UNIT 5 DAY 6 - The Dark Side Flashcards
(38 cards)
natural selection
favours only limited and selective altruism directed towards kin and in proportion how closely the kin are related
3 categories of the dark side
- infanticide of kin (females killing young offspring of unrelated females)
- siblicide (killing ones siblings)
- infanticide of non-kin (males killing offspring on unrelated males)
infanticide of kin
- most mammalian species, males disperse and females remain in natal groups
- females commit infanticide, killing kin
What is the prevalence of infanticide in mammals?
A wide range of social mammals, including primates, rodents, and carnivores
What are the three categories of infanticide?
-Infanticide by members of other social groups
-Infanticide by male immigrants unrelated to the juveniles or the infants they kill
-Infanticide by female competitors
For the six observed infanticides which females did the killing and when? (Meerkats
-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
How closely related were they to the pups they killed? (Meerkats)
-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
What does the indirect evidence indicate about dominant females commonly killing pups born to subordinates?
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
What are the results of the experiment?
-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
benefits of infanticide
-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
costs of infanticide
-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
siblicide (in birds)
- 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
obligate suicide (black eagles)
- older siblings attack younger siblings to death
- parents don’t interfere
- relatively uncommon
facultative suicide
- agression occurs among siblings
- varies in intensity
- sometimes leads to death
- environmental conditions can affect these
why? insurance hypothesis
- 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
siblicide (spotted hyenas)
- 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)
spotted hyenas at birth
- emerge with open eyes, all teeth, intense aggressions towards sibling
- 1-1.65kg at birth
- fully erupted incisors
precocial
- born in an advanced state, independent
how long is gestation
about 110 days
What are their hormone levels like at birth and into the next months?
Aggression is most intense on the day of birth falls rapidly after
Androgens
male hormones such as testosterone, a steroid type of hormone
How are levels of androgen related to aggression?
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
Where do females give birth and what are their litters like?
-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
What are the expected twin sex ratios compared to the observed data?
-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
