Lecture 5 - manipulation and spite

Question 1

what is manipulation?

Answer 1

manipulation looks like altruism but the host is actually tricked - One individual may be ‘tricked’ or ‘coerced’ into behaving cooperatively towards another…
…what looks like altruistic cooperation is actually manipulation
Negative effect on host but positive effect on the parasite

Question 2

describe interspecific brood parasitism of reed warblers to feed cuckoo chicks

Answer 2

Parasites manipulate their hosts to be altruistic

• Cuckoo chicks are many times the size of the host chicks (reed warblers in this case), yet the host still ends up feeding them
• Host has to invest far more than it normally would when feeding their own young
• Host responds to two signals it receives from the chicks as signals of hunger- calls and gape
• When you quantify total gape area of chicks - they beg more the more hungry they become - as they get older the gape area is bigger
• The hungrier they become the louder they beg - older chicks need more food than young chicks they beg more

Question 3

describe the experiment testing gape size and begging calls of cuckoos

Answer 3

they increased the sound component (using playback) and gape size (by brood size) of the nests and found that parents responded to bigger signals (either gape or call)

• Hosts feed single cuckoo chick at similar rate to 4 reed warbler chicks
• Cuckoos have much smaller gape area than the host broods, so they make up for this by their begging calls - Cuckoo chick mimics begging calls of >4 reed warbler chicks
• Older cuckoo chicks beg at higher rate than 4 reed warbler chicks
• Cuckoos do not simply mimic reed warbler hosts. Instead, they exploit hosts’ provisioning rules and their integration of visual/auditory cues

Question 4

the host of horsfields hawk-cuckoo nests on the ground so loud begging just attracts predators, what adaptation have they evolved to avoid this but still get more food from host?

Answer 4

cuckoo has bright yellow patch of skin underneath wing that makes it looks like it has a larger gape area instead of begging loudly as a signal of hunger

Question 5

give an example of parasitism switching to mutualism

Answer 5

great spotted cuckoo v carrion crow
The cuckoos benefit hosts by emitting foul-smelling secretion that repels predators
-Tested this hypothesis by adding and removing cuckoo chicks - when they were removed, they had a high rate of nest predation
-In this case there isn’t much cost because the great spotted is similar size to the carrion crow and doesn’t evict the other chicks is instead just reared alongside so doesn’t have must cost to the host - rare example

Question 6

what is an example of mutualism leading to interspecific manipulation

Answer 6

Lycaenid butterfly and ants

• ants protect the larvae from predators and in return ants can feed on nectar organ - however the butterfly larva actually manipulate the ants behaviour
• If the ants haven’t fed on the dorsal nectary organ, they walk around a lot more - the more they are fed the more the ants hang around on the larvae protecting them
• They also produce a pheromone which induces aggression in ants
• Ants that feed on the nectary organ are more likely to attend the larva
• Larva enlists a ‘standing guard’ of aggressive ants to defend them, using a manipulative drug that decreases dopamine in ant brains - this has a likely cost to the ants for a benefit to the butterfly larva

Question 7

it is initially unclear why spite should evolve, under hamiltons rule when can spiteful behaviour evolve?

Answer 7

rB > C

B is negative and C is positive, so relatedness must be negative

Question 8

how can r be negative?

Answer 8

• Relatedness coefficient = genes shared identically by descent
• Relatedness is measure relative to the population

Question 9

when may a spiteful gene spread through the population?

Answer 9

if it harms individuals not carrying that gene, thereby benefitting other carriers of the spiteful gene - spite like this is extremely rare in nature

Question 10

give an example of spite occuring in nature

Answer 10

polyembryonic parasitoid wasps

• male and female larvae occupy host moth
• some females develop as sterile soldiers that attack other larvae - preferentially directing this behaviour towards males (low relatedness = 0.25 - females = 1)
• behaviour is costly because female soldiers are sterile close - kin benefit from this behaviour

Question 11

what provides the framework to understanding the evolution of social behaviours?

Answer 11

hamiltons concept of inclusive fitness theory and table of social interactions

Question 12

describe how often these social interactions occur;

1) mutually beneficial
2) altruism
3) selfish
4) spite

Answer 12

1) mutually beneficial = reciprocity = rare, mutualism = common - intra and interspecific
2) altruistic= occurs either as manipulation or kin selection
3) selfish - common
4) spiteful - rare

Question 13

why is the spiteful behaviour in polyembryonic parasitoid wasps an unusual situation?

Answer 13

because it’s a closed population - any harm to the males benefits clonal sisters - in open populations spiteful acts may not only benefit your relative but also many others in the population which might not be good - so this works due to it being a closed population