Conflict and aggression: Family conflict Flashcards
When does conflict occur?
Conflict can occur whenever the fitness interests of individuals do not allign.
Conflict often involves individuals being selfish and inflicting harm on others.
The payoffs of selfish behaviours, including aggression, depend on the costs, benefits and relatedness between individuals.
When can selfishness occur? (inclusive fitness model)
Whether an individual behaves selfishly or cooperates depends on the relatedness between the individuals and the balance between costs and benefits.
- Conflict can be intraspecific and interspecific
-rB+C>0
-B: Costs the the recipient
+C: Benefits to the actor
Selfishness is more likely to occur when r is low and individuals are more distantly related.
Selfishness is more likely to occur when the cost to the recipient is low and the benefit to the actor is high.
Example: Nematodes
- Study compared the aggresin levels of nematodes in varying levels of genetic diversity
- When there is higher genetic diversity, and individuals are less closely related, agression increases.
Example:
- studies found that individuals can hold territories large than required to spitefully harm others -> they have less resources therefor pose less of a competition to actor and offspring
- less likely to do this if relatedness is high as -rB will be more negative
- reduced dispersal limits larger territory size
What causes conflict within families
Althoug r is high within families conflict can occur due to:
- Variation in relatedness within the family
- Life history selection
- -> Number vs size of offsrping
- -> Current vs future investment
- -> The reproductive strategy: Optimism vs pesimism
Basically when individuals have different fitness optimum.
Types of family conflict
- Sexual conflict (less complicated at mates are not related)
- Sibling conflict
- parent -offspring conflict
Cause of family conflict: life history selection
Parents have optimal investment determined by the difference between costs and benefits. Depends on:
- how parental investment is distributed
- how much reproduction costs in terms of future reproduction
This optimum varies in different environments as the shape of the benefits curve changes in the optimsation model (picture them in your head- Benign, normal, harsh).
There are trade-offs which shape this optimum:
- Number vs quality of offspring
- Current vs future reproduction
Parents and offspring can have different optima.
conflict within families:
Number vs quality conflict between parent and offspring
Future vs current investment between offspring and future offspring
Environment can lead to specific strategies:
- pessimism
- optimism
Pessimism vs optimism
The reproductive strategy used by the parents shapes the conflict between siblings and parents vs offspring.
There are many strategies of reproduction depending on the physiology and environment of the organism.
Pessimism vs optimism:
Parental optimism is selected for in upredicatble encironments. Parents produce an optimistic number of offsrping incase there is a optimal year.
Example: Snowy owl
- Food supply (lemmings) is very variable
- Large clutch size are produced in a staggered nature
- Good year: all owls survive
- Bas year: the owl that hatches first eat the others (sibling conflict)
Parental pessimism is selected for in species with low fertility and hatching success.
Example: Boobies
- They produce 2 eggs even though they only have enough resources for one
- Low hatch rate so producing 2 increases chances that one will hatch.
Conflict between Siblings
Offspring vs future offspring
There is a trade off between parents reproducing now and reproducing later as reproduction is costly and uses resources that could be put into survival.
Reproduction effects chance of parent survival and thus the chance of future reproduction.
There is active competition between offspring and offspring that have not been born yet.
Selection on life hisotry is different in different environment
- Harsh: reduction in life span so strengthens selection for early investment.
- Benign : longer life spans so weaker selection-> grow now and reproduce later, if reproduce don’t invest too heavily.
Current offspring
There is active competition between offspring as they compete for resources.
Offspring may kill each other (Parasitoid wasps) if the costs are not too great in order to recieve greater investment.
Example: begging in birds
- Chicks beg for food
- They are competing with their offspring and also offspring that have not yet been born.
- Begging/ dishonest signals are more likely when chicks have competition with future/ current offspring
Dishonest signals are also an example of conflict between parent and offspring.
Causes of family conflict: Relatedness
Difference in relatedness is key driver of family conflict
Parents are related to their offsrping by 0.5 and offspring are related to each other by 0.5, but they are related to themselves by 1.
Increasing parental investment by same amount has greater benefit to offspring than parents (different diminishing returns) leading to different optima
This means that parents and offspring have different optimal levels of parental investment. (Offspring optimal PI is higher than parents)
Conflict between parents and offspring
Parents and offspring have different parental investment optimas and their fitness interests don’t always align meaning there is often conflict: parents want to invest less than offspring want them to invest.
Example: Analyses of turtles
- The mass of turtle eggs were measure and compared to parents optimum mass and offsprings optimum mass
- Mass was on parents optima as parents control investment
- Offspring can control investment in placental species.
Example: Sheep
- Mother’s fitness is maximised when she has multiple medium offspring so there is stabilising selection on wieght.
- Offspring’s fitness is maximised when they are large and the only offspring so there is directional selection on weight.
- There are two different selection pressure’s acting in different directions.
Example: Araneae spider
- offspring eat their mother following reproduction leading to 2.5 fold greater weight gain, advancements in moulting, larger size at dispersal leading to higher survival rate.
- mothers able to desert reproduce a second clutch but the estimated reproductive outputs are lower from this strategy.
- selection have favoured extreme parental investment into offspring
Increased conflict with lowered relatedness
When relatedness between parent and offspring reduces than the assymetry between fitness increases.
Example: Brood mates
- There is greater conflict between broodmates than full siblings as they are less related
- Very loud begging in brood mates as they compete for food (sibling conflict)
- Very loud begging to gain food from father (parent- offsrping conflict)
Low relatedness can lead to dishonest signals of need and increased aggression
More aggression when
- Smaller brood sizes
- Longer nestling periods
Parent offspring conflict can stop the optimum production of offspring
Example: parasitoid wasps
- parasitoid wasps lay eggs into hosts
- When intermediate number of eggs (2/3) are laid there is a high level of aggression as large c/b payoff of killing offspring
- As a result either 1 egg (no agression possible) or multiple eggs (low c/b) are laid
Sexual conflict over care
Parents typically want to provide the least amount of care possible.
This leads to conflict over care between parents.
How is biparental care possible?
- Incomplete compensation means that if one parent reduces care then there is a cost to both parents.
- Incomplete compensation is a ESS.
Example:
- study looked at 54 avian species
- If one parent was removed, the other did not fully compensate
- If one parent had weights attatched the other also did not fully compensate.
Some species do show complete compensation
- Common when mate for life and fitness costs completely align -> Rifleman fish
- Or associated with tracking/ punishment-> if they take turns in provisioning they must also track the other
In most cases males show more dessertation but there are scenarios where both parent do.
Example: pendulum tits
- 30% full dissertation
- make deserts: female suffer (offspring die) from reduced care while males benefit (more offspring) -> widely accepted
- In these tits both experienced parallel increased RS when one individual abandons and effect RS of other.
- high frequency dissertation due to intense sexual conflict
- try to be first t desert. One deserting reduces chance of other due to big reduction in RS.
Paternity uncertainty impacts parental care conflict and the liklihood of a male to adjust his care.
- Multiple paternity reduces male incentive to care/ adjust care
- Cost of care also reduces the incestive to care/ adjust care
Overview
Conflict occures whenever fitness interests do not align.
Selfishness leads to conflict and depends on the level of relatedness and the c/b ratio. (hamilton’s equation)
- Less conflict generally expected when relatedness is high, however, conflict is still possible if fitness interests diverge significantly.
Reasons for familty coflict:
- Different relatedness between relatives leading to different optima
- Life history selection leading to trade-offs which shape conflict
- -> Current vs future offsrping
- -> Number vs quality of offspring
- -> pesimism vs optimism
Family conflict
1) Parent - parent
- There is sexual conflict over care
- -> Impacted by the level of paternity
2) Parent offspring
- Different parental investment optima
3) siblings
- Competition for parental care
4) siblings with future siblings
- Indirect competition for investments
