Flashcards in Infanticide and aggression Deck (75):
What species is the typical model for infanticide?
Langurs can live in polygynous or polygynandrous systems. What causes polygyny?
Desynchronisation to the environment, resulting from a lack of seasonality or provisioning by locals
In langurs which sex is philopatric?
One harem resident will fertilise all offspring in the harem. What can be said about the relatedness of offspring?
They are all half siblings.
What two things contribute to cooperation in langurs?
1. Female philopatry
2. Half sibship
HIGH DEGREE OF RELATEDNESS
Due to the high relatedness between females, what is commonly observed?
Allomothering (baby sitting)
How does the harem resident threaten invading males?
Why does bachelor males not cooperate to overthrow the harem resident?
There is always an alpha in the bachelor group. He is the only one able to challenge the harem resident, and if the bachelors are able to overthrow the resident the alpha will turn on them. There is no point in cooperating.
What is the average term for a langur harem resident?
Why must the new male kill nursing infants in a takeover? Give 2 reasons.
1. He wants to propagate his genes ASAP in case he is overthrown
2. Mothers cannot have his offspring if they already have a nursing infant due to lactational amenorrhea
What is lactational amenorrhea?
The hormone prolactin (that stimulates milk production) prevents ovulation.
What happens when a new harem resident attempts to kill a nursing baby? Why?
All the females rush in to protect their sister and her baby because they are highly related
Do female langurs have affiliative relationships with each other?
Does the male attack females when they try and stop him committing infanticide? Why, why not?
No, because he wants to mate with them all
If her baby is killed, what happens to a nursing mother?
Her milk will dry up in ~10-11 days and then she will mate with her attacker
Do females drink their own milk if their baby is killed?
Are male langurs skilled or messy killers? Why?
Messy: they are folivores so are not used to or skilled at killing prey
Do langurs cannibalise dead infants after infanticide?
No, they are folivores
Will a male ever kill his own offspring? Why?
No, because he wishes to proliferate his genes
What is the Sexual Selection Hypothesis (SSH) for infanticide?
Males kill the offspring of their competitors, thus infanticide is a form of intrasexual competition
If a harem resident dies of natural causes, will his successor still kill his offspring?
Yes; even if there is no direct competition, the successor does not want the genes of another male proliferated.
What are the 4 predictions of the SSH for infanticide?
1. Males will not kill their own offspring
2. Males must sire the next offspring
3. Changes in harem resident should induce miscarriages/abortions in pregnant females
4. Killing shortens inter-birth intervals
In order to ensure he sires his own offspring, what must a new harem resident do?
Maintain his residency for as long as possible
The age of a lost baby determines the inter-birth interval for the mother. True or false?
True: if the baby was younger when it was killed, the mother returns to fertility quicker
Usually langurs mate in cycles. Are these time periods longer or shorter if the mother has lost a baby to infanticide?
When a new resident takes over he will harass and mock bite ALL females, even those without babies. Why?
To induce stress that causes spontaneous abortions. He cannot tell if a female is pregnant with another male's offspring and it is in his interests to kill any babies.
Do female langurs mourn dead babies?
Their behaviour is altered for the first few days afterwards. It can be assumed this is mourning.
If a baby dies from external causes like a bite or a fall, does the mother abandon it?
If the baby dies from internal causes, does the mother abandon it?
No, they will often carry dead babies around for ages. Unclear why, ignorance?
Can females physically defend against infanticide?
Yes, by forming coalitions
Give examples of female coalitions against infanticide in a) philopatric females and b) non-philopatric females
a) Langurs due to high relatedness
b) Bonobos due to ano-genital rubbing to form affiliative relationships
Does the tendency for infanticide usually spread?
Yes, because being infanticidal pays off for the male as it is more likely he will sire his own offspring
When does being infanticidal not pay?
If a new harem resident takes over and kills all nursing babies, sires his own offspring but is then overthrown, it is obvious that all the babies are his and they will be killed by his successor
How can being non-infanticidal pay?
A new harem resident DOES NOT kill all babies, and fertilises the females when they are ready, but he is then overthrown. Due to the time lag created when he waited to mate, his babies will be born during his successor's residency and the successor will think they are his.
Therefore what can be said of infanticide in evolutionary terms?
It is a mixed evolutionary sustainable strategy (MESS)
Therefore if a male could predict how long his residency will be then he could vary his strategy. True or false?
Do males know how long their residencies will last?
Do females know how long a male's residency will last?
Yes, although it is unclear how
Because females seem to know how long a male's residency will last, they can manipulate the sex of their baby. True or false?
If a male will be resident for a long time, which sex offspring will be produced and why?
A male will not kill his own sons, and males are more likely to be killed than females as they serve as competition
If a male will only be resident for short time, which sex will the offspring be and why?
Females are less likely to be killed as they are future mating partners
What proportion has been calculated at Jodhpur for how many of her infants a mother will see killed in her lifetime?
4 (out of an average 17 babies had)
There are 6 female counter strategies to infanticide (in all primates not just langurs). What are they?
1. Defence of offspring
2. Promiscuous mating (in multi-male groups)
3. Sex during pregnancy
4. Delay copulation
5. Adjust offspring sex ratio
6. Synchronise fertility
How do promiscuous mating, sex during pregnancy and fertility synchronisation protect offspring from infanticide?
For paternity confusion, a male will not risk killing an offspring that might be his
Why might a female delay copulation to prevent infanticide?
To punish the male, negative conditioning
How does adjusting the sex ratio of offspring prevent infanticide?
Females can produce daughters if they think the male is likely to be overthrown
In Hanuman langurs, what is the most common counterstrategy against infanticide?
Defence against the male
In Hanuman langurs, which counterstrategies are observed?
Defence against the male, promiscuous mating (in polygynandrous systems), sex during pregnancy, adjustment of the sex ratio, synchronisation (in some locations)
In Hanuman langurs, why is sex during pregnancy usually ineffective against infanticide?
The males have 'clocks' and can apparently figure out that the time between copulation and birth do not match up
Which two forms of infanticide counterstrategy are not observed in langurs?
In multi-male langur troops, where the female has mated with numerous males, when an infant is born who protects it?
All males that mated with the female in that cycle, as none of them know who the father is.
In multi-male langur troops, where the female has mated with numerous males, when an infant is born who attacks it?
Males that did not mate with the female during her cycle
What is the Lorenzian theory of aggression?
Aggression is evolutionarily beneficial as it distributes individuals across space to avoid competition, whilst also selecting for the strongest competitors to defend a bloodline.
Under Lorenzian theory, is aggression a naturally occurring behaviour?
Yes; aggression is an endogenous 'drive' that builds up periodically
Under Lorenzian theory, what is the nature vs. culture standpoint?
In nature animals often refrain from killing defeated conspecifics, whereas humans do not.
Under Lorenzian theory, why is there cultural pessimism?
It is thought that humans 'de-humanise their competitors' as a result of indoctrination and by using distance weapons.
What is the de-humanisation of competitors called?
Pseudo-speciation, humans perceive themselves to be different from one another
Give 3 pieces of evidence AGAINST Lorenzian theory.
1. Aggression is reactive, not spontaneous
2. Infanticide occurs in non-human animals
3. Killing of adult conspecifics occurs among non-human animals, e.g. chimpanzees
What is central to theories about aggression?
Nature vs. culture
Why do adult male chimpanzees kill neighbouring males?
To steal their food and females
Why do adult male chimpanzees kill older females?
To destroy the mother-daughter bond and kidnap females into their own group
Why do adult male chimpanzees kill 'foreign' babies? Give 3 reasons
1. For food
2. To eliminate future male competitors
3. If there is paternity uncertainty
Why does monogamy eliminate infanticide?
There is paternity certainty
What are the killing patrols of male chimps called?
How do chimps kill each other?
The group will pin down an enemy, bite them and rip them apart
Will chimps drink the blood of those they've murdered?
What are fights between neighbouring chimps called?
Inter-community warfare, can sometimes go on for years
Only male chimps will commit infanticide. True or false?
False: there is often mother-daughter cooperation to snatch and kill the babies of others.
This example comes from Passion and Pom in Gombe, documented by Jane Goodall. These chimps apparently were doing it for cannibalism.
Infanticide is observed in callitrichids. Who carries it out? Why?
The grandmother in 'grandmaternal cannibalism'
In polyandrous systems the dominant female (grandmother) recruits everyone else as babysitters for her offspring.
She releases a pheromone to prevent her daughters ovulating.
Should one of them mate and give birth she will eat the infant.
Why would daughter callitrichids risk grandmaternal cannibalism and get pregnant?
The mortality risk for the dominant female is high, and whoever has babies next becomes the new queen
Why do females mate with the killer of their infant?
Because at the end of the day they want to propagate their genes, to do so they need a new baby
Female langurs in polygynandrous groups become proceptive and copulate before ovulation. What effect does this have on males?
They cannot tell when she is ovulating and so when the baby is born no one is sure who the father is
Female langurs in polygynous groups openly show menstrual bleeding, whereas those in polygynandrous groups do not. Why?
By showing menstrual bleeding it is obvious what part of the cycle you are in; in a polygynous group there is no need to confuse paternity as only one male is mating
Why don't females synchronise to prevent against infanticide?
Because then a polygynandrous group would form and they will have to share food with extra males.