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Conflict between individuals. 8.1 Sex Allocation Conflict Conflict: when the sex allocation optima for individuals differ sexes have different worth to.

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Presentation on theme: "Conflict between individuals. 8.1 Sex Allocation Conflict Conflict: when the sex allocation optima for individuals differ sexes have different worth to."— Presentation transcript:

1 Conflict between individuals

2 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

3 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)

4 8.3 Conflict under LMC, LRC & LRE 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

5 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.

6 8.5 Polyembryonic parasitoids Copidosoma sp. Polyembryony = production of multiple genetically identical embryos from single egg

7 if a male and female egg are laid, 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 males As male pre-mating dispersal increases, so does the degree of conflict

8 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) Sex ratio conflict and sterile soldiers

9 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) Spite and Sterile Soldiers

10 8.6 Sex allocation conflicts in the eusocial hymenoptera

11 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 1.Lower LRC 2.RA is reduced 5.Fisherian SR are favoured by workers when 1.Termites = diploid 2.Solitary haplodiploids 3.Slave-making ants (workers and queens are unrelated) Queen-worker conflict     

12 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 Relatedness asymmetry and Split Sex Ratio: Theory

13 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 Relatedness Asymmetry and Split Sex Ratio: Tests  Ants  Ants & Wasps  Bees

14 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 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 from Split sex ratios can result from different selection pressures polygynous pop of Formica exsecta SSR from LRC only, not RA.

15 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 Conflict, control and manipulation

16 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 Resolving Sex Ratio Conflicts

17 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 Conflict over male production

18 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!! Implications of Sex Ratio Conflicts

19 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


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