Lecture 12 - Eusociality

Question 1

why did Darwin question eusociality?

Answer 1

how can sterility evolve and be selected for in a population considering natural selection involves the capacity to reproduce

Question 2

describe the diversity of eusociality

Answer 2

1) Hymenoptera - bees, wasps, ants
2) isoptera - termites
3) homoptera - aphids

Question 3

what are 3 key features of eusociality

Answer 3

• Cooperative brood care
• Sterile castes
• Overlapping generations

Question 4

why are eusocial systems ecologically important?

Answer 4

• 14,000 spp of social insect (cf. 10,000 birds, 4,000 mammals)
• driver ant colony: 22 million ants
• Brazilian rainforest: 70-80% of insect, 33% animal biomass
• sophisticated communication: waggle dance
• specialisation
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Question 5

brief explanation of the lifecycle of a typical hymnoptera insect

Answer 5

1) queen founds nest and produces sterile workers
2) takes 9 years before the colony is big enough to stat reproducing
3) after 9 years the queen switches from just producing female workers to also producing winged females and males that reproduce
4) males and females fly up and mate - male then dies and females lose winds and found a new nest

Question 6

what are the 2 models for how eusociality evolved?

Answer 6

• both start off assuming ancestors were solitary parasitoids
  1) staying at home hypothesis
  2) sharing a nest

Question 7

describe the ‘staying at home’ hypothesis

Answer 7

solitary parasitoid -> nest guarding by female -> young stay and help defend/build -> young permanently at home and never breed

Question 8

what is the genetic predisposition for the ‘staying at home’ hypothesis

Answer 8

For daughters, raising full siblings (coeff of relatedness, r = 0.5), is as good as raising own offspring (r = 0.5).

For queen, producing offspring (r = 0.5) is better than producing grand-offspring (r = 0.25).

Queen should prefer daughters to stay as workers

Question 9

describe the ‘sharing a nest’ hypothesis

Answer 9

sisters build nest close together -> cooperative defence, separate reproduction -> one female dominates reproduction -> young females become workers

Question 10

what is the genetic predisposition for the ‘sharing a nest’ hypothesis

Answer 10

• For sisters that cooperate, there is a benefit from raising dominant’s offspring (i.e. nieces and nephews).
• This may outweigh the benefit of breeding alone if that is a high risk activity

Question 11

in what species is the ‘staying at home’ (subsocial) hypothesis seen

Answer 11

halictine bees

Question 12

in what species is the ‘sharing a nest’ (parasocial) hypothesis seen

Answer 12

polistes and stenogastrine wasps

Question 13

what did hamilton say about haplodiploidy?

Answer 13

haplodiploidy predisposes Hymenoptera to evolve sterile castes

Question 14

what is the difference between males and females that are haplodiploids?

Answer 14

• Males from unfertilized eggs – haploid
• Females from fertilized eggs – diploid
• Males form gametes without meiosis
• Females form gametes with meiosis

Question 15

where do sons and daughters in haplodiploid species receive their genes from?

Answer 15

• daughters receive identical genes from their father and the other half from diploid mother
• sons dont have a father - receive genes only from their mother

Question 16

what is the consequence of haplodiploidy for relatedness for sister-sister?

Answer 16

Via mother:
r = 0.5 x 0.5 = 0.25

\+

Via father:
r = 0.5 x 1 = 0.5

r = 0.75

Question 17

what is the consequence of haplodiploidy for relatedness for sister-brother?

Answer 17

Via mother:
r = 0.5 x 0.5 = 0.25

\+

Via father:
r = 0.5 x 0 = 0

r = 0.25
- the father passes no genes to his son

Question 18

what is the consequence of haplodiploidy for relatedness for brother-sister ?

Answer 18

Via mother:
r = 1 x 0.5 = 0.5

\+

Via father:
r = 0 x 1 = 0

r = 0.5
- a brother is more related to his sister than she is too him - asymmetry in relatedness

Question 19

what affect does the asymmetry in relatedness have on female workers

Answer 19

for a female worker it is better to produce sisters than daughters
- explains why females (not males) rear sisters

Question 20

compare haplodiploidy to diploid termites

Answer 20

males and females equally related to siblings and both sexes become sterile workers

Question 21

compare haplodiploidy to clonal aphids

Answer 21

sterility is not an evolutionary puzzle because there’s no conflict over reproduction - every individual is related to each other by 1, they just want to maximise overall reproductive output of the clonal group

Question 22

describe the conflict between queens and workers over sex ratio of broods

Answer 22

• queens are equally related to sons and daughters
• workers are more closely related to their sisters
• queens want to produce an even sex ratio
• workers have a preference for females
• queens can choose to fertilise eggs or not to produce different sexes but workers can choose which sex to invest more into

Question 23

what did trivers and hare test in their haplodiploidy experiement?

Answer 23

• tested sex ratio in 21 ant species

- results suggest the workers ‘win’

Question 24

what are the 2 main criticisms with the trivers and hare experiment?

Answer 24

1) Local mate competition - brothers may compete to mate so it may pay females to bias sex ratio too
2) Queen mating frequency affects relatedness - if the female mates more than once the relatedness gets reduced

Question 25

what is now known about multiple mating?

Answer 25

• multiple mating is actually frequent making the patterns of relatedness less extreme
• this messes up with the predictions of what workers would prefer- actually depends more on the queens mating frequency