L13

Question 1

Diversity of eusocial systems

Answer 1

• Evolved in hymenoptera eg bees, wasps and ants
  • Isoptera (termites)
  • Homoptera (aphids)
  • Their level of eusociality is not the same as hymenoptera

Question 2

What three features define eusociality?

Answer 2

• Cooperative brood care
• Sterile castes
• Overlapping generations

Question 3

Ecological importance of eusociality

Answer 3

• 14,000 species of eusocial insects
  • Driver ant colony can have up to 22 million ants from the same queen
  • 70-80% of insect biomass in Brazilian rainforest and 33% of whole animal biomass
  • Sophisticated communication: waggle dance
  • Specialisations as they are not reproducing so can direct resources

Question 4

Life history strategies of Myrmica rubra

Answer 4

• Nuptial flights synchronised after warm weather, they emerge and mate
  • Female stores sperm for many years and female can selectively manipulate sperm
  • Female initially produces sterile workers, 9 years later colony produces reproductive individuals

Question 5

How did eusociality evolve Hypothesis 1

Answer 5

• Staying at home
  • Ancestors were parasitoid wasps
  • These females nest guard
  • The young stay and help defend/ build nest
  • Young are permanently at home and never breed

Question 6

Genetic predisposition for hypothesis 1 to occur

Answer 6

• Mother mating once, for daughters, raising full siblings is as good as raising own offspring
  • For queen, producing offspring is better (r=0.5) than producing grand offspring (r= 0.25)
  • Queen should prefer daughters to stay as workers

Question 7

How did eusociality evolve Hypothesis 2

Answer 7

• Cooperate in building and defending nest benefits
  • Occurs in tropical and temperate wasps
  • Strategy helps to defend reproduction against predation/ parasites
  • If one female dominates it turns into hypothesis 1 eventually

Question 8

Genetic predisposition for hypothesis 2 to occur

Answer 8

• For sisters that cooperate there is a benefit from raising dominants offspring
  • This may outweigh the benefit of breeding alone if that is a high risk activity

Question 9

Hypothesis 1

Answer 9

• Subsocial
• Halictine bees

Question 10

Hypothesis 2

Answer 10

• Parasocial
• Polistes and stenogastrine wasps
  
  • Small nests
  • Founded by a few sister females

Question 11

Haplodiploidy

Answer 11

• Males develop from unfertilised eggs - haploid
  • Females develop from fertilised eggs - diploid

Males form gametes without meiosis
- Mitosis
- Exact copy
- Genetically identical

Females form gametes with meiosis
- Independent assortment
- Half of complement of gene
- Variation

- Daughters receive identical genes from father and the other half from diploid mother

- Sons receive genes only from mother-

Question 12

Working out relatedness

Answer 12

• Go back to most related common ancestor
  • Via mother focal females are related to sister by 0.5x0.5 = 0.25 0.25
  • Via father father females 0.5x1 = 0.5 + 0.25
  • Sisters are more related to each other than their offspring

Question 13

Sister- brother relationship

Answer 13

• Via mother = 0.25
  • Via father = 0

No link between father and son

- Lower than normal siblings

Question 14

Brother- sister relationship

Answer 14

• Focal male = all from mother
  • Via mother = 0.5
  • Via father = 0

R = 0.5

Question 15

Female worker production perspective

Answer 15

• Better to produce sisters than daughters
  • Explains why females (not males) rear sisters

Question 16

Diploid termites

Answer 16

• Males and females are equally related to siblings and both sexes become sterile worker

Question 17

Clonal aphids

Answer 17

• Sterility is not an evolutionary puzzle because there is no conflict over reproduction

Question 18

Conflict between queen and workers over sex ratio

Answer 18

• Queen has equal relatedness to daughters and sons
  • Preferred sex ratio for queen is 1:1

Worker

- More related to sister

- Prefer sex ratio 3:1

Question 19

Who wins the sex ratio conflict?

Answer 19

• Queen can decide when to fertilise eggs etc
  • Workers look after eggs so could preferentially feed females and kill males

Question 20

Trivers & Hare 1976

Answer 20

• Sex: weight ratio
  • Suggests workers win
  • 3:1 line

Question 21

Criticisms of trivers and hare

Answer 21

• Too simplistic
  1. Local mate competition
  2. Queen mating frequency affects relatedness

Question 22

Local mate competition

Answer 22

• Always assumed 1:1 sex ratio is ESS
  • Brothers may compete to mate
  • No point in producing sons that just spend time fighting
  • Happens in fig wasps
  • Males and females are dimorphic
  • Early fertilisation of females before they emerge
  • Females fly off and lay eggs in other figs
  • One male can fertilise many females so no point in a male sex ratio

It pays females to bias sex ratio towards females

Question 23

Queen mating frequency affects relatedness

Answer 23

• Relies on assumption queen has only related once
  • If a female has two mates, each male has equal probability of fathering offspring
  • R = 0.25
  • If two possible fathers focal female r = 0.5
  • Two fathers = 50% chance of fatherhood
  • Overall relatedness of sisters is 0.5 not 0.75 reduced relatedness
  • Infinite no of mates = lower relatedness