L13 Flashcards
Diversity of eusocial systems
- Evolved in hymenoptera eg bees, wasps and ants
- Isoptera (termites)
- Homoptera (aphids)
- Their level of eusociality is not the same as hymenoptera
What three features define eusociality?
- Cooperative brood care
- Sterile castes
- Overlapping generations
Ecological importance of eusociality
- 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
Life history strategies of Myrmica rubra
- 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
How did eusociality evolve Hypothesis 1
- 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
Genetic predisposition for hypothesis 1 to occur
- 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
How did eusociality evolve Hypothesis 2
- 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
Genetic predisposition for hypothesis 2 to occur
- 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
Hypothesis 1
- Subsocial
- Halictine bees
Hypothesis 2
- Parasocial
- Polistes and stenogastrine wasps
- Small nests
- Founded by a few sister females
Haplodiploidy
- 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-
Working out relatedness
- 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
Sister- brother relationship
- Via mother = 0.25
- Via father = 0
No link between father and son
- Lower than normal siblings
Brother- sister relationship
- Focal male = all from mother
- Via mother = 0.5
- Via father = 0
R = 0.5
Female worker production perspective
- Better to produce sisters than daughters
- Explains why females (not males) rear sisters
Diploid termites
- Males and females are equally related to siblings and both sexes become sterile worker
Clonal aphids
- Sterility is not an evolutionary puzzle because there is no conflict over reproduction
Conflict between queen and workers over sex ratio
- 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
Who wins the sex ratio conflict?
- Queen can decide when to fertilise eggs etc
- Workers look after eggs so could preferentially feed females and kill males
Trivers & Hare 1976
- Sex: weight ratio
- Suggests workers win
- 3:1 line
Criticisms of trivers and hare
- Too simplistic
- Local mate competition
- Queen mating frequency affects relatedness
Local mate competition
- 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
Queen mating frequency affects relatedness
- 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
