UNIT 5 DAY 6 - The Dark Side

Question 1

natural selection

Answer 1

favours only limited and selective altruism directed towards kin and in proportion how closely the kin are related

Question 2

3 categories of the dark side

Answer 2

1. infanticide of kin (females killing young offspring of unrelated females)
2. siblicide (killing ones siblings)
3. infanticide of non-kin (males killing offspring on unrelated males)

Question 3

infanticide of kin

Answer 3

• most mammalian species, males disperse and females remain in natal groups
• females commit infanticide, killing kin

Question 4

What is the prevalence of infanticide in mammals?

Answer 4

A wide range of social mammals, including primates, rodents, and carnivores

Question 5

What are the three categories of infanticide?

Answer 5

-Infanticide by members of other social groups
-Infanticide by male immigrants unrelated to the juveniles or the infants they kill
-Infanticide by female competitors

Question 6

For the six observed infanticides which females did the killing and when? (Meerkats

Answer 6

-In two cases the infanticidal animal was a pregnant, dominant female
-In three cases it was a pregnant subordinate female
-In one case it was a non-pregnant subordinate female
-They killed less than 24 hr after birth

Question 7

How closely related were they to the pups they killed? (Meerkats)

Answer 7

-In all six cases, females killed the offspring of their maternal siblings
-In one case each, they killed the offspring of their mother, daughter, maternal cousin and maternal niece

Question 8

What does the indirect evidence indicate about dominant females commonly killing pups born to subordinates?

Answer 8

commonly kill pups born to subordinates
-Litters born to subordinates most frequently died within 24 hrs of birth
-The period when directly observed indicates that infanticide is most likely to occur
-Dominant females frequently expelled subordinate females from the group during the latter months of their own pregancy, but allowed them to return soon after birth

Question 9

What are the results of the experiment?

Answer 9

-Five out of the six cases of observed infanticide involved pregnant female relatives killing pups less than 24 hr old
-Males and lactating females were not observed to kill pups born in their own groups, and a female that was not evidently pregnant was only observed to do so one occasion
-Evidence suggests that pregnant, dominant females frequently killed pups born to suboridnate females

Question 10

benefits of infanticide

Answer 10

-Breeding females probably beneftis from infanticidal behavior as the amount of food received by pups from other groups members declines as the pup: helper ratio increases
-By ensuring there is no older pups in group at the same time her own, mother ensure that their pups have an advantage in competition for food

Question 11

costs of infanticide

Answer 11

-By expelling subordinate females from the group during the later stages of gestation, breeding females presumably reduced the risk of infanticide
-Removal of adult females from the group probably improved the survival chances of the dominant female’s pups during the neonatal period
-Expelling subordinates had appreciable costs as the presence of additional helpers reduced the workload of breeders and survival increased with the group size
-The costs of allowing subordinate females to return to the group once pups had been born were probably low

Question 12

siblicide (in birds)

Answer 12

• evolves when killing siblings increases ones own survival chance
• evolves when competition among nestlings for food is fierce, nestling vary in ability to compete for food, parents deliver food in spatially confined nest where one nestling can obtain most of the food delivered

Question 13

obligate suicide (black eagles)

Answer 13

• older siblings attack younger siblings to death
• parents don’t interfere
• relatively uncommon

Question 14

facultative suicide

Answer 14

• agression occurs among siblings
• varies in intensity
• sometimes leads to death
• environmental conditions can affect these

Question 15

why? insurance hypothesis

Answer 15

• better to lay more eggs and give one up if it is a bad year than to miss out on fitness, increase if she can support more babies
• if first egg is competent, laying more ensures furthering of gene line

Question 16

siblicide (spotted hyenas)

Answer 16

• killing sibling increases killers access to food, also elevates killer in the dominance hierarchy
• native to sub-saharan africa, most complex social structure, live in large groups, females are larger and dominate males
• females have pseudo-penises which copulate an give birth
• females –> care for own cubs, males –> no care at all
• females produce androstenedione (turns into oestrogen and testosterone)

Question 17

spotted hyenas at birth

Answer 17

• emerge with open eyes, all teeth, intense aggressions towards sibling
• 1-1.65kg at birth
• fully erupted incisors

Question 18

precocial

Answer 18

• born in an advanced state, independent

Question 19

how long is gestation

Answer 19

about 110 days

Question 20

What are their hormone levels like at birth and into the next months?

Answer 20

Aggression is most intense on the day of birth falls rapidly after

Question 21

Androgens

Answer 21

male hormones such as testosterone, a steroid type of hormone

Question 22

How are levels of androgen related to aggression?

Answer 22

The presence of substantial plasma androgen levels during fetal and neonatal life would be compatible with the organisation of activation of neonatal aggression by these steroids

Question 23

Where do females give birth and what are their litters like?

Answer 23

-They give birth at the mouth of a natal den, usually an abandoned aardvark burrow
-Tunnels diverge from this den entrance, becoming smaller in diameter at greater distances from the opening, forcing even small hyenas to crawl on their carpals
-This arrangement protects young from predation, but also prevents the mother from entering the burrow system, infants must emerge to nurse
-First litters are usually singletons
Second litters are generally twins or triplets

Question 24

What are the expected twin sex ratios compared to the observed data?

Answer 24

-Among twins the expected distribution of litter sex ratios was not observed
-Given an equal probability of males and females at birth, the expected ratio of 1:2:1 for male:male:male:female:female:female

Question 25

What happened to triplets?

Answer 25

The ratio of single- to mixed-sexed sets is 1:1 as expected

Question 26

How common is siblicide in other animals?

Answer 26

It is common in predatory birds

Question 27

What are the advantages of siblicide between twin sisters and between twin brothers?

Answer 27

-Competition within same-sex pairs may occur for different reasons
-For females elimination of a sister results in the removal of a close-ranking competitor b/c females acquire the mother’s rank in the socal hierarchy
-For males, confronting the difficult task of integration into a new clan, large size may be a particular advantage, and elimination of a brother does result in a more rapid weight gain during the first year of life

Question 28

How do neonates have more influence in these interactions than the mother?

Answer 28

Fatal outcome of fighting may thus be in part a result of ecological factors limiting potential parental influence on infant behavior, resolving parent-offspring conflict in favor of offrspring

Question 29

infanticide of non-kin (males)

Answer 29

• killing offspring to unrelated female to gain access to her for breeding

Question 30

Sarah Hrdy’s grey langurs (Old World Monkeys)

Answer 30

• infanticide evolved in males by sexual selection to increase access to fertile females

Question 31

sexual selection hypotheses

Answer 31

1. sexual selection should favour infanticides by males if doing so will return a mother to sexual receptively more rapidly
2. favoured in social (not solitary) species, especially in polygynous species, where access to reproductive females can be controlled
3. counterstrategies should evolve in females, so that males doesn’t know whether he is killing own offspring

Question 32

What is the distribution of infanticide among mammals?

Answer 32

Infanticide by males is widespread in mammals

Question 33

In what mammalian groups is it most common?

Answer 33

-New world monkeys, great apes, old world primates, hares, squirrels, marmots, mice, marsupials, bats, mongooses, felids, canids, bears, seals & sea lions, martens, ungulates, lemurs

Question 34

Has it evolved repeatedly or just once?

Answer 34

-Evolved independently multiple times

Question 35

How common is it in social vs solitary vs monogamous species?

Answer 35

• It mostly occurs in social species and less in solitary species and least in monogamous species

Question 36

What are the three features of a species that make infanticide by males likely?

Answer 36

• Social groups containing more females per male
• Dominant males obtain higher share of reproduction in a given season
• Maintain their dominant position for shorter periods

Question 37

lions

Answer 37

• also male infanticidal

Question 38

meerkat social groups, infanticide can occur when

Answer 38

females in group kill young of related, competitor females