Evolution of Social Behavior Flashcards
Neuroethology & Evolutionary theory
- arise between 1960s-1975 to influence modern animal behavior studies
Diverse criteria of sociality, Sociobiology (E.O. Wilson, 1975)
- # of animals that come together
- length of time group remains together
- amount of time spent in social behavior
- reciprocal communication
- division of labor (“roles”) in group
- overlap of generations & parental care
- aid-giving: “altruism”
- “eusociality”
Eusociality
- reproductive division of labor (with sterility)
- overlapping generations
- cooperative care of young
- seen in insects
Ladybugs
- form dense aggregations during winter –> release warming chemical allomones to ward off predators
- temporary increase in sociality to be antipredatory
also done by stiped catfish
Allomones
chemical substance produced & released by individual of one species that affects behavior of another species –> benefit originator, not receiver + costly to make alone
Also produced by leaf-footed coreid bugs
Japanese macaque grooming
- grooming primarily seen by females
- who is groomed can distinguish hierarchy or potential allyship –> identify “social climbers”
Some benefits of sociality
- anti-predation
- increased feeding efficiency and information sharing
- facilitation of reproduction
- increased competitive ability
- division of labor
- energy efficiency
- social transmission of information
Predation detection & numbers
- goshawks are less successful when they attack larger flocks of wood pigeons
- same is seen with smooth-billed ani on butterflies
Chimpanzee predation
- prey on mothers w/ young
- males eat first, reward others w/ sex or some food
- males to show allyship
- columnist monkeys X fight back from slow feeding –> reduced energy
Physiological benefits of sociality
- penguins & bats huddle –> minimize heat loss
Costs of sociality
- increased competition for resources
- increased predation pressure
- increased transmission of disease
“Selfish herd” hypothesis (W.D. Hamilton)
- origins of sociality are “selfish”
- initially, animals derive a benefit from being next to others simply because reduced likelihood that any one individual will be captured
V.C. Wynne-Edwards
- animals “self-regulate” their populations through social behaviors
- for the benefit of species
- case for “group selection” - related to the view that animals sacrifice personal survival & fertility to control population growth (not a conscious choice)
- control devices: territoriality, dominance hierarchies, grouping in large flocks
Group selection
S = selfish individuals
A = altruistic individuals
- differential survival of groups or populations
Levels of Selection
A. individual
B. kin
C. group selection
Richard Dawkins
- selection operates on genes, not individuals
- individual is embodiment of selection of thousands of selfish genes, each trying to perpetuate itself
- gene not a survival unit
Why group selection (usually) won’t work (Williams)
- by generation 14, over 99% of population would be fit to “mutant” (in model of producing 3 offspring vs. 2)
The problem of the “selfish” mutant (Larson)
- lemming suicide
- falsified data/observations
Wynne-Edwards vs. Williams
- debate over whether traits like epideictic displays evolve for benefit of group/species
- Evolutionary biologists conclude the answer is almost always NO
- while can superficially appear as such, it’s actually the individuals that benefit
David Lack
- 30+ year study of great tit (reproductive patterns, studied factors controlling numbers in natural populations)
- clutch size in great tits: selection against extremes: stabilizing selection
Size vs. number
- average weight of nestlings decreases with clutch size
- more mouths to feed –> more effort
- survival of offspring is related to weight of fledging
Experimental increase in clutch size
- CS 9 ideal
- Why don’t we see directional/selection impact? –> answer in adult survival (lifetime reproductive success vs. success in any one year)
- Lack’s CS hypothesis suggests birds will produce # of eggs that improve survival of adults
Pseudomonas fluorescens
- cooperating groups formed due to production of adhesive (mutation, not in response to conditions) –> interests of indivduals to align w/ that of group (access to oxygen @ surface)
- as group: all survive even though most do not contribute adhesive
- if “freeloaders” reproduce too much –> mat sinks –> selection on freeloaders to reproduce less
- groups that contain enough “altruists” float survive better than groups w/ fewer altruists than that minimum number
- groups will grow + split into daughter groups –> altruistic individuals will benefit despite cost of expending resources to produce adhesive or reproducing less
- looks like group selection - but benefits for individual
Cooperation examples
- cooperative prey capture
- shared thermoregulation
- defense of teritories
- sharing food
- guarding + feeding young
- parasite removal
- alarm calls
- aiding attacked conspecifics
- dying in defense of others
Mutualism
- ex. cooperative prey capture
- not based on equal benefit –> as long as all get more than as an individual –> cooperation
Haldane
- would risk life to save 2 brothers or 8 cousins
Wright’s coefficient of relatedness “r”
- r = probability that any randomly selected allele in focal individual has copy (identical by descent) in the related individual
- r = (0.5)^L (L = generation links)
Calculating “r” for different kin classes
- Parent & offspring = 0.5 (fixed)
- Grandparent & grandchild = 0.25 (fixed)
- Full siblings = 0.5 (probabalistic)
- Half siblings = 0.25 (probabalistic)
- Cousins = 0.125 (probabalistic)
Kin selection
- selection of gene’s due to an individual’s promoting the survival and reproduction of relatives (other than offspring) who possess the same genes through common descent
Inclusive fitness
- the sum of an individual’s fitness + all its influence on fitness of relatives other than direct descendents
Fitness
- the contribution to the next generation of one genotype relative to the contributions of other genotypes
Hamilton’s kin selection rule
rB - C > 0
* r = coefficient of relatedness of donor to recipient
* B = benefit gained by recipient
* C = cost to donor
Altruisim between relatives: is kin selection responsible (examples)?
- honeybees (reproductive castes, defending hive by workers (females))
- monkeys (agnostic aiding)
- ground squirrels & prairie dogs (alarm calls, burrow defense)
- jackals, red-cockaded woodpeckers, scrub jays (“helpers at nest”)
Wasps vs. bees altruism
- wasps can sting indefinitely –> more aggressive
- bees die after one sting –> more kind
- queen related to honeybees –> kin selection?
Kin selection in honeybees
- sex determination: males haploid, females diploid
- –> Relatedness among all sisters: 0.5 paternal, 0.25 maternal –> r = 0.75
- –> Relatedness of queen to offspring = 0.5
- high relatedness amongst siblings gives genetic advantage to siblings & reason to defend hive (females more sacrificial)
- avg degree of relatedness among sisters decreases by # of males mating w/ queen –> beneficial for workers to give up reproduction
Honeybee queen mating
- queen first leaves hive at ~1 week old
- males die while mating
- flaw in video: males only mate with own queen –> actually, goes out & emits pheromones to attact males from other hives –> increased genetic diversity to increase survival & productivity
What is the role of kin selection in honey bee eusociality?
- Ancestral honeybee: haplodipoid sex determination & monogamous mating –> kin selection
- Evolution of eusociality: worker sterility –> subsequent selection
- Evolution of polygamy (queen mates w/ multiple males)
- Extant honeybees: workers no longer derive same benefit from sterility
- haplodiploidy neuther necessary nor sufficient for eusociality
- kin selection alone X explains eusociality in extant honeybees –> many pathways
Termites
diploid but eusocial –> haplodiploidy not a requirement for eusociality
Honeybee subgenera (Danforth et al)
- eusociality evolved once in the group –> trait has been lost 6 times (species coming from eusocial lineages subsequently becoming solitary or parasitic
Agnostic aiding in monkeys (Kurland, 1977)
- Kin-correlated behavior (not necessarily kin selection) but does Hamilton’s Rule apply?
- Recruitment screams –> directed at relatives for aid
- X know B or C –> cannot be measured
Alarm calling in black-tailed prairie dogs
- high alarm rate w/ offspring or w/ only non-descendant/close-gen rels. in home cot
- still call w/o close gen rels in home cot (but low)
White-fronted bee-eaters
- alloparental care –> does kin selection explain?
- increased helpers –> increased survival –> increased supporting family
- studies show kin-correlated behavior (X show rB-C>0)
- siblings help parents –> X show Hamilton’s rule –> X kin selection
Florida scrub jay helpers
- defend nest against predators
- defend territory
- help feed nestlings –> does not directly increase chick survival (total amount of food is constant) –> lessens burden on parents
- helpers tend to be young of breeding pair or other relatives
- technically increased benefit in rearing own offspring
So why do Florida scrub jays help?
- increase chances of helper’s survival
- lielihood of successful dispersal to a breeding site is low (difficult habitat)
- males may inherit all or part of father’s territory (low chance but >0)
- helping increases survival of helper’s parents
- increases sibling production
- may result in increase in territory size
Pied kingfisher
Abandon helper status when mated
White-winged choughs
- helpers aren’t always related to young
- bug out eyes to entice outsider young –> kidnapping to take care of
Kin recognition (or kin discrimination)
the ability to identify, distinguish, or classify kin from non-kin regardless of the mechanism
Kin recognition mechanisms
- location (behavior varies relative to some reference point (ex. brooding parasite in nest))
- association (if they become familiar at sensitive times during development)
- phenotype mechanism (comparing expression of some genetically influenced trait in another animal with its expression in the individual or others recognized through association)
- recognition alleles (green beard effect)
Phenotype matching in sweat bees
- guards allow entry based on odors of bees (increased relatedness to guard –> increased permits)
Paper wasp nest
- primitively eusocial
- workers can reproduce but queen denies opportunity (dominance hierarchy)
- relatively small colonies –> increased face-to-face interactions –> increased individual recognition
- ALSO can visually recognize nest mates through facial and abdominal markings
“green beard effect” (Dawkins)
genes that confers on their bearer a distinctive phenotypic trait (like a green beard) and also a bias to provide assistance to all other owners of the same trait –> form self-serving clique –> gene spreads in population
red ants –> kill new queens that X have certain allele
ground squirrel kin recognition experiment (Sherman & Holmes)
- lab-reared under conditions: siblings together, siblings apart, non-siblings together, non-siblings apart
- later tested on altruism
- reduced antagonism in ST & NST
- reduced fights & increased cooperation in full sisters (rather than half)
reciprocal altruism (Trivers)
individual provides a benefit to an unrelated individual w/ likelihood that recipient will return similar benefit in future encounters
ex. cleaner fish
ex. in literature: anubis baboons, black hamlet fish, vampire bats, alliances in vervet monkeys
Anubis baboons reciprocal altruism (Packer)
- dom male possessive over female –> stay together, sex, etc
- sub male attacks dom male –> other sub male mates w/ female –> return favor to each other
- problem: hasn’t been seen since
Hamlet fish mating (eggs as altruism) (S)
- eggs more demanding to make than sperm
- hermaphrodites: take turns expositing eggs & sperm rather than all at once to reduce “cheating”
Vampire bats (Wilkinson) (S)
- beg for blood from colony member if unsuccessful in hunt –> return on later occasion
- hard to prove altruism but can prove cognitive recognition among members –> how do we know not mistaken identity?
Vervet monkeys (Seyfarth)
- reciprocal altruism involving different “currencies?”
- B groomed by A –> does B return favor when A gets in fight?
- recorded respective screams & play back after grooming to see response –> increased duration of response to non-related members post-grooming
- problem: too much screaming –> reduced response –> no control group
Key issues in evaluating evidence for reciprocal altruism
- Significant cost to behavior?
- Occur w/ frequency?
- Involve unrelated individuals?
- “Favor” returned?
Docility
species typical tendency to accept knowledge & advice transmitted through social channels
Why is reciprocal altruism rare in animals?
- cognitively demanding to identify & categorize individuals –> small groups = less demanding
Prisoner’s dilemma & reciprocal altruism (Axelrod & Hamilton)
- likelihood of playing the same choice (cooperate vs. defect) as previous round’s opponent in game
Evolution of “docility” (Simon)
- proposed simple & robust mechanism based on human docility & bounded rationality that can (indirectly) account for the evolutionary success of genuinely altruistic behavior
- Yes, altruism exists but such X selected for –> instead indirect outcome of “docility”
- Proximate dimension of docility & bounded rationality: reward areas of brain underpin why allegiance, conformity & acceptance result in positive experiences
on avg, adaptive bc humans learn quickly & faithfully - but can be maladaptive costs to some individuals
Bounded rationality
rationality of individuals is limited by information they have, the cognitive limitations of their minds, and the finite amount of time they have to make a decision
