Eusociality Flashcards
what does eusociality mean?
‘truly’ social
what four characteristics does a eusocial animal show?
- communal living
- cooperative care for the young
- overlap of generations
- reproductive division of labour
what is meant by reproductive division of labor?
cannot pass on their genes
what is relatedness?
- probability that two individuals share an allele due to recent common ancestry
- represented as the coefficient of relatedness
what are solitary animals?
show none of the 4 charactersitics
what is pre - sociality?
some of the 4 characterics
what is sub social?
parents and offspring cooperate
what is parasocial?
individuals of the same generation live in a single dwelling and interact
why is eusociality important?
it is one of the 9 major transitions in evolution (solitary individuals to colonies)
what are some examples of eusocial animals?
bees, wasps, ants, termites, shrimp, mole rats
how many times has eusociality occurred?
there are around 20 independent origins
what does eusociality challenge?
natural selection
how did eusociality evolve?
- the parasocial route
2. the subsocial route
outline the steps of the parasocial route.
- reproductives build nests close together
- cooperate in nest construction and defence but all reproduce
- one female dominates reproduction, others hope to inherit the nest later on
- overlap of generations, young females become workers
why share a nest?
- ecological constraints
- protestion and nest
what are the genetic benefits of the parasocial route?
individuals found in the nest are related
use wasps as an example of the parasocial route
2 sisters - one dominates reproduction
joint nesters more likely to be succesful - alpha females benefit
beta females do no worse than solitary nesters
- if alpha dies the beta could inherit the nest
what does the parasocial route lead to?
lead to helping behavior but not to irreversible sterility (not a major transition)
outline the steps of the subsocial route.
- solitary wasp, safe site to rear young
- female guards nest
- young help defend the nest
- young permanently at home and never breed
why will ecological constraints lead to the subsocial route?
- nests are vulnerbale to predators and parasties
- nest building is time consuming and costly
- saves a ;pt of time and effort
why will genetic gains and losses lead to the subsocial route?
mothers gain from having helpers - get offspring
helpers are on average related to siblins and offspring by 0.5 so they don’t lose
how does haplodiploidy affect eusociality?
can be conflicts due to genetic systems as there is asymmetric sibling relatedness
outline the problems of haplodiploidy
- works normally females
- have half the mother genome
- sex is determined by whether the egg is ferilised
- unfertilised = male
- fertilised = female
- unequal relatedness
how do different sexes occur in an insect colony?
- queen has a sperm storage organ and decides whether to let the sperm fertilise the egg
- males can’t have sons
in haplodiploidy how related are sisters to sisters?
0.75
in haplodiploidy how related are sisters to brothers?
- 25
- there is no male genetics
describe the queen/worker conflict over sex ratio
- Queen daughter and queen son relatedness is 0.5
- Worker sibling relatedness is 0.75 and 0.25
- 3x as related to females
- Females are 3x as valuable passing on her genes
what sex ratio does the queen favour?
1:1
what sex ratio do the workers favour?
3:1
how is the sex ratio determined?
- workers can decide who gets fed
- queen decides the primary sex ratio
- if workers have no control over the sex ratio then the benefits of helping are reduced
what happens if the sex ratio deviates from 1:1?
- one sex becomes more common
- find it harder to mate and the other sex will do better
how is genetic value calculated?
relatedness x frequency x relative mating success
what happens when the sex ratio is 3:1 in haplodiploidy?
helping is not advantageous
describe halicitine mining bees as an example
- Mated females overwinter
- Females produce an early brood
- These mate and produce later summer brood
- The later mated females overwinter
when is C low?
when ecological conditions mea the chances of being successful alone are low
when is B high?
when ecological conditions mean that having a helper brings significant benefit
