Social insects: Eusociality

Question 1

Which groups is eusociality found in?

Answer 1

• Hymenoptera: Bees, wasps and ants
• Also seen in Isoptera (termites) and homoptera (aphids)

Question 2

What three features in a colony define eusocial systems?

Answer 2

1. Cooperative brood care
2. Sterile castes
3. Overlapping generations

Question 3

What are sterile castes?

Answer 3

• Individuals within the group that are unable to reproduce from the point of development
• A colony has different castes within that have different jobs
• Specialisation increases in castes that don’t reproduce - allows all resources to be put in to specialising

Question 4

How did eusociality evolve?: Staying at home hypothesis (subsocial)

Answer 4

• Solitary parasitoid: nest guarding by female: young stay and help defend/build: young permanently staying home and never breed.
• Natural genetic predisposition for this to occur - daughters have same coefficient relatedness to siblings as to offspring (r = 0.5).
• For queen it is better to produce offspring than grand offspring so keeping daughters near is better and allows more offspring.

Question 5

How did eusocilaity evolve?: Sharing a nest hypothesis (parasocial)

Answer 5

• Sisters build nest close together: cooperative defence, separate reproduction: one female dominates reproduction: young females become workers.
• 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
• Not as good as breeding alone

Question 6

What is Haplodiploidy?

Answer 6

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

Question 7

How do males and females form gametes in haplodiploidy insects?

Answer 7

• Males form gametes without meiosis - only used mitosis
• Females form gametes with meiosis
• Daughters receive identical genes from father and the other half from diploid mother
• Sons receive genes only from mother

Question 8

What is the relatedness between family members of haplodiploid insects?

Answer 8

• Male (brother) would have all genes passed down from mother so is 1 in relatedness to the mother
• Sisters are very related to each other so it is better to produce female offspring then male
• Males are not related to ‘father’ or sons at all

Question 9

What causes conflict to arise in colonies?

Answer 9

Conflict between queen and workers over sex ratio

Question 10

Why does the sex ratio conflict occur?

Answer 10

• Queen has equal relatedness to sons and daughters
• Workers and queen have different relatedness and so different preferences on sex ratio of the colony

Question 11

How could workers vs queens skew the sex ratio?

Answer 11

• Workers feed and look after so could kill off males and keep females
• Queen lays eggs so can choose which to fertilise or not and get 50:50 sex ratio

Question 12

Study that showed who won the sex ratio conflict?

Answer 12

• Trivers and hare 1976
• Paper that showed worker ants were in control of this conflict
• Study had been questioned

Question 13

What two things could be confounding the results of the trivers and hare study?

Answer 13

1. Local mate competition
2. Queen mating frequency affects relatedness