Presentation on theme: "Social Behaviors: Altruism to Spite. Social Behaviors Animals often cooperate with each other – But in most cases this cooperation is mutually beneficial."— Presentation transcript:
Social Behaviors Animals often cooperate with each other – But in most cases this cooperation is mutually beneficial and is explained by self interest
Classification of Social Behaviors Effect on actorEffect on Recipient +- + Mutually beneficialSelfish - AltruisticSpiteful
Altruism A behavior is altruistic if it is costly to the personal reproduction of the actor who performs the behavior, but beneficial to other individuals Was initially a puzzle to behavioral ecologists since evolution acts on individuals Dawkins The Selfish Gene
Kin Selection and Inclusive Fitness Animals often cooperate with each other because they are related to each other- kin selection The likelihood that individuals share a same gene that is identical by descent provides a coefficient of relatedness or r
Coefficient of Relatedness How to calculate r – r = Σ (0.5) L – At each generation link there is a 0.5 probability that a copy of a gene will get passed on – For L generation links the probability is (0.5) L Parent and offspring R=1(0.5) 1 =0.5 Grandparent and grandchild R=1(0.5) 2 =0.25
How to calculate r – r = Σ (0.5) L – At each generation link there is a 0.5 probability that a copy of a gene will get passed on – For L generation links the probability is (0.5) L Full siblings R=2(0.5) 2 =0.5 Grandparent and grandchild R=1(0.5) 2 =0.25 Coefficient of Relatedness
Or just memorize it rDescendant KinNon-descendant Kin 0.5OffspringFull siblings 0.25GrandchildrenHalf-Siblings Nephews and Nieces 0.125Great-grandchildrenCousins Coefficient of Relatedness
Inclusive Fitness From the view of a selfish gene – It can increase its transmission to the next generation by increasing the reproductive success of the individual in which it is in (direct fitness) – Or by increasing the reproductive success of other individuals who carry that gene (indirect fitness) Inclusive fitness is the sum of direct and indirect fitness
Hamilton’s Rule An altruistic act will spread due to kin selection if Altruistic cooperation can be favored if the benefits to the recipient (B) weighted by the genetic relatedness of the recipient to the actor (r), outweigh the costs to the actor (C) Benefits are usually measured in the offspring you can produce by helping, and the costs are the number of offspring you lose by helping BCBC 1r1r > or rB-C >0
Hamilton’s Rule Imagine an individual can a) rear its own offspring or b) help its mother produce offspring – If full sibling, the individuals own offspring and its mothers offspring have r=0.5, so B/C>1 Helping will be favored if you can help your mother rear more full siblings than you can produce
Altruism The most extreme example of altruism is suicide and sterility in social insects – Worker bees sting predators and die as a result – Also do not reproduce themselves and instead facilitate others to produce offspring
Altruism The marine insect equivalent: the snapping shrimp- Synalpheus regalis The marine insect equivalent: the snapping shrimp – colonies contain over 300 individuals, but only one reproductive female – kin-structured aggregations may promote evolution of specialized defenders that raise their own and the breeders' inclusive fitness by defending the colony.
Altruism The marine insect equivalent: the snapping shrimp- Synalpheus regalis The marine insect equivalent: the snapping shrimp – Because few predators can enter the narrow canals of the sponges, the greatest competition comes from enemies that are of the same or closely related species – Since most of the defenders do not breed, the only way to secure their genes in future generations is to protect their juvenile siblings, allowing them to grow to adulthood free from predation and survive long enough to reproduce. – The only example of marine eusociality
Eusociality Eusociality- the highest level of social behavior and is defined by cooperative brood care (including brood care of offspring from other individuals), overlapping generations within a colony of adults, and a division of labor into reproductive and non-reproductive groups
Belding’s ground squirrels – Males leave the nest leaving their mother and female siblings to stay in a closely related cohort – Females cooperate to defend each other’s young against other infanticidal ground squirrels – Also give off alarm calls when predators are nearby Altruism
Kin discrimination In order for their to be kin selection, animals should have some mechanism to recognize their kin How might this occur?
1) Greenbeard allele – Recognition allele that expresses itself phenotypically, enabling those possessing the gene to recognize that gene in others A single allele that a) causes the signal, b) causes it to be recognized in others, and c) produces cooperative behaviors Is highly subject to cheating! Kin discrimination
Most greenbeard alleles are in microbes But one is in fire ants- Gp-9 locus – New queens recruit into nests after dominant queens mate – Workers with a b allele at the G9 locus use odor to determine if recruiting queens possess the allele And kill them if they don't Kin discrimination
2) genetic kin discrimination- shared genes are recognized phenotypically – Chemical cues or odours- be altruistic to neighbors who smell like you- ‘armpit effect’ 3) Environmental cues – Simple rules: Treat anyone at home as your kin – Learning: imprinting Kin discrimination
Beldings ground squirrells – Recognize kin by learning Unrelated ground squirrels raised together are not treated aggressively – There is also phenotype matching amongst females – Odors from squirrel glands also give cues of relatedness Kin discrimination
Kin Selection and discrimination But kin discrimination isn't necessarily needed for kin selection – Populations with limited dispersal could lead to high relatedness between interacting individuals, favoring indiscriminate altruism
Kin selection in oysters??? Oyster broadcast their gametes and larvae spend a few weeks in the plankton before settling on other oysters – Oyster populations taken from different bays and clumped together attract more spat than monocultures of oysters from one bay Genetics being worked on…so stay tuned
Spite Hamilton’s rule also shows that natural selection can favor spiteful harming behaviors – rB-C>0………. C is + behavior is costly to the actor, B is - ; behavior is harmful to the recipient R is -; recipeint is less related to the actor than an average member of the population – Spite is favored when it is directed at non-relatives and spiteful behavior frees up resources for relatives of the actor
Spite But many behaviors thought to be spiteful were actually just selfish as the behaviors provided a benefit in the long term Table 11.3
Spite Some wasp larvae develop soldiers to attack other larvae – Female soldier larvae attack brother larvae to free up resources for the other females
Spite Only spiteful if 1) Behavior is really costly and doesn’t give some benefit – Soldier larvae aren't reproductive 2) Harming behaviors are directed towards relatively unrelated individuals – Soldiers preferentially attack larvae to which they are less related 3) There is strong competition for local resources and variability in relatedness
Cooperation But what about those animals that cooperate that aren't kin? – How do we explain them?
Cooperation A behavior is cooperative if it provides a benefit to another individual and has been selected for because of its benefit to the recipient
Why should an individual carry a behavior that benefits another individual? – Especially if that cooperation is cheated – The prisoners dilemma The prisoners dilemma Cooperation
The prisoners dilemma is an illustration of how difficult a problem cooperation is….. Both individuals would benefit from mutual cooperation, but both are tempted to cheat So cooperation is not an necessarily an ESS, because a mutant cheater can spread Cooperation
HypothesisDescription Kin selectionHelping individuals that share copies of the same gene By-product benefitsCooperation acts as a byproduct of an otherwise selfish act ReciprocityHelping another individual because the individual will help them back; tit for tat EnforcementRewarding cooperation and/or punishment for free riding
Cooperation: By-product benefit Foraging cooperatively is an example of by- product benefit – Animals can catch and consume more prey when they work together – Everybody wins – Humpback whale feed cooperatively Humpback whale feed cooperatively
Cooperation: Reciprocity Short term costs of helping another individual can be more than repaid by the help that is exchanged at a later point But how is it stable and not cheated?
Animals must not only meet once – In terms of the prisoner’s dilemma, they must be repeat offenders! Tit-For-Tat Strategy – cooperate on the first move, and thereafter do whatever your opponent did on a previous move Start off nice and cooperate, punish defection, and forgive (respond to cooperation of others, even if they initially defected) Cooperation: Reciprocity
Cooperation: Enforcement Cooperation is much more likely if free-riders are punished Cleaners – Cleaner fish will eat parasites,but prefer to eat the mucous or tissue of fish If the fish bites its client, the larger fish aggressively chases away the cleaner fish, making it less likely to take advantage in the future
The Ultimate Cooperation Interspecific Mutualism- a +/+ interaction in which each has behaviors that benefit the other species, but beneficial behaviors from the other species outweigh the costs Snapping Shrimp and Gobies Many sessile species have mutualistic guards Crab and Corals – The enemy of my enemy is my friend!