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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. QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.
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
Reasoning• Group selection theory:
H H H F F F
Grandchildren:
24 24
Total: 48
Grandchildren:
18.7 21.3
Total: 40
Grandchildren:
16 16
Total: 32
ESS sex ratio determined by relative strength of within/between group selection, influenced by N!!
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H
CAN ONLY GROUP SELECTION EXPLAIN LMC?
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F
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
LMC under different scenarios
0
0.1
0.2
0.3
0.4
0.5
0.6
0 5 10 15 20 25 30
number of foundresses
sex ratio (% males)
Diploid
Haplodiploid inbreedingdepends on N
Haplodiploid fixedsibmating k=0.5
Haplodiploid completesibmating k=1.0
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Support for LMCLMC 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
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ScelionidaeComparative 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
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Pollinating fig wasps
Pollinating fig wasps
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Herre 1985
Low inbreeding
High inbreeding
Data from 3 different species of fig wasp
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Pollinating fig waspsConstraints to facultative SR adjustment:
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N variableN stable
Herre 1987
If LMC is constant, less selection pressure for facultative SR adjustment
Data from 13 species of fig wasp
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
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