4/6 & 4/8 - Aggression, Dominance, Kinship

What is a dominance relationship? How is it communicated? Would it be

possible to label an individual as "dominant" if you had never seen it interact with

any other individuals, but you knew its age and weight?

• An asymmetric agonistic relationship (not an attribute)

• Dominance is relative, x is dominant to y

• communicated: Subordinate usually retreats, dominant usually prevails

• physical traits can contribute to dominance but need to observe relationships, cannot select for dominance bc not an individual trait, is a relationship

What three factors cause asymmetric outcomes (winners/losers) in agonistic

interactions?

• Experience (learned asymmetry)

  • A loses to B, A may be likelier to lose to B again

• RHP (resource holding potential) 

  • higher RHP monopolizes food, gets more, stronger, natural ability to win

  • Lemurs, high cost, selection on fem to be dom to get food needed

• Allies

  • Females get allies with “GG rubbing”

  • allies critical, more important than RHP sometimes

How do animals communicate dominance?

• Formalized communication of dominance status, mostly by subordinate individual

How do dominance “styles” vary among species?

• Frequency and severity of aggression

• Symmetry within contests

• Post-fight reconciliation (usually sub initiate)

• How often subordinates initiate approaches

• Fights: despotic vs egalitarian (rhesus macaque (just take loss in fight) vs stumptail macaque)

What is meant by dominance rank? Can natural selection act on rank?

• “Rank”: an animal’s position in a dominance hierarchy

• Dominance hierarchy: an ordering of individuals based on their pairwise dominance relationships

• Can selection act on rank? -> NO!

  • rank position not always correlated w rep success, traits that act on success can act on other things, alliances, personalities, success in things, ambition, confidence

How does a researcher assess rank? (You

should be able to deduce a rank order for a small number of animals given the

appropriate data.)

• Dominance status must be transitive to be organized in a linear hierarchy

• Chart to read who wins and loses, winner on left, loser on top, AB = a beat B x times, analyze total fights, total wins, % won, # out-ranked

  • Shows rank isn’t based on total fights, total wins, % won

  • Find rank with who wins over one another, A wins more against each person in a fight, look at pair to est dominance in linear form

How is male rank expected to relate to male reproductive success in non-human

primates? How does it actually relate? Why is there a mismatch between reality

and expectation (hint: other factors)?

• Rank and reproductive success in males

  • expect rank to correlate w rep success

  • Mixed results

  • Some studies show positive, a few are negative

  • Some how no correlation, some show positive sometimes

  • Relationship not stronger bc other factors influence male rep success: estrus synchrony, female choice, amount of MM comp varies, alt male strategies

Male rank could influence lifetime reproductive success by affecting (1) mating

opportunities and/or (2) longevity. What do studies relating male stress hormone

profiles and immune functino to rank position reveal about the linkage between

dominance rank and longevity (and thus lifetime reproductive success)?

• Cortisol levels are chronically elevated in low-ranking male baboon

• Among highest ranked males, lowest cortisol if:

  • Differentiated response to rivals

  • Control situation, initiate fight

  • Differentiated response to win/loss

  • Redirect aggression

• higher rank can be stressed bc have to maintain rank

• But when society unstable, advantages of high rank disappear, cortisol is now higher in high-rankers, who lose ability to change levels w/ stressors

What is the HPA axis, and where in this system does rank have an effect? for males

• Physiological proxies -> rank and stress resp, rank and immune fn

• The HPA axis (hypothalamus-pituitary-adrenal)

  • Hypothalamus -*> anterior pituitary -*> adrenal cortex -> cortisol

    • *Hypo-antpit: CRH - corticotropic releasing hormone

    • *Antpit-adrcor: ACTH - adreno-corticotropic hormone

  • In brain: hypoth and antpit

  • Negative feedback to hypoth and ant pit from too much cortisol, stops production of CRH and ACTH

  • Cortisol mobilizes an adaptive fight or flight response to stressors, but chronically high cortisol is bad for health

how does male rank relate to immune function?

• Positive correlation between rank and immune response

• higher rank = better immune response

What are the main mechanisms that might lead high-ranking females to have an

advantage relative to low-ranking females in terms of reproductive success?

What actual patterns are observed when one relates rank to female reproductive

success?

• expect positive correlation bc higher rank f might have better nutrition, safer position, or free from stress

• Overall, half of studies show advantage of high rank and positive correlation, no has neg, half no correlation

What causes variation in the relationship between female rank and

reproductive success?

• Why isnt relationship stronger?

  • High rank is costly for females because:

    • Higher mortality from predation or infanticide

    • Higher miscarriage rate

    • More likely sterile

  • Other factors influence female reproductive success

    • Food availability

    • Mortality from predation and infanticide

    • Group size

    • Female age

• High rank is usually an advantage for high reproductive success, if rank had effect, but doesnt always have expected positive effect, variation

How does female rank affect stress responses and immune function? Why are

these physiological important if one is interested in lifetime reproductive success?

• How a female experiences low rank is critical

  • How often is she getting attacked?

  • Is she getting less food?

  • Can she displace tension?

  • Does she have a support network?

• These factors, not rank itself, influence cortisol levels, overall a variable relationship between rank and cortisol

• Females of different rank may have offspring with different cortisol levels

• importnant bc indicate health, high stress kills, in a study low-rankers show elevated inflammatory responses, unhealthy if no pathogens present

Why should kinship be related to patterns of cooperation? altruism? What is the theory of kin selection, and how is it a solution to the puzzle of the evolution of altruistic behavior?

• indirect reproduction to carry on genes, altruism and coop helps them survive

• Kin selection = a solution to the puzzle of the evolution of altruism (among kin)

  • Two ways of reproducing: direct (your own offspring), indirect (copies of your genes in your relatives

  • despite being costly to the actor may benefit relative and carry on genes

define cooperation and altruism

Cooperation: a behavior that provides a benefit to another individual (the recipient) and that is selected (natural selection) because it benefits the recipient (and thus the actor)

Altruism: a form of cooperation that benefits the recipient, but is costly to the actor

What is “inclusive fitness”?

• Via kin selection, genes are favored if they cause behavior that maximizes “inclusive fitness”

• “inclusive fitness”: altruism among organisms who share a given percentage of genes enables those genes to be passed on to subsequent generations

What is Hamilton's Rule? What is its significance? What general predictions

does it make about the distribution of kin-biased altruistic (and by extension,

cooperative) behavior?

• Rule: Altruism will evolve via kin selection only when Br > C

  • Only when B benefit to recipient of altruism * r coefficient of relatedness > C cost to altruist

Significance:

• Varying kinship relations influence the evolution of altruism via kin selection

• Establishes a theoretical framework that altruism toward kin can evolve via kin selection

Predictions:

• More distantly related, more s/he must benefit relative to altruist’s cost for altruistic behavior to evolve

• Predictions: altruism is more likely to evolve via kin selection when altruist and recipient more closely related

• More costly altruism will be limited to more closely related kin

• Cooperation should also be kin-biased to maximize inclusive fitness, alt diff bc actor pays cost

how do we measure kin relations and how much two primates are related? (letter)

r = coefficient of relatedness (ranges from 0-1) = proportion of genes shared through common descent = probability of sharing same allele inherited from a common ancestor, 1 is self

how measure nepotism in non human primates?

Cant measure B or c precisely, but can look for nepotism and if degree of kinship is correlated w degree of coop or alt behavior

What evidence exists for nepotism in non-gregarious species?

• kin-structured neighborhoods

• Not very social but show some nepotism, have kin structured neighborhoods with non random spacing of families

What evidence exists for nepotism in cooperatively breeding species?

• Families! older sbilings forgo reproducing and help raise younger siblings

• Very family based structure, one breeding pair in family

• Nepotistic biases in non-human primates, more allomaternal care corresponds w proactive prosociality / handle pulling to give food

What evidence exists for nepotism in species with male philopatry?

• not a guarantee, but sometimes happens

• In muriquis males are friendly avoid comp and share paternity

• In chimps males not coop w kin, “best friends” not necessarily related

• Male philopatry not guarantee kin bias

What evidence exists for nepotism in species with female philopatry (give some examples)?

• intervening in fights, coalition formation

• Grooming interpreted as altruistic, recently called into question bc weak evidence of it being costly (not paying attention to env for predators or members of species, animals groomed tend to be harassed more, social cost of not grooming someone else), but may be beneficial (cement bond with prim who may help in future, unlikely to get attacked when grooming high rank)

what is a coalition, kinds

• Coalitions: individual forming coalition incurs a cost (risk of injury) while benefitting the animal it supports 

• 2 kinds of coalition, both kin-biased:

  • C supports aggressor, A against B supp A

  • C defends victim, A against B supp B

• Kin intervene on behalf of one another more than non kin

Coalition formation may be the best example of altruistic behavior in non-human

primates, at least when it takes particular forms. Under what circumstances is

coalition formation most likely to be altruistic, and how – in such circumstances –

does it relate to kinship?

• victim support more kin baised, defense is more dangerous, stronger kin relationship needed for this altruism

• Most informative: victim support against higher ranked attacker, more kin bias

  • Moms helping their kids usually

Under what circumstances might coalition form NOT be viewed as altruistic?

• lower cost to primate

• expects help later

Nepotism appears to have limits in non-human primates: discuss.

• Nepotism varies across species, more extreme in despotic hierarchies

• Distant kin (r > 0.125-0.25) treated like non-kin, only differentiate up to a point w kin

• Paternal kin are not preferred as consistently as maternal kin

• demographic effects: nepotism stronger in larger groups w greater kinship differentials

methods of kin recognition?

• Two most likely mechanisms: 

  • Developmental association (westermark)

  • Phenotype matching (unfamiliar relatives could recognize each other)