Local mate competition In 1967 Hamilton described his classic LMC model: –When populations are structured such that mating takes place locally and related.

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.

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:

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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