r<0) but will benefit those carrying the gene (relatives)

  

e.g. polyembryonic parasitoid wasps-

• lay eggs into moth larva- develop in the larva

• females lay one male and one female- eggs divide asexually and produce thousands of larvae

• some females develop as sterile soldiers and attack other larvae

• haploid-diploid sex determination→

  • soldier - females→ r = 1 (clonal)

  • soldier - males→ r = 0.25

• is this spite?

  • behaviour is costly to actor→ soldiers cannot reproduce

  • behaviour targets unrelated individuals→ soldiers never attack own sisters, often attack brothers and unrelated females and males

  

  • close kin benefit from the harmful behaviour→ less competition for food

  → is evidence that this is spite

There are few other examples→ one in the handout, discuss why spite is so rare in nature in coursework

Social Interactions:

• selfish behaviour is common→ every individual wants to maximise their own fitness

• see lots of mutualism

• see lots of altruism→ arises through kin selection and manipulation- can link to mutualism

• spite is rare