M6+7 Grefen- Cooperation I, II + III

what is hamilton’s rule of cooperation and how can we use it to classify social behaviours depending on the values involved?

an action will be favoured by natural selection when rb-c>0, where:

• r is the fraction of relatedness between the actor and the recipient (proportion of own genes that will be passed on via the recipient’s offspring)

• b is the benefit to the recipient (how many more offspring the recipient will be able to produce)

• c is the cost to the actor (how many fewer offspring the actor will be able to produce)- if c is negative, the action also benefits the actor

what are direct, indirect and inclusive fitness?

direct fitness- the offspring the actor has

indirect fitness- the offspring the recipient has X the relatedness between the actor and recipient (how many of the actor’s genes will be passed down via the recipient’s offspring)

inclusive fitness- the sum of the direct and indirect fitness

what are fraternal and egalitarion cooperation?

fraternal cooperation is between cooperators that are closely related, eg:

• the cells within a multicellular organism cooperate

• the individuals within a population can cooperate (or may not, depending on degree of relatedness)

egalitarian cooperation is between cooperators of that are unrelated or distantly related, eg:

• different genes contribute to a genome

• different genomes (nuclear, mitochondrial…) contribute to a complex cell

• populations of different species can cooperate

what is unenforced direct benefit cooperation? give an example

• a kind of direct cooperation- no real reason/benefit to cheat

• it’s just very beneficial to cooperate, so no enforcement is needed

eg. cooperative nest founding by queen ants:

• burrowing through soil to form a nest is difficult, so it helps to have multiple queens doing so (they then fight to the death)

• possible cheat- to not work and wait until the nest is done

• but the chance of a successful nest increases greatly with each additional queen, so not cooperating isn’t beneficial

what is reciprocity cooperation? give an example

• a kind of direct, enforced cooperation- two partners do repeated actions that help eachother with consequences for cheating

• each action looks altruistic, but the exchange becomes direct benefit

eg. cleaner fish:

• cleaner gets to feed on ectoparasites and don’t get eaten, big fish ‘client’ gets cleaned

• possible cheat- client eats the cleaner, cleaner takes a bit of the client

• but the client would then not find another cleaner, and the cleaner would lose clients, so there are consequences for breaking reciprocity

‘prisoners dilemma’

what is policing cooperation? give an example

• a kind of direct, enforced cooperation- cheating is prevented by systematic action

eg. worker laying of male eggs in eusocial insects

• queen mates with many males

• this produces female workers which all collaborate to raise subsequent offspring as relatives

• possible cheat- a laying worker could lay its own eggs (to produce males that can mate with the queen)

• but worker-laid eggs get routinely removed by workers very effectively (because they have a greater regression relatedness to queen-laid eggs than worker-laid eggs in a multi-father population), so cheating is unsuccessful

• the best route to passing on your genes is by raising queen-laid eggs, so slacking is also not beneficial

what is imposed incentive cooperation? give an example

• a kind of direct,enforced cooperation- cooperation is encouraged by one individual to others via rewards, punishments and sanctions

eg. soybeans and Rhizobium

• soybean plants supply Rhizobium bacteria with oxygen and carbohydrates in return for fixed nitrogen

• possible cheat- Rhizobia could stop fixing nitrogen

• but the soybean plants withhold oxygen from Rhizobium that do not fix enough nitrogen- this is an imposed incentive

what is limited dispersal cooperation? include the calculations

• also called population viscosity

• a theoretical kind of indirect cooperation- offspring don’t move far from where they were born, so they are surrounded by close relatives and can all help eachother

• however, this has been shown to not be a valid theory, as the degree of relatives helping eachother is cancelled by the local resource competition between them

applied to hamilton’s rule:

• an altruistic action is favoured by selection if rb-c > 0

• however the gain to the recipient must be balanced by a cost (of b - c) to another group of individuals (which the actor may also be related to)

• relatedness to this ‘density-dependent group’ is called r_e

• so hamiltons rule becomes rb - c - r_e(b - c) > 0

• if the cost is spread across the whole population (isn’t density dependent), r_e = 0, so hamilton’s rule stays the same

• if the actor is closely related to the density-dependent group (in the case of limited dispersal), r = r_e, so the expanded rule cancels down to rc - c > 0

• in this case, the benefit b to the recipient becomes irrelevant, so there is no reason to be altruistic (theory isn’t valid)

overall altruistic actions are favoured with low comp/high r (and vice versa):

• high relatedness to the recipient, where the cost comes to a wider, less related population (global competition)

what is kin discrimination cooperation? give an example

• a kind of indirect cooperation- individuals are able to recognise their relatives, so they can be altruistic to just their kin and pass on their genes indirectly

eg. long-tailed tits (and other birds)

• long-tailed tits try to mate on their own, but if they fail, they try to help at another nest- most of the time they select a relative to help

• the more helpful the individual is, the more likely they are to be discriminant in helping only relatives

what is greenbeard cooperation? give an example

• a semi-theoretical kind of indirect cooperation- a gene that can cause the individual to have a distinctive trait (a green beard), recognise it in other individuals, and behave altruistically to other bearers

eg. invasive fire ants (potential example?)

• workers carrying the b allele kill young queens which don’t have it (BB), relying on a chemical odour