conflict between individuals. 8.1 sex allocation conflict conflict: when the sex allocation optima...
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8.1 Sex Allocation ConflictConflict:
when the sex allocation optima for individuals differ
sexes have different worth to individuals
Haplodiploidy
egg + sperm daughter (2n)
egg son (n)
Father’s have only daughters no sons
Relatedness Asymmetries
brother > sister = 0.5
sister > brother = 0.25
8.2 Conflict under Fisherian Selection
Fisher: equal investment into each sex
investment: 10g SONS 5g daughters
produce: two daughters for every son
rv: sons twice as high as daughters
offspring prefer to be male
= conflict
Is there really conflict?
not much work
Post-conception:
amount and cost of investment to parent depends on sex of offspring and parent. (T C-B 1991)
8.3 Conflict under LMC, LRC & LRE
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
-1 1 3 5 7 9 11 13 15
Number of Foundresses
Sex Ratio (Percentage Male)
Mother's ESS Sex RatioOffspring's ESS Sex Ratio
Fisherian benefits to the minority sex
Offspring prefer less biased SR than mother.
Mat-Pat conflict:
males only pass on sperm to daughters -> prefer a more female biased SR
8.4 Sibling conflict in haplodiploids & single-sex broods
Relatedness Asymmetry in haplodiploid broods of mixed sex.
sisters are worth more to brothers than brothers are to sisters.
bro>sis = 0.25 sis>bro=0.5
Pickering (1980) - can this lead to Split Sex Ratios?
SSR = some broods are male biased, others female ***
sisters are worth more to brothers than brothers are to sisters.
so males should be less selfish toward sisters than sisters are towards brothers.
but not that straight forward.
8.5 Polyembryonic parasitoids
Copidosoma sp.
Polyembryony = production of multiple genetically identical embryos from single egg
if a male and female egg are laid,
8.5.1 Sex ratio conflict and sterile soldiers
Solid = no female pre-mating dispersal
Dashed = female pre-mating disperal
No pre-mating dispersal = simple LMC situation, no conflict over SR, minimum number of malesAs male pre-mating dispersal increases, so does the degree of conflict
Conflict leads to evolution of morphological castes:
reproductive larvae
precocious larvae
usually females, seek out and kill males
resolves SR conflict in the favour of their clonal reproductive sisters, at the expense of males (brothers)
8.5.1 Sex ratio conflict and sterile soldiers
Spite = a behaviour costly to actor and receiver.
only favoured if there is negative relatedness between actor and receiver.
Relatedness is defined in relation to the average level in the population,
negative relatedness means the recipient is less related than other competitors to the actor.
In the polyembryonic, soldiers are less related to their brothers (r=0.5) than their sisters (r=1)
8.5.2 Spite and Sterile Soldiers
Eusocial hymenoptera: queen favours Fisherian sex allocation but workers (more related to sisters than brothers)
prefer a more female biased sex ratiorelatedness asymmetry!
Trivers and Hare (1972) Predictions:1. Queens favour equal investment2. Singly mated queens workers ESS = 75% female3. Multiply mated queens RA reduces, so does worker preference for
biased SR.4. Poylgynous colonies less females biased SR
1. Lower LRC2. RA is reduced
• Fisherian SR are favoured by workers when• Termites = diploid• Solitary haplodiploids• Slave-making ants (workers and queens are unrelated)
8.6.1 Queen-worker conflict
Boomsma & Grafen: sources of Relatedness Asymmetry reduction.
1. 1♀ Multiple mating reduces sis-sis relatedness,
2. n ♀ : if queens are related, with increasing queen number
3. 1 ♀ : worker production of males (nephews = 0.375, brothers = 0.25)
4. ♀ is replaced by daughter: (nieces=nephews=0.375)
What is the response to RA reduction?
Low RA (low rel to females) specialise on producing MALES
High RA (high rel to females) specialise on producing FEMALES
What effect of colony productivity?
colony = very productive large contribution to population
population SR = biased to colony’s favoured sex
Fisherian costs to producing sex decrease in SR bias.
8.6.2 Relatedness asymmetry and Split Sex Ratio: Theory
Evidence for worker control in sex ratios:
Boomsma & Grafen: sources of Relatedness Asymmetry reduction.
1. 1♀ Multiple mating reduces sis-sis relatedness,
2. n ♀ : if queens are related, with queen number
3. 1 ♀ : worker production of males (nephews = 0.375, brothers = 0.25)
4. ♀ is replaced by daughter: (nieces=nephews=0.3755)
How robust is the evidence?
- shifts in SR observed can be huge
- observational and experimental data
8.6.3 Relatedness Asymmetry and Split Sex Ratio: Tests
Ants
Ants & Wasps
Bees
Sex allocation is under very fine control by workersSundstrom (2000) Formica truncorumqueens mate multiply - does the sperm mix?
less mixed RA is higher female biased SRmore mixed RA is lower male biased SR
8.6.4 Relatedness Asymmetry and Split Sex Ratio: Complications
Queen control in some species leads to split SR Fire ant Solenopsis invicta colonies accept a new unfamiliar queen (!) sex allocations strategy of a colony predicted by strategy of the colony she came fromSplit sex ratios can result from different selection pressures polygynous pop of Formica exsecta SSR from LRC only, not RA.
2 Conflicts:
Sex Allocation
Prop of females that develop as reproductives***
COSTS to manipulation are key:
workers selectively kill males
workers bias final caste of developing females
Constraints:
can workers bias caste fate?
can workers asses SR early enough to reduce costs?
can workers asses RA in colony?
Queens fight back:
adjust primary SR to make females limited forcing them to be raised as workers.
8.6.5 Conflict, control and manipulation
Is the answer a SR between the queen & worker optima?Resolution models - depends on the species biology.
need to understand the COSTS to sex ratio manipulation
Example: monogynous colonies, singly mated queens, queen determines primary SR, workers control caste
1. Sex allocation is intermediate of queen & workers2. Cost to colony productivity, males overproduced and too
many females become reproductives not workers.3. Sequential decision: q>w, queen “wins” by having strategy
closer to her optimum4. Cost of SR decelerating (?) to q or w, split sex ratios are
favoured.
8.6.6. Resolving Sex Ratio Conflicts
Worker production of males
Worker-son r= 0.5, worker-brother r=0.25
unmated workers can do this
Is this observed?
not as much as predicted
policing
by queens - always selected for
by workers - selected for if brothers are more related than nephews.
- if colony production suffers a cost
8.6.7 Conflict over male production
If workers have some control, SR is more biased to females than preferred by queens
queens fitness is higher if she is in a male-biased colony
so queen should mate multiply for workers to favour this
But - males prefer queens to mate singly so the resulting colony has a more female biased SR.
[fathers have only daughters no sons]
CONFLICT
Multiple males mating same female want their sperm to be used separately - sperm clumping!!
8.6.8 Implications of Sex Ratio Conflicts