Aggression Flashcards
agression/agonistic behaviour
- Animals sending threatening signals (often organism-specific – ex. Showing of canine teeth)
- Engaging in physical combat
- Involves 2+ organisms (usually conspecifics)
how/why do aggressive interactions occur?
- Array of animal “weapons” used in aggressive interactions (ex. Antlers)
- Mating, competition for food sources, protecting territory, protecting young
- Activation of HPG (Hypothalamic Pituitary Gonadal Axis)
- Testosterone levels
Activation of HPG (Hypothalamic Pituitary Gonadal Axis) and aggression
Hypothalamus -> pituitary -> testes -> testosterone (that can shut system off as well)
testosterone (in general)
- more testosterone = higher aggression, sexual behaviour, spermatogenesis, BUT suppresses parental care, changes fat stores and immune function, and impairs immune function over time -> increases mortality
- Ex. Spike in testosterone during spring increases fighting for territory and mates in song sparrows
testosterone levels and human aggression
- Challenge hypothesis: testosterone levels in men are affected by recent challenges with men (ex. Winners in sports have higher testosterone than losers)
- Basal group: saliva taken before and after they watched documentary
- Treatment group: watched documentary of their hockey team winning and losing
- Win = higher testosterone; loss = neutral testosterone
what info can be gained through observing aggressive interactions?
dominance hierarchy (dominant vs. subordinate organisms)
dominance hierarchy
- Measured in social conspecifics
- Defined as the rank of the individuals, based on results of aggressive interactions
- Top of dominance hierarchy: access to more food and mating opportunities, safer territories
- Rank within the hierarchy has an impact on hormone levels
experimental assessment of dominance hierarchy in rats
Give rats access to chocolate; dominant one is one that’s always swiping the others away from it, subordinate is the one getting swiped
winner and loser effects in aggression context
- Prior experience with an opponent can influence future aggressive interactions
- Ex. Animal 1 defeats animal 2; at next interaction, animal 1 would be more aggressive and animal 2 would be less aggressive
- Ex. Animal 3 witnesses animal 4 lose a fight to animal 5, animal 3 will be more aggressive when engaging with animal 4
- Winning streaks vs. Losing streaks: winning increased probability of future wins (and vice versa); proximate cause = glucocorticoids
blue-footed boobies: basics
- Boobies have asynchronous hatching (offspring don’t hatch at same time -> size differences in siblings -> creates brood hierarchy)
- Advantages: more time to secure resources, less of a burden at time of birth, decrease sibling rivalry
- Can result in facultative siblicide under conditions of food scarcity (only largest chick will be fed)
- Males and females share parental responsibilities (incubating eggs, feeding chicks, etc.)
- Model used to study aggression: parent/offspring aggression and aggression between siblings
blue-footed boobies: winner-loser effects (generally)
- “winner-loser” effects between siblings: older chicks aggressive/dominant, younger chicks submissive/subordinate
- Winner/loser effects persist throughout life, even in aggressive situations with others (not just siblings) - ie. Losers lose for life
study: winner-loser effects in blue-footed boobies
- put subordinates vs. neutral boobies and dominant vs. neutral boobies
- hypothesized that subordinates would have low probability of winning and dominant would have high probability
- Took big subordinates (big birds usually tend to win, so by using bigger subs they’re making sure that the loser effect is really what’s at work, not size) and vice versa for dominants
- Saw strong loser effect, moderate winner effect
copperhead snakes winner-loser effects
- Will a win or a loss in aggressive interaction influence future contest outcomes?
- Big snakes more likely to win
- Study showed that when pairing winner and neutral snake, the winner effect didn’t occur, but when pairing loser and neutral snake, the loser effect did occur
- Even losers with size advantage continue to lose
take-home point about boobies and snakes
loser effect stronger than winner effect
hormones and aggression in winner-loser effect
Losers have higher level of glucocorticoids
