Infanticide and aggression Flashcards
What species is the typical model for infanticide?
Hanuman langurs
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?
Females
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?
- Female philopatry
- 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?
Teeth grinding
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?
27 months
Why must the new male kill nursing infants in a takeover? Give 2 reasons.
- He wants to propagate his genes ASAP in case he is overthrown
- 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?
Yes
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?
Yes
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?
- Males will not kill their own offspring
- Males must sire the next offspring
- Changes in harem resident should induce miscarriages/abortions in pregnant females
- 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?
Shorter.
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?
Yes, immediately
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