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Local mate competition

Explore the Local Mate Competition (LMC) model and its role in shaping female-biased sex ratios in populations due to competition between related males. Understand the inclusive fitness and group selection theories, haplodiploidy, and support for LMC through comparative studies in various species.

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Local mate competition

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  1. Local mate competition • In 1967 Hamilton described his classic LMC model: • When populations are structured such that mating takes place locally and related males compete for mates a female biased sex ratio is favoured.

  2. : : ?

  3. Reasoning • Inclusive fitness: • Competition between related males, reduces the fitness returns for producing males • Some of males mate with their sister, which increases the fitness return from producing daughters

  4. H H H F F F Grandchildren: Grandchildren: Grandchildren: 24 24 18.7 21.3 16 16 Total: 48 Total: 40 Total: 32 Reasoning H F • Group selection theory: ESS sex ratio determined by relative strength of within/between group selection, influenced by N!! CAN ONLY GROUP SELECTION EXPLAIN LMC?

  5. Haplodiploidy • In haplodiploids an extra factor favours female biased SR • Sons are haploid, daughters diploid • Sibmating increases relatedness between mother and daughters, no effect R sons • Inbreeding leads to more females biased ESS SR Sibmating directly influences LMC and in only haplodiploids it has an additional effect on SR

  6. LMC under different scenarios

  7. Support for LMC LMC has been applied to explain female biased SR adjustment in many species • Comparative studies: compare sr across species/population that differ in LMC • Directly testing facultative sex ratio adjustment

  8. Scelionidae Comparative study across species: • Egg parasite, only one wasp per egg • Host (lepidoptera and hemiptera) clutch sizes vary (1 - 1000) • Strenght LMC decreases with amount of eggs • Data across 31 show positive relationship between number of eggs and SR Waage, 1982

  9. Pollinating fig wasps

  10. Pollinating fig wasps Low inbreeding High inbreeding Data from 3 different species of fig wasp Herre 1985

  11. Pollinating fig wasps Constraints to facultative SR adjustment: If LMC is constant, less selection pressure for facultative SR adjustment Data from 13 species of fig wasp N stable N variable Herre 1987

  12. Conclusions • LMC can explain: • Female biased SR in many organisms • Variation in SR across species/populations • Facultative SR adjustment • Futher directions: • More taxa (e.g. social vs. non social, winged vs. nonwinged • Use of molecular methods to better estimate N, f • Comparative methods based on phylogeny • Focus on mechanisms • Focus on species that do not show SR adjustment to LMC

  13. Problems testing LMC: • Ability to test theory limited because: • Population SRs can be obscured by facultative SR adjustment • Individual/patch SRs can be obscured by other additional factors Comparative approach within species most powerful

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