6 - Social Insects Flashcards
What is in eusociality?
Cooperative care of young by sterile casta
Across all generations
Occurs in social insects and some others
For example naked mole rats but the most common in hymenoptera
One pair reproduces while the rest of the colony is sterile
Only hymenoptera and termites display obligate eusociality
This is irreversible reproduction is impossible
What is a Haplodiploid?
Males are from unfertilised eggs 1N
Females are from fertilized eggs 2N
Sisters share all paternal genes so 50% identical and other 50% have 50% of mother’s genes so 75% related
More related to each other than to own young
How does Hamilton’s rule work under Haplodiploidy?
b/c > roffspring/rrecipient(eg. sister) therefore b/c > 0.5/0.75
b/c > 0.6 (1.3)
Need to produce 2 sisters per 3 offspring sacrificed for same fitness
If b/c is greater then 0.6, cooperation can evolve even if less efficient than raising own offspring
Summarise the haplodiploid hypothesis
Cooperation only evolves in haplodiploid species
What the problems with the haplodiploid hypothesis?
Only compares sisters to daughters
Females are 0.25 r to brothers
Need to compare value of helping produce brothers and sisters to sons and daughters
If investment is equal, average to siblings is 0.5 and not different from own offspring
In diploids, b/c > 1 for cooperation
No advantage in haplodiploids
What is the Trivers and Hare study, 1976
3x r means selection favours sex ratio of 3:1 f:m
A worker should produce 3 females per drone
Average r to offspring of queen?
(0.75x0.75) + (0.25x0.25) = 0.625 (sex ratio x relatedness)
There fore, critical value for cooperation, b/c > 0.5/0.625 = 0.8
Need four siblings for 5 offspring sacrificed and b/c < 1
How does to value of offspring contribute to the negation of the haplodiploid hypothesis?
Value = contribution to future generation
If f:m is 3:1, males are 3x as valuble as females
Tradeoff is:
Siblings: (0.75x1x0.75)+(0.25x3x0.25) = 0.75
Offspring: (0.75x1x0.5)+(0.25x3x0.5) = 0.75
Where: (sex ratio x value x relatedness) for males and females
As sex ratio is female biased, haplodiploidy offers no extra advantage to cooperation
If overall population ratio of sex is 1:1, b/c > 0.8 (0.5/0.625)
In male based colonies, this scenario will be selected against
As r is same overall, and biased sex ratios do not contribute, haplodiploidy is probably not needed for evolution of cooperation
What is the monogoamy hypothesis?
r is reduced if there are multiple matings, therefore monogamy is important
If half siblings, sisters are r = 0.25, sister and brother 0.25 also
Under monogamy, equal relation to siblings as offspring
Any small advantage of siblings > offspring favours eusociality
Can’t be due to r as seems impossible to increase it
Many social insects mate for life
Monogamy and other factors lead to high b/c
What factors might contribute to b/c in haplodiploid species?
Life insurance: workers care for dependent offspring in case of death, confirmed by Godagkar, 1991
Helpers have x2 reproductive success benefit than individual breeders
Field et al found this by removing all helpers from a colony
Communal defence: helpers defend resources. eg harvested foo, as in some aphids and termites
Key poiny: r means b/c must be greater than 1
What is the sex ratio conflict?
Queens v workers
Queen’s equal relation to m/f means that, according to Fider’s theory, there should be a 1:1 m:f input ratio
Workers prefer 3:1 f:m, therefore there is conflict
Trivers and Hare (1976) compared 21 soecies and found 3:1 f:m average
Workers use their power eg. feeding to make sure desired ratio is produced
Evidence is not obvious
How does sex ratio impact mating?
Must predict optimal sex ratio based on how many times queen mates
Can predict correlations between matings and ratio
Workers know how many matings queen has had due to scent variation of young
More matings means greater diversity of hydrocarbons - some evidence to suggest workers can sense this
Workers manipulate sex ratio by destroying males and deciding who gets to be queen
