Sibling Rivalry

Question 1

sibling rivalry

Answer 1

a form of competition between siblings for food, resources or parental attention

Question 2

what factors intensify sibling rivalry?

Answer 2

• being close in age
• being of the same gender
• if one child is intellectually/physically gifted

Question 3

why does sibling rivalry occur?

Answer 3

individuals are 50% related to siblings, but 100% related to themselves.
the benefit of giving a resource to a sibling must be 2x the benefit of keeping it to themself.

Question 4

siblicide

Answer 4

most extreme form of sibling rivalry
killing of an individual by its sibling

Question 5

facultative siblicide

Answer 5

siblicide that depends on the environment and conditions. if the circumstances determine that it would be beneficial for the individual to kill their sibling, they will

Question 6

obligate siblicide

Answer 6

siblicide that always happens. innate nature of the species is to be highly aggressive towards, and kill siblings.

Question 7

why does siblicide exist?

Answer 7

a way to deal with overproduction: sometimes parents produce more offspring than they can raise, and brood reduction is a mechanism to solve this problem. siblicide is a method of brood reduction.

a consequence of asynchronous birth: young can be born at different times, and so first born get a head start at monopolizing resources. unequal feeding rates and aggression exaggerate the size difference and kill the youngest offspring.

Question 8

hyena sibling rivalry

Answer 8

hyenas are born in twins. if the twins are the same sex they will fight to the death

Question 9

sibling rivalry in herons vs egrets

Answer 9

siblicide is rare in herons, common in egrets.

Question 10

egret siblicide

Answer 10

obligate siblicide
parents feed a chick a bolts, partially digested small fish. this is small enough to be monopolized. Since eggs are laid asynchronously, the oldest chick is strong enough to outcompete its siblings and grab the parent’s beak to monopolize the bolts.
to keep younger chick away from food it is beat up and killed

Question 11

heron siblicide

Answer 11

not common. their food is one large fish, which is too big to monopolize. siblicide uncommon

Question 12

cross foster experiment

Answer 12

fostered herons didnt fight much, but they showed increased levels of siblicide once the food was smaller (facultative siblicide)

fostered egrets showed decreased levels of siblicide, but still fought even when food wasn’t monopolizable

Question 13

sibling rivalry in pigs

Answer 13

sibling competition contributes to piglet mortality, that usually happens anyways. prevents a piglet from getting milk, or the good milk that is closest to the mother’s head.
piglets are born with canine teeth, may have evolved to help piglets fight for their milk and their place among siblings.

Question 14

parental responses to too many kids

Answer 14

neglect
feed food that can be monopolized by strongest offspring
direct brood reduction (infanticide)
asynchronous vs synchronous incubation
make first eggs bigger
put more androgens into earlier eggs
promote/ignore sibling rivalry

Question 15

what controls variation in siblicide?

Answer 15

hatch asynchrony
size asymmetry
hunger
environmental conditions (food)