Conflict between individuals
8.1 Sex Allocation Conflict
Conflict:
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
0.5
0.45
Sex Ratio (Percentage Male)
0.4
0.35
Fisherian benefits to the
minority sex
 Offspring prefer less
biased SR than mother.
0.3
0.25
0.2
0.15
0.1
Mother's ESS Sex Ratio
Offspring's ESS Sex Ratio
0.05
0
-1
1
3
5
7
9
11
13
15
Number of Foundresses
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
8.5.1 Sex ratio conflict and sterile
soldiers
if a male and female egg are laid,
Solid = no female pre-mating dispersal
Dashed = female pre-mating disperal
As
Nomale
pre-mating
pre-mating
dispersal
dispersal
= simple
increases,
LMC situation,
so does no
the
degree
conflict of
over
conflict
SR, minimum number of males
8.5.1 Sex ratio conflict and sterile
soldiers
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)
8.5.2 Spite 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)
8.6 Sex allocation conflicts in the
eusocial hymenoptera
8.6.1 Queen-worker conflict
Eusocial hymenoptera:
queen favours Fisherian sex allocation
but workers (more related to sisters than brothers)
prefer a more female biased sex ratio
relatedness asymmetry!
Trivers and Hare (1972) Predictions:
1.
 Queens favour equal investment
2.
 Singly mated queens  workers ESS = 75% female
3.
Multiply mated queens  RA reduces, so does worker preference for
 biased SR.
4.
 Poylgynous colonies  less females biased SR

5.
1.
2.
Lower LRC
RA is reduced
Fisherian SR are favoured by workers when
1.
2.
3.
Termites = diploid
Solitary haplodiploids
Slave-making ants (workers and queens are unrelated)
8.6.2 Relatedness asymmetry and Split
Sex Ratio: Theory
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.
8.6.3 Relatedness Asymmetry and Split
Sex Ratio: Tests
Evidence for worker control in sex ratios:
Boomsma & Grafen: sources of Relatedness Asymmetry reduction.
1♀ Multiple mating reduces sis-sis relatedness,
2.
 Ants
n ♀ : if queens are related, with queen number  Ants & Wasps
3.
1 ♀ : worker production of males (nephews = 0.375, brothers = 0.25)
4.
♀ is replaced by daughter: (nieces=nephews=0.3755)
1.
How robust is the evidence?
- shifts in SR observed can be huge
- observational and experimental data
 Bees
8.6.4 Relatedness Asymmetry and Split
Sex Ratio: Complications
Sex allocation is under very fine control by workers
Sundstrom (2000) Formica truncorum
queens mate multiply - does the sperm mix?
less mixed  RA is higher  female biased SR
more mixed  RA is lower  male biased SR
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 from
Split sex ratios can result from different selection pressures
polygynous pop of Formica exsecta
SSR from LRC only, not RA.
8.6.5 Conflict, control and manipulation
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.
8.6.6. Resolving Sex Ratio Conflicts
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 & workers
2. 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 optimum
4. Cost of SR decelerating (?) to q or w, split sex ratios are
favoured.
8.6.7 Conflict over male production
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
8.6.8 Implications of Sex Ratio Conflicts
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!!
8.7 Discussion
Kin selection = great
Formica truncorum
- num Queens
- colony productivity
- mating
- sperm mixing
- kin recognition
Future?
resolution of conflicts
extend of selective forces: RA, LRC, LRE,
theory & manipulative experiments