Conflict between individuals

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

8.6 Sex allocation conflicts in the eusocial hymenoptera

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

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

8.7 Discussion